Zhou Tan

Philippe Agard

Jun Gao
email: gaojun@mail.iggcas.ac.cn

Timm John

Jilei Li

Tuo Jiang

Léa Bayet

Xinshui Wang

Xi Zhang

Tan Zhou

Agard Philippe

Gao Jun

Implications for exhumation processes in SW Tianshan

Keywords: UHP metamorphism, eclogite, P-T path, pseudosection modeling, thermobarometry, zircon U-Pb, zircon oxygen isotope, exhumation pattern, Chinese UHP oceanic eclogite, garnet zoning, Zr-in-rutile thermometry, diffusion modeling, cold subduction regime, Chinese SW-Tianshan

This study attempts to characterize, using a field, petrological, geochemical and isotopic approach, some key fossil fragments of material equilibrated along the subduction plate boundary, now exhumed and exposed in the Chinese South Tianshan Metamorphic Belt (STMB) as high-pressure low-temperature (HP-LT) metamorphic rocks. Subduction zone processes (e.g., earthquake generation, mass/fluid transfer or mechanical coupling), which control Earth dynamics or material recycling into the mantle and impact a large fraction of the human population, remain indeed poorly constrained and inaccessible to direct observation. We herein shed light on some of these processes, across a critical depth range of ~80 km, beyond which geophysical evidence and models infer a change in mechanical coupling and oceanic rocks are usually not recovered. This study focuses on an unusually thick (~5 km) pile of wellpreserved HP/UHP metavolcanoclastics, wrapping eclogite boudins/slices and preserving pervasive coesite relics in both lithologies, along a ~30km-long transect across the Akeyazi metamorphic complex (AMC) in the Kebuerte valley.

Structural investigations reveal that the present-day geometry of the AMC is that of a metamorphic dome preserving evidence for internal nappe stacking. What was previously described as a HP/UHP "mélange" should be subdivided into several coherent, km-scale, essentially metavolcanoclastic tectonic units bearing contrasting P-T-time-deformation histories. At least four of the six sub-units identified here, namely the UH (480-560°C and 2.75 GPa), EB (~2.1 GPa and 505°C), MU (~1.45 GPa and 485°C) and GT units (>~0.7-1.0 GPa and 470-520°C) experienced subduction and were buried to depths of ~85, 65, 45 and 30 km respectively. Pervasive deformation following eclogite and/or blueschist-eclogite peak burial is marked by pervasive BS facies, exhumation-related shear senses with a top to the north component.

The reconstruction of the detailed P-T-time-isotopic history of a representative coesite-bearing oceanic eclogite suggests pre-peak burial to UHP conditions at 318 Ma (~2.95 GPa ±0.2 and 510 °C ± 20) and peak ages around 315 ±5 Ma. In situ laser probe 40 Ar-39 Ar radiometric dating of phengite and zircon U-Pb dating on thirteen samples About three years ago, I arrived the 'Capitale romantique'-Paris to seek further studying, with feeling like 'a homeless ranger'. Not exaggerated, the fact that I am a 26 years old father with a 2 years old daughter essentially gave me a very limited time for abroad studying, before she really grew up enough to remember the time she should have with her father. Family issues also make it impossible to move my wife and daughter to stay with me in Paris, that is why when everybody joked to me that you worked too hard, I always replied time is not enough for me to enjoy the life and work in Paris.

As a poor self-control guy with also poor foundation of geology, hard-working is probably the only way, for me, to manage to finish this PhD thesis, a prerequisite of a promising future. The beginning of my PhD thesis here is difficult and the rest time before I really finished the writing of this PhD thesis, for sure, is not easy at all, since as a young and 'remote' father I am always struggling between work and family stuff.

The accompanying of several TACATACA & close friends (Guillaume, Michele and Mathieu) really dilutes those pressures and makes me survived. They tolerate and enjoy the difference of culture, behavior and habit between eastern and western, and help me a lot in both life living and working. Despite some complaints, from my wife and parents, to remind me of coming back as soon as possible that really make me depressed, I inwardly understand their 'misunderstanding'. Because the foundation of a promising future that I am seeking abroad, in fact, stands on the sacrificing of their life, especially for my daughter. Heartfelt gratefulness, therefore, must be typed down in this thesis for Supplementary Figures and Tables: ......

Résumé

Les zones de subduction sont des frontières de plaques convergentes le long desquelles une plaque plonge sous une autre. Les processus associés à la dynamique des zones de subduction (séismes, transfert de matière ou de fluide ou encore le couplage mécanique à l'interface des plaques) contrôlent au première ordre la tectonique des plaques et le recyclage de matière dans le manteau, et impactent fortement une large partie de la population mondiale vivant au niveau de ces frontières de plaques. Cependant, ces processus restent relativement peu contraints car inaccessibles à l'observation directe.

Ainsi, ce projet de thèse a pour objectif de contraindre les processus gouvernant les zones de subduction à environ 80 km, profondeur critique au-delà de laquelle des données géophysiques et des modèles montrent un changement du couplage mécanique et les roches océaniques ne sont la plupart du temps pas récupérées. Pour ce faire, notre travail s'est concentré sur la caractérisation de matériels fossiles équilibrés à de telles profondeurs le long d'une zone de subduction fossile, qui se trouve à présent exhumée au niveau de la Ceinture Métamorphique du Sud Tianshan (Chine).

Cette ceinture métamorphique est en partie structurée d'un empilement de roches métavolcanoclastiques de haute pression (HP) à ultra haute pression (UHP) sur une épaisseur (inhabituelle) de 5 km. Ces unité contiennent localement des fragments d'éclogites préservant des reliques de coésite. Cette séquence d'environ 30 km d'épaisseur forme le complexe métamorphique d'Akeyazi (AMC) dans la vallée de la Kebuerte. Des études structurales portant sur l'AMC ont précédemment révélé que sa géométrie actuelle est semblable à celle d'un dôme métamorphique formé d'un « mélange » de roches HP/UHP.

A partir d'une étude de terrain détaillée, couplée à une fine étude pétrologique, géochimique et isotopique, il nous a été cependant possible de subdiviser la structure de complexe métamorphique en six sous-unités d'échelles kilométriques possédant des histoires P-T-temps-déformations bien distinctes. Au moins quatre de ces six unités ont été enfouies en zones de subductions: l'unité UH (480-560°C et 2,75 GPa, soit ~ 85 km de profondeur), l'unité EB (505°C et ~2,1GPa, soit ~65 km de profondeur), l'unité MU (485°C et ~1,45GPa, soit ~ 45 km de profondeur) et l'unité GT (470-520°C et > 0,7-1,0 GPa, soit > 30 km de profondeur). Ces unités sont également caractérisées par une déformation pénétrative développée dans le facies des schistes bleus et associée à un cisaillement top vers le nord synchrone de leur exhumation.

La reconstitution de l'histoire détaillée P-T-temps d'un échantillon représentatif des éclogites océaniques à coésite suggère un pré-pic d'enfouissement dans des conditions de UHP il y a 318 Ma (à ~2,95 ± 0,2 GPa et 510 ± 20°C) suivi d'un pic d'enfouissement à environ 315 Ma ± 5. D'autre part, des datations 40Ar-39Ar in situ à la sonde laser sur des phengites et U-Pb sur zircon pour treize échantillons donnent des âges pour le pic d'enfouissement de 320 ±1, 332±2, 359±2 et 280-310 Ma pour les sous-unités UH, EB, MU et GS (GS1, GS2 et GT) respectivement. Cela suggère l'existence de plusieurs épisodes transitoires de détachement de matériel de la plaque plongeante lors de la subduction du Sud Tianshan sous la marge continentale Paléo-Kazakhstan. Le gradient métamorphique diminue d'environ 12°C/km à environ 5-7°C/km au cours du temps, ce qui reflète possiblement le refroidissement progressif du système en subduction. La juxtaposition et l'exhumation des sous-unités UH, EB, MU et GT à des profondeurs crustales (environ 20 km) et à une vitesse de l'ordre de 1-3mm/an s'est terminée aux alentours de 290-300 Ma. L'existence d'unités métavolcanoclastiques à glaucophane âgées d'environ 300 Ma (GT et une partie de l'unité GS1) suggère que la subduction était encore active à la fin du Carbonifère.

L'étude des compositions en éléments majeurs et traces des grenats révèle une zonation annulaire (notamment en Mn, Y et terres rares lourdes) contemporaine d'une augmentation transitoire de la température d'environ 80°C (montrée par le Zr dans le rutile). Les modèles de croissance à diffusion limitante du grenat supportent l'idée d'une excursion thermique transitoire d'une durée d'environ 300 000 ans afin de reproduire la zonation observée dans les grenats (en prenant en compte une durée de croissance totale de 5 Ma pour le grenat). Nous proposons qu'une telle excursion thermique est liée au mouvement rapide des morceaux océaniques UHP vers le coin de manteau plus chaud. yield peak burial ages of 320 ±1, 332 ±2, 359 respectively, for the UH, EB, MU and GS facies units (GS1, GS2 and GT). This suggests the existence of several short-lived episodes of detachment of material from the downgoing plate during subduction of the South Tianshan ocean beneath the Paleo Kazakhstan Continent. The tectono-metamorphic evolution from ~12°C/km to ~5-7 °C/km with time may reflect progressive cooling of the subduction system. Juxtaposition and exhumation of the UH, EB, MU and GT units to mid-crustal depth (~20 km), at rates on the order of 1-3 mm/yr, was accomplished around 290-300 Ma. The existence of ~300 Ma glaucophane-bearing metavolcanoclastic units (i.e., GT and part of the GS1 unit) suggests that subduction was still active during the Late Carboniferous. Petrological investigations on garnet major and trace element chemistry reveal a specific zoning (i.e., in Mn, Y and heavy rare earth elements) coeval with a transient ~80 °C increase in temperature (revealed by Zr-in-rutile thermometry). Diffusioncontrolled garnet growth modeling supports the necessity of a ~300 kyr transient thermal excursion to reproduce this garnet zonation (assuming a 5 Myr duration for the overall garnet growth). Such a transient thermal excursion is tentatively tied to the fast movement of detached UHP oceanic slices towards the hotter mantle wedge.

⎯⎯⎯⎯ An untouched photography took by sony a77 (17mm, F8, 1/100) during the 1 st year (fall 2013) field excursion of the PhD candidate in the Akeyazi-Kongguerbulake area, Zhaosu county, Xinjiang province, China. This beautiful scenery indeed inspires my interest and love for natural earth sciences and unknown fields. Just as Liu CiXin wrote down in <the ball lightning>: the key to a wonderful and unrepentant life is to fascinate something, forever young. whatever supports or pressures from my family. It is my responsibility and pleasure to live for them.

Last but the most important, the gratefulness for my two PhD superiors. As a Chinese, our 5000 years history civilized us to keep best respect to our teacher--'One day as a teacher, a life as a father'. Great thanks should be given to my Chinese superior prof. Jun Gao who always tolerated my weakness and guided me with unwearied helps.

Although there are some argument and misunderstanding between us, mainly because of my immature behavior and bad performance. Speechless acknowledgement must be typed down to my French 'boss' prof. Philippe Agard. His meticulous help, during my three years PhD life in Paris, really motivates me to move forward. The unrestrained thought of his guided me to think more logically and independently. He also led by example to teach me how to behave as a rigorous, neutral and selfless geologist. For sure, I am still way far away from the standard of a good student if considering how good and unsurpassable their previous PhD students are (e.g., S. Angiboust, P. Yamato for P.A.; Ji-Lei Li, Xin-Shui Wang for J.G.), I therefore never dare to dream that they will be proud of me. However, no matter what happens in the future, whatever be rich or poor, be in power or stay unknown in a quiet corner of the world, I sincerely and honestly maintain proud and grateful to the fact that I used to be they PhD student, and they indeed sharped my thought, civilized my ages and visualized my time. (M≥4, depth<70 Km, 1964(M≥4, depth<70 Km, -1998) ) with locations presented as black dots; (b) The surface subdivision with the major tectonic plates of earth. 3: (a) Structure of subducted slabs as inferred from mantle tomography (Engdahl et al., 1998)

Table of figures

••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -- Figure 2: Schematic illustration of the Plate tectonics theory. •••••••••••••••••••••• -- Figure
. •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -- Figure 4:
The global distribution pattern of fossil subduction remnants along plates sutured boundaries. 6: Schematic sketch of the plate interface in subduction setting, according to present understanding. 9: Simple sketch showing the relationship between main contacts and tectonic units in the South Tianshan Orogen and adjacent region. 10: Geological map of the Southwestern Tianshan HP/UHP metamorphic belt (STMB). . 11: Brief geological map of the AMC, with emphasizing the finding of key lithologies and coesite.

••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --
••••••••••••••••••••••••••••••••••••••••• -- Figure
••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --
••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -- Figure
••••••••••••••••••••••••••••• -- Figure
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -- Figure
••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -- Figure 12:
The collection of the protolith feature of samples of previous works. --Figure 13: The compilation of previous P-T estimates for diverse lithologies in the STMB.

•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -- Figure 14:
The compilation of regional age reports. 16: Simplified geological map of (a) the Chinese Western Tianshan and (b) close-up map for the area. 21: Thin-section scale shear senses in eclogite and greenschist facies for the UHP eclogite and its meta-volcano-sedimentary host-rock, respectively. [START_REF] Sun | Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes[END_REF]) REE abundances of the various zircon (a) and garnet domains (b). 30: Sketch depicting the petrologic evolution of mineral growth within metabasalts and inferred mobility of elements (mainly REEs) within the garnet-zirconmatrix metamorphic system during subduction and exhumation. 31: Previous radiometric data (see Table 2) and results from this study place constraints on the main tectonic stages for the area. 32: Simplified geodynamic cartoon setting back the studied samples and the overall time constraints inferred from this study within the evolution of the Chinese Southwestern Tianshan HP-UHP/LT metamorphic belt. 34: Rutile armored by sphene in both omphacite matrix (a, b) and later stage retrograde-growth quartz (c, d) 35: Rb vs K, Nb/U vs U, K/Th vs Ba/Th and Ba/Nb vs U/Nb diagrams [START_REF] Bebout | Metamorphic chemical geodynamics of subduction zones[END_REF][START_REF] Bebout | Metasomatism in Subduction Zones of Subducted Oceanic Slabs, Mantle Wedges, and the Slab-Mantle Interface[END_REF] for discriminating between LILE enrichment by metamorphism and seafloor alteration. 38: Key features of the specific garnet zoning investigated here, examplified by garnet A1. 43: Simplified sketches depicting the impact of diffusion-controlled garnet growth (here during a transient thermal pulse 44: Tentative interpretation of the thermal excursion in terms of rock dynamics along a cold subduction plate interface.

•••••••••••••••••••••••••••••••••• -- Figure 15: Sampling location of this thesis in the AMC. ••••••••••••••••••••••••••••• -- Figure
••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --
••••••••••••••••••••••••••••••• -- Figure 19: Whole-rock discrimination diagrams for the samples. •••••••••••••••••• --
••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -- Figure
••••••••• --
••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -70 -
••••••••••••••••••••••••••••••••••••••••••••••••••••• -75 - Figure 24: Chondrite-normalized
•••••••••••••••••••••••••••••••••••••••••••••• -78 -
••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -79 -
••••••••••••••••••••••••••••••••••••••••••• -90 - Figure
••••••••••••••••••• -91 - Figure
••••••••••••••••••••••••••••••••••• -92 - Figure
••••••••••••••••••••••••••••• -93 - Figure 33: BSE imaging of mineral inclusion distribution in the studied garnet porphyroblast. •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -103 - Figure
.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -103 - Figure
••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -104 -
•••••••••••••••••••••••••••••••••••••••••••• -104 -
••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -107 - Figure
••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -109 -
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --
••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -- Figure
). ••••••••••••••••••••••••••••••••••••••• -- Figure
•••••••••••••••••••••••••••••••••••••••••••••••• --
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -- Figure 47:
The Ca, Mg and Mn mapping as well as corresponding compositional profiles of the rest of investigated garnet grains. 48: Systematic garnet size survey. The three main groups and estimated mineral modes (vol %) for investigated UHP eclogite samples are shown. 49: Polynomial fitting for estimating effective bulk rock compositions during garnet growth (and uptake of major elements, HREEs and Y).

•••••••••••••••••••••••••••••••••••••• -- Figure
••••••••••••••••• -- Figure
••••••••••••••••••••• --
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --
••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -- Figure 54: (a)
The structural sketch showing the extension on E-W of the revised AMC, with (b, c) the detail data of field structural measurements for the schistosity and lineation. 58: Mineral plots of compositions determined with the electron probe microanalysis.

•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --
••••••••••••••••••• --
•••••••••••••••••••••••••••••••••••••••••••••••••••••••• -- Figure
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --
Figure 59: P-T plot showing the results of our P-T estimates using THERMOCALC [START_REF] Holland | An enlarged and updated internally consistent thermodynamic dataset with uncertainties and correlations: the system K2O-Na2O-CaO-MgO-MnO-FeO-Fe2O3-Al2O3-TiO2-SiO2-C-H2-O2[END_REF] together with estimates of metamorphic temperature by the Raman spectroscopy of carbonaceous material (RSCM, [START_REF] Beyssac | Raman spectra of carbonaceous material in metasediments: A new geothermometer[END_REF][START_REF] Beyssac | Thermal metamorphism in the lesser Himalaya of Nepal determined from Raman spectroscopy of carbonaceous material[END_REF] and Ti-in-biotite geothermometry [START_REF] Henry | The Ti-saturation surface for lowto-medium pressure metapelitic biotites: Implications for geothermometry and Tisubstitution mechanisms[END_REF] 60: (a) Radiometric ages obtained for all samples, with respect to respective localities on Kebuerte section. b,c,d) The compilation of regional age reports with respect to sampling localities (ages versus latitude). Ages reported in key valleys are listed respectively from the top to bottom. 63: Panoramic views of the main north and south contacts in between the AMC and the SCTSZ mylonitized shear zone (GS1, GS2). 67: The phengite 40 Ar-39 Ar step-heating results of regional GS to lower BS facies samples (J2, 22, 157 and 147), and the LA-ICP-MS zircon U-Pb radiometric results of meta-basite sample (158) 71: Major elements composition of selected samples in this PhD thesis and those from previous works. 72: P-T-density pesudosections conducted for representative compositions of metavolcanoclsatics (regional and global) 73: P-T-density pesudosections conducted for representative compositions of regional eclogitie, blueschist and serpentinite. [START_REF] Su | U-Pb zircon geochronology of Tianshan eclogites in NW China: implication for the collision between the Yili and Tarim blocks of the southwestern Altaids[END_REF].

.••••••••••••••• -191 - Figure
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -202 -
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -206 - Figure
•••••••••••••••••••••••••••••••• -211 -
•••••••••••••• -214 - Figure
. •••••••••••••••••••••••••••••••••••••••••••••••••••• -215 -
••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -216 -
••••••••••••••••••••••••• -219 - Figure
••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -221 - Figure
••••••••••••••••••••••••••••••••••••••••••••• -224 - Figure
•••••••••••••••••••••••••••••••••••••••• -224 -
worldwide and repeatedly impact half of the world's population living on top or nearby one of them.

Subduction earthquakes were first tied to the plate tectonics theory by [START_REF] Mckenzie | The North Pacific: an example of tectonics on a sphere[END_REF], following up on the imagination and observations from the paper "Die Entstehung der Kontinente" of [START_REF] Wegener | Die Entstehung der Kontinente[END_REF], which proposed that the surface of Earth is covered by large, rigid mosaic-like continents that move relative to each other causing tectonic activity at their boundaries. In the zone of convergence one plate is dragged down or overridden by another one along the subduction zone, namely at the junction of two plates (Figure 2). The first models of asymmetrical subduction zones were soon after proposed by [START_REF] Dewey | Mountain belts and the new global tectonics[END_REF], who described them as the direct result of lateral buoyancy contrasts between convergent plates and [START_REF] Wilson | Mantle plumes and plate motions[END_REF] introduced the direct correlation between subduction zones and seismicity, pointing out the earthquake generation in correspondence to the plates' interface. Famous examples of devastating earthquakes in active subduction zones include are Tohoku in 2011 (M~9.0; [START_REF] Simons | The 2011 magnitude 9.0 Tohoku-Oki earthquake: Mosaicking the megathrust from seconds to centuries[END_REF]), Alaska in 1964 (M~9.4;[START_REF] Plafker | Tectonic Deformation Associated with the 1964 Alaska Earthqiake[END_REF] and the 1960 Valdivia earthquake (considered the most powerful earthquake ever recorded, with M~9.5; [START_REF] Moreno | Impact of megathrust geometry on inversion of coseismic slip from geodetic data: Application to the 1960 Chile earthquake[END_REF].

Fossil Subduction Remnants: An Ideal Target?

Subduction zones are almost inaccessible to direct observation (even the ongoing NantroSeize drilling project will reach no deeper than ~7 km) and, as a result, the nature, structure and properties of the plate interface are still largely unknown. Even if the developing geophysical data acquisition technology (e.g., tomography), to some (Engdahl et al., 1998). Red lines show the surface projection of each section. The base of each section is the core-mantle boundary (CMB); dashed lines show the location of mantle discontinuities at 410, 660, and 1700 km. Red and blue colors in each section denote regions where the P wave velocities are relatively slow and fast, respectively, compared to average mantle at the same depth. (b) P wave velocity structure across the Cascadia Subduction zone depicting the structure and the expected depth for typical seismic events in subduction zones.

extent, shed a light on the deep structure of subduction zone down to mantle depth, instrumental uncertainties within the range of several hundred meters to a few kilometers indeed affect the relocation of earthquake hypocenter, with depth even more poorly constrained than the epicenter [START_REF] Kuge | Rupture characteristics of the 2005 Tarapaca, northern Chile, intermediate-depth earthquake: Evidence for heterogeneous fluid distribution across the subducting oceanic plate?[END_REF][START_REF] Waldhauser | Large-scale relocation of two decades of Northern California seismicity using cross-correlation and double-difference methods[END_REF].

Alternatively, one can use former subducted materials, ultimately exhumed to the surface along fossil subduction/suture zones [START_REF] Agard | Exhumation of oceanic blueschists and eclogites in subduction zones: timing and mechanisms[END_REF][START_REF] Agard | The subduction plate interface: Rock record and mechanical coupling (from long to short time scales)[END_REF], to track both chemical and mechanical processes operating along the subduction interface [START_REF] Ague | Carbon dioxide released from subduction zones by fluid-mediated reactions[END_REF][START_REF] Angiboust | Eclogite breccias in a subducted ophiolite: A record of intermediate-depth earthquakes?[END_REF][START_REF] Gao | Mobilization of Ti-Nb-Ta during subduction: Evidence from rutile-bearing dehydration segregations and veins hosted in eclogite, Tianshan, NW China[END_REF][START_REF] John | Generation of intermediate-depth earthquakes by self-localizing thermal runaway[END_REF][START_REF] Li | Fluid-mediated metal transport in subduction zones and its link to arc-related giant ore deposits: Constraints from a sulfide-bearing HP vein in lawsonite eclogite (Tianshan, China)[END_REF][START_REF] Sverjensky | Important role for organic carbon in subduction-zone fluids in the deep carbon cycle[END_REF], even deep to > 150 km depth [START_REF] Ye | The possible subduction of continental material to depths greater than 200 km[END_REF].

However, the interplay between fluids, rheology and seismicity, and the way they impact mechanical coupling along the interface, earthquake triggering and/or overall subduction dynamics is still largely circumstantial. Besides, the mechanisms and processes accounting for (i) the exhumation of dense oceanic (ultra-) high pressure low temperature (UHP/HP-LT) rocks that are negatively buoyant with respect to te surrounding mantle (unlike the relatively lighter continental material, sedimentary rocks or serpentinites) and are commonly irreversibly buried, and (ii) the juxtaposition of HP and UHP tectonic slices on exhumation are still to some extent perplexing [START_REF] Agard | The subduction plate interface: Rock record and mechanical coupling (from long to short time scales)[END_REF][START_REF] Agard | Exhumation of oceanic blueschists and eclogites in subduction zones: timing and mechanisms[END_REF][START_REF] Burov | Mechanisms of continental subduction and exhumation of HP and UHP rocks[END_REF][START_REF] Chen | Exhumation of oceanic eclogites: thermodynamic constraints onpressure, temperature, bulk composition and density[END_REF][START_REF] Gerya | Exhumation of high-pressure metamorphic rocks in a subduction channel: A numerical simulation[END_REF]Guillot et al., 2009;Warren, 2013;Warren et al., 2008). It is thus important to retrieve information from exhumed, fossil fragments of subduction plate interface through field investigations. Well-exposed, typical fossil subduction remnants preserving a pristine tectonic and/or mineralogical record are extremely rare within former suture zones, particularly those recording deep subduction of oceanic crust (down to 70~100km).

A compilation of worldwide key HP/UHP fossil subduction remnants is presented in Figure 4 with grouping strategies based on index minerals (i.e., lawsonite, coesite and diamonds) for high or ultra-high pressure metamorphism and peak metamorphic timing. The occurrence of lawsonite in metamorphic rocks outlines typical cold fossil subduction (e.g., [START_REF] Tsujimori | Very-lowtemperature record of the subduction process: A review of worldwide lawsonite eclogites[END_REF][START_REF] Tsujimori | Lawsonite blueschists and lawsonite eclogites as proxies for paleo-subduction zone processes: A review[END_REF]Vitale Brovarone et al., 2014), with metamorphic gradients as low as 5℃ /km, while coesite and diamond (generally as inclusions) are proxies for UHP metamorphism (e.g., [START_REF] Chopin | Coesite and pure pyrope in high-grade blueschists of the Western Alps: a first record and some consequences[END_REF][START_REF] Okay | Coesite from the Dabie Shan eclogites, central China[END_REF][START_REF] Shutong | Diamond from the Dabie Shan metamorphic rocks and its implication for tectonic setting[END_REF][START_REF] Smith | Coesite in clinopyroxene in the Caledonides and its implications for geodynamics[END_REF]. As shown in Figure 4, almost all UHP fossil subduction remnants relate to continental subduction, with exhumation assisted by buoyancy forces following the subduction of light continental crust and/or serpentinite (e.g., W. Alps and Dabieshan; [START_REF] Agard | Exhumation of oceanic blueschists and eclogites in subduction zones: timing and mechanisms[END_REF]Guillot et al., 2015). In contrast, only a few of HP fossil subduction remnants are associated within a metavolcanoclastics-dominated accretionary wedge, with exhumation mechanism yet unknown but possibly related to tectonic thinning/underthrusting/underplating (e.g., analogous but deeper than the Schistes Lustrés, W. Alps. [START_REF] Agard | Exhumation of oceanic blueschists and eclogites in subduction zones: timing and mechanisms[END_REF].

Burial and Recovery of Formerly Subducted Lithologies

Opposite routes characterize burial (i.e., subduction s.s.) and recovery (i.e., detachment and exhumation) of subducted lithologies. Slices of the upper part of the down-going lithosphere make their way back to the surface only at certain time periods and in minor amounts [START_REF] Agard | Exhumation of oceanic blueschists and eclogites in subduction zones: timing and mechanisms[END_REF]Guillot et al., 2009;Warren, 2013). These fragments can be relatively complete sections of oceanic lithosphere (i.e., seafloor sediments, basalts, gabbros and serpentinized peridotite; e.g., Monviso/Zermatt-Saas, W.Alps), oceanic and/or terrigenous sediments offscraped from the accretionary wedge (e.g., Schistes Lustrés, W.Alps; Franciscan complex, California), detrital material basally eroded from the upper plate (e.g., [START_REF] Cloos | Shear-zone thickness and the seismicity of Chilean-and Marianas-type subduction zones[END_REF]Vannucchi et al., 2012, 2008) and/or subducted seamounts (e.g., [START_REF] Bassett | Gravity anomalies, crustal structure, and seismicity at subduction zones: 2. Interrelationships between fore-arc structure and seismogenic behavior[END_REF][START_REF] John | Subducted seamounts in an eclogite-facies ophiolite sequence: The Andean Raspas Complex, SW Ecuador[END_REF]. In addition, ashes formed by arc volcanism could be transport over long distance and later incorporated into the trench (e.g., [START_REF] Kutterolf | Pacific offshore record of plinian arc volcanism in Central America: 3. Application to forearc geology[END_REF]. The different subduction types (i.e., accretionary versus erosive, Figure 5) also result in contrasting material supply within wedge or even down to mantle depths, and play a significant role on material recycling [START_REF] Clift | Controls on tectonic accretion versus erosion in subduction zones: Implications for the origin and recycling of the continental crust[END_REF]Cloos andShreve, 1996, 1988).

In contrast (to the burial), the recovery of subducted lithologies is of prerequisite on i) how rock/block/slice can detach from subducting slab and ii) subsequently exhume along the plate interface (Figure 6). On one hand, the detachment is essentially facilitated either by the existence of a décollement layer (i.e., decoupling zone) where the ductile-brittle transition, mechanical coupling (i.e., strain localization and stress accumulation) and/or serpentinization had taken place in oceanic subduction settings (e.g., [START_REF] Agard | Exhumation of oceanic blueschists and eclogites in subduction zones: timing and mechanisms[END_REF][START_REF] Blake | The role of serpentinite melanges in the unroofing of UHPM rocks: An example from the Western Alps of Italy[END_REF]Guillot et al., 2009;[START_REF] Philippot | Deformation processes in eclogitic rocks: evidence for the rheological delamination of the oceanic crust in deeper levels of subduction zones[END_REF][START_REF] Tsujimori | Very-lowtemperature record of the subduction process: A review of worldwide lawsonite eclogites[END_REF], or by the separation of the buoyant upper crust from the denser lithosphere when shearing exceeds the strength of the binding [START_REF] Bassett | Gravity anomalies, crustal structure, and seismicity at subduction zones: 2. Interrelationships between fore-arc structure and seismogenic behavior[END_REF].

force of rocks in continental subduction zones (e.g., Norway; [START_REF] Jolivet | Softening trigerred by eclogitization, the first step toward exhumation during continental subduction[END_REF]. On other hand, a 'weak' channel will be required for the exhumation of HP/UHP lithologies.

Fluid released from subducting slab during progressive metamorphic dehydration could not only facilitate the lubrication of the subduction plane but also assist the formation of low strength minerals (e.g., lawsonite, phengite, antigorite and talc) (Guillot et al., 2009;[START_REF] Stöckhert | Rheology of crustal rocks at ultrahigh pressure[END_REF]. This concept was mainly used to discuss exhumation of rigid mafic blocks wrapped in a soft serpentinite matrix within a serpentinite subduction channel [START_REF] Blake | The role of serpentinite melanges in the unroofing of UHPM rocks: An example from the Western Alps of Italy[END_REF][START_REF] Federico | Ophiolite mélange zone records exhumation in a fossil subduction channel[END_REF][START_REF] Gerya | Exhumation of high-pressure metamorphic rocks in a subduction channel: A numerical simulation[END_REF], but not so much for continental exhumation since their buoyancy is considered sufficient for their return, even from UHP conditions (e.g., [START_REF] Chemenda | A mechanism for syn-collisional rock exhumation and associated normal faulting: Results from physical modelling[END_REF][START_REF] Ernst | Preservation/exhumation of ultrahigh-pressure subduction complexes[END_REF]Guillot et al., 2009).

The recovery (of subducted lithologies) frequently occurs during a ~15 Ma shortlived period in a given subduction zone, as concluded by recent compilations (Agard et al., 2018(Agard et al., , 2009)). This, in fact, suggests that a steady-state regime such as proposed by [START_REF] Platt | The uplift of high-pressure-low-temperature metamorphic rocks[END_REF][START_REF] Platt | Dynamics of orogenic wedges and the uplift of high-pressure metamorphic rocks[END_REF], i.e., underplating coupled with shallow extension that would allow HP rocks to be exhumed to upper crustal levels, is in general not effective since only punctuated exhumation is observed. Moreover, most sedimentary accretionary prisms (reaching about ~20 km depth on average, and exceptionnally ~40-60 km: Chile, [START_REF] Glodny | Internal dynamics of a paleoaccretionary wedge: Insights from combined isotope tectonochronology and sandbox modelling of the South-Central Chilean forearc[END_REF]Cascadia, Hyndman (1995); Schistes Lustrés, [START_REF] Agard | Exhumation of the Schistes Lustrés complex: in situ laser probe 40Ar/39Ar constraints and implications for the Western Alps[END_REF][START_REF] Agard | Tectonometamorphic evolution of the Schistes Lustres Complex; implications for the exhumation of HP and UHP rocks in the Western Alps[END_REF]) are not deep enough to form UHP or even HP rocks (Guillot et al., 2009).

Importantly too, no exhumation of HP/UHP lithologies is happening at present in most subduction zones (e.g., Cascadia), further implying that the exhumation of HP/UHP only take place during potential perturbations of a subduction setting [START_REF] Agard | The subduction plate interface: Rock record and mechanical coupling (from long to short time scales)[END_REF][START_REF] Agard | Exhumation of oceanic blueschists and eclogites in subduction zones: timing and mechanisms[END_REF][START_REF] Agard | Transient, synobduction exhumation of Zagros blueschists inferred from P-T, deformation, time, and kinematic constraints: Implications for Neotethyan wedge dynamics[END_REF], for example in response to a change in slab geometry (i.e., subduction angle and convergence velocity) and/or transient increase in mechanical coupling (e.g., docking of a subducted seamount).

1.4. Using The STMB to probe the plate interface: a fossil, deeply buried and cold package (dominantly) made of metavolcanoclastics Regardless of various subduction types, subducted materials and contrasting exhumation mechanisms, mechanisms and processes responsible for the occasional recovery of ocean-derived HP-UHP/LT metavolcanics/metavolcanoclastics equilibrated along the subduction plate interface are essential to constrain subduction dynamics and gain insights on long-/short-term processes along the plate boundary (Bachmann et al., 2009;Stöckhert, 2012;Agard et al., 2018 and references therein).

The diversity of subducted material ( §1.3) is likely to influence viscosity, density and thus buoyancy, and to control chemical and mechanical behaviors within the plate interface [START_REF] Bebout | Metamorphic chemical geodynamics of subduction zones[END_REF][START_REF] Bebout | Metasomatism in Subduction Zones of Subducted Oceanic Slabs, Mantle Wedges, and the Slab-Mantle Interface[END_REF][START_REF] Yamato | Burial and exhumation in a subduction wedge: Mutual constraints from thermomechanical modeling and natural P-T-t data (Schistes Lustrés, western Alps)[END_REF]Krebs et al., 2011). In particular there is a strong need for 'good' exposures recording plate interface processes in a critical depth range around 80 km, beyond which no deeper oceanic rocks are recovered in general [START_REF] Agard | The subduction plate interface: Rock record and mechanical coupling (from long to short time scales)[END_REF]; the only exception so far is a 10-50 m thick UHP slice in Lago di Cignana from Zermatt-Saas, W.Alps; [START_REF] Frezzotti | Carbonate dissolution during subduction revealed by diamond-bearing rocks from the Alps[END_REF][START_REF] Groppo | The P -T path of the ultra-high pressure Lago Di Cignana and adjoining high-pressure meta-ophiolitic units : insights into the evolution of the subducting Tethyan slab[END_REF] and where geophysicists and modellers infer a change in large-scale mechanical coupling between the plates (e.g., [START_REF] Wada | Common depth of slab-mantle decoupling: Reconciling diversity and uniformity of subduction zones[END_REF][START_REF] Syracuse | The global range of subduction zone thermal models[END_REF][START_REF] Van Keken | Subduction factory: 4. Depth-dependent flux of H2O from subducting slabs worldwide[END_REF].

To document key processes operating in that depth range, the Chinese South Tianshan Metamoprhic Belt (STMB) is a potentially important/exceptional example.

The

STMB is indeed

characterized by an unusually thick (~5 km) pile of well-preserved HP/UHP metavolcanoclastics [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF] wrapping eclogite boudins/slices (e.g., [START_REF] Gao | Formation of HP-LT rocks and their tectonic implications in the western Tianshan Orogen, NW China: Geochemical and age constraints[END_REF], resembling classic accretionary type subduction (e.g., Schistes Lustrés Corsica/W.Alps and Franciscan complex), but still very distinct because of (i) its pervasive coesite findings not only in oceanic metabasites [START_REF] Lü | Petrology of coesite-bearing eclogite from Habutengsu Valley, western Tianshan, NW China and its tectonometamorphic implication[END_REF]Lü and Zhang, 2012) but also in the metavolcanoclastic matrix [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF][START_REF] Yang | Petrology and U-Pb zircon dating of coesite-bearing metapelite from the Kebuerte Valley, Western Tianshan, China[END_REF] and (ii) relatively high peak metamorphic records at ~3.0 GPa (~550˚C; e.g., Wei et al., 2009;[START_REF] Yang | Petrology and U-Pb zircon dating of coesite-bearing metapelite from the Kebuerte Valley, Western Tianshan, China[END_REF][START_REF] Zhang | Forbidden zone" subduction of sediments to 150 km depth -The reaction of dolomite to magnesite + aragonite in the UHPM metapelites from western Tianshan, China[END_REF]. To explain its recovery, the SMTB both lacks significant serpentinite exposures (<<5 vol%; [START_REF] Li | Petrology of rodingite derived from eclogite in western Tianshan[END_REF]; see §2), making the existence of a serpentinite channel unlikely, and evidence for continental subduction (i.e., coesite/diamond gneisses ± felsic amphibolites ± garnet-bearing peridotites, such as in Dora Maira, Dabie-Sulu, or Kokchetav; Guillot et al., 2009), although it was recently tentatively proposed for the STMB [START_REF] Loury | Tectonometamorphic evolution of the Atbashi highpressure units (Kyrgyz CAOB, Tien Shan): implications for the closure of the Turkestan Ocean and continental subduction-exhumation of the South Kazakh continental margin[END_REF]. When set back against the global compilation (e.g., [START_REF] Agard | The subduction plate interface: Rock record and mechanical coupling (from long to short time scales)[END_REF][START_REF] Agard | Exhumation of oceanic blueschists and eclogites in subduction zones: timing and mechanisms[END_REF]Guillot et al., 2009), the STMB sits somewhere in the middle in terms of P-T record and lithological composition, between accretionary-/serpentinite-types and continental-type subduction (Figure 7).

Overall, the pervasively coesite-bearing metavolcanoclastics-dominated STMB may serve as a nicely preserved remnant in the right depth range (~80km depth) to address questions regarding material rheology/viscosity, fluid-rock interactions and deformation (i.e., stress accumulation & strain localization). This PhD thesis focuses on the following ones:

1) why is it so thick so deep, and what can we learn from this 'exceptional' example across a depth range critical for mechanical coupling (~80 km; [START_REF] Syracuse | The global range of subduction zone thermal models[END_REF][START_REF] Wada | Common depth of slab-mantle decoupling: Reconciling diversity and uniformity of subduction zones[END_REF]?

2) How well constrained are processes occurring at such depth?

3) What is the role of coupling-decoupling mechanisms on the rock recovery at such depth?

4) Are we able to track short-lived processes within the plate interface? So far, despite numerous studies providing detailed petrological, geochemical evolutions, fluid activity or geochronology data (e.g., [START_REF] Gao | Mobilization of Ti-Nb-Ta during subduction: Evidence from rutile-bearing dehydration segregations and veins hosted in eclogite, Tianshan, NW China[END_REF][START_REF] John | Trace-element mobilization in slabs due to non steady-state fluid-rock interaction: constraints from an eclogite-facies transport vein in blueschist (Tianshan, China)[END_REF][START_REF] Klemd | Changes in dip of subducted slabs at depth: Petrological and geochronological evidence from HP-UHP rocks (Tianshan, NW-China)[END_REF]Meyer et al., 2016;[START_REF] Van Der Straaten | Tracing the effects of high-pressure metasomatic fluids and seawater alteration in blueschist-facies overprinted eclogites: Implications for subduction channel processes[END_REF] from the STMB, especially in the Akeyazi metamorphic complex (AMC, Figure 11), contrasting hypotheses still exist on i) the fundamental architecture of the SMTB, i.e. internal structures and tectonic evolution (HP/UHP mélange versus HP-UHP sub-belts; [START_REF] Klemd | Changes in dip of subducted slabs at depth: Petrological and geochronological evidence from HP-UHP rocks (Tianshan, NW-China)[END_REF]Li et al., 2016;Lü et al., 2012) and ii) the timing of peak metamorphism and of ocean basin closure (i.e., Triassic versus Late Carboniferous; [START_REF] Su | U-Pb zircon geochronology of Tianshan eclogites in NW China: implication for the collision between the Yili and Tarim blocks of the southwestern Altaids[END_REF]Zhang et al., 2007). In order to refine our understanding of the overall architecture and evolution of the STMB (which, incidentally, is a prerequisite for any further study of deep subduction processes; e.g., fluid-rock interaction), more local and specific questions will be addressed in this PhD thesis:

1) Can we refine the architecture and deformation pattern of the STMB?

2)

Can we assess the P-T conditions in a more evenly distributed way (i.e., P-T mapping)?

3) When do HP/UHP rocks detach from the slab, and is this happening continuously or at specific times?

4)

Can we get an idea about how these tectonic slices were assembled (or 'mélanged')?

5)

When did the Paleo South Tianshan ocean basin close? a general integration of the results and discuss their implications for subduction dynamics and for regional scale tectonics.

Structure of the Thesis

Geological Setting of the STMB

Geological Background

The Chinese Southwestern Tianshan high-to ultrahigh-pressure low-temperature (HP/UHP-LT) accretionary complex constitutes the eastern part of the Kazakhstan collage system [START_REF] Gao | Large-scale porphyry-type mineralization in the Central Asian metallogenic domain: A review[END_REF]; and references therein) within the Altaids (also called the Central Asian Orogenic Belt; Figure 8). It extends for about 200 km along the Southwestern Central Tianshan Suture Zone (SCTSZ, Figure 9), and correlates with the Atbashi (Hegner et al., 2010;[START_REF] Loury | Tectonometamorphic evolution of the Atbashi highpressure units (Kyrgyz CAOB, Tien Shan): implications for the closure of the Turkestan Ocean and continental subduction-exhumation of the South Kazakh continental margin[END_REF][START_REF] Simonov | Conditions of formation of the Atbashi Ridge eclogites (South Tien Shan)[END_REF], Chatkal [START_REF] Loury | Late Paleozoic evolution of the South Tien Shan: Insights from P -T estimates and allanite geochronology on retrogressed eclogites (Chatkal range, Kyrgyzstan)[END_REF][START_REF] Mühlberg | Late Carboniferous high-pressure metamorphism of the Kassan Metamorphic Complex (Kyrgyz Tianshan) and assembly of the SW Central Asian Orogenic Belt[END_REF] and Fan-Karategin (U)HP metamorphic complexes [START_REF] Volkova | Geochemical discrimination of metabasalt rocks of the Fan-Karategin transitional blueschist/greenschist belt, South Tianshan, Tajikistan: seamount volcanism and accretionary tectonics[END_REF] in the Kyrgyzstan part of the South Tianshan Orogenic Belt (STOB). The SCTSZ bounds to the north the Chinese section of the HP-UHP/LT metamorphic complex, known as the Akeyazi metamorphic complex (AMC, Figure 10). This contact, now a ~0.5 km-wide dextral strike-slip shear zone, was active from the Early Permian to Early Triassic [START_REF] Gao | but not systematically[END_REF][START_REF] Laurent-Charvet | Late Paleozoic strike-slip shear zones in eastern central Asia (NW China): New structural and geochronological data[END_REF].

To the north lies a LP-HT Palaeozoic active continental margin [START_REF] Allen | Palaeozoic collisional tectonics and magmatism of the Chinese Tien Shan[END_REF]Gao et al., 1998;[START_REF] Klemd | Metamorphic evolution of (ultra)-highpressure subduction-related transient crust in the South Tianshan Orogen (Central Asian Orogenic Belt): Geodynamic implications[END_REF], mainly made of amphibole-and granulite-facies rocks, along with Late Silurian and Early Carboniferous continental arc-type volcanic, volcaniclastic rocks and granitoids (Gao et al., 2009a;Xia et al., 2014). To the south the AMC is overlain by unmetamorphosed and/or low grade Palaeozoic sedimentary strata, which also represent the northern, passive continental margin of the Tarim plate (Carroll et al., 1995).

The Akeyazi Metamorphic Complex

The AMC is predominantly composed of strongly schistosed metavolcanoclastics hosting mafic metavolcanics as pods, lenses, boudins, thin layers (Figure 11a) or massive blocks (Figure 11b; [START_REF] Gao | but not systematically[END_REF] and marble horizons [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF], as well as very rare ultramafic rocks (Li et al., 2010;[START_REF] Shen | UHP metamorphism documented in Ti-chondrodite-and Ti-clinohumite-bearing serpentinized ultramafic rocks from Chinese southwestern Tianshan[END_REF]. Some well-preserved pillow-shape eclogitic meta-basalts were also identified (Figure 11c).

Whole-rock geochemical data for the mafic metavolcanics suggest oceanic basalt or arc-related affinities [START_REF] Gao | but not systematically[END_REF][START_REF] John | Trace-element mobilization in slabs due to non steady-state fluid-rock interaction: constraints from an eclogite-facies transport vein in blueschist (Tianshan, China)[END_REF]Liu et al., 2014;Meyer et al., 2016;[START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF] while the metavolcanoclastics have characteristics similar to upper continental crust and trench sediments (Liu et al., 2014;Meyer et al., 2016;[START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF] (Figure 12).

Previous work mostly focused on individual HP/UHP rocks/outcrops for the reconstruction of P-T-(time) histories (e.g., Li et al., 2016;Lü et al., 2012;[START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF], fluid-rock interaction processes and/or geochemical budgets (e.g., Beinlich et al [START_REF] Ganguly | Cation Diffusion Kinetics in Aluminosilicate Garnets and Geological Applications[END_REF][START_REF] John | Volcanic arcs fed by rapid pulsed fluid flow through subducting slabs[END_REF][START_REF] Van Der Straaten | Blueschist-facies rehydration of eclogites (Tian Shan, NW-China): Implications for fluid-rock interaction in the subduction channel[END_REF]. The compilation of regional P-T (-time) constraints (Figure 13; also see [START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF] indicates that most peak metamorphic estimates for eclogite and prograde blueschist yield eclogite facies (EC facies) HP-LT conditions within the range 480-580°C and 1.5-3.0 GPa. A range of P- T conditions ~450-570°C at 2.7-3.3 GPa was obtained for some EC facies metavolcanoclastics (Figure 13). Evidence for UHP metamorphism comes from both coesite relics in garnet (from several localities: stars in Figure 11) and thermodynamic calculation. The spread of regional P-T estimates (Figure 13a, Table 1), whatever the lithologies, could a priori arise from contrasting assumptions for thermodynamic modeling (e.g., difficulties in determining effective bulk rock composition and Fe 3+ content and/or assessing H2O activity) or from the complexity of metamorphic evolutions in individual HP-UHP tectonic slices [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF].

The exhaustive compilation of age data (Figure 14a, Table 2), and the comparison of previous age data versus their assessed Pmax estimates (Figure 14b, c), evidence a considerable spread in ages too, with an overlap between eclogite and blueschist ages, whatever the protolith. The timing of peak metamorphic conditions falls in the range 325-305 Ma (Figure 14c). Garnet growth by multi-point Lu-Hf isochron was dated at ca. 315 Ma [START_REF] Klemd | Changes in dip of subducted slabs at depth: Petrological and geochronological evidence from HP-UHP rocks (Tianshan, NW-China)[END_REF], for both eclogites and blueschists from a variety of valleys within AMC. U-Pb SIMS ages from metamorphic zircon rims in eclogites are indistinguishable within error, at 319 ± 3 Ma and 321 ± 2 Ma (Liu et al., 2014;Su et al., 2010) and similar to a U-Pb age of 318 ± 7 Ma obtained for eclogite-facies rutile [START_REF] Li | SIMS U-Pb rutile age of low-temperature eclogites from southwestern Chinese Tianshan, NW China[END_REF]. Du et al. (2014) also reported a suite of relative consistent Sm-Nd isochron ages of 309 ± 4.6 M, 306 ± 15 Ma and 305 ± 11 Ma for eclogites from the Habutengsu river (Fig. 1b). An age of 317 ± 5 Ma was obtained on high-pressure veins crosscutting a blueschist wall-rock, interpreted as the prograde dehydration-related transformation of blueschist to eclogite (Rb-Sr multi-point isochron; [START_REF] John | Volcanic arcs fed by rapid pulsed fluid flow through subducting slabs[END_REF].

Recent Sm-Nd and Lu-Hf isochron ages of 318.4 ± 3.9 Ma and 326.9 ± 2.9 Ma on blueschists (Soldner et al., 2017) were interpreted as peak eclogite-facies and prograde metamorphism, respectively. Post-peak cooling was constrained by white mica K-Ar, Ar-Ar and Rb-Sr ages at around 310 Ma [START_REF] Klemd | New Age Constraints on the Metamorphic Evolution of the High-Pressure/Low-Temperature Belt in the Western Tianshan Mountains, NW China[END_REF]. Ages < 280 Ma or > than ~325 Ma were considered by most authors as resulting from limitations of isotopic dating (e.g. excess Ar in Ar-Ar system; Nd disequilibrium in Sm-Nd system; difficulties to relate zircon U-Pb ages to metamorphic stages) or taken as evidence for distinct HP-UHP episodes. S1.

detailed P-T-time-isotopic studies; ii) representative lithologies with interesting mineral zonation were also chosen for in-depth investigation; iii) ~20 samples with relative clear senses of shear, and representative in terms of lithologies and sampling locations along the ~ 30km transect, were selected for P-T-in situ Ar-Ar probingdeformation mapping. [START_REF] Qian | Petrogenesis and tectonic settings of Carboniferous volcanic rocks from north Zhaosu, western Tianshan Mountains: constraints from petrology and geochemistry[END_REF]. Relative standard deviations (RSD) are within ±10% for most trace elements but reach ±20% for V, Cr, Co, Ni, Th and U according to analyses of rock standards.

Mineral Major and Trace Elements

Major element compositions of minerals and relevant mapping ( §4, 5, 6) were obtained from polished thin sections by electron microprobe analyses at IGGCAS with JEOL JXA 8100 and ISTeP with CAMECA SX Five. Quantitative analyses were performed using wavelength dispersive spectrometers with an acceleration voltage of 15 kV, a beam current of 15 nA, a 3 μm beam size and 30 s counting time. Natural minerals and synthetic oxides were used as standards, and a program based on the ZAF procedure was used for data correction.

Concentrations of Zirconium in rutile ( §5) were determined by electro microprobe following the method outlined by [START_REF] Zack | Temperature dependence of Zr in rutile: empirical calibration of a rutile thermometer[END_REF]. All analyses were conducted with a CAMECA SX Five in ISTeP, Sorbonne Université, France. EMPA conditions were optimised specifically for Zr so that detect limitation could be improved by four times (20 µg/g compared with 80 µg/g). Acceleration voltage was set at 20 kV with 120 nA beam current and 5 µm beam diameter. A H-type spectrometer was chosen for measuring Zr-Lα because of its highest sensitivity for this element. Detailed settings for spectrometers followed the Table . 2 of [START_REF] Zack | Temperature dependence of Zr in rutile: empirical calibration of a rutile thermometer[END_REF]. Every 10 analyses of unknown rutile were bracketed by 2 analyses of synthetic rutile standard for true zeroconcentration count rates on the peaks and to exclude any machine drift.

In situ trace element point and profile analyses of zoned garnet, zircon and associated matrix mineral were performed by LA-ICP-MS at IGGCAS with a single collector quadrupole Agilent 7500a ICM-MS, equipped with an UP193Fx argon fluoride New Wave Research Excimer laser ablation system. Glass reference material NIST SRM 610 and NIST SRM 612 were used as standards for external calibration.

LA-ICP-MS measurements were conducted using a spot size diameter of 60 μm with a laser frequency of 15 Hz and 0.63 GW/cm 2 and a fluence of 3.32 J/cm 2 . Acquisition time was 20 s for the background and 120 s for the mineral analyses. The relevant element content of minerals determined by EMPA was used as internal standards.

Reproducibility and accuracy, which were determined for NIST SRM 610 and NIST SRM 612, are usually < 8% and < 6%. Trace element concentrations were then calculated using GLITTER Version 3 [START_REF] Van Achterbergh | GLITTER: On-line interactive data reduction for the laser ablation inductively coupled plasma mass spectrometry microprobe[END_REF].

Zircon Oxygen Isotope

Oxygen isotope analyses ( §4) at the exact locations of U-Pb isotope zircon were also processed with the use of the Cameca IMS-1280 SIMS at IGGCAS. After U-Pb dating, the mount was carefully repolished for the O isotope analyses. The Gaussian focused Cs+ ions are used as a primary beam to sputter zircon for O-isotope analyses.

The primary beam size is ~10 µm in diameter, and 2.

P-T Constraints

Perple_X Pseudosection Modeling

Pseudosection modeling ( §4, 5) was performed in the system MnNCKFMASHTO for key metavolcanic eclogite samples (No. 11AT06, §4) with excess SiO2 (i.e., quartz or coesite), for either P-T estimates or investigation of mineral mode evolution. TiO2 must be considered due to the presence of rutile and/or titanite in the matrix or as inclusions in porphyroblasts. The fluid phase in assumed to be pure H2O and was set in excess or specific aH2O value. CO2 was neglected as only small amounts of carbonate occur as thin secondary veins. Fe2O3 was set at fixed ratio of total FeO according to XRF data.

In order to take into account the sequestration of elements induced by the growth zoning of garnet porphyroblast, effective bulk compositions were adjusted from XRF compositions by removing part of the garnet modal abundance, following the method of Carson et al. (1999). For the modelling of prograde and peak conditions, half of the modal abundance of zoned garnet (e.g., [START_REF] Warren | Oxidized eclogites and garnet-blueschists from Oman: P-T path modelling in the NCFMASHO system[END_REF]Wei et al., 2009) was removed from the XRF composition. For the retrograde path, the entire fractionated composition by garnet porphyroblasts were subtracted from the bulk-rock composition.

The P-T pseudosections were calculated using the software Perple_X 6.68 [START_REF] Connolly | Computation of phase equilibria by linear programming: a tool for geodynamic modeling and its application to subduction zone decarbonation[END_REF][START_REF] Connolly | Multivariable phase diagrams; an algorithm based on generalized thermodynamics[END_REF]) and an internally consistent thermodynamic dataset (hp02ver.dat or hp04ver.dat; [START_REF] Connolly | Metamorphic controls on seismic velocity of subducted oceanic crust at 100-250 km depth[END_REF]Holland and Powell, 2003) based on the effective recalculated bulk rock composition. Mineral solid-solution models are Gt(HP) for garnet [START_REF] Holland | An internally consistent thermodynamic data set for phases of petrological interest[END_REF], Omph(GHP) for omphacite (Green et al., 2007), Amph (DP) for amphibole [START_REF] Diener | A new thermodynamic model for clino-and orthoamphiboles in the system Na2O-CaO-FeO-MgO-Al2O3-SiO2-H2O-O[END_REF], Mica(CHA) for white mica (Coggon and Holland, 2002), Chl(HP) for chlorite [START_REF] Holland | An internally consistent thermodynamic data set for phases of petrological interest[END_REF], Ep(HP) for epidote/clinozoisite [START_REF] Holland | An internally consistent thermodynamic data set for phases of petrological interest[END_REF], and H2O-CO2 fluid solution model is from [START_REF] Connolly | Petrogenetic grids for metacarbonate rocks: pressure-temperature phase-diagram projection for mixed-volatile systems[END_REF]. P-T conditions were further constrained by comparing predicted garnet end-member isopleths with measured garnet compositions and incorporate typical uncertainties on EMPA analyses (ca. 3% to 5%; [START_REF] Lifshin | Minimizing Errors in Electron Microprobe Analysis[END_REF]Williams and Jercinovic, 2006).

THERMOCALC Multi-equilibrium Average PT

THERMOCALC multi-equilibrium average PT calculations ( §6) were conducted for metavolcanoclastics/metavolcanics for the regional P-T-time mapping.

The internally consistent thermodynamic dataset (tc-ds55) of [START_REF] Holland | An internally consistent thermodynamic data set for phases of petrological interest[END_REF] and the program THERMOCALC v3.33 (Holland andPowell, 1998, 1990) were applied for multi-equilibrium P-T estimates. Recalculation of the analyses (e.g., the calculations of Fe 3+ and mineral end-member activities) was performed with the program AX of Holland and Powell (ftp://www.esc.cam.ac.uk/pub/minp/AX/). Only P-T estimates, which satisfies the equilibrium test criteria (e.g., sigfit, hat [START_REF] Holland | An internally consistent thermodynamic data set for phases of petrological interest[END_REF], have been considered. The accuracy of P-T estimates, as predicted by the error ellipse parameters, is generally on the order of 0.05-0.2GPa for pressure and 10-30°C for temperature. Some end-members merely present in small amounts (e.g., Fe-celadonite/celadonite for some phengite), which yield a large uncertainty on the results, were removed during calculation.

Zr-in-Rutile Thermometry

Diffusion of Zr in rutile generally depends on both oxygen fugacity and temperature, via interstitial tetravalent ion migration [START_REF] Sasaki | Tracer impurity diffusion in single-crystal rutile (TiO2-x)[END_REF]. [START_REF] Zack | Temperature dependence of Zr in rutile: empirical calibration of a rutile thermometer[END_REF][START_REF] Zack | Trace element abundances in rutiles from eclogites and associated garnet mica schists[END_REF] with A = 7.420 ± 0.105 and B = -4530 ± 111. The activity of the quartz was assumed =1, as quartz was always present in most of our samples. in which P is in kbar and R is the gas constant, 0.0083144 kJ/K.

Raman Spectrometry Carbonaceous Material Thermometry (RSCM)

The Raman spectroscopy of carbonaceous material (RSCM, [START_REF] Beyssac | Raman spectra of carbonaceous material in metasediments: A new geothermometer[END_REF] is applied here ( §6) as the independent peak temperature estimate to be compared with those from THERMOCALC. It was calibrated as a geothermometer (±50°C) in the range 330-650°C. Relative, intersample uncertainties on temperature can be much smaller, around 10-15°C [START_REF] Beyssac | Thermal metamorphism in the lesser Himalaya of Nepal determined from Raman spectroscopy of carbonaceous material[END_REF]. Since the degree of organization of the carbonaceous material is irreversible, temperatures deduced from the Raman spectra represent peak temperature conditions reached by the rocks. RSCM was done on thin sections of graphite-bearing metavolcanoclasts oriented perpendicular to the foliation by focusing the laser beam beneath a transparent crystal. Raman spectra were obtained with a Renishaw INVIA Reflex Raman microspectrometer at the Laboratoire de Géologie of the Ecole Normale Supérieure, France. Spectra were excited at room temperature with the 514.5 nm line of a 20 mW Ar Spectra Physics laser through a LEICA 100X objective (NA 0.90). Detail procedure of analysis follows that of [START_REF] Agard | Transient, synobduction exhumation of Zagros blueschists inferred from P-T, deformation, time, and kinematic constraints: Implications for Neotethyan wedge dynamics[END_REF]. We recorded at least 13 spectra for each sample to take into account the CM heterogeneities. The program Peak Fit 4.0 was then used to process the spectra.

Ti-in-Biotite Thermometry

An empirical Ti-in-biotite geothermometer [START_REF] Henry | The Ti-saturation surface for lowto-medium pressure metapelitic biotites: Implications for geothermometry and Tisubstitution mechanisms[END_REF] is also used here ( §6) to serve as the independent temperature estimates for regional GS facies metamorphism recorded by biotite-bearing metavolcanoclasts. It was calibrated from rocks equilibrated at roughly 0.4-0.6GPa and 480-800°C with composition range of XMg = 0.275-1.000 and Ti = 0.04-0.60 apfu. Precision of the Ti-in-biotite thermometer is estimated to be ±24°C at the lower temperature range and improves to ±12 °C at higher temperatures. the Cameca IMS-1280 SIMS. U-Th-Pb ratios and absolute abundances were determined relative to the standard zircon 91500 [START_REF] Wiedenbeck | Three natural zircon standards for U-Th-Pb, Lu-Hf, trace element and REE analyses[END_REF], analyses of which were interspersed with those of unknown grains, using operating and data processing procedures similar to those described by Li et al. (2009). A long-term uncertainty of 1.5% (1 RSD) for 206 Pb/ 238 U measurements of the standard zircons was propagated to the unknowns (Q.-L. Li et al., 2010) despite that the measured 206 Pb/ 238 U error in a specific session is generally around 1% (1 RSD) or less. Measured compositions were corrected for common Pb using non-radiogenic 204 Pb. Further details on instrument parameters, analytical method, calibration and correction procedures can be found in Li et al. (2010).

Radiometric Constraints

The U-Pb dating and trace element analysis of zircon grains in metabasite (No. 158, §6) was simultaneously conducted by LA-ICP-MS at the Wuhan SampleSolution Analytical Technology Co., Ltd., China. Detailed operating conditions for the laser ablation system and the ICP-MS instrument and data reduction are the same as description by [START_REF] Zong | The assembly of Rodinia: The correlation of early Neoproterozoic (ca. 900 Ma) high-grade metamorphism and continental arc formation in the southern Beishan Orogen, southern Central Asian Orogenic Belt (CAOB)[END_REF]. Laser sampling was performed using a GeolasPro laser ablation system that consists of a COMPexPro 102 ArF excimer laser (wavelength of 193nm and maximum energy of 200mJ) and a MicroLas optical system. An Agilent 7700e ICP-MS instrument was used to acquire ion-signal intensities. Helium was applied as a carrier gas. Argon was used as the make-up gas and mixed with the carrier gas via a T-connector before entering the ICP. A "wave" signal smoothing device is included in this laser ablation system [START_REF] Hu | Wave" signal-smoothing and mercury-removing device for laser ablation quadrupole and multiple collector ICPMS analysis: Application to lead isotope analysis[END_REF]. The spot size and frequency of the laser were set to 60µm and 6Hz, respectively, in this study. Zircon 91500 and glass NIST610 were used as external standards for U-Pb dating and trace element calibration, respectively. Each analysis incorporated a background acquisition of approximately 20-30s followed by 50s of data acquisition from the sample. An Excel-based software

ICPMSDataCal was used to perform off-line selection and integration of background and analyzed signals, time-drift correction and quantitative calibration for trace element analysis and U-Pb dating [START_REF] Liu | Continental and oceanic crust recycling-induced melt-peridotite interactions in the Trans-North China Orogen: U-Pb dating, Hf isotopes and trace elements in zircons from mantle xenoliths[END_REF]. Concordia diagrams and weighted mean calculations were made using Isoplot/Ex_ver3 [START_REF] Ludwig | A Geochronological Toolkit for Microsoft Excel[END_REF].

Sm-Nd Geochronology

Sm-Nd isotopic analyses were performed for the oriented sample of coesite- Argon isotopic interferences on K and Ca were determined by irradiation of KF and CaF2 pure salts from which the following correction factors were obtained. Argon analyses were performed at Géosciences Montpellier, France with two analytical devices that each consist of: (a) an IR-CO2 laser of 100kHz used at 5-15% during 60s, (b) a lenses system for beam focusing, (c) a steel chamber, kept at 10 -8 -10 -9 bar, with a drilled copper plate, (d) an inlet line for purification of gases including two Zr-Al getters, (e) a multi-collector mass spectrometer (Argus VI from Thermo-Fisher). A custom-made software controls the laser intensity, the timing of extraction/purification and the data acquisition. To measure the Ar background within the system, one blank analysis was performed every three sample analyses. ArArCalc v2.5.2 was used for data reduction and plotting. The two-sigma errors reported on plateau, isochron and total gas ages include the error on the irradiation factor J. Atmospheric 40 Ar was estimated using a value of the initial 40 Ar/ 36 Ar of 295.5.

40 Ar-39 Ar In Situ Laser Ablation Probing Geochronology

The 40 Ar-39 Ar in situ laser ablation technical procedure ( §6) was first proposed by [START_REF] Schaeffer | Laser Ar-39-Ar-40 study of Apollo 17 basalts[END_REF] and modified by [START_REF] Maluski | 40Ar-39Ar laser probe multi-dating inside single biotites of a Variscan orthogeneiss (Pinet, Massif Central, France)[END_REF]. Sample preparation and analysis (procedure as in [START_REF] Agard | Exhumation of the Schistes Lustrés complex: in situ laser probe 40Ar/39Ar constraints and implications for the Western Alps[END_REF][START_REF] Agard | Transient, synobduction exhumation of Zagros blueschists inferred from P-T, deformation, time, and kinematic constraints: Implications for Neotethyan wedge dynamics[END_REF][START_REF] Augier | Exhumation, doming and slab retreat in the Betic Cordillera (SE Spain): in situ40Ar/39Ar ages and P-T-d-t paths for the Nevado-Filabride complex[END_REF] were conducted at Géosciences Montpellier, France. The laser system consists of a continuous 6W argon ion laser, a beam shutter for selection of lasering exposure time, with typically 5ms pulses separated by 40ms, and a set of lenses for beam focusing.

The number of pulses depends on the nature of the analyzed mineral, its K content and its presumed age. Argon extraction, purification and analyses are performed within three distinctive parts with the sample chamber where gas extraction is done, the purification line with hot getters and nitrogen liquid traps (cold) traps, and a MAP 215-50 noble gas mass spectrometer equipped with an electron multiplier. Rock sections 500µm thick, which had been used to make the petrographic thin sections, were double polished within 1µm tolerance. Whole section and detailed area photographs of both the rock section and corresponding thin section were taken for an accurate selection of favorable areas during lasering experiments. All samples were ultrasonically rinsed in ethanol and distilled water, wrapped in pure aluminum foils and then irradiated in the

McMaster nuclear reactor (Canada) with several aliquots of the MMHb-1 international standard (520. 4 ± 1.7Ma, Samson & Alexander Jr, 1987). After irradiation, both the monitors and the sections were placed on a Cu holder inside the sample chamber and heated for 48h at 150-200°C.

For each age determination, argon was extracted from a 150×300µm surface corresponding to a mixture of several phengite grains, given grain size (Figs. 10b,S6).

The crater is a 30-40µm approximate hemisphere surrounded by a circular wall made of melted material. Incision of the sample did not exceed 10-20µm deep depending on the three-dimensional orientation of the phengite crystals. Once the extraction was completed, about four minutes were required for gas cleaning of the line and 15 min for data acquisition by peak jumping from mass 40 to mass 36 (8 runs). For each experiment, ages have been obtained after correction with blanks, mass discrimination, radioactive decay of 37 Ar and 36 Ar and irradiation-induced mass interferences. They are reported with one sigma uncertainty (Table 4) and were evaluated assuming an atmospheric composition for the initially trapped argon (i.e., ( 40 Ar-36 Ar) i ~295.5).

Introduction

Mechanisms and processes responsible for the occasional recovery of negatively buoyant, ocean-derived high-to ultra-high pressure low temperature (HP-UHP/LT) eclogites equilibrated along the subduction plate interface and for their juxtaposition as tectonic slices or blocks during exhumation remain a matter of debate [START_REF] Agard | Exhumation of oceanic blueschists and eclogites in subduction zones: timing and mechanisms[END_REF][START_REF] Burov | Mechanisms of continental subduction and exhumation of HP and UHP rocks[END_REF][START_REF] Chen | Exhumation of oceanic eclogites: thermodynamic constraints onpressure, temperature, bulk composition and density[END_REF][START_REF] Federico | 39Ar/40Ar dating of high-pressure rocks from the Ligurian Alps: Evidence for a continuous subduction-exhumation cycle[END_REF][START_REF] Gerya | Exhumation of high-pressure metamorphic rocks in a subduction channel: A numerical simulation[END_REF]Guillot et al., 2009;[START_REF] Klemd | Changes in dip of subducted slabs at depth: Petrological and geochronological evidence from HP-UHP rocks (Tianshan, NW-China)[END_REF]Lü et al., 2012;Warren, 2013;Warren et al., 2008). The Southwestern Tianshan Akeyazi HP-UHP/LT metamorphic belt potentially provides an interesting test example, with well-preserved mafic horizons or tectonic blocks/slices/boudins of different sizes (from the cm-to km-scale) embedded in volumetrically dominant meta-volcanosedimentary rocks [START_REF] Gao | Formation of HP-LT rocks and their tectonic implications in the western Tianshan Orogen, NW China: Geochemical and age constraints[END_REF][START_REF] Gao | PT path of highpressure/low-temperature rocks and tectonic implications in the western Tianshan Mountains[END_REF]Meyer et al., 2016).

However, despite numerous previous works (on UHP relicts, detailed petrology, P-T estimates on isolated blocks/slices and time constraints on the timing of metamorphism; section 2), the area is still a matter of controversy as to (i) the exact P-T evolution and age of metamorphism, (ii) whether the metamorphic belt may be composed of two distinct HP and UHP slices and (iii) whether mafic bodies represent a tectonic mélange (Du et al., 2014;[START_REF] Gao | PT path of highpressure/low-temperature rocks and tectonic implications in the western Tianshan Mountains[END_REF][START_REF] Klemd | Changes in dip of subducted slabs at depth: Petrological and geochronological evidence from HP-UHP rocks (Tianshan, NW-China)[END_REF][START_REF] Li | A common high-pressure metamorphic evolution of interlayered eclogites and metasediments from the "ultrahigh-pressure unit" of the Tianshan metamorphic belt in China[END_REF]Meyer et al., 2016) or an assembly of km-scale tectonic slices (Lü et al., 2012).

Uncertainties partly arise from the fact that conclusions were drawn on spectacular but isolated samples (sometimes from loose scree and river beds) rather than on an extensive coverage of the area, and do not tightly enough link recrystallization observations with P-T data. In order to contribute to clarifying these issues, we herein review and reappraise available P-T-t constraints for the area (Figure 16) and perform a combined P-T-radiometric-isotopic study on several eclogitic samples from a key location. Samples come from a thick (~ 5m) layered eclogite outcrop close to where UHP was previously reported (Lü and Zhang, 2012, Figure 16b) and were chosen to provide detailed constraints on their tectono-metamorphic and geochronological evolution (prograde, peak and exhumation stages) using SIMS high precision U-Pb isochron dating of zircon grains and whole-rock the TIMS Sm-Nd technique.

Implications for recrystallization and exhumation processes are discussed and set back within the frame of the regional geodynamic evolution. The Chinese Southwestern Tianshan high-to ultrahigh-pressure low-temperature metamorphic complex extends for about 200 km along the Southwestern Central Tianshan Suture Zone (SCTSZ; Figure 16). It is correlated with the Atbashi metamorphic complex in the Southwestern Tianshan Accretionary Complex (Hegner 3) of this study. Letters on the lower-left corner of the age boxes refer to lithology: "M" for mafic (typical eclogite), "m" for matrix (mainly meta-volcanic sediment with abundant amphibole) and "m" for micaschist (mainly felsic). Numbers on the upper-right corner of the boxes correspond to publications listed in Table 2 and follow those of Figure 14 in chapter 2.

et al., 2010) and the Fan-Karategin metamorphic belt [START_REF] Volkova | Geochemical discrimination of metabasalt rocks of the Fan-Karategin transitional blueschist/greenschist belt, South Tianshan, Tajikistan: seamount volcanism and accretionary tectonics[END_REF]. Gao et al. (1998) proposed that this HP-UHP/LT complex formed from the northward subduction of the South Tianshan ocean and subsequent collision between the already amalgamated Kazakhstan-Yili-Central Tianshan terrane, in the north, and the Tarim-Karakum plates in the south. Subduction polarity is still debated, however, with alternative suggestions of southward subduction (e.g. [START_REF] Lin | Palaeozoic tectonics of the southwestern Chinese Tianshan: new insights from a structural study of the highpressure/\rlow-temperature metamorphic belt[END_REF].

The Southwestern Central Tianshan Suture Zone bounds to the north the Chinese section of the HP-UHP/LT metamorphic complex, known as the Akeyazi metamorphic complex. This contact, now a ~0.5 km wide sinistral strike-slip shear zone, was active from the late Permian to early Triassic [START_REF] Gao | The mineralogy, petrology, metamorphic PTDt trajectory and exhumation mechanism of blueschists, south Tianshan, northwestern China[END_REF]Gao andKlemd, 2000, 2003).

To the north lies a LP-HT Palaeozoic active continental margin [START_REF] Allen | Palaeozoic collisional tectonics and magmatism of the Chinese Tien Shan[END_REF]Gao et al., 1998;[START_REF] Klemd | Metamorphic evolution of (ultra)high-pressure subduction-related transient crust in the South Tianshan Orogen (Central Asian Orogenic Belt): Geodynamic implications[END_REF], mainly made of amphibolite-and granulite-facies rocks, along with Late Silurian and Early Carboniferous continental arc-type volcanic and volcaniclastic rocks and granitoids [START_REF] Gao | Formation of HP-LT rocks and their tectonic implications in the western Tianshan Orogen, NW China: Geochemical and age constraints[END_REF]Gao et al., 2009;Xia et al., 2014). The Akeyazi metamorphic complex (AMC) is overlain to the southwest by unmetamorphosed Palaeozoic sedimentary strata representing the northern, passive continental margin on margin of the Tarim plate [START_REF] Allen | Palaeozoic collisional tectonics and magmatism of the Chinese Tien Shan[END_REF]Carroll et al., 1995).

The Akeyazi metamorphic complex is predominantly composed of strongly schistosed meta-volcanosedimentary rocks hosting mafic metavolcanics, marbles and rare ultramafic rocks. Mafic metavolcanics are eclogites and/or blueschists showing gradual transitions or interlayering [START_REF] Li | Coexisting carbonate-bearing eclogite and blueschist in SW Tianshan, China: petrology and phase equilibria[END_REF]. They are distributed as pods, boudins, thin layers or massive blocks in the host rocks [START_REF] Gao | Formation of HP-LT rocks and their tectonic implications in the western Tianshan Orogen, NW China: Geochemical and age constraints[END_REF]. The AMC was interpreted by some as a tectonic mélange and thought to have formed in a subduction accretionary wedge during subduction of the Southwestern Tianshan ocean [START_REF] Gao | Formation of HP-LT rocks and their tectonic implications in the western Tianshan Orogen, NW China: Geochemical and age constraints[END_REF][START_REF] Gao | PT path of highpressure/low-temperature rocks and tectonic implications in the western Tianshan Mountains[END_REF]. Both the metavolcanics and the matrix metavolcanosedimentary were variably retrogressed under blueschist and/or greenschist facies conditions.

Whole-rock geochemical data for the mafic metavolcanics suggest ocean basalt or arc-related affinities [START_REF] Gao | Formation of HP-LT rocks and their tectonic implications in the western Tianshan Orogen, NW China: Geochemical and age constraints[END_REF][START_REF] John | Trace-element mobilization in slabs due to non steady-state fluid-rock interaction: constraints from an eclogite-facies transport vein in blueschist (Tianshan, China)[END_REF][START_REF] Klemd | New Age Constraints on the Metamorphic Evolution of the High-Pressure/Low-Temperature Belt in the Western Tianshan Mountains, NW China[END_REF]. A recent study indicated that some eclogite boundins also have a continental arc affinity protolith, possibly originating from the basement of a Palaeozoic continental arc setting (Liu et al., 2014a).

Previous age constraints on the P-T evolution of tectonic slices/blocks

Most peak metamorphic estimates for eclogites and prograde blueschists (differences are largely controlled by lithology) yield eclogite-facies HP-LT conditions Table 2). Sources listed in the captions of Figure 16 and Table 2. "1": Pmax range for previous "blueschist" ages lacking precise P-T constraint; "2": same for eclogites; "3": range of zircon U-Pb data from SP leucogranite dikes [START_REF] Gao | The collision between the Yili and Tarim blocks of the Southwestern Altaids: Geochemical and age constraints of a leucogranite dike crosscutting the HP-LT metamorphic belt in the Chinese Tianshan Orogen[END_REF]; "4": range of zircon (inherited core) U-Pb data from regional rodingite (Li et al., 2010c).

within the range 480-580℃ and 1.5-3.0 GPa [START_REF] Beinlich | Trace-element mobilization during Ca-metasomatism along a major fluid conduit: Eclogitization of blueschist as a consequence of fluid-rock interaction[END_REF][START_REF] Gao | PT path of highpressure/low-temperature rocks and tectonic implications in the western Tianshan Mountains[END_REF][START_REF] John | Trace-element mobilization in slabs due to non steady-state fluid-rock interaction: constraints from an eclogite-facies transport vein in blueschist (Tianshan, China)[END_REF][START_REF] Klemd | P-T evolution of glaucophaneomphacite bearing HP-LT rocks in the western Tianshan Orogen, NW China:new evidence for 'Alpine-type' tectonics[END_REF]Li et al., 2016;Meyer et al., 2016;Soldner et al., 2016;[START_REF] Wei | Eclogites from the south Tianshan, NW China: petrological characteristic and calculated mineral equilibria in the Na2O-CaO-FeO-MgO-Al2O3-SiO2-H2O system[END_REF]. A range of P-T conditions of 570-630℃ at 2.7-3.3 GPa was obtained for eclogite-facies micaschists (Wei et al., 2009;[START_REF] Yang | Petrology and U-Pb zircon dating of coesite-bearing metapelite from the Kebuerte Valley, Western Tianshan, China[END_REF], and 470-510℃ at 2.4-2.7 GPa for eclogites (e.g. Meyer et al., 2016, see Table 2 for references).

Evidence for UHP metamorphism comes from both relict coesite inclusions in garnet in several localities (stars in Figure 16b) and thermodynamic pseudosection modeling [START_REF] Lü | Coesite inclusions in garnet from eclogitic rocks in western Tianshan, northwest China: convincing proof of UHP metamorphism[END_REF][START_REF] Lü | Petrology of coesite-bearing eclogite from Habutengsu Valley, western Tianshan, NW China and its tectonometamorphic implication[END_REF]Lü et al., 2012;[START_REF] Tian | Metamorphism of ultrahigh-pressure eclogites from the Kebuerte Valley, South Tianshan, NW China: phase equilibria and P-T path[END_REF]Wei et al., 2009). The spread of P-T estimates [START_REF] Du | Lawsonite-bearing chloritoidglaucophane schist from SW Tianshan, China: Phase equilibria and P-T path[END_REF][START_REF] Gao | The mineralogy, petrology, metamorphic PTDt trajectory and exhumation mechanism of blueschists, south Tianshan, northwestern China[END_REF][START_REF] Gao | PT path of highpressure/low-temperature rocks and tectonic implications in the western Tianshan Mountains[END_REF][START_REF] Klemd | P-T evolution of glaucophaneomphacite bearing HP-LT rocks in the western Tianshan Orogen, NW China:new evidence for 'Alpine-type' tectonics[END_REF][START_REF] Li | A common high-pressure metamorphic evolution of interlayered eclogites and metasediments from the "ultrahigh-pressure unit" of the Tianshan metamorphic belt in China[END_REF]Li et al., 2016;[START_REF] Li | Coexisting carbonate-bearing eclogite and blueschist in SW Tianshan, China: petrology and phase equilibria[END_REF][START_REF] Lü | Petrology of coesite-bearing eclogite from Habutengsu Valley, western Tianshan, NW China and its tectonometamorphic implication[END_REF]Lü et al., 2012;[START_REF] Tian | Metamorphism of ultrahigh-pressure eclogites from the Kebuerte Valley, South Tianshan, NW China: phase equilibria and P-T path[END_REF][START_REF] Wei | Eclogites from the south Tianshan, NW China: petrological characteristic and calculated mineral equilibria in the Na2O-CaO-FeO-MgO-Al2O3-SiO2-H2O system[END_REF] may a priori arise from contrasting assumptions for thermodynamic modeling (and/or difficulties in determining Fe 3+ content and assessing H2O activity) or from the complexity of metamorphic evolutions in individual HP-UHP tectonic slices.

The exhaustive compilation of age data (location on Figure 16b), and the comparison of previous age data versus their assessed Pmax estimates (Figure 17), evidence a considerable spread in ages too, with an overlap between eclogite and blueschist ages, whatever the protolith (Figure 17). The timing of peak metamorphic conditions falls in the range 325-305 Ma. Garnet growth by multi-point Lu-Hf isochron was dated at ca. 315 Ma [START_REF] Klemd | Changes in dip of subducted slabs at depth: Petrological and geochronological evidence from HP-UHP rocks (Tianshan, NW-China)[END_REF], for both eclogites and blueschists from a variety of valleys within AMC. U-Pb SIMS ages from metamorphic zircon rims in eclogites are indistinguishable within error, at 319 ± 3 Ma and 321 ± 2 Ma (Liu et al., 2014a;[START_REF] Su | U-Pb zircon geochronology of Tianshan eclogites in NW China: implication for the collision between the Yili and Tarim blocks of the southwestern Altaids[END_REF] and similar to a U-Pb age of 318 ± 7 Ma obtained for eclogitefacies rutile [START_REF] Li | SIMS U-Pb rutile age of low-temperature eclogites from southwestern Chinese Tianshan, NW China[END_REF]. Du et al. (2014) also reported a suite of relative consistent Sm-Nd isochron ages of 309 ± 4.6 M, 306 ± 15 Ma and 305 ± 11 Ma for eclogites from the Habutengsu river (Figure 16b). An age of 317 ± 5 Ma was obtained on high-pressure veins crosscutting a blueschist wall-rock, interpreted as the prograde dehydrationrelated transformation of blueschist to eclogite (Rb-Sr multi-point isochron, [START_REF] John | Volcanic arcs fed by rapid pulsed fluid flow through subducting slabs[END_REF]. Recent Sm-Nd and Lu-Hf isochron ages of 318.4 ± 3.9 Ma and 326.9 ± 2.9 Ma on blueschists (Soldner et al., 2016) were interpreted as peak eclogite-facies and prograde metamorphism, respectively. Post-peak cooling was constrained by white mica K-Ar, Ar-Ar and Rb-Sr ages at around 310 Ma [START_REF] Klemd | New Age Constraints on the Metamorphic Evolution of the High-Pressure/Low-Temperature Belt in the Western Tianshan Mountains, NW China[END_REF]. Ages < 280

Ma or > than ~325 Ma were considered by most authors as resulting from limitations of isotopic dating (e.g. excess Ar in Ar-Ar system; Nd disequilibrium in Sm-Nd system;

difficulties to relate zircon U-Pb ages to metamorphic stages) or taken as evidence for distinct HP-UHP episodes.

Controversy on regional exhumation

The Akeyazi metamorphic complex is either interpreted as a tectonic mélange or as made of two main units. In the first interpretation, mafic slices/blocks derived from different depths (UHP and HP conditions) were juxtaposed and mixed during exhumation in a meta-volcano-sedimentary subduction channel-like setting (Klemd et al., 2011;Li et al., 2016;Meyer et al., 2016). Despite, indications that rocks may have partly re-equilibrate with fluids in equilibrium with serpentinites (van der [START_REF] Van Der Straaten | Blueschist-facies rehydration of eclogites (Tian Shan, NW-China): Implications for fluid-rock interaction in the subduction channel[END_REF][START_REF] Van Der Straaten | Tracing the effects of high-pressure metasomatic fluids and seawater alteration in blueschist-facies overprinted eclogites: Implications for subduction channel processes[END_REF], serpentinites, which can act as buoyant material during exhumation processes (Guillot et al., 2015), are extremely rare [START_REF] Shen | UHP Metamorphism Documented in Ti-chondrodite-and Ticlinohumite-bearing Serpentinized Ultramafic Rocks from Chinese Southwestern Tianshan[END_REF]. Metavolcanosedimentary rocks could also act as buoyant material and promote the exhumation of denser, negative-buoyant oceanic HP-UHP/LT rocks in a subduction channel [START_REF] Gerya | Exhumation of high-pressure metamorphic rocks in a subduction channel: A numerical simulation[END_REF].

In contrast, the coherent sub-belt model (Lü et al., 2012), based on several individual UHP occurrences in the northern part of the AMC and the prevalence of blueschist facies rocks without UHP "signal" in the south, considers that the AMC consists of two internally coherent metamorphic "sub-belts": a UHP in the north and a HP belt in the south, separated by a major fault contact (only inferred at present) and later juxtaposed during exhumation.

Sample selection and whole-rock composition

Samples were collected from the second eastern tributary up the Atantayi valley (Figure 16b) in a ~six meter thick, layered eclogitic mafic slice. In order to detailedly reconstruct its tectono-metamorphic evolution (pro-and retrograde), three fresh eclogite samples were chose from the core of the thick-layered eclogite outcrop (Figure 18; oriented samples: GJ01-6, 11AT06-2; for geochemistry: 11AT06-1) and one garnet-clinopyroxene-quartz bearing micaschist from the meta-volcanosedimentary host-rock (GJ01-1). Considering the relative low Zr content (only ca. 50 ug/g) of the metabasalts (Table 4), about 100 kilograms of eclogite were sampled for the zircon study and approximately 500 zircon grains were collected and mounted (detailed processing is given in the Analytical methods in the Appendix).

Bulk-and trace-element geochemical data are shown in Table 4 and Figure 19.

Loss on ignite on ranges between 1.8 and 3.3 wt. %, in agreement with modal abundances of hydrous mineral such as amphibole (5 to 8 vol%).

Chondrite-and primitive mantle-normalized [START_REF] Sun | Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes[END_REF] rare earth element (REE) and trace-element patterns of the eclogites are similar to N-MORB (Figure 19), as further supported by a Th/Yb vs. Nb/Yb plot (Figure 19c) and by the εNd(t) value of +8.5 (t = ca. 312 Ma,Table. 7). They show a positive slope in LREEs to MREEs and flat in HREEs, with (La/Yb)N = 0.542 -1.097, (La/Sm)N = 0.524 -0.666, (Gd/Yb)N = 0.999 -1.536 and a ΣREE concentration of 49.9 to 58.2 ppm (Table 4). Primitive mantle-normalized trace-element variations show moderate Rb, Ba, U and Pb enrichments (Figure 19b) for these three eclogite samples. As expected for MORB type samples, there is no Nb-Ta depletion recorded. Table 3: NOTES: Mineral modes were determined from the thin section by point counting on the basis of petrographic observations. The uncertainty of modal abundances of minerals was estimated to be less than 10% by repeating the same operations. Modeled abundances of mineral assemblage for peak T condition are calculated by pseudosection modeling with EBC-1.

Petrology

Mineral occurrences and modal abundances are given in "Fetota" means the total amount of iron oxide analysed from XRF;

The Fe2O3 content of bulk-rock is constrained from potassium permanganate titration method; The Fe2O3 and FeO contents of EBCs were calculated based on the constant ratio of Fe 3+ /Fe 2+ from XRF data for evaluated composition;

Garnet in sample 11AT06 occurs as idioblastic porphyroblasts (~0.4 to 2.5 mm in diameter; Figure 20d, e) in a medium-grained omphacite matrix. The inclusion-rich cores (Figure 20e) host omphacite, epidote, chlorite, paragonite, quartz and glaucophane/barroisite (Figure 33). Box-shaped inclusions of aggregates of paragonite and epidote could represent pseudomorphs after lawsonite (Figure 34). Coesite inclusions (Figure 22b, c) were found in the garnet mantle (Figure 22d), where inclusions are much less than in the core.

Omphacite occurs as small subhedralanhedral grains (~0.05 to 0.1 mm across), either as the main matrix phase or as inclusions in garnet, epidote and paragonite (Figure 20b,d,f,i). Epidote is subhedral and contains inclusions of omphacite, quartz and rutile (Figure 20d). Blue amphibole is found as inclusions in some garnets (Figure 20h) and in the core of late-stage blue-green amphibole (Figure 20g). Rutile is present both in garnet porphyroblasts (Figure 20e), paragonite and amphibole grains as armored relicts, and in the matrix (Figure 20g), where it is replaced by helicitic rims of titanite (Figure 33). Retrograde albite is rare and xenoblastic.

Chlorite replaces or cuts across garnet (Figure 20e).

In oriented eclogite samples (11AT06-2 and GJ01-6), omphacite defines a weak to moderate foliation, and contain aggregates of epidote group minerals and paragonite aligned along the matrix foliation (Figure 20f, 21a-b). In the XZ plane of deformation,

Mineral chemistry

A selection of representative EPMA analyses is provided in Table 5. Mineral abbreviations are after [START_REF] Whitney | Abbreviations for names of rock-forming minerals[END_REF].

Garnet

Garnet porphyroblasts in eclogite sample 11AT06-1 exhibit systematic compositional zoning (e.g., Figure 22e) with a core-mantle increase in pyrope (Xprp) (Morimoto, 1988) outlining the distinct omphacite generations; (g) Chemical composition of amphiboles in studied eclogite after [START_REF] Hawthorne | On the classification of amphiboles[END_REF]. Mineral abbreviations as for Figure 20.

and a slight decrease in spessartine and grossular content (Xsps and Xgrs). The almandine (Xalm) profile is fairly constant from core to mantle then decreases steadily towards the outermost part of the rim (Figure 22e). Second-order fluctuations in Xgrs and Xsps but also in Xalm can be observed (Figure 22e). Garnet profiles may show a rim-outer rim coeval increase in Xalm and decrease in Xprp, which is generally attributed to retrograde reequilibration by diffusion (Wei et al., 2009).

Garnet zoning in eclogite is highlighted by seven spots along the EMPA profile (Figure 22e), which are used in pseudosection modeling (section 8.2). Overall, garnet composition changes from core to mantle and rim from Alm67Py10Grs20Sps4 to Alm70Py12Grs18Sps1 to Alm57Py21Grs22Sps0.3 (Table 5). These average values correspond to the Grt-C, Grt-M1 to M2 and Grt-M5 to R zones defined in Figure 22d, and to the approximate location of the LA-ICPMS trace element analyses of the garnet core, mantle and rim.

Omphacite

Clinopyroxene is always omphacitic, but inclusions in garnet and matrix clinopyroxene show distinct compositional variations (Figure 22f). Inclusions have a lower jadeite content (31-45 mol.%, average 38 mol.%) and a higher total FeO content (4.3-12.9 wt.%, average 7.7 wt.%) than matrix omphacite (40-51 mol.% Jd and 2.5-6.5

wt.% FeO, respectively). Both have similar values of NaN/(NaN+CaN) (~0.48; Table 5).

Omphacite inclusions in paragonite lie on the upper bound for jadeite content and NaN/(NaN+CaN) but on the lower bound for the total FeO content.

Representative microprobe analyses

Mineral

Grt-C Grt-M1 Grt-M2 Grt-M3 Grt-M4 Grt-M5 Grt-R Gln-in-grt Gln-c-matrix Brs-in-grt Brs-r-matrix Omp-in-grt-c Omp-in-grt-m Omp-in-pg Omp-matrix
+ Mn + Mg + Ca), X (omp) = Xjd, X (Brs, gln, chl) = Fe 2+ (Fe 2+ + Mg), X (Ph, pa) = Mg 2+ ; Y(grt) = Xgr = Ca (Fe 2+ + Mn + Mg + Ca), Y (omp) = j(o) = Na (Na + Ca), Y (gln,ep,czo) = Fe 3+
(Fe 3+ + AlVI), Y (Brs) = (Na)M4; c, core; m, mantle; r, rim; -in-phase: inclusion mineral in phase, -matrix: mineral in the matrix; "-" means did not calculate.

Amphibole

Amphibole in the layered eclogite is either glaucophane or barroisite (Figure 22g).

Glaucophane occurs as euhedral porphyroblasts (~0.5 mm across) with barroisite rims (Figure 20g). Both glaucophane and barroisite appear as inclusions in garnet, with a wide range of compositions for the latter, across the magnesio-katophorite field [START_REF] Leake | Nomenclature of amphiboles[END_REF] and a systematic decrease in (Na)M4 (Figure 20h). Glaucophane inclusions have higher Fe 2+ /(Fe 2+ +Mg) and Fe 3+ /(Fe 3+ +Al) ratios. Some amphibole grains have a clear zonation, with glaucophane in the core and barroisite in the rim, similar to the Tianshan garnet-omphacite blueschist samples described by [START_REF] Klemd | P-T evolution of glaucophaneomphacite bearing HP-LT rocks in the western Tianshan Orogen, NW China:new evidence for 'Alpine-type' tectonics[END_REF].

Epidote-group minerals

Epidote-group minerals occur as 0.5-0.7 mm large porphyroblasts or as subhedral grains close to garnet porphyroblasts (Figure 20c-e). Porphyroblasts are randomly oriented in the matrix with mineral inclusions of omphacite and rutile (Figure 20c). The pistacite (=Fe 3+ /(Fe 3+ +Al)) contents of epidote range from 0.09 to 0.17 (Table 5).

Chlorite

Chlorite appears as matrix minerals filled into the fractures of garnet porphyroblasts or as inclusions in garnet (Table 5).

Rutile/Titanite

Rutile appears as acicular or irregular crystals inclusions in paragonite (Figure 20g), glaucophane/barroisite (Figure 20g), garnet (Figure 34) and matrix minerals (Fig. S1). A titanite-armor around rutile is observed in both matrix omphacite (Figure 33ab) and quartz (Figure 33c-d). The TiO2 and Al2O3 contents of titanite are respectively about 37.9 wt % and 2.11 wt % (Table 5).

Trace-element pattern of zircon and garnet

Zircon in layered eclogite occurs as 30 to 50 um grains in the matrix (Figure 22a)

or in garnet (Figure 22a,34). Cathodoluminescence images of zircon grains are used below as a proxy for variations in zircon chemistry (whereas trace-element patterns are discussed in next section). Zircon grains from eclogitic samples show two to four growth zones preserved (Figure 23, 34a-l). A dull-luminescent core domain is found in all zircon grains (Figure 23, 34a-l), with typical sector zoning. A large overgrowth is generally present and herein referred to as the 'mantle'. Complex zoning patterns (chaotic and wavy zoning) were also observed (Figure 23a, e and 34). A lightluminescent outer rim can also be distinguished in many grains (e.g., Figure 23 and Figure 35). A metamorphic origin may be attribute to these zircon domains when considering the < 0.01 Th/U ratios and the presence of diagnostic HP minerals, such as omphacite and rtile, detected via Raman spectroscopy (with peaks at 682 cm -1 and 609 cm -1 , respectively; Figure 35m-n). Quartz was observed but never coesite.

Trace-element pattern and oxygen isotopes of zircon

Based on differences in cathodoluminescence (CL) images and chondritenormalized REE patterns (and U-Pb chronology, which will be discussed in section 7.1), four zircon domains (or growth stages) have been defined from core to rim:

respectively (1) the zircon core, (2) a zone enriched in HREE (with the same CL characteristics as the core, but more rarely preserved), (3) a mantle zone and ( 4) the zircon rim.

Chondrite-normalized REE patterns of zircon cores (Figure 24a) show a typically positive slope from LREE to MREE, a relative enrichment in HREE ((Lu/Sm)N ~ 7). Other zircon grains are shown in Figure 35.

22.94) and flat HREE patterns ((Lu/Tb)N ~ 1.53). This core is also characterized by low Th/U ratios (< 0.01), medium U (~980 ppm), low Th (~4 ppm) and moderate Y, Ti, P and Nb contents (~89, 2670, 27 and 6 ppm, respectively; Table 6). 6). They are also distinct in terms of U-Pb isotopic composition (Figure 25), but have similar Th/U ratios (< 0.01), U and Th contents.

The zircon mantle domain (Figure 24b) shows a more gentle positive slope from LREE to MREE and a flat HREE distribution with lower HREE and Y absolute contents ((Lu/Eu)N ~ 3.17; (Lu/Tb)N ~ 0.94; Y content ~ 45 ppm; Table 6).

The REE pattern of zircon rims differ largely from that of the former three zones discussed above by a steeper MREE to HREE distribution (with (Lu/Gd)N ~ 10 and

(Lu/Tb)N ~ 34, Table 6) and the absence of a HREE plateau. Its Y, P, Th and U contents are also much lower (i.e., respectively, ~ 48, 21, 0.17 and 30 ppm). The Th and U contents are about 30 times less than in the other three zircon domains. Table 6: Average Laser-ICP-MS trace-element compositions of various garnet and zircon domains. NOTES: "bd" means below detected; "-" do not calculated; Here the Std-dev is 1 sigma;

Trace-element pattern of garnet

Laser spots for the analysis of garnet core, mantle and rim corresponding to EPMA analyses of the C, M1 to M2 and M5 to R areas (shown in Figure 22b).

Chondrite-normalized REE patterns of garnet core, mantle and rim (Figure 24b) negative slope for HREE. Garnet rims show the strongest depletion in MREE and a slightly lower HREE content compared to that of mantle. Fifty spots of twenty-seven zircon grains from eclogite sample 11AT06 have been analyzed to unravel the oxygen isotope composition and data the four growth domains (Table 7; Th/U ratios vary between 0.001 to 0.005). Core domains give apparent 25f).

are
Owing to the low U contents of the outer rims (5 of 8 analyzed spots have U contents mostly ranging from 1 to 49 ppm; Table 7), U-Pb results for this domain are presented on the Tera-Wasserburg plot and of poorer quality than the other domains.

Common lead contents of the 8 analyzed spots are highly variable, with values of f206 between 0.09 % and 34.21 % (Table 7). The linear regression of the data points (MSWD = 0.81, n = 8) gives a lower intercept age of 280.8 ± 4.9 Ma and the upper intercept with 207 Pb/ 206 Pb = 0.381 for the common Pb composition (Figure 25g). The weighted mean 206 Pb/ 238 U age of this rim domain is 280.5 ± 4.3 Ma (MSWD = 0.64, n = 8) using the 207 Pb-based common-lead correction [START_REF] Williams | U-Th-Pb geochronology by ion microprobe[END_REF] with the terrestrial Pb isotope composition from [START_REF] Stacey | Approximation of terrestrial lead isotope evolution by a two-stage model[END_REF], which is consistent with the lower intercept age within errors.

By contrast, oxygen isotope δ 18 O compositions measured in the four zircon domains are very similar, with most values ranging between 8.9 ‰ and 9.5 ‰ (Figure 25b; mean value = 9.13 ± 0.09 ‰, MSWD = 5.6, n = 56; Table 8).

Sm-Nd isotopic chronology

Whole rock, omphacite and garnet (including core and rim) Sm-Nd isotopic data of the oriented eclogite sample 11AT06-2 are given in Table 8: 'a', the δ 18 O values have been corrected by the instrumental mass fractionation; Modeled results were calculated based on methods and relevant factors from [START_REF] Zheng | Calculation of oxygen isotope fractionation in metal oxides[END_REF]Zheng ( , 1993)); P peak is setted on 530℃.

good agreement with results obtained from whole-rock trace-elements analyses by ICP-MS (Table 5).

Whole rock and omphacite separates have 147 Sm/ 144 Nd ratios of 0.2841, 0.2452 and 0.2510 respectively. Garnet separates have a Sm/Nd ratio of about 2.13 and 147 Sm/ 144 Nd ratios of 1.2828 and 1.2843, which are close to values reported for other SW Tianshan eclogites [START_REF] Gao | Formation of HP-LT rocks and their tectonic implications in the western Tianshan Orogen, NW China: Geochemical and age constraints[END_REF].

The WR-Omp-Grt isochron yields a Sm-Nd age of 312.1 ± 2.4 Ma (MSWD = 0.78, Figure 26), close to the Omp-Grt isochrone isochron (311.9 ± 2.6 Ma), with εNd(t) of + 8.5 (t = ca. 312 Ma, Table 9). age for the oriented sample (11AT06-2; Table 9)

equilibrium thermobarometry (Holland andPowell, 1998, 2011;version 3.33 with updated database tc-ds55). Average PT results and used representative mineral compositions are given in Table 10.

P-T estimates of 495 ± 20 ℃ and 2.75 ± 0.05 GPa were derived assuming equilibrium between garnet cores and inclusions of omphacite and amphibole (i.e., red square #1 in Figure 22d). Equilibrating omphacite inclusions and the garnet mantle (red square #2 in Figure 22d), in the vicinity of coesite inclusion, yield higher P-T estimates of 520 ± 15 ℃ and 3.0 ± 0.75 GPa but with considerable pressure uncertainties. Lower P but higher T values, around 570 ± 35 ℃ and 2.4 ± 0.3 GPa, are obtained for garnet rims, considering an omp-grt-ph-amp equilibrium assemblage (i.e., red square #3:

Figure 22d; Table 10). Quartz (or coesite) was assumed to be present in all calculations

Phase equilibrium modeling

Pseudosection modeling for sample 11AT06-1 was performed in the system MnNCKFMASHTO (Tables 3,4,5), with excess SiO2 (i.e., quartz or coesite). TiO2 must be considered due to the presence of rutile and/or titanite in the matrix or as inclusions in porphyroblasts. The fluid phase in assumed to be pure H2O and was set in excess. CO2 was neglected as only small amounts of carbonate occur as thin secondary veins. Fe2O3 was set at 22.5 mol% of total FeO according to XRF data (Table 4).

In order to take into account the sequestration of elements induced by the growth zoning of garnet porphyroblast, effective bulk compositions were adjusted from XRF compositions by removing part of the garnet modal abundance, following the method of Carson et al. (1999). For the modelling of prograde and peak conditions (EBC-1), half of the modal abundance of zoned garnet [START_REF] Warren | Oxidized eclogites and garnet-blueschists from Oman: P-T path modelling in the NCFMASHO system[END_REF]Wei et al., 2009) was removed from the XRF composition. For the retrograde path (EBC-2), garnet porphyroblasts were subtracted from the bulk-rock composition (see Table 4 for XRF, EBC-1 and EBC-2 compositions).

The P-T pseudosections were calculated using the software Perple_X 6.68 [START_REF] Connolly | Multivariable phase diagrams; an algorithm based on generalized thermodynamics[END_REF][START_REF] Connolly | Computation of phase equilibria by linear programming: a tool for geodynamic modeling and its application to subduction zone decarbonation[END_REF] and an internally consistent thermodynamic dataset (hp02ver.dat, [START_REF] Connolly | Metamorphic controls on seismic velocity of subducted oceanic crust at 100-250 km depth[END_REF]Holland and Powell, 2003) based on the effective recalculated bulk rock composition (EBC-1 and EBC-2; Table 4). Mineral solid-solution models are Gt(HP) for garnet [START_REF] Holland | An internally consistent thermodynamic data set for phases of petrological interest[END_REF], Omph(GHP)

for omphacite (Green et al., 2007), Amph (DP) for amphibole [START_REF] Diener | A new thermodynamic model for clino-and orthoamphiboles in the system Na2O-CaO-FeO-MgO-Al2O3-SiO2-H2O-O[END_REF], Mica(CHA) for white mica (Coggon and Holland, 2002), Chl(HP) for chlorite [START_REF] Holland | An internally consistent thermodynamic data set for phases of petrological interest[END_REF], Ep(HP) for epidote/clinozoisite [START_REF] Holland | An internally consistent thermodynamic data set for phases of petrological interest[END_REF], and H2O-CO2 fluid solution model is from [START_REF] Connolly | Petrogenetic grids for metacarbonate rocks: pressure-temperature phase-diagram projection for mixed-volatile systems[END_REF].

The pseudosection for sample 11AT06-1 is shown in Figure 27. It is dominated by tri-and quadrivariant fields with a few di-and quini-variant fields. P-T conditions were further constrained by comparing predicted garnet isopleths with measured garnet compositions (boxes on Figure 27b incorporate typical uncertainties on EMPA analyses, ca. 3% to 5%, [START_REF] Lifshin | Minimizing Errors in Electron Microprobe Analysis[END_REF]Williams and Jercinovic, 2006).

Stage I, as defined by core-mantle zoning (i.e., garnet zoning from Grt-C to Grt-M3 in Figure 22e; see compositions in Table 5), is marked by an increase in both T and 4). Seven spots across the core-rim EMPA profile (Figure 22e; Table 5) were used to estimate PT conditions based on calculated isopleths. Blue boxes also consider ca. Stage II is constrained by the mantle-rim zoning (corresponding to Grt-M4, Grt-M5 and Grt-R in Figure 22d, Table 5) and the mineral assemblage omp-amp1(gln)-mica1(ph)-lws-grt-rt. It is marked by a slight increase in T at 550~560℃ and a pressure decrease at 2.35~2.60 GPa, further constrained by the Si content of phengite included in garnet (3.43 p.f.u.; Table 5). Later retrograde re-equilibration, based on the EBC-2 whole-rock composition, is estimated from measured (Na)M4 contents in amphibole and

(Na)M4 isopleths modeled from pseudosection (Figure 27c) at ca. 1.20 GPa and 548℃. The studied mafic eclogites show LREE-depleted and HREE-flat N-MORB patterns [START_REF] Sun | Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes[END_REF], with enrichments in Rb, Ba, U, Pb, and Sr. δ 18 O values for multistage zircons (~ 9.13 ± 0.09 ‰; Figure 25b) with modelled bulk-rock δ 18 O P peak of ca. 8.47 ‰ (Table . 6, oxygen fractionation factors from [START_REF] Zheng | Calculation of oxygen isotope fractionation in metal oxides[END_REF]Zheng, , 1993) ) are similar to those of typical altered ocean crust (AOC, ~ 7.9 to 9.5 ‰ from [START_REF] Cocker | Oxygen and carbon isotope evidence for seawater-hydrothermal alteration of the Macquarie Island ophiolite[END_REF][START_REF] Miller | Distinguishing between seafloor alteration and fluid flow during subduction using stable isotope geochemistry: examples from Tethyan ophiolites in the Western Alps[END_REF], suggesting that the metamorphic zircons may have inherited the composition of the bulk (e.g., [START_REF] Rubatto | Oxygen isotope record of oceanic and highpressure metasomatism: a P-T-time-fluid path for the Monviso eclogites (Italy)[END_REF] Some characteristic element patterns (e.g., in Rb vs K, Nb/U vs U, K/Th vs Ba/Th and Ba/Nb vs U/Nb diagrams, [START_REF] Bebout | Metamorphic chemical geodynamics of subduction zones[END_REF][START_REF] Bebout | Metasomatism in Subduction Zones of Subducted Oceanic Slabs, Mantle Wedges, and the Slab-Mantle Interface[END_REF] suggest that the N-MORB protolith was later slightly enriched in LILE during metamorphism. By contrast, the metavolcanosedimentary host rock yields an Upper Continental Crust-like trace-element and REE-distribution pattern, with notable Nb and Ta anomalies (Figure 19). External fluids derived from subduction-related lithologies would indeed have likely , 2012). We therefore hypothesize that external fluid infiltration was limited and/or δ 18 O was internally buffered [START_REF] Martin | The isotopic composition of zircon and garnet: A record of the metamorphic history of Naxos[END_REF][START_REF] Martin | Mobility of trace elements and oxygen in zircon during metamorphism: Consequences for geochemical tracing[END_REF].

The P-T evolution followed by mafic eclogites (Figure 27) is characterized by burial along a typical subduction gradient (~7°C/km) with a moderate heating (up to 50-80℃) during decompression. This is consistent with recent results of thermodynamic modeling [START_REF] Li | A common high-pressure metamorphic evolution of interlayered eclogites and metasediments from the "ultrahigh-pressure unit" of the Tianshan metamorphic belt in China[END_REF]Li et al., 2016;[START_REF] Lü | Petrology of coesite-bearing eclogite from Habutengsu Valley, western Tianshan, NW China and its tectonometamorphic implication[END_REF][START_REF] Tian | Metamorphism of ultrahigh-pressure eclogites from the Kebuerte Valley, South Tianshan, NW China: phase equilibria and P-T path[END_REF][START_REF] Wei | Eclogites from the south Tianshan, NW China: petrological characteristic and calculated mineral equilibria in the Na2O-CaO-FeO-MgO-Al2O3-SiO2-H2O system[END_REF], though in contrast to some early claims of counterclockwise [START_REF] Lin | Prograde pressure-temperature path of jadeite-bearing eclogites and associated high-pressure/low-temperature rocks from western Tianshan[END_REF] or hairpin-shaped P-T trajectories [START_REF] Gao | PT path of highpressure/low-temperature rocks and tectonic implications in the western Tianshan Mountains[END_REF].

Thermodynamic modelling of successive re-equilibration stages yield P-T estimates within ~ 0.2 GPa and 20 ℃ (1σ-error, see also discussion by Li et al., 2016), considering uncertainties on solid solution models and thermodynamic properties [START_REF] Dachs | The uncertainty of the standard entropy and its effect on petrological calculations[END_REF][START_REF] Worley | High-precision relative thermobarometry: theory and a worked example[END_REF], effective bulk composition (Carson et al., 1999;[START_REF] Evans | A method for calculating effective bulk composition modification due to crystal fractionation in garnet-bearing schist: implications for isopleth thermobarometry[END_REF] and microprobe analyses [START_REF] Lifshin | Minimizing Errors in Electron Microprobe Analysis[END_REF]Williams and Jercinovic, 2006). Conventional thermobarometry give consistent and robust P-T results (Figure 28a) but with larger uncertainties for the pressure peak (Figure 27a, Table S1). When considering these uncertainties, most previous published P-T paths in fact will overlap (Figure 28b, except for [START_REF] Li | A common high-pressure metamorphic evolution of interlayered eclogites and metasediments from the "ultrahigh-pressure unit" of the Tianshan metamorphic belt in China[END_REF]Li et al., 2016;[START_REF] Van Der Straaten | Blueschist-facies rehydration of eclogites (Tian Shan, NW-China): Implications for fluid-rock interaction in the subduction channel[END_REF][START_REF] Wei | Eclogites from the south Tianshan, NW China: petrological characteristic and calculated mineral equilibria in the Na2O-CaO-FeO-MgO-Al2O3-SiO2-H2O system[END_REF]. Most studies concord on Tmax conditions for peak burial in the range 510-570 ℃ (Figure 28b). Our results (520 ± 30℃ for UHP peak burial and 550 ± 30℃ for the temperature peak) are consistent with the recent independent results obtained by Raman spectroscopy of carbonaceous matter (ca. 540 ± 30℃, Meyer et al., 2016).

Future studies should help clarify their contrasts in Pmax estimates, which cluster in three distinct groups (dashed boxes; Figure 28b): 1) a UHP group ranging from ca.

2.7 to 3.3 GPa (e.g., [START_REF] Tian | Metamorphism of ultrahigh-pressure eclogites from the Kebuerte Valley, South Tianshan, NW China: phase equilibria and P-T path[END_REF]Wei et al., 2009;[START_REF] Yang | Petrology and U-Pb zircon dating of coesite-bearing metapelite from the Kebuerte Valley, Western Tianshan, China[END_REF] (and this study), 2) a HP group in the range of ca. 1.8-2.5 GPa (e.g., [START_REF] Beinlich | Trace-element mobilization during Ca-metasomatism along a major fluid conduit: Eclogitization of blueschist as a consequence of fluid-rock interaction[END_REF][START_REF] Du | [END_REF][START_REF] Li | A common high-pressure metamorphic evolution of interlayered eclogites and metasediments from the "ultrahigh-pressure unit" of the Tianshan metamorphic belt in China[END_REF]Li et al., 2016 ;[START_REF] Liu | Paleozoic subduction erosion involving accretionary wedge sediments in the South Tianshan Orogen: Evidence from geochronological and geochemical studies on eclogites and their host metasediments[END_REF]Meyer et al., 2016;Soldner et al., 2016) and 3) a blueschist-facies group ranging from ca. 1.3 to 1.9 GPa (e.g., [START_REF] Gao | PT path of highpressure/low-temperature rocks and tectonic implications in the western Tianshan Mountains[END_REF][START_REF] Klemd | P-T evolution of glaucophaneomphacite bearing HP-LT rocks in the western Tianshan Orogen, NW China:new evidence for 'Alpine-type' tectonics[END_REF][START_REF] Van Der Straaten | Blueschist-facies rehydration of eclogites (Tian Shan, NW-China): Implications for fluid-rock interaction in the subduction channel[END_REF][START_REF] Wei | Eclogites from the south Tianshan, NW China: petrological characteristic and calculated mineral equilibria in the Na2O-CaO-FeO-MgO-Al2O3-SiO2-H2O system[END_REF].

Linking garnet with zircon growth

This section attempts to link the potential of garnet as thermobarometer (e.g., Konrad-Schmolke et al., 2008) with that of zircon as geochronometer (e.g., [START_REF] Rubatto | Zircon trace element geochemistry: partitioning with garnet and the link between U-Pb ages and metamorphism[END_REF] to closely tie U-Pb ages to metamorphic conditions and finally derive a precise P-T-time path.

Figure 24b shows that REE patterns for successive garnet and zircon metamorphic growth are almost parallel, except for the zircon rim. Partitioning data for REE between zircon and garnet [START_REF] Rubatto | Zircon trace element geochemistry: partitioning with garnet and the link between U-Pb ages and metamorphism[END_REF][START_REF] Rubatto | Zircon formation during fluid circulation in eclogites (Monviso, Western Alps): implications for Zr and Hf budget in subduction zones[END_REF] suggest that zircon preferentially sequesters Y and HREE over garnet, with D-values of ~2-4 (Figure 29a).

Data show that only the zircon high HREE core and/or core domains (and not the zircon mantle and rim) have higher HREE contents than garnet (Figure 29b, Table 6) and may therefore have equilibrated with it.

Zircon high-HREE cores may have co-crystallized either with the garnet core or mantle domains (Figure 29b), but the D Y+HREEs zrn/grt pattern of the second option is more similar to the one reported in eclogite vein by [START_REF] Rubatto | Zircon formation during fluid circulation in eclogites (Monviso, Western Alps): implications for Zr and Hf budget in subduction zones[END_REF]. For the zircon core domain, the most likely candidate would be the garnet rim. We thus tentatively propose (Figure 29c, 30) that zircon high-HREE core grew in equilibrium with the garnet mantle at ~ ca. 318 Ma at UHP conditions (~ ca. 2.6-3.1 GPa; Grt-M1 to M2 stages with coesite inclusions; Figure 22), while zircon core grew in equilibrium with the garnet rim at ~ ca. 316 Ma (~ ca. 2.3-2.7 GPa; Grt-M5 to R stage). The zircon mantle domain (~ ca. 303 Ma, Figure 25f), with similar but lower HREE patterns (Figure 24a), could have inherited its HREE content from the partial resorption of garnet (and/or zircon cores, i.e., [START_REF] Degeling | Zr budgets for metamorphic reactions, and the formation of zircon from garnet breakdown[END_REF], while garnet abundance was still buffering the HREE budget. By contrast, the different REE pattern of the last zircon rim overgrowth (~ ca. 280 Ma, Figure 25g), hints to the breakdown of another Zr-bearing mineral during greenschist/blueschist-facies exhumation, possibly rutile [START_REF] Kohn | The fall and rise of metamorphic zircon[END_REF][START_REF] Lucassen | Redistribution of HFSE elements during rutile replacement by titanite[END_REF]. Similar multi-stage zircon growth from the Dabie mountain (but with zircon from separate eclogite and quartz vein, Liu et al., 2014b;[START_REF] Zheng | Fluid flow during exhumation of deeply subducted continental crust: zircon U-Pb age and O-isotope studies of a quartz vein within ultrahigh-pressure eclogite[END_REF] was interpreted as a witness of channelized fluid flow during exhumation. (~500-850℃, [START_REF] Li | Sm-Nd and Rb-Sr isotopic chronology and cooling history of ultrahigh pressure metamorphic rocks and their country rocks at Shuanghe in the Dabie Mountains, Central China[END_REF] and omphacite (~1050℃, [START_REF] Sneeringer | Strontium and samarium diffusion in diopside[END_REF], questioning Nd equilibrium between these phases at a peak temperature of 530 ± 30°C, consistent mineral pair and whole rock Sm-Nd isochron were reported for similar finegrained eclogites from distinct localities in the Dabie mountains [START_REF] Li | Sm-Nd and Rb-Sr isotopic chronology and cooling history of ultrahigh pressure metamorphic rocks and their country rocks at Shuanghe in the Dabie Mountains, Central China[END_REF].

This WR-garnet-omphacite Sm-Nd age of ca. 312 Ma (Figure 26, Table 9) can therefore be treated as constraining the post-peak eclogite-facies deformation event coeval with omphacite growth in the matrix (Figure 21a-b), slightly after or coeval with the growth of zircon cores in equilibrium with garnet rims (i.e., ~ ca. 316 Ma). These age constraints are broadly consistent with a recent Sm-Nd WR-grt-omp age of ~ 307 2) and results from this study place constraints on the main tectonic stages for the area (i.e., detachment, exhumation, etc), as well as on exhumation rates.

± 11 Ma interpreted as dating the timing of HP metamorphism (Du et al., 2014) and a Sm-Nd WR-grt-gln age of 318.4 ± 3.9 Ma for a blueschist equilibrated close to HP peak metamorphism (Soldner et al., 2016). Ages between 318 and 312 Ma are also consistent with the 320.4 ± 3.7 Ma zircon-rim U-Pb age obtained on coesite-bearing metavolcanosedimentary rocks [START_REF] Yang | Petrology and U-Pb zircon dating of coesite-bearing metapelite from the Kebuerte Valley, Western Tianshan, China[END_REF] and with the 315.2 ± 1.6 Ma garnet-multipoint Lu-Hf age obtained for eclogites [START_REF] Klemd | Changes in dip of subducted slabs at depth: Petrological and geochronological evidence from HP-UHP rocks (Tianshan, NW-China)[END_REF].

Overall, the present study allows to conclude that 315 ± 5 Ma can be taken as a reliable value for the attainment of HP to UHP conditions in the Chinese Southwestern Tianshan UHP-HP/LT metamorphic complex. The dispersion of Ar/Ar ages (Fig. 16b, Gao et al., 2000;[START_REF] Klemd | New Age Constraints on the Metamorphic Evolution of the High-Pressure/Low-Temperature Belt in the Western Tianshan Mountains, NW China[END_REF]Wang et al., 2010;[START_REF] Shen | UHP Metamorphism Documented in Ti-chondrodite-and Ticlinohumite-bearing Serpentinized Ultramafic Rocks from Chinese Southwestern Tianshan[END_REF] may therefore be due to a problem of excess argon, at least in some eclogite/blueschist samples.

Indeed the same outcrop yielded very distinct Ar-Ar plateau ages (e.g., 401 ± 1 and 364 ± 1 Ma by Gao et al., 2000) versus ca. 320 Ma by [START_REF] Klemd | New Age Constraints on the Metamorphic Evolution of the High-Pressure/Low-Temperature Belt in the Western Tianshan Mountains, NW China[END_REF], and similar ages were obtained for Rb/Sr and Ar/Ar ages by [START_REF] Klemd | New Age Constraints on the Metamorphic Evolution of the High-Pressure/Low-Temperature Belt in the Western Tianshan Mountains, NW China[END_REF], for which white mica closure temperatures (if strictly under fluid-assisted recrystallization-free assuming) differ by 100 ℃ or more (Li et al., 1994;Ruffet et al., 1997;Villa, 1998;[START_REF] Villa | Geochronology of the Larderello geothermal field: new data and the "closure temperature[END_REF].

The 303 Ma age derived from zircon mantle recrystallization (Figure 25f) is here taken as a minimum age for the garnet-free or garnet resorption greenschist-facies metamorphism. This conclusion is strengthened by a greenschist-facies Ar-Ar plateau age of ~ 293.1 ± 1.7 Ma reported by [START_REF] Shen | UHP Metamorphism Documented in Ti-chondrodite-and Ticlinohumite-bearing Serpentinized Ultramafic Rocks from Chinese Southwestern Tianshan[END_REF]. Later recrystallization of zircon rims at ~280 Ma, though of poor quality (Figure 25g) could correspond to the late exhumation movements, as similar ages were reported for the extensive ductile strikeslip deformation of the Southwestern Central Tianshan Suture zone (i.e., [START_REF] De Jong | New 40Ar/39Ar age constraints on the Late Palaeozoic tectonic evolution of the western Tianshan (Xinjiang, northwestern China), with emphasis on Permian fluid ingress[END_REF][START_REF] Laurent-Charvet | Late Paleozoic strike-slip shear zones in eastern central Asia (NW China): New structural and geochronological data[END_REF]. Note that late, post-exhumation rodingitization was constrained at 291 ± 15.0 Ma (Li et al., 2010c) and that crosscutting, undeformed leucogranites were dated at ~ 284.9 ± 2.0 Ma [START_REF] Gao | The collision between the Yili and Tarim blocks of the Southwestern Altaids: Geochemical and age constraints of a leucogranite dike crosscutting the HP-LT metamorphic belt in the Chinese Tianshan Orogen[END_REF].

These age constraints point to decreasing exhumation velocities, from ca. 12.0 ± 6.5 mm/yr for early UHP to HP exhumation (if < 2 Ma) to 3.6 ± 2.0 mm/yr for blueschist-facies exhumation (within ca. 13 Ma) and 0.8 ± 0.4 mm/yr for greenschistfacies exhumation (within ca. 22 Ma). The average exhumation rate, ca. 2.6 mm/yr, falls within the range of 1-5 mm/yr for exhumed oceanic rocks worldwide (Agard et al., 2009). Importantly, the timing of HP-UHP metamorphism appears very restricted (at 315 ± 5 Ma; i.e., < 10 Ma) compared to the likely duration of active subduction (> 50-100 My, since an oceanic domain existed in the region from at least ~422 ± 10 Ma to ca. 280-300 Ma, Li et al., 2010c).

Although this study focuses on a single key exposure, a simple geodynamic reconstruction is provided (Figure 32) to set back our results in a tentative evolution of the Chinese Southwestern Tianshan metamorphic complex. HP-UHP/LT rocks were detached or exhumed after their peak burial only at about 315 ± 5 Ma (Figure 31) and brought back to the surface to greenschist-facies conditions between ca. 310 and 300

Ma (Figure 32b). Pervasive north-trending shear senses deduced from eclogite-, blueschist-and greenschist-facies recrystallizations (this study, Fig. 6, see also [START_REF] Lin | Palaeozoic tectonics of the southwestern Chinese Tianshan: new insights from a structural study of the highpressure/\rlow-temperature metamorphic belt[END_REF]Wang et al., 2010) are interpreted to result from southwest-trending extrusion of the AMC (Figure 32b).

At present, thorough large-scale structural studies and/or extensive P-T(-t) mapping across the whole HP/UHP complex are still missing to assess whether the ponctated exhumation at 315 ± 5 Ma is associated with chaotic block-in-matrix mixing, with heterogeneous P-T and/or fluid conditions (e.g., extremely complex zoning of both garnet and amphibole, Li et al., 2016) or to accretion of tectonic slices of volcanosedimentary material hosting stripped pieces from the seafloor (i.e., mafic meta-volcanics).

Conclusions

This study provides P-T-radiometric-isotopic constraints on several eclogitic samples from a key coesite-bearing location in the Chinese Southwestern Tianshan UHP-HP/LT metamorphic complex. Together with an exhaustive review of available P-T (-time) constraints for the area, the following conclusions can be drawn from these new data:

(1) Mafic eclogites have slightly LILE-enriched N-MORB like features with δ 18 Ozircon values of ~ ca. 9.0 ‰ typical of an AOC protolith. The constant δ 18 O values for the successive zircon growths suggest a metamorphic system closed (or very limited)

to external fluid infiltration.

(2) Thermodynamic modeling permits a complete recovery of their P-T trajectory from pre-peak burial to UHP conditions (~ 2.95 GPa ± 0.2 and 510°C ± 20) and later exhumation. REE partitioning between multistage zircon and garnet growth domains allows for a critical assessment of the P-T-time path: the ca. 318 Ma and 316 Ma zircon ages are tied to UHP and HP metamorphism, respectively, along with a consistent ca. 312 Ma Sm-Nd age for HP eclogite-facies deformation. Thus, peak burial can be constrained at about 315 ± 5 Ma. These P-T-t constraints point to decreasing exhumation velocities, from ca. 12.0 ± 6.5 mm/yr for early UHP to HP exhumation to 3.6 ± 2.0 mm/yr for blueschist facies exhumation and 0.8 ± 0.4 mm/yr for greenschist facies exhumation.

(3) The comparison of P-T (-time) estimates between this study and the compilation of previous works outlines the existence of a short-lived detachment of subducted eclogites (< 10 Ma) with respect to the "long-term" subduction duration (> 50-100

Ma).

ACKNOWLEDGMENTS

This study was essentially funded by the National Natural Science Foundation of China (41390440, 41390445, 41025008)

APPENDIX Analytical methods

Bulk-rock analyses

Four bulk-rock chemical analyses were performed at the Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS) on three samples from one eclogite outcrop (see location in Fig. 4; 11AT06-1, 11AT06-2 and GJ01-6), and one sample from the wall-rock mica schist ~3 meters away (GJ01-1). Major oxides were determined by a PHILLIPS PW1480 X-ray fluorescence spectrometer (XRF) on fused glass discs. Loss on ignition (LOI) was measured after heating to 1,000 °C.

Uncertainties for most major oxides are ca. 2%, for MnO and P2O5 ca. 5%, and totals are within 100 ± 1 wt.%. Whole rock Fe2O3 content is constrained by potassium permanganate titration. Trace element concentrations were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) using a Finnigan MAT ELEMENT spectrometer at the IGGCAS. The detailed analytical procedure is identical to that used by [START_REF] Qian | Petrogenesis and tectonic settings of Carboniferous volcanic rocks from north Zhaosu, western Tianshan Mountains: constraints from petrology and geochemistry[END_REF]. Relative standard deviations (RSD) are within ±10% for most trace elements but reach ± 20% for V, Cr, Co, Ni, Th and U according to analyses of rock standards. Detail major and trace elements analyses are presented in Table 4.

Mineral major elements

In situ major element compositions of garnet and inclusion minerals were obtained from polished thin sections by electron microprobe analyses at the IGGCAS with the use of JEOL JXA 8100. Quantitative analyses were performed using wavelength dispersive spectrometers with an acceleration voltage of 15 kV, a beam current of 15 nA, a 3 μm beam size and 30 s counting time. Natural minerals and synthetic oxides were used as standards, and a program based on the ZAF procedure was used for data correction. Representative microprobe analyses for pseudosection modeling and for Thermocalc averagePT calculations are presented in Table 5 andTable 10, Reproducibility and accuracy, which were determined for NIST SRM 610 and NIST SRM 612, are usually < 8 % and < 6 %. Trace element concentrations were then calculated using GLITTER Version 3 [START_REF] Van Achterbergh | GLITTER: On-line interactive data reduction for the laser ablation inductively coupled plasma mass spectrometry microprobe[END_REF]. Representative average trace element data of the relevant garnet and zircon domains are given in Table 6.

Raman analyses

In order to identify coesite inclusions in garnet or small high-pressure mineral inclusions in zircon (e.g. omphactie or rutile), Raman spectroscopy was performed at IGGCAS using a Renishaw Raman MKI-1000 system equipped with a CCD detector and an Ar ion laser. The laser beam with a wavelength of 514.5 nm was focused on the coesite inclusion through 50× and 100× objectives of a light microscope. The laser spot size was focused to 1 μm. The reproduction of spectra for the same spot is better than 0.2 cm -1 .

Sm-Nd isotope chronology analyses

Sm-Nd isotopic analyses were obtained at the Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing. 100 mg of samples were first mixed with 149 Sm-150 Nd diluent, dissolved afterwards in a purified HF-HClO 4 -HNO 3 mixture, and finally heated on an electric hot plate for a week. Separation and purification of bulk REE were conducted by a silica-column with an AG50W-X12 exchange resin (200-400 mesh, 2ml), those of Sm and Nd by a silica-column with Teflon powder (1 ml) as exchange medium. Isotopic ratios of Sm and Nd were measured using a Finnigan MAT-262 thermal ionization mass spectrometer. Nd isotopic data of unknowns were normalized to 146 Nd/ 144 Nd of 0.7219 and corrected using Ames ( 143 Nd/ 144 Nd = 0.512138) as external standard. Errors in element concentrations and 147Sm/144Nd-ratios are less than 0.5% (2σ). Sm-Nd data for the studied sample is shown in Table 9.

U-Pb isotope chronology and Oxygen isotope of zircon

For the preparation of zircon study, and considering the relative low Zr content (only ca. 50 ug/g) of this N-MORB type meta-basalt (Table 4), about 100 kilograms analyses. Measurements of U, Th and Pb were conducted using the Cameca IMS-1280 SIMS. U-Th-Pb ratios and absolute abundances were determined relative to the standard zircon 91500 [START_REF] Wiedenbeck | Three natural zircon standards for U-Th-Pb, Lu-Hf, trace element and REE analyses[END_REF], analyses of which were interspersed with those of unknown grains, using operating and data processing procedures similar to those described by Li et al. (2009). A long-term uncertainty of 1.5% (1 RSD) for 206 Pb/ 238 U measurements of the standard zircons was propagated to the unknowns (Li et al., 2010a) despite that the measured 206 Pb/ 238 U error in a specific session is generally around 1% (1 RSD) or less. Measured compositions were corrected for common Pb using non-radiogenic 204 Pb. Further details on instrument parameters, analytical method, calibration and correction procedures can be found in (Li et al., 2010b). Results of U-Pb isotopic chronology of zircon for sample 11AT06 are listed in Table 7.

Oxygen isotope analyses at the exact locations of U-Pb isotope zircon were also 8. [START_REF] Bebout | Metamorphic chemical geodynamics of subduction zones[END_REF][START_REF] Bebout | Metasomatism in Subduction Zones of Subducted Oceanic Slabs, Mantle Wedges, and the Slab-Mantle Interface[END_REF] for discriminating between LILE enrichment by metamorphism and seafloor alteration. 1: eclogite/blueschist/amphibolite [START_REF] Sorensen | Phengite-hosted LILE enrichment in eclogite and related rocks: implications for fluid-mediated mass transfer in subduction zones and arc magma genesis[END_REF]; 2: eclogite/gabbro/metagabbro (GIIE+GIII, [START_REF] John | Trace element fractionation during fluid-induced eclogitization in a subducting slab: trace element and Lu-Hf-Sm-Nd isotope systematics[END_REF]; 3: typical altered oceanic crust rocks from ODP Sites 801 [START_REF] Kelley | Composition of altered oceanic crust at ODP Sites 801 and 1149[END_REF]. and was detected in other eclogites in the region. This transient thermal excursion is tentatively tied to the fast movement of detached UHP oceanic slices towards the hotter mantle wedge.

Introduction

Garnet plays an ultimate role in disclosing mechanical and thermal processes at plate boundaries, by constraining complex pressure-temperature-time histories (e.g., [START_REF] Baxter | Garnet: A rock-forming mineral petrochronometer[END_REF][START_REF] Caddick | Garnet: Witness to the Evolution of Destructive Plate Boundaries[END_REF], and references therein) and kinetics of metamorphic processes (e.g., [START_REF] Angiboust | Eclogite breccias in a subducted ophiolite: A record of intermediate-depth earthquakes?[END_REF][START_REF] Berg | Strain rates at high temporal resolution from curved inclusion trails in garnet, Passo del Sole, Central Swiss Alps[END_REF][START_REF] King | Ultrahigh-pressure metabasaltic garnets as probes into deep subduction zone chemical cycling[END_REF][START_REF] Moore | Origins of yttrium and rare earth element distributions in metamorphic garnet[END_REF][START_REF] Prior | Some garnet microstructures: an illustration of the potential of orientation maps and misorientation analysis in microstructural studies[END_REF][START_REF] Skora | Diffusion-limited REE uptake by eclogite garnets and its consequences for Lu-Hf and Sm-Nd geochronology[END_REF][START_REF] Yang | The origin of Mn and Y annuli in garnet and the thermal dependence of P in garnet and Y in apatite in calc-pelite and pelite, Gagnon terrane, western Labrador[END_REF]. Garnet also yields unique information about nucleation and growth [START_REF] Carlson | Porphyroblast crystallization: linking processes, kinetics, and microstructures[END_REF], fluid- infiltration events [START_REF] King | Ultrahigh-pressure metabasaltic garnets as probes into deep subduction zone chemical cycling[END_REF][START_REF] Li | Fluid-mediated metal transport in subduction zones and its link to arc-related giant ore deposits: Constraints from a sulfide-bearing HP vein in lawsonite eclogite (Tianshan, China)[END_REF] and timescales of peak metamorphic heating, burial/exhumation and retrogression [START_REF] Caddick | Preservation of Garnet Growth Zoning and the Duration of Prograde Metamorphism[END_REF][START_REF] Skora | The duration of prograde garnet crystallization in the UHP eclogites at Lago di Cignana, Italy[END_REF].

In particular, crucial information can be retrieved by studying special garnet compositional zoning, e.g. (i) oscillatory/rhythmic zoning of major elements recording fluid infiltration or subtle P-T path perturbations [START_REF] García-Casco | Oscillatory zoning in eclogitic garnet and amphibole, Northern Serpentinite Melange, Cuba: a record of tectonic instability during subduction?[END_REF][START_REF] Li | Fluid-mediated metal transport in subduction zones and its link to arc-related giant ore deposits: Constraints from a sulfide-bearing HP vein in lawsonite eclogite (Tianshan, China)[END_REF][START_REF] Schumacher | Subtle oscillatory zoning in garnet from regional metamorphic phyllites and mica schists, western Erzgebirge, Germany[END_REF], (ii) healed fracture zoning in major elements related to subduction zone seismicity [START_REF] Angiboust | Eclogite breccias in a subducted ophiolite: A record of intermediate-depth earthquakes?[END_REF], (iii) Y+REEs secondary peak zoning revealing major or accessory mineral breakdown [START_REF] King | Ultrahigh-pressure metabasaltic garnets as probes into deep subduction zone chemical cycling[END_REF][START_REF] Pyle | Yttrium zoning in garnet: coupling of major and accessory phases during metamorphic reactions[END_REF][START_REF] Yang | The origin of Mn and Y annuli in garnet and the thermal dependence of P in garnet and Y in apatite in calc-pelite and pelite, Gagnon terrane, western Labrador[END_REF] or diffusion-controlled dynamic growth [START_REF] Skora | Diffusion-limited REE uptake by eclogite garnets and its consequences for Lu-Hf and Sm-Nd geochronology[END_REF].

This study focuses on the evolution of deeply subducted, coesite-bearing oceanic eclogites from the SW-Tianshan UHP metamorphic complex, whose P-T-time evolution was recently reappraised [START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF]. In some rocks we noted an unusual garnet zoning with concordant, annular enrichment in Mn, HREEs and Y (Figure 38a-c), but not in other major (Fe, Ca, Mg) or key trace elements (L/MREEs, Ti, Sr, Zr, Sc, Rb and P; Figure 39). Based on Zr-in-rutile thermometry and detailed petrology, geochemical diffusion and thermodynamic modeling, we show that a ~80°C short-lived (~300 kyrs) thermal pulse is required to account for this joint Mn, HREEs & Y enrichment. We then discuss implications for element mobility and transient rock dynamics along a deep cold subduction plate interface.

Geological setting

The Chinese Southwestern Tianshan HP/UHP-LT metamorphic complex extends for about 200 km along the Southwestern Central Tianshan Suture Zone (SCTSZ;

Figure 37a-b). It is correlated with the Atbashi metamorphic complex in the Southwestern Tianshan Accretionary Complex (Hegner et al., 2010) and the Fan-Karategin metamorphic belt [START_REF] Volkova | Geochemical discrimination of metabasalt rocks of the Fan-Karategin transitional blueschist/greenschist belt, South Tianshan, Tajikistan: seamount volcanism and accretionary tectonics[END_REF]. The SCTSZ bounds to the north the Chinese section of the HP-UHP/LT metamorphic complex, known as the Akeyazi metamorphic complex (AMC). To the north lies a LP-HT Palaeozoic active 13) using four different calibrations, pointing to a ~80 ˚C thermal pulse.

continental margin (Gao et al., 1998), mainly made of amphibolite-and granulite-facies rocks, along with Late Silurian and Early Carboniferous continental arc-type volcanic and volcaniclastic rocks and granitoids (Gao et al., 2009). To the south the AMC is overlain by unmetamorphosed Palaeozoic sedimentary strata, which also represent the northern, passive continental margin of the Tarim plate (Carroll et al., 1995).

The AMC is predominantly composed of strongly schistosed metavolcanoclastics hosting mafic metavolcanics, marble horizons [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF] and rare ultramafic rocks as pods, lenses, boudins, thin layers or massive blocks [START_REF] Gao | Formation of HP-LT rocks and their tectonic implications in the western Tianshan Orogen, NW China: Geochemical and age constraints[END_REF].

The AMC was mainly interpreted as a tectonic mélange and thought to have formed in a subduction accretionary wedge during norward subduction of the Southwestern Tianshan Ocean [START_REF] Gao | PT path of highpressure/low-temperature rocks and tectonic implications in the western Tianshan Mountains[END_REF][START_REF] Klemd | Metamorphic evolution of (ultra)high-pressure subduction-related transient crust in the South Tianshan Orogen (Central Asian Orogenic Belt): Geodynamic implications[END_REF]. Whole-rock geochemical data for the mafic metavolcanics suggest oceanic basalt or arc-related affinities [START_REF] Gao | Formation of HP-LT rocks and their tectonic implications in the western Tianshan Orogen, NW China: Geochemical and age constraints[END_REF][START_REF] John | Trace-element mobilization in slabs due to non steady-state fluid-rock interaction: constraints from an eclogite-facies transport vein in blueschist (Tianshan, China)[END_REF].

According to our compilation of regional P-T-time constraints [START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF], most peak metamorphic estimates for eclogites and prograde blueschists yield eclogitefacies HP-LT conditions within the range 480-580°C and 1.5-3.0 GPa. A range of P-T conditions of 450-570°C at 2.7-3.3 GPa was obtained for eclogite-facies micaschists.

Evidence for UHP metamorphism comes from both relict coesite inclusions in garnet from several localities (stars in Figure 37b) and thermodynamic calculation. The timing of peak metamorphism falls at 315 ± 5 Myrs, i.e. in a very restricted range with respect to a ~100 Myr-long subduction [START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF]their figures 13, 16).

Metavolcanoclastic rocks from SW-Tianshan preserve P-T conditions slightly higher

Sample description

Three fresh samples of coesite-bearing UHP eclogite (A, B, C; Figure 37d, 46, 48)

were collected from a hm-scale eclogitic mafic slice (in the second eastern tributary up the Atantayi valley; Figure 37b), along adjacent meter thick fresh eclogite layers ( Figure 37d; N42°31′57″, E81°12′37″; [START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF]. They mainly consist of garnet, omphacite, glaucophane, phengite/paragonite, epidote/clinozoiste and rutile/titanite in variable amounts (Figure 46,48). Their N-MORB type bulk-rock compositions, together with analysed εNd(t) ~+8.5 (t=312 Ma) and modeled bulk-rock δ 18 O ~8.47‰, suggest that the protolith was a piece of altered oceanic crust [START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF]. Peak burial conditions, in part recorded by garnet compositions, is in the range 470-550 °C, 2.7-3.2 GPa, similar to other reported UHP slices in the region [START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF]; their figure 13b).

Garnet occurs as idioblastic porphyroblasts with radius ~0.12-1.58 mm (Figure 46, 48) in the fine-grained omphacite matrix. Garnet size distribution was systematically surveyed for each sample (Figure 48; see Appendix A for details). Garnet cores are generally inclusion-rich and host tiny crystals (~5 to 50 µm in diameter, Figure 40c) of omphacite, epidote, chlorite, paragonite, quartz and glaucophane/barroisite (as examplified by garnet A1; Figure 40c,46a). Box-shaped inclusions of aggregates of paragonite+epidote (±chlorite) are interpreted as pseudomorphs after lawsonite [START_REF] Tan | Temperature estimates (Figure 38e) for core, rim and matrix range from ca. 380 to 540[END_REF]. Coesite in the mantle of garnet A1 (Figure 38a,40c) is located immediately outside the annular, concordant MnYHREE pulse (Figure 38a-c). Omphacite occurs as subhedral-anhedral fine grains (~0.05 to 0.1 mm across), either as the main matrix phase or as inclusions in garnet (Figure 40c). Blue-green amphibole is found as glaucophane inclusions in garnet (Figure 40c) and barroisite with glaucophane cores in the matrix. Rutile (Figure 38d,45a) is present both in garnet porphyroblasts as armored relicts and in the matrix, where partly replaced by titanite. Chlorite is included in or cuts across garnet (Figure 40c, 46a).

Mineral geochemistry

Systematic major and trace element analyses were performed for garnet of all sizes, for relevant inclusions hosted in garnet (i.e., A1) and for matrix minerals.

Representative data are shown in Table 12. In detail, Mn, Ho and Dy present relatively wide central peaks (~1/3 of garnet diameter, Figure 39b-d; Mn ~6072 ± 1269 µg/g; Ho ~3.38 ± 0.788 µg/g; Dy ~13.9 ± 2.74 µg/g; Table 12) compared to the rest of HREEs (i.e., Tm, Er, Lu and Yb) and Y (~1/9 of the diameter; Figure 39b-d; Tm ~1.56 ± 4.55 µg/g; Er ~10.0 ± 2.64 µg/g; Lu ~1.54 ± 0.535 µg/g; Yb ~11.2 ± 3.58 µg/g, Table 12). A secondary peak is observed at a rather constant corepeak-secondarypeak distance (~0.77 ± 0.06 mm for garnet A1, considering uncertainties from LA-ICP-MS analyses spots interval ca. 0.12 mm; Figure 38c) before the outermost rim is depleted again to approximately 1/5 to 1/3 of the absolute concentrations with respect to their core peaks (Figure 39, Table 12). Note that only punctual Y concentrations determined by LA-ICP-MS analyses are shown in Figure 38b since concentrations of ~40 to 110 µg/g are too low to be detected by microprobe analyses.

In contrast, neither central nor secondary peaks can be observed on the profiles and mapping of other garnet major components (i.e., Fe, Mg and Ca; Figure 39a,45cd). The Xgrs (mol % of grossular) gradually decreases from 0.18~0.20 to 0.15~0.16 then increases to 0.22~0.24 in the outermost rim, while the Xprp monotonously increases from 0.09~0.10 to 0.22~0.23 but shows minor oscillations at the outermost rim (Figure 39). The Xalm evolution is quite simple with almost constant values from core to mantle (i.e., 0.67~0.7), then gradually decreases to 0.54~0.57 at the outermost rim (with a small near-edge plateau; Figure 39).

Compositional profiles of MREEs and key trace elements (most LREEs analyses are below detect limitation; Table 12) also largely differ from the MnYHREE zoning (Figure 39e-h). None of the central peaks can be identified (e.g., Sm and Eu are even depleted in the core; Figure 39e). Secondary peaks can be noticed among the profiles of some elements (e.g., Sc, Sm), but their position varies for each element. Ti and P mapping (Figure 45a-b) suggests joint growth of garnet with Ti-and P-bearing phases. These relationships between garnet size and Mn zoning suggest that large garnets nucleated almost simultaneously, before middle and then small garnets, explaining a different record of yet similar MnYHREE enrichment. The fact that this is observed for samples meters apart (Figure 37d) suggests the existence of an external control (at outcrop-or km-scale) on diffusion-controlled nucleation and growth mechanism.

Major/trace elements composition of associated minerals

In order to assess the potential mass contribution of Mn, Y and HREEs from associated minerals to investigated unusual garnet zonation, major and trace elements analyses were performed for minerals either included in garnet A1 (i.e., omphacite,

Thermodynamic modeling

Thermodynamic modelling was used to predict the evolution of mineral modes during garnet growth (notably chlorite and lawsonite; Figure 40d-e) and evaluate their impact as a source and/or local buffer on the Mn, Y and HREEs budget of the rock. In order to account for element fractionation during garnet growth, three pseudosections were calculated based on evolving effective bulk rock compositions (EBC0-1-2; Figure 40f, Table 11). The evolution of relevant mineral modes was calculated along a pressure-constant heating path (Figure 40f), starting from 450 °C to 490 °C, followed by a transient 80 °C T pulse (to 580 °C), then later heating to 500°C, broadly consistent with regional Tmax ~500-600 °C by Zr-in-rutile and RSCM thermometers [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF][START_REF] Chen | Zr-in-rutile thermometry in eclogite and vein from southwestern Tianshan, China[END_REF]Meyer et al., 2016). Details on effective bulk rock compositions (EBCs), estimates and related pre-settings are given in Appendix A (see also Table 11 for EBCs).

Calculations were performed for different water activity scenarios. Under watersaturated conditions (i.e., αH2O = 1), moderate amounts of chlorite and lawsonite (~ca.

4-5 vol %) break down during the T pulse (for similar eclogite-facies dehydration see [START_REF] Groppo | Prograde P-T evolution of a lawsonite eclogite from the Monviso meta-ophiolite (Western Alps): dehydration and redox reactions during subduction of oceanic FeTi-oxide gabbro[END_REF][START_REF] Martin | Lawsonite geochemistry and stability-implication for trace element and water cycles in subduction zones[END_REF][START_REF] Tsujimori | Lawsonite blueschists and lawsonite eclogites as proxies for paleo-subduction zone processes: A review[END_REF]Vitale Brovarone et al., 2014). For a lower water activity of 0.8, chlorite and lawsonite breakdown increases slightly to ca. 6-7 vol %. Additional chlorite and lawsonite could break down before the T pulse for a water activity down to ~0.6. In the scenario where the T pulse coincides with a change in αH2O (i.e., from 0.6 to 1.0 on heating, and 1.0 to K D E 0.6 on cooling), the extent of chlorite and lawsonite breakdown can be quite limited around 1-1.5 vol % (Figure 40f).

Diffusion modeling

Diffusion modeling (Figure 41) is herein used to evaluate the conditions required to match the concordant MnYHREE enrichment during the ~80°C T pulse revealed by petrological data. Details of diffusion modeling are presented in Appendix B. 14. [START_REF] Skora | Diffusion-limited REE uptake by eclogite garnets and its consequences for Lu-Hf and Sm-Nd geochronology[END_REF] explained the existence of central peaks or annular maxima in garnet (for both Y and HREEs, but spatially discordant) by thermally accelerated diffusion REE uptake in the surrounding matrix, assuming a constant crystal growth rate and a non-linear T increase. Similar crystal diffusion modelling was performed with a prescribed interface velocity/growth rate, instead of calculated as part of the solution [START_REF] Alexander | Modeling diffusive dissolution in silicate melts[END_REF][START_REF] Ketcham | Numerical simulation of diffusion-controlled nucleation and growth of porphyroblasts[END_REF][START_REF] Watson | Non-equilibrium isotopic and elemental fractionation during diffusion-controlled crystal growth under static and dynamic conditions[END_REF].

However, porphyroblast growth rate depends on the exact growth mechanism [START_REF] Ague | Metamorphism as garnet sees it: The kinetics of nucleation and growth, equilibration, and diffusional relaxation[END_REF][START_REF] Carlson | The significance of intergranular diffusion to the mechanisms and kinetics of porphyroblast crystallization[END_REF] and on the competition between crystals interacting during diffusion-controlled growth, suggesting time-dependent growth rates with an important stochastic component [START_REF] Carlson | Porphyroblast crystallization: linking processes, kinetics, and microstructures[END_REF][START_REF] Hesse | A finite volume method for trace element diffusion and partitioning during crystal growth[END_REF]. A time-dependent growth rate (see App. B) is therefore applied throughout the diffusion modeling (except for the parametric study performed with a linear T-t path and growth rate: Figure 41b, g-j).

Influence of key parameters (for a linear T-t path)

The key input parameters, i.e. system size ( ), garnet radius ( ), pre-exponential factor ( ) of diffusion coefficient in matrix and activation energy ( ), were first tested along a linear T-time path (450 to 600 °C in 5 Myrs: black line in Figure 41b) to evaluate their impact on the existence and location of trace element peaks, using Y as a reference (Figure 41g-j; Table 14).

Increasing system size ( ) from 0.2 to 0.5 cm (Figure 41g) can lead to an outward shift of the annular Y peak of ~0.35 mm (i.e. ~1/4 of fixed garnet radius, Table 14).

Increasing the garnet radius ( ) from 0.72 to 1.44 mm (Figure 41h) will also produce

r R f D 0 m Q m r R f
an outward shift of ca. 0.20 mm. However, changing the pre-exponential factor ( ) -garnet radius ( ) strictly follows the measurements of the four large garnets (A1, A2, B1, C1) preserving the whole MnYHREE pulse.

and
-system size ( ) controls the overall element mass balance. Estimating it is difficult because it requires 3D investigation of the nucleation and growth history of the nearest neighbors [START_REF] Carlson | Porphyroblast crystallization: linking processes, kinetics, and microstructures[END_REF][START_REF] Skora | Diffusion-limited REE uptake by eclogite garnets and its consequences for Lu-Hf and Sm-Nd geochronology[END_REF]. Element accessibility for the earliest-grown (and largest) garnets suggests an initially large system size, decreasing with time as new (relative smaller) garnets nucleate in the vicinity of pre-existing porphyroblasts [START_REF] Skora | Diffusion-limited REE uptake by eclogite garnets and its consequences for Lu-Hf and Sm-Nd geochronology[END_REF]. According to our garnet survey (in 2D), the distance

D 0 m Q m D 0 m Q m r R f D 0 m Q m R f r
between the nearest neighbors and the large garnet B1 is ca. 0.52 cm (red line in Figure 48), suggesting that the half-distance from center to center to the nearest neighbor is a reasonable estimate for its system size (~ca. 0.26 cm); a similar assumption was made for all garnets.

-the garnet growth rate used here is expressed as a function of the final garnet radius ( ) and time duration of the various steps of T-t path ( , and ). It is neither a linear nor square root function of time, contrary to previous studies (e.g., [START_REF] Baumgartner | Modeling diffusion limited uptake of trace elements by eclogite garnets[END_REF][START_REF] Skora | Diffusion-limited REE uptake by eclogite garnets and its consequences for Lu-Hf and Sm-Nd geochronology[END_REF][START_REF] Weare | Diffusion metasomatism and mineral reaction zones; general principles and application to feldspar alteration[END_REF]. This assumption allows to reproduce corepeak to secondarypeak distance and to fit the joint annular MnYHREE pulse observed in any given garnet and the similar Mn zoning among diverse size garnets (taking place at = 0.077 ± 0.004 cm, Figure 40).

-initial element concentrations in the matrix are those of the unfractionated bulk rock composition (i.e., EBC0, calculated by normalized XRF+ICP-MS data, Table 11).

-the activation energy ( ) and pre-exponential diffusion factor are theoretically covariant for each element in both the porphyroblast ( , , garnet) and matrix ( , , mainly clinopyroxene) but generally poorly constrained [START_REF] Brady | Diffusion in minerals: an overview of published experimental diffusion data[END_REF] or missing (e.g., in the P-T window considered here, UHP and Tmax<500-600°C). For the sake of simplicity, the activation energy is here fixed at ~300 kJ/mol ( ), following experiments for Mn, HREEs & Y diffusivities in garnet/diopside (at ~ca. 1000 °C) giving ~ca. 220 to 480 kJ/mol [START_REF] Carlson | Rates of Fe, Mg, Mn, and Ca diffusion in garnet[END_REF][START_REF] Carlson | Rates and mechanism of Y, REE, and Cr diffusion in garnet[END_REF][START_REF] Chu | Analysis of experimental data on divalent cation diffusion kinetics in aluminosilicate garnets with application to timescales of peak Barrovian metamorphism[END_REF][START_REF] Dimanov | Average" interdiffusion of (Fe,Mn)-Mg in natural diopside[END_REF][START_REF] Dimanov | Fe, Mn)-Mg interdiffusion in natural diopside: effect of pO2[END_REF][START_REF] Van Orman | Rare earth element diffusion in diopside: influence of temperature, pressure, and ionic radius, and an elastic model for diffusion in silicates[END_REF][START_REF] Van Orman | Rare earth element diffusion in a natural pyrope single crystal at 2.8 GPa[END_REF]. Similarly,

R f t n t p t n' R p Q k D 0 k Q g D 0 g Q m D 0 m Q g = Q m Q k D 0 g
is set at a fixed 1×10 6 cm 2 /yrs for Mn, HREEs and Y diffusivities in garnet (yet, at ~ ca. 1000 °C, experiments yield estimates one order of magnitude smaller; [START_REF] Carlson | Rates of Fe, Mg, Mn, and Ca diffusion in garnet[END_REF][START_REF] Carlson | Rates and mechanism of Y, REE, and Cr diffusion in garnet[END_REF][START_REF] Chu | Analysis of experimental data on divalent cation diffusion kinetics in aluminosilicate garnets with application to timescales of peak Barrovian metamorphism[END_REF][START_REF] Van Orman | Rare earth element diffusion in a natural pyrope single crystal at 2.8 GPa[END_REF].

-by contrast, we vary the pre-exponential diffusion factor in the matrix to fit the observed garnet zonation profiles. The fitted hence represents the bulk diffusive response of the matrix to a "sink" or source term for a specific divalent/trivalent cation, and serves as a macroscopic effective property of each sample (i.e., it includes potential effects of the structure of grain boundaries, of porosity, as well as of the conceivable contribution of the trace elements' accumulation on the grain boundaries and intra-grain diffusion; e.g., [START_REF] Dohmen | Mechanism and kinetics of element and isotopic exchange mediated by a fluid phase[END_REF][START_REF] Ganguly | Cation Diffusion Kinetics in Aluminosilicate Garnets and Geological Applications[END_REF][START_REF] Hiraga | Grain boundaries as reservoirs of incompatible elements in the Earth's mantle[END_REF].

-the duration of investigated garnet A1 growth is set at 5 Myrs, broadly agree with an estimated duration of garnet growth ( ) of 7.6 ± 6.8 Myrs, inferred from the gap between Lu-Hf and Sm-Nd ages of regional blueschists (Soldner et al., 2016).

Relevant boundary conditions for each modeling round are listed in Table 14.

Three distinct T-t trajectories with fixed T0 (at 450°C; Figure 41b-f) and variable

Tf associated with a 80°C T pulse of 1 Myr were tested to evaluate the impact of different Tf (500 to 550°C) and pre-exponential diffusion factors in matrix (8×10 10 to 8×10 13 cm 2 /yrs). The Mn profile of garnet A1 is taken as reference (Figure 41c-f; modeling Runs 16 to 27, Table 14). The linear T-t path within 5 Myrs from 450 to 600°C (without 80 °C T pulse in anytime) is used for comparison.

D 0 m D 0 m t f D 0 m
With a relatively fast ~8×10 13 cm 2 /yrs (Fig. 5c; i.e., a value comparable to experimental constraints at ca. 1000°C for Mn diffusivity in natural diopside, converted with applying Qm=300kJ/mol; [START_REF] Dimanov | Average" interdiffusion of (Fe,Mn)-Mg in natural diopside[END_REF][START_REF] Dimanov | Fe, Mn)-Mg interdiffusion in natural diopside: effect of pO2[END_REF], no secondary peak is produced, whatever the T-t path and with or without T pulse. All profiles resemble a classical "Rayleigh fractionation" pattern (e.g., [START_REF] Hollister | Garnet zoning: an interpretation based on the Rayleigh fractionation model[END_REF][START_REF] Otamendi | Rayleigh fractionation of heavy rare earths and yttrium during metamorphic garnet growth[END_REF]. Decreasing by one to three log10 units in magnitude (Figure 41d-f) reduces the gap between modeled and observed profiles, especially for the Mn secondary peak (Figure 41e-f). However, depending on , the early part of the modeled Mn profiles, before the secondary peak, may largely deviate from the observed profile. The best fit is observed for of 8×10 11 cm 2 /yrs. Further tests 14). See text for details.

D 0 m D 0 m D 0 m D 0 m
explore the duration of garnet growth ( ) versus that of the T pulse ( ; Figure 41k-l;

Runs 28 to 33, Table 14). At fixed ~8×10 11 cm 2 /yrs, a transient of 0.3 Myrs ( set as 5 Myrs) fits measured profiles much better than a longer lived of 1 Myr ( set as 2 Myrs).

Overall, the best-fit (red profile in Fig. 41l) is obtained with conditions of Tf = 500°C, = 8×10 11 cm 2 /yrs and ~5 Myrs accompanied by transient (~ca. 1/20 of ) ~80°C T pulse (Run 30; Table 14).

Modeling garnet zoning with a transient thermal pulse

Further tests were performed to try and reproduce 1) annular Mn zonation among diverse size garnets and 2) annular joint MnYHREE pulse in garnet A1 under the same scenario.

In order to account for differences in radius and grain distribution in the different samples (i.e., garnets A1-2, B1, C1, Figure 42a), some minor adjustment of the and (for Mn) parameters is needed with respect to those used to best fit Mn zoning in garnet A1 (Figure 41), allowing to vary by less than one order of magnitude only.

Best-fit results and fitting parameters are presented in Figure 42a 14).

Potential differences in diffusion rate of HREEs and Y in the matrix need to be considered to account for the concordant MnYHREE zoning, since experiments show

t f t p D 0 m t p t f t p t f D 0 m t f t f t f D 0 m D 0 m R p
that differences in ionic radius amongst the HREES impact diffusivity in diopside, from Dy to Lu, by ~1 log10 unit (converted into Q = 300kJ/mol, [START_REF] Van Orman | Rare earth element diffusion in diopside: influence of temperature, pressure, and ionic radius, and an elastic model for diffusion in silicates[END_REF].

Additional tests, increasing diffusion rates by about one log10 unit with decreasing ionic radius (Dy to Lu), were therefore applied to obtain best-fit value of for each HREE and Y profile (see Figure 42c-i and Table 14; Run 37 to 43). The main carriers of L/MREEs (± HREEs), Sc, and Sr in blueschists/eclogites (i.e., within the "subduction factory") are epidote group minerals and lawsonite.

Discussion

Apatite, ilmenite, titanite, rutile and zircon, respectively, serve as important carriers of P + Mn + HREEs, Ti + Mn + REEs, Ti + HREEs and Zr + HREEs [START_REF] Spandler | Redistribution of trace elements during prograde metamorphism from lawsonite blueschist to eclogite facies; implications for deep subduction-zone processes[END_REF][START_REF] Spandler | Element recycling from subducting slabs to arc crust: A review[END_REF]. The lack of corresponding secondary peaks of MREEs and key trace elements (Ti, Sr, Zr, Sc, Rb, P; Figure 39e-h) essentially allows to discard mineral breakdown as a major cause. Furthermore, no breakdown of apatite and titanite/rutile is observed together with garnet growth, as shown by Ti and P mapping (Figure 45a-b).

Predicted amounts of chlorite and lawsonite breakdown accompanying garnet growth along a temperature pulse such as revealed by Zr-in-rutile data (Figure 48d), lie in the range 1.5-7.0 vol % (lws) and 1.0-6.0 vol % (chl), whatever the aH2O value (Figure 40f). Their breakdown predicts a joint supply of major and trace elements with a 40/35/30 wt% increase in L/M/HREEs and 21% in CaO (for lawsonite) and a 11/3/22 wt% increase in MnO, MgO and FeO for chlorite. These joint enrichments conflict, however, with the decoupled trends observed for Fe, Mg, Ca and Mn, HREEs, Y in the various garnet profiles/maps (Figure 38,39,47). We therefore conclude that this specific garnet zoning cannot be ascribed to the breakdown of potential Mn-and/or REE-rich major minerals (i.e., epidote, lawsonite, chlorite, apatite, Ti-rich phases). The observation that the metamorphic system remained isotopically closed [START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF]) also indicates minimum external fluid infiltration.

Zr concentrations found in rutile grains (Figure 38e, Table 13) match those reported in nearby eclogites [START_REF] Chen | Zr-in-rutile thermometry in eclogite and vein from southwestern Tianshan, China[END_REF][START_REF] Li | Fluid-mediated metal transport in subduction zones and its link to arc-related giant ore deposits: Constraints from a sulfide-bearing HP vein in lawsonite eclogite (Tianshan, China)[END_REF][START_REF] Zhang | Nb-Ta mobility and fractionation during exhumation of UHP eclogite from southwestern Tianshan, China[END_REF].

Given the relatively moderate regional Tmax (<500-600°C), these Zr signatures can probably be considered as pristine and not affected by later intracrystalline diffusive resetting [START_REF] Cherniak | Zr and Hf diffusion in rutile[END_REF][START_REF] Kohn | Implications of near-rim compositional zoning in rutile for geothermometry, geospeedometry, and trace element equilibration[END_REF][START_REF] Penniston-Dorland | A mélange of subduction temperatures: Evidence from Zr-in-rutile thermometry for strengthening of the subduction interface[END_REF], thereby providing a faithful record of the temperature evolution. An alternative interpretation could be that the lower Zr concentrations of matrix rutile grains (e.g., ~20

µg/g Zr, Figure 38d-e, Table 13) result from retrograde reequilibration, implying exsolution of high Zr-phases to produce lower-Zr rutile during cooling [START_REF] Penniston-Dorland | A mélange of subduction temperatures: Evidence from Zr-in-rutile thermometry for strengthening of the subduction interface[END_REF]. No Zr-bearing phase was however found rimming investigated rutile grains (e.g., zircon, very bright in BSE image, than rutile, Figure 45e-f), strengthening the view that the estimated T pulse of ~80°C is real.

Necessity of a transient thermal pulse and implications for thermodynamic modeling

Control on Y+REEs concentrations in garnet by diffusion through the intergranular medium was first proposed by [START_REF] Skora | Diffusion-limited REE uptake by eclogite garnets and its consequences for Lu-Hf and Sm-Nd geochronology[END_REF] and reappraised by [START_REF] Hesse | A finite volume method for trace element diffusion and partitioning during crystal growth[END_REF] and [START_REF] Moore | Origins of yttrium and rare earth element distributions in metamorphic garnet[END_REF]. This predicts, however, that the location of Y+REEs (mantle) peaks will differ for each element [START_REF] Skora | Diffusion-limited REE uptake by eclogite garnets and its consequences for Lu-Hf and Sm-Nd geochronology[END_REF] this study; Figs 5g-j) owing to the significant dependence of uptake on competing rates of crystal growth ( , Eq. ( 7)), intergranular diffusion ( , Eq. ( 8), Figure 41i), changes in system size ( , Figure 41g), crystal radius ( , Figure 41h) and activation energy ( , Figure 41j). 14; red-line, Figure 41l). By contrast, no secondary peaks can be retrieved, even for small (Figure 41f), by applying a linear T-time path with identical growth rate derived from fixed (Eq. ( 7b)).

R(t)

D m (T ) r R f Q D 0 m R f t f t p R p T f D 0 m t f t p t p t f D 0 m R p
The zoning patterns described here reveal an increase in Mn concentration coincident with a temperature increase, which goes against usual thermobarometric inferences (e.g., [START_REF] Baxter | Garnet: A rock-forming mineral petrochronometer[END_REF][START_REF] Caddick | Garnet: Witness to the Evolution of Destructive Plate Boundaries[END_REF]. Diffusion-controlled garnet growth is generally not considered when applying thermobarometry, however, and this study suggests that care should be taken in directly relating major element zoning with T and P evolutions. The lack of significant zoning in Ca, Fe and Mg associated with the thermal pulse is also surprising: this may indicate that the thermal pulse may have been too short to effectively modify the diffusion of these cations in the system.

Geodynamic significance of a transient thermal pulse

The existence of a transient thermal pulse is identified based on (i) variations in Zr concentration in rutile grains accompanying garnet growth (i.e., ∆T ~80°C) and (ii) modeling of the specific annular MnYHREE zoning through a T-time pulse. This chemical zoning is observed for garnet grains from samples meters apart (Figure 37d), demonstrating that this thermal pulse is at least an outcrop-scale phenomenon. Its spatial extension is in fact probably much larger, since a similar concordant MnYHREE zoning can be observed in eclogites and mafic schists in two adjacent valleys ~10 km apart [START_REF] Klemd | Changes in dip of subducted slabs at depth: Petrological and geochronological evidence from HP-UHP rocks (Tianshan, NW-China)[END_REF]: samples FTS9-2 and FTS5-15, their figures 2a-c, 2k-i;

annular Mn garnet zoning was also documented in eclogitic mafic boudins ~12km to the east: samples 11-06-5 and 11-06-6, their figures 4d, 4g in Meyer et al., 2016).

Further evidence can thus probably be gathered from the STMB. However, preservation/formation of this type of zoning requires an almost closed system behaviour (which is probably not the case for most samples across the region, as shown by the distributed blueschist/eclogite veins arguing for efficient fluid circulation; e.g., [START_REF] Gao | Mobilization of Ti-Nb-Ta during subduction: Evidence from rutile-bearing dehydration segregations and veins hosted in eclogite, Tianshan, NW China[END_REF][START_REF] John | Trace-element mobilization in slabs due to non steady-state fluid-rock interaction: constraints from an eclogite-facies transport vein in blueschist (Tianshan, China)[END_REF][START_REF] Li | Fluid-mediated metal transport in subduction zones and its link to arc-related giant ore deposits: Constraints from a sulfide-bearing HP vein in lawsonite eclogite (Tianshan, China)[END_REF], since final patterns of garnet Mn profiles are extremely sensitive to the variation of (Figure 41c-f). Any external supply of Mn, HREEs and Y could similarly boost intergranular diffusivities, thereby hindering the formation of a pulse and producing a monotonic profile (i.e., Rayleigh Fractionation. [START_REF] Hollister | Garnet zoning: an interpretation based on the Rayleigh fractionation model[END_REF][START_REF] Otamendi | Rayleigh fractionation of heavy rare earths and yttrium during metamorphic garnet growth[END_REF] or oscillatory zoning [START_REF] Li | Fluid-mediated metal transport in subduction zones and its link to arc-related giant ore deposits: Constraints from a sulfide-bearing HP vein in lawsonite eclogite (Tianshan, China)[END_REF][START_REF] Moore | Origins of yttrium and rare earth element distributions in metamorphic garnet[END_REF].

D 0 m
petrological observations (e.g., [START_REF] Blanco-Quintero | Tectonic blocks in serpentinite mélange (eastern Cuba) reveal large-scale convective flow of the subduction channel[END_REF]. Although tectonic slices rather than mélange formation characterize the STMB [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF][START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF], any fast translation of UHP slices nearer to a relatively hotter mantle wedge (for example following detachment from the slab; Figure 44) might trigger a transient thermal excursion. To match a ~80°C thermal pulse a ca. 1-5 cm/yr up-dip movement of detached UHP slices would be required, considering a ~3.5 km wide plate interface with a ~150°C temperature difference across [START_REF] Abers | Seismic low-velocity layer at the top of subducting slabs: observations, predictions, and systematics[END_REF][START_REF] Gerya | Exhumation of high-pressure metamorphic rocks in a subduction channel: A numerical simulation[END_REF][START_REF] Ruh | Tectonic slicing of subducting oceanic crust along plate interfaces: Numerical modeling[END_REF]. So far the (few) estimates for the duration of garnet growth point to Myr [START_REF] Ernst | Subduction, ultrahigh-pressure metamorphism, and regurgitation of buoyant crustal slices-implications for arcs and continental growth[END_REF][START_REF] Green | Psychology of a changing paradigm: 40+ years of high-pressure metamorphism[END_REF][START_REF] Rubatto | Exhumation as fast as subduction?[END_REF]. Some numerical models of oceanic crust subduction with fast convergence and steep cold slab show ~cm/yr movements during early detachment which could match our observations (12 cm/yr, 60˚ angle. [START_REF] Ruh | Tectonic slicing of subducting oceanic crust along plate interfaces: Numerical modeling[END_REF]. Appendix A. Thermodynamic modeling for the estimate of mineral modes evolution and effective partition coefficient

Conclusion

Garnet size distribution (Figure 48) was investigated to derive effective bulk rock compositions (EBCs, Figure 49, Table 11), i.e. taking into account progressive garnet fractionation from the whole-rock composition, and to evaluate the evolution of mineral mode (Figure 40f) under a specific P-T loop (i.e., T pulse, Figure 40f). This allows estimating dynamic effective partition coefficient of specific elements during the modeling of diffusion-controlled garnet growth (App. B.).

Garnet size distribution (Figure 48) was estimated using Photoshop manual coloring (for each garnet grain) and assuming euhedral garnet ranges from pentagonto octagon-shape to derive radius (and corresponding uncertainties). Modal proportions of each garnet group (large, middle and small; see main text for grouping strategy and

where represent the fitted polynomial equations for given element concentration profile as a function of . The fractionated mass from the matrix, as a result of garnet growth, can be calculated by integrating within the relevant range :

(

Successive fractions were thus substracted XRF bulk rock composition to account for the growth of garnet core, mantle and rim and estimate EBCs used for thermodynamic and diffusion modelling. Calculated EBCs are shown in Table 11.

Thermodynamic modeling was performed with Perple_X [START_REF] Connolly | Multivariable phase diagrams; an algorithm based on generalized thermodynamics[END_REF][START_REF] Connolly | Computation of phase equilibria by linear programming: a tool for geodynamic modeling and its application to subduction zone decarbonation[END_REF] using successively the unfractionated bulk-rock composition (i.e., EBC0, Table 11) and garnet-fractionated effective bulk rock compositions (EBC1-2, Table 11) to estimate minerals modes along the near-peak prograde path. Pressure is fixed at 2.75 GPa for simplification, and temperature increases from 450 to 500 °C, with a short-lived ~80

V g R g a a = V grt-x measured / R grt-x max grt -x V grt-x measured R grt-x max c g = f (V g ) f c (V g ) V g C g f c (V g ) V [0, V g ] C g = f (V g )dV 0 V grt -x ò V grt -x x=L,M ,S
å °C T excursion. The database and solid solutions are the same as in [START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF].

Different values of αH2O (Figure 40f), as well as a temperature-dependent change in αH2O, were applied via T-αH2O pseudosections to test its influence on the predicted mineral modes.

Generally, garnet central peak concentrations (of given element) of the profiles were compared to the bulk rock composition to estimate the bulk distribution coefficient [START_REF] Hollister | Garnet zoning: an interpretation based on the Rayleigh fractionation model[END_REF], assuming that the effective matrix concentration during garnet growth equals that of the bulk rock composition [START_REF] Skora | Diffusion-limited REE uptake by eclogite garnets and its consequences for Lu-Hf and Sm-Nd geochronology[END_REF].

is treated as constant at a given temperature and pressure, for a sufficiently dilute trace component between two phases (e.g., [START_REF] Hesse | A finite volume method for trace element diffusion and partitioning during crystal growth[END_REF][START_REF] Skora | Diffusion-limited REE uptake by eclogite garnets and its consequences for Lu-Hf and Sm-Nd geochronology[END_REF]. Two values of effective , before and after the concordant pulse in concentrations, were considered (Figure 43): , which describe the ratio between P-T dependent activity coefficients v g i and v EBC 0,1 i , is treated to approach unity. Calculations of initial (i.e., c g-c i c EBC 0 i

K D E = c g-c i c EBC 0 i ; c g-ml i c EBC1 i ae è ç ç ö ø ÷ ÷ v g i v EBC 0,1 i ae è ç ç ö ø ÷ ÷ P ,T ( ) (4
) will be particular sensitive to uncertainties in the location of the central cuts with respect to garnet cores. Potentially

K D K D K D E i K D
missed central peaks of some garnets were estimated in proportion of the sharp central peak pattern of the largest garnet B1 (for Mn) and relative smaller garnet A1 (for Y, Tm, Lu, Yb and Er). Values of for each element are listed in Table 14.

Appendix B. Finite volume diffusion modeling

The finite volume method from Hesse (2012), with spherical geometry in a uniform matrix, is used to compute the diffusion and partitioning of trace elements during porphyroblast growth (Figure 41a). Diffusion on both sides of the moving crystal-matrix interface are explicitely considered in this study (i.e., intragranular and matrix diffusion), whereas most previous studies only consider diffusion in the matrix (e.g., [START_REF] Castro | Timescales of spherulite crystallization in obsidian inferred from water concentration profiles[END_REF][START_REF] Skora | Diffusion-limited REE uptake by eclogite garnets and its consequences for Lu-Hf and Sm-Nd geochronology[END_REF][START_REF] Skora | Estimation of a maximum Lu diffusion rate in a natural eclogite garnet[END_REF][START_REF] Watkins | Diffusion-controlled spherulite growth in obsidian inferred from H2O concentration profiles[END_REF] or inside the growing porphyroblast (e.g., [START_REF] Alexander | Modeling diffusive dissolution in silicate melts[END_REF]. The motion of the crystalmatrix interface and the thermal evolution are prescribed as time functions. The appropriate conditions for the diffusion flux across the crystal-matrix interface are derived from discrete mass conservation.

The evolution of the concentration profiles is controlled by:

(1a) (1b)
Where and represent the accumulation and the diffusive flux of the trace element in the k-phase. The phase subscript refers to garnet and to the matrix.

The exponential factor on reflects the radial dependence of volume and area in spherical coordinates. The Diffusive flux in k-phase is defined by:

K D E ¶ ¶t (r 2 c g ) + ¶ ¶r (r 2 F g (c g )) = 0, on W g [r min , R] ´[0,t f ] ¶ ¶t (r 2 c m ) + ¶ ¶r (r 2 F m (c m )) = 0, on W m [R,r max ] ´[0,t f ] r 2 c k F k g m 2 r F k (2)
Where is the diffusion coefficient in k-phase, and initial conditions in each spatial domain are given by:

(3a) (3b)
Four boundary conditions are required. Two are at the internal interface (i.e., garnet radius, Figure 41a) and the other two are at the outer boundaries of the domain (i.e., system size, Figure 41a). Hesse (2012) assumed that concentration profiles are symmetric across the center of the porphyroblast and that the matrix surrounding it acts as a closed system, so that: (6a)

F k = -D k ¶c k ¶r D k c g (r,0) = c g 0 , on W g [r min , R] c m (r,0) = c m 0 , on W m [R,r max ] R r F g (r min ) = F m (r max ) = 0 F I c g = K D E c m K D E lim r®R -F g (r ) = lim r®R + F m (r ) = F I (R) lim r®R -c g (r ) = K D E lim r®R + c m (r ) T(t) R(t) T(t) = (T f -T 0 )t t n + t p + t n' + T 0 , t [0, t n ] (6b) (6c) (6d)
Where and represent the initial and final value at and , respectively. represents the absolute change of temperature during the thermal pulse and is fixed at a constant 80°C following estimates of Zr-in-rutile thermometry (Figure 38, 45, Table 13; Table 14). , and are the variable on different modeling runs for constraining the time duration of processes before ( ), during (

) and after ( ) the T pulse. To account for the concordant Mn zoning among diverse size garnets (i.e. at = 0.77 ± 0.04 mm; Figure 40), the garnet growth rate is computed using a polynomial power-law equation with variable exponent :

(7a) (7b)
Where = 0, and are 1.22, 1.10, 1.58 and 1.12 mm respectively (for A1-2, B1 and C1 garnets; Figure 40,46). , in contrast, was set constant at 0.77 mm (Figure 40a), except for test calculations performed along an ordinary T-t path (Figure 41b, gj) for which R(t) follows a linear evolution. Since all garnet growth rates are the same and set to follow that of garnet A1 (i.e., in Eq (7a); n=6.34), slight to moderate differences are predicted for their total growth duration.

R p R(t) n R(t) = R 0 + (R f -R 0 )( t t n + t p + t n' ) n , t [0, t n + t p + t n' ] n = log t n +0.5t p t n +t p +t n' ae è ç ö ø ÷ R p -R 0 R f -R 0 ae è ç ö ø ÷ R 0 R f R p
The diffusion coefficient of divalent/trivalent cations in matrix and growing porphyroblast is expressed as a function of temperature by Arrhenius equation:

Where is the pre-exponential factor, is the constant activation energy, is the universal gas constant, and is the phase subscript (herein, represent garnet porphyroblast and matrix respectively). In this study, the constant activation energy will be fixed at 300 kJ/mol (except for benchmarks tests for varying , Table 14) for simplification since the finite volume model from Hesse ( 2012) is mostly sensitive to variations on (Figure 41j). The interested reader is refered to [START_REF] Hesse | A finite volume method for trace element diffusion and partitioning during crystal growth[END_REF] for further modelling details.

Appendix C. Analytical methods

Major elements electron microprobe analyses and mapping

Most major element compositions of garnet, mineral inclusions and matrix minerals, as well as relevant profiles and mapping analyses, were obtained by electron microprobe analyses at IGGCAS with JEOL JXA 8100 under presettings of wavelength dispersive spectrometers with an acceleration voltage of 15 kV, a beam current of 15 nA, at 1 to 3 μm beam size and 30 s counting time. Additional high resolution Mn, Y, P and Ti mapping for key garnet grain (A1, Figure 38a-b, 45) with 15 kV acceleration voltages and 200 nA beam current under 60 ms dwell time was conducted on CAMECA SX Five FE at IGGCAS. Natural minerals and synthetic oxides were used as standards,

T D k = D 0k exp( -Q k UT ) D 0 k Q k U k Q k Q k Q k
and a program based on the ZAF procedure was used for data correction. Average compositions for mineral chemistry of studied UHP eclogite are presented in Table 12.

Laser-ablation ICP-MS trace elements analyses

In situ trace element point and profile (Figure 38b-c LA-ICP-MS measurements were conducted using a spot size diameter of 60 μm with a laser frequency of 15 Hz and 0.63 GW/cm2 and a fluence of 3.32 J/cm2. Acquisition time was 20 s for the background and 120 s for the mineral analyses. The Ca-content of garnet determined by EMPA was used as internal standard. Reproducibility and accuracy, which were determined for NIST SRM 610 and NIST SRM 612, are usually <8% and <6%. Trace element concentrations were then calculated using GLITTER Version 3 [START_REF] Van Achterbergh | GLITTER: On-line interactive data reduction for the laser ablation inductively coupled plasma mass spectrometry microprobe[END_REF]. Average trace element composition of the relevant garnet domains and associated minerals are given in Table 12, following their microprobe data.

Zirconium contents of rutile electron microprobe analyses

Concentrations of Zirconium in rutile were determined by electron microprobe following the method outlined by [START_REF] Zack | Temperature dependence of Zr in rutile: empirical calibration of a rutile thermometer[END_REF], since the size of most rutile euhedral inclusions in garnet A1 (Figure 38d) were too small (ca. 5 to 30 um in dia., Figure 38d, 45) to be analysed by LA-ICP-MS. All analyses were conducted with a optimised so that detect limits on Zr could be improved by four times (20 µg/g compared with 80 µg/g). Acceleration voltage was set at 20 kV with 120 nA beam current and 5 um beam diameter. A H-type spectrometer was chosen for measuring Zr-Lα because of its highest sensitivity for this element. Detailed settings for spectrometers followed the Table 2 of [START_REF] Zack | Temperature dependence of Zr in rutile: empirical calibration of a rutile thermometer[END_REF]. Every 10 analyses of unknown rutile were bracketed by 2 analyses of synthetic rutile standard for true zero-concentration count rates on the peaks and to exclude any machine drift. Summary of rutile measurements with respect to their location is presented in Table 13. This study Garnet (A1 as example)

12. 5Major oxides (wt%) Trace elements (ug/g) Table 12: NOTES: "bd" means below the detect limitaion of LA-ICP-MS. "-" means do not calculated or analysed. Oxides/elements with bold italic mark mean those used in thermodynamic modeling for the estimate of mineral mode evolution and the modeling of elements-uptake during garnet growth and the recovery of relevant garnet profiles based on diffusion modeling.

Considering the limitation of the tiny size (≪45um*45um) of garnet mineral inclusions, the trace elements composition of omphacite and amphibole are analysed from corresponding minerals in the matrix around garnet1. Lawsonite is assumed to be existed around peak metamorphism because of the thermodynamic modeling results and the finds of box-sharp inclusions of lwspseudomorph in garnet1 [START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF], and corresponding data are cited from Spanlder et al ( 2003) and Vitale Brovarone et al ( 2014). The Zr concentrations of garnet mantle annular peak domain and amphibole in matrix are marked with "*" and present quite distinct absolute values and uncertainties compared with the rest of garnet domains, cause some of its analysis points had Zr concentration as high as 50 to 550 ppm, respectively, but the rest still bear Zr concentration level as low as ca. 2 ppm, similar to that of the rest of garnet domains, probably because of the existence of micro-grain zircon inclusions.

Introduction

Mechanisms and processes responsible for the occasional recovery of oceanderived high-to ultra-high pressure low temperature (HP-UHP/LT) metavolcanics/metavolcanoclastics equilibrated along the subduction plate interface [START_REF] Agard | Exhumation of oceanic blueschists and eclogites in subduction zones: timing and mechanisms[END_REF] are essential to constrain subduction dynamics and gain insights on the meter-to hectometer-scale constitution of the plate boundary (Bachmann et al., 2009;Stöckhert, 2012;Agard et al., 2018 and references therein). The diversity of subducted material, either from the downgoing plate (generally the uppermost section, i.e. pelagic sediments with basaltic oceanic crust and/or seamounts) or upper plate derived (i.e., ashes from arc-volcanism and/or detrital sediments in the accretionary wedge, and/or basement material if basal erosion occurs), is likely to influence viscosity, density and thus buoyancy, and to control chemical and mechanical behaviors within the plate interface [START_REF] Bebout | Metamorphic chemical geodynamics of subduction zones[END_REF][START_REF] Bebout | Metasomatism in Subduction Zones of Subducted Oceanic Slabs, Mantle Wedges, and the Slab-Mantle Interface[END_REF][START_REF] Yamato | Burial and exhumation in a subduction wedge: Mutual constraints from thermomechanical modeling and natural P-T-t data (Schistes Lustrés, western Alps)[END_REF]Krebs et al., 2011).

Regardless of their origin, subducted material transported on top of the subducting plate may be stripped from the slab as mélange (e.g., [START_REF] Blanco-Quintero | Tectonic blocks in serpentinite mélange (eastern Cuba) reveal large-scale convective flow of the subduction channel[END_REF][START_REF] Wakabayashi | Mélanges of the Franciscan Complex, California: Diverse structural settings, evidence for sedimentary mixing, and their connection to subduction processes[END_REF][START_REF] Wakabayashi | Anatomy of a subduction complex: Architecture of the Franciscan Complex, California, at multiple length and time scales[END_REF] or tectonic slices (e.g., [START_REF] Angiboust | Insights on deep, accretionary subduction processes from the Sistan ophiolitic "mélange" (Eastern Iran)[END_REF][START_REF] Bonnet | Tectonic slicing and mixing processes along the subduction interface: The Sistan example (Eastern Iran)[END_REF][START_REF] Locatelli | Intermediatedepth brecciation along the subduction plate interface (Monviso eclogite, W. Alps)[END_REF] and later juxtaposed during exhumation. To unravel the fate of deeply subducted material (down to ~80 km depth), the Chinese South Tianshan Metamoprhic Belt (STMB) is a potentially important example. It is indeed characterized by an unusually thick (~5km) pile of well-preserved HP/UHP metavolcanoclastics [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF] wrapping eclogite boudins/slices with numerous coesite findings (e.g., [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF]Lü & Zhang, 2012;[START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF].

However, despite numerous studies providing detailed petrological, geochemical evolutions or geochronology data (e.g., [START_REF] Gao | Mobilization of Ti-Nb-Ta during subduction: Evidence from rutile-bearing dehydration segregations and veins hosted in eclogite, Tianshan, NW China[END_REF][START_REF] John | Trace-element mobilization in slabs due to non steady-state fluid-rock interaction: constraints from an eclogite-facies transport vein in blueschist (Tianshan, China)[END_REF]Klemd et al., 2011;[START_REF] Van Der Straaten | Tracing the effects of high-pressure metasomatic fluids and seawater alteration in blueschist-facies overprinted eclogites: Implications for subduction channel processes[END_REF]Tan et al., 2017 and references therein), the internal structures and tectonic evolution of the STMB remain poorly constrained: why is it so thick so deep, and what can we learn from this exceptional example across a depth range critical for mechanical coupling (~80 km; [START_REF] Syracuse | The global range of subduction zone thermal models[END_REF][START_REF] Wada | Common depth of slab-mantle decoupling: Reconciling diversity and uniformity of subduction zones[END_REF]? The present study provides for the first time a detailed, fully coupled tectono-metamorphic-radiometric study across the STMB, combining a composite ~30 km long cross-section, average PT estimates for each domain and in-situ Ar-Ar dating (together with zircon U-Pb and step-heating measurements) to provide age constraints with deformation control. Results allow to discuss the conditions of recovery, exhumation rates and implications for subduction processes and regional geodynamics.

Geological Setting of SW-Tianshan Accretionary Complex

The Chinese Southwestern Tianshan high-to ultrahigh-pressure low-temperature (HP/UHP-LT) accretionary complex constitutes the eastern part of the Kazakhstan collage system [START_REF] Gao | Large-scale porphyry-type mineralization in the Central Asian metallogenic domain: A review[END_REF]and references therein) within the Altaids (also called the Central Asian Orogenic Belt; Figure 50a). It extends for about 200 km along the Southwestern Central Tianshan Suture Zone (SCTSZ, Figure 50b), and correlates with the Atbashi (Hegner et al., 2010;[START_REF] Loury | Tectonometamorphic evolution of the Atbashi highpressure units (Kyrgyz CAOB, Tien Shan): implications for the closure of the Turkestan Ocean and continental subduction-exhumation of the South Kazakh continental margin[END_REF][START_REF] Simonov | Conditions of formation of the Atbashi Ridge eclogites (South Tien Shan)[END_REF], Chatkal [START_REF] Loury | Late Paleozoic evolution of the South Tien Shan: Insights from P -T estimates and allanite geochronology on retrogressed eclogites (Chatkal range, Kyrgyzstan)[END_REF][START_REF] Mühlberg | Late Carboniferous high-pressure metamorphism of the Kassan Metamorphic Complex (Kyrgyz Tianshan) and assembly of the SW Central Asian Orogenic Belt[END_REF] and Fan-Karategin (U)HP metamorphic complexes [START_REF] Volkova | Geochemical discrimination of metabasalt rocks of the Fan-Karategin transitional blueschist/greenschist belt, South Tianshan, Tajikistan: seamount volcanism and accretionary tectonics[END_REF] in the Kyrgyzstan part of the South Tianshan Orogenic Belt (STOB). The SCTSZ bounds to the north the Chinese section of the HP-UHP/LT metamorphic complex, known as the Akeyazi metamorphic complex (AMC, Figure 50c). This contact, now a ~0.5 km-wide dextral strike-slip shear zone, was active from the Early Permian to Early Triassic [START_REF] Gao | but not systematically[END_REF][START_REF] Laurent-Charvet | Late Paleozoic strike-slip shear zones in eastern central Asia (NW China): New structural and geochronological data[END_REF]. To the north lies a LP-HT Palaeozoic active continental margin [START_REF] Allen | Palaeozoic collisional tectonics and magmatism of the Chinese Tien Shan[END_REF]Gao et al., 1998;[START_REF] Klemd | Metamorphic evolution of (ultra)-highpressure subduction-related transient crust in the South Tianshan Orogen (Central Asian Orogenic Belt): Geodynamic implications[END_REF], mainly made of amphibole-and granulitefacies rocks, along with Late Silurian and Early Carboniferous continental arc-type volcanic, volcaniclastic rocks and granitoids (Gao et al., 2009a;Xia et al., 2014). To the south the AMC is overlain by unmetamorphosed and/or low grade Palaeozoic sedimentary strata, which also represent the northern, passive continental margin of the Tarim plate (Carroll et al., 1995).

The AMC is predominantly composed of strongly schistosed metavolcanoclastics hosting mafic metavolcanics as pods, lenses, boudins, thin layers or massive blocks [START_REF] Gao | but not systematically[END_REF] and marble horizons [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF], as well as very rare ultramafic rocks (Li et al., 2010;[START_REF] Shen | UHP metamorphism documented in Ti-chondrodite-and Ti-clinohumite-bearing serpentinized ultramafic rocks from Chinese southwestern Tianshan[END_REF]. Whole-rock geochemical data for the mafic metavolcanics suggest oceanic basalt or arc-related affinities [START_REF] Gao | but not systematically[END_REF][START_REF] John | Trace-element mobilization in slabs due to non steady-state fluid-rock interaction: constraints from an eclogite-facies transport vein in blueschist (Tianshan, China)[END_REF]Liu et al., 2014;Meyer et al., 2016;[START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF] while the metavolcanoclastics have characteristics similar to upper continental crust and trench sediments (Liu et al., 2014;Meyer et al., 2016;[START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF].

Previous work mostly focused on individual HP/UHP rocks/outcrops for the reconstruction of P-T-(time) histories (e.g., Li et al., 2016;Lü et al., 2012;[START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF], fluid-rock interaction processes and/or geochemical budgets (e.g., [START_REF] Beinlich | Trace-element mobilization during Ca-metasomatism along a major fluid conduit: Eclogitization of blueschist as a consequence of fluid-rock interaction[END_REF][START_REF] John | Volcanic arcs fed by rapid pulsed fluid flow through subducting slabs[END_REF][START_REF] Van Der Straaten | Blueschist-facies rehydration of eclogites (Tian Shan, NW-China): Implications for fluid-rock interaction in the subduction channel[END_REF]. A recent compilation of regional P-T (-time) constraints [START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF] indicates that most peak metamorphic estimates for eclogite and prograde blueschist yield eclogite facies (EC facies) HP-LT conditions within the range 480-580°C and 1.5-3.0 GPa. A range of P-T conditions ~450-570°C at 2.7-3.3 GPa was obtained for some EC facies metavolcanoclastics.

Evidence for UHP metamorphism comes from both coesite relics in garnet (from several localities: stars in Figure 50c, 51a, d, 52a, 69) and thermodynamic calculation.

The spread of regional P-T estimates [START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF] Figure 13) could a priori arise from contrasting assumptions for thermodynamic modeling (e.g., difficulties in determining effective bulk rock composition and Fe 3+ content and/or assessing H2O activity) or from the complexity of metamorphic evolutions in individual HP-UHP tectonic slices [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF].

Our recent compilation of previous P-T-time works [START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF] suggests that the timing of peak HP/UHP metamorphism falls within 315 ± 5 Ma, i.e., in a restricted range with respect to a ~100 Ma-long subduction (also see Table 22 and Figure 69 for the compilation), in support of a Late Carboniferous accretionary system (Gao et al., 2009b). Some controversy exists, however, to the east of SCTSZ, in the Beishan arc terrane of South Tianshan Orogenic Belt: some workers propose that accretion may have lasted until the Early Triassic [START_REF] Tian | Triassic deformation of Permian Early Triassic arc-related sediments in the Beishan (NW China): Last pulse of the accretionary orogenesis in the southernmost Altaids[END_REF], while others suggest a Permian collision (e.g., [START_REF] Xiao | Paleozoic accreationary and collisional tectonics of the eastern Tianshan (China): Implications for the continental growth of central Asia[END_REF]. Regional ages <280 Ma (e.g., Zhang et al., 2007) or > 325 Ma (e.g., [START_REF] Gao | The mineralogy, petrology, metamorphic PTDt trajectory and exhumation mechanism of blueschists, south Tianshan, northwestern China[END_REF]Gao et al., , 2000[START_REF] Gao | South Tianshan: Late Paleozoic or Triassic collision orogenic belt?[END_REF] were previously considered as either resulting from intrinsic limitations of isotopic dating (e.g., excess Ar, Nd disequilibrium in Sm-Nd system; difficulty to link zircon U-Pb ages to precise metamorphic stages) or taken as evidence for distinct HP-UHP episodes [START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF].

Structural Data

Structural information for the SW-Tianshan Metamorphic Belt is scarce [START_REF] Gao | PT path of highpressure/low-temperature rocks and tectonic implications in the western Tianshan Mountains[END_REF], with only few recent reports for the Akeyasi Metamorphic Complex [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF][START_REF] Lin | Palaeozoic tectonics of the southwestern Chinese Tianshan: new insights from a structural study of the highpressure/\rlow-temperature metamorphic belt[END_REF]Soldner et al., 2017;[START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF] and for the nearby and Du et al. (2014). Samples with black frame were studied with the electron probe microanalysis (Table 15). (b, c) Simple sketches showing the controversy about the regional geodynamic model: Tectonic mélange (e.g., [START_REF] Klemd | Changes in dip of subducted slabs at depth: Petrological and geochronological evidence from HP-UHP rocks (Tianshan, NW-China)[END_REF]Li et al., 2016) versus UHP/HP sub-belts (e.g., Lü et al., 2012). (d) Reappraisal geological map of the AMC (this study).

investigations in this study and previous regional structural works, a revised structural map is proposed for the area (Figure 51a-d). Also check Figure 63 for the rest panoramic pictures.

Overall structural organization of the Akeyasi Metamorphic Complex

An approximately 30 km-long N-S cross-section was constructed along the Kebuerte valley (Figure 51d,52a,d). It cuts across the whole South Tianshan Orogenic Belt, namely, from north to south: the south margin of Central Tianshan continental arc, the AMC, and the unmetamorphosed to low grade Palaeozoic sedimentary strata bounded by the North Haerkeshan Peak Fault (NHF). A recently published cross-section along the adjacent Akesayi valley [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF] is shown for comparison (Figure 52e).

In the study area, the AMC is a metamorphic dome structure (Figure 52d) that can be further divided into six sub-units bounded by hm-/km-scale contacts (Figure 53,63) on the basis of petrological, lithological and structural characteristics (e.g., Figure 52-54):

1) Unit GS1: this ~3 km-wide GS facies unit (Figure 52a, d, 53a, 63a) separates the CTB continental arc from the HP/UHP exposures (e.g., [START_REF] Klemd | Changes in dip of subducted slabs at depth: Petrological and geochronological evidence from HP-UHP rocks (Tianshan, NW-China)[END_REF]Li et al., 2016, Figure 51b). It consists of strongly schistosed chl-phengite-biotite-quartz schist (Figure 64d, 65a) and actinolite-epidote-chlorite-quartz/albite schist (Figure 55g, 65b), with few garnet-bearing, significantly retrograded metapelites (Figure 56h), m-/hmscale marble horizons and magmatic intrusions [START_REF] Pu | Silurian arc volcanic slices and their tectonic implications in the southwestern Tianshan UHPM belt[END_REF]. Mylonitic horizons are found in places;

2) Unit UH: this corresponds to the so-called HP/UHP metamorphic 'mélange' (e.g., [START_REF] Klemd | Changes in dip of subducted slabs at depth: Petrological and geochronological evidence from HP-UHP rocks (Tianshan, NW-China)[END_REF]Li et al., 2016, Figure 51b), host to most previous P-T-time(-fluid) works (Table 22; Figure 69) and coesite reports (Figure 50c, 51a, d;[START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF][START_REF] Lü | Petrology of coesite-bearing eclogite from Habutengsu Valley, western Tianshan, NW China and its tectonometamorphic implication[END_REF]Lü & Zhang, 2012;[START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF][START_REF] Yang | Petrology and U-Pb zircon dating of coesite-bearing metapelite from the Kebuerte Valley, Western Tianshan, China[END_REF]. This unit crops out for ~9km along section (Figure 51a,d,52a,d) and is separated by two normal shear sense faults (Figure 52, 53a-b, 63a) from the GS1 unit to the north and a EC/BS facies blueschist unit to the south. Noteworthily, [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF] identified several internal, km-scale individual tectonic slices in this unit (Figure 51a,d,52e). It is predominantly composed of strongly schistosed meta-pelitic/-psammitic volcanoclastics (Figure 55ab, 56a, 65c) hosting mafic metavolcanics as pods, lenses, boudins, thin layers or massive blocks (e.g., Figure 55a; Soldner et al., 2017;[START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF] as well as some marble horizons (Figure 52e; [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF];

3) Unit EB: this ~4km-large EC/BS facies unit (Figure 51a,d,52a,) occupies the central and lowermost portion of the AMC on this transect. It lies structurally below the UH unit to the north (Figure 53b), and is overthrust on its southern side by a metamafic/-ultramafic unit (MU, Figure 53c) through a GS facies contact zone. It is characterized by relatively homogeneous, moderately schistosed blueschist horizons (Figure 55c-d, 56b-c) hosting lenses and/or pillow-shaped eclogite/blueschist blocks (Figure 55c).

4) Unit MU: this unit comprises metamorphosed mafic and ultramafic rocks (Figure 53c), which is the first report of meta-ultramafic rocks within the AMC. Similar lithologies have so far been reported only in the Changawuzi-Muzaerte valley (~40 km to the west, Figure 50c; [START_REF] Gao | PT path of highpressure/low-temperature rocks and tectonic implications in the western Tianshan Mountains[END_REF][START_REF] Li | Petrology of rodingite derived from eclogite in western Tianshan[END_REF]. To the north, the metaultramafic rocks are closely associated with a GS facies, weakly schistosed phengitechlorite-quartz/albite schist shear zone (Figure 64e, 65d) and overthrust by a ~1kmwide metabasic slice to the south (Figure 53c, 55e, 56e-g). The mutual relationships between the MU and UH units (both overlie the EB unit) cannot be ascertained due to glaciar coverage (Figure 52a, 54a, c), but the attitude of schistosity and aerial views suggest that MU overlies UH.

5) Unit GT: this ~5km-wide GS facies transitional zone (Figure 52a,d,53d,63d) is located at the southern side of the MU. The boundary between GT and MU could be more complex than the simple contact drawn on Figure 52d. GT is overthrust by a strongly retrograded meta-mafic slice (Figure 65g), which could represent the southern margin of the MU or a local small sub-unit. The GT unit is bounded by a km-scale normal shear zone to the south (Figure 53d, 63b-c). The GT mainly consists of moderately to strongly schistosed GS facies chlorite-phengite-quartz schist ± garnet relics or pseudomorphs (Figure 55f, 56i, 64g-h, 65g-i), with few blueschist blocks previously reported close to its northern margin (Figure 69, Gao et al., 2000); 6) Unit GS2: this unit shows lithologies and structural patterns very similar to those of the GS1 unit, with mainly strongly deformed phengite-chlorite-albite/quartz (Figure

Deformation stages and deformation patterns

Deformation stages are herein essentially defined based on textures and mineralogy.

The main schistosity (noted S2 in the north of the study area by Soldner et al., 2017) most commonly corresponds to a blue amphibole bearing, blueschist facies schistosity (S1 is only seldom preserved in eclogitic or eclogite to blueschist facies boudins, in UH or EB units for example, Figure 64a; Soldner et al., 2017;[START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF]. This schistosity is in fact composite, depending on the extent of retrogression and exhumation-related deformation, and may encompass a range of P-T conditions, from late eclogite to incipient blueschist and even down to a transitional blueschist to greenschist facies. A detailed mapping of regional schistosity by facies should in principle be feasible but was not performed here, in part because eclogite and/or blueschist facies schistosities may correspond to diachronous events in the different sub-units. Crenulation of the dominant schistosity is also evidenced in several exposures (as in [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF] and more strongly developed in the GS1 and GS2 units. For the sake of comparison with thin-sections and radiometric constraints, deformation are hereafter termed De, Db and Dg. White micas analyzed in situ by laser ablation (for Ar-Ar dating) were denoted S if following the schistosity and C along shear planes.

The dominant schistosity and various stretching lineations are reported in Figure 50c, 52a-c, and 54. The schistosity varies from place to place but dominantly strikes NW- Despite ample evidence for recumbent folding and flattening (e.g., Figure 64b-c), regional deformation is relatively non-coaxial, as examplified by pervasive S-C structures (Figure 55, 56i, 60b, 64-66) and asymmetric folding (although less conspicuous in the EB unit). Shear senses associated with EC/BS and GS facies metamorphism, whether at outcrop scale or in thin-section, are very consistent throughout the area, and respectively top to NNW and top to NEE (Figure 52a-c).

Sampling strategy and sample description

Sample selection (Figure 51a, 52) was intended at providing samples for average PT comparison between the different sub-units (rather than detailed individual trajectories by thermodynamic modelling; e.g., [START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF], ideally for each of the metamorphic equilibration stages, seeking enough textural control on deformation and/or recrystallisation stages that in-situ Ar-Ar dating could be used to provide age constraints with deformation control. Sampling strategy, geographic coordinates and parageneses are given in Table 15. A brief sample description is given below:

-UH unit:

#135 is a strongly schistosed pelitic metavolcanoclastic rock hosting eclogite lens (Figure 55a) with well-preserved eclogitic paragenesis of Grt-Gln-LwsPs-Omp-Ph-Qz-Rt±Ttn±Brs±Chl (Figure 56a, 60b) and clear top to N shear sense as indicated by elongated glaucophane, phengite and quartz along the schistosity and shear band (Figure 60b, 66). Omphacite was detected both as inclusion in garnet (Figure 56a) and as relict in the gln+qz matrix. Fresh Lawsonite was not found but only pseudomorphs in garnet (Ep+Pg, Figure 56a). This sample represents the host rock of the coesitebearing HP/UHP eclogite (Figure 51, 52, 69; [START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF] and is taken here to represent De.

#26 is a strongly schistosed felsic metavolcanoclastic rock with Grt-Ph-Qz-LwsPs-Chl-Rt±Ttn±Carb (Figure 65c), sampled close to the coesite-bearing felsic metapelite of Yang et al. (2013) (Figure 51, 52, 69). Top to N sense of shear is indicated by stretched recrystallized quartz (Figure 55b) and elongated phengite along the schistosity and shear band (Figure 66). As for sample #135, no fresh lawsonite was detected but only pseudomorphs in garnet (Ca-Grt+Pg, Figure 65c). It is also representative of the metavolcanoclastic matrix host rock of the UH unit.

-EB unit:

#117 is a strongly to moderately schistosed pelitic metavolcanoclast hosting eclogite lens (Figure 55c) with Grt-Gln/Brs-Ph-Qz-Rt±Ttn±Chl assemblage (Figure 56b, 66) and relatively obvious top to N shear sense (Figure 66) as indicated by elongated glaucophane, phengite and quartz along the along the schistosity and shear band. It locates close to the north margin of the EB unit, as representative lithology of the blueschist horizon.

#32 is a strongly schistosed pelitic metavolcanoclastic rock with Grt-Gln/Brs-Qz-Ctd-Rt±Ttn±Chl assemblage (Figure 56c, 60b, 66) and clear top to N shear sense (Figure 60b, 66) as indicated by elongated glaucophane, phengite and quartz along the along the schistosity and shear band. No fresh lawsonite was detected but pseudomorph in garnet (Ep+Pg; Figure 56c). It locates at the central part of the EB unit, as representative lithology of the blueschist horizon (Figure 55d).

-MU unit:

#157 is a moderately to weakly schistosed felsic metavolcanoclastic rock with GS facies Ph-Chl-Ab-Qz assemblage (Figure 65d, 66) and relatively obvious top to NE shear sense from outcrop observation (Figure 64e). It locates at the north margin of the MU unit associated with the meta-ultramafic rock and probably represents an individual contact between the EB and MU units (Figure 53c). Both in situ and step-heating 40 Ar-39 Ar radiometric analyses were performed for this sample.

#156-1 is a moderately to strongly schistosed metamafic/ultramafic schist with MgChl-Ttn assemblage (Figure 65e). It is associated with the serpentinite slice in the MU unit as vein or thin layers (Figure 64f).

#156-2 is a metaultramafic (rodingite?) vein with Grs-Di-Chl assemblage (Figure 65f). It locally crosscuts the serpentinite slice in the MU as vein (Figure 64f).

#156-3 is the mainly representative lithology of the serpentinite slice in the MU unit, with Srp-Di assemblage (Figure 56d). It was strongly schistosed but no sense of shear can be observed (Figure 64f). It is locally closely associated to south with the metabasite slice with inferred contact (Figure 53c). As for the other two former samples, only microprobe work was performed for this sample.

#158 is more mafic than typical samples from the EB unit. It was sampled next to probably former pillows (Figure 55e). It shows a complex mineral assemblage with Grt-Czo-Gln/Brs/Act±Ph±Ttn±Omp±Ab±Chl (Figure 56e-g). Elongated euhedral actinolite is wrapped by a relatively anhedral glaucophane matrix, and both are replaced by later barroisite. Phengite and omphacite are rare and only found as relic in the matrix (Figure 56f-g) or as inclusion in epidote. Zircon separation was performed for LA-ICPMS trace elements and U-Pb measurements for this sample.

-GT unit:

#147 is a weakly schistosed, relatively mafic rock with a Grt-Ph-Pg-Chl-Ab-Qz-Ep±relict Gln±Carb±Bi assemblage (Figure 65g). The appearance of relict glaucophane implies it probably experienced lower BS facies metamorphism prior to the regional GS facies overprinting marked by the significant replacement of garnet/phengite by biotite+chlorite (Figure 65g). No clear shear sense could be found on the outcrop, and only 40 Ar-39 Ar step-heating was performed for this sample.

#148-1 is a strongly schistosed felsic metavolcanoclastic rock with Grt-Ph-Chl assemblage (Figure 65h, 66). Top to NEE sense of shear was observed as indicated by stretched recrystallized quartz vein (Figure 64g) and mica "fish" (Figure 65h, 66). It locates at the central part of the GT unit. The sample was prepared for in situ phengite 40 Ar-39 Ar radiometric, specifically testing whether the large mica "fish" (~3mm across;

Figure 65h, 66) recorded potential excess Ar.

#148-2 is a strongly schistosed felsic metavolcanoclastic rock with Grt-Ph-Chl assemblage (Figure 65i, 66), sampled close to #148-2 but with contrasting sense of shear in the GT unit. Top to N shear sense was indicated by relict 𝜎-porphyroblast, elongated phengite and quartz along the schistosity and shear band (Figure 65i, 66).

#71 is a strongly schistosed pelitic metavolcanoclastic rock with Ph-Chl-Qz±Ab assemblage (Figure 56i, 60b, 66) sampled close to the southern margin of the GT unit.

Top to S sense of shear was indicated by stretched recrystallized quartz vein (Figure 55f) and phengite+chlorite+quartz along the schistosity and shear plane (Figure 56i, 66).

-GS1 and GS2 units:

#J2 is a strongly schistosed pelitic metavolcanoclastic rock with Ph-Bi-Chl-Qz assemblage (Figure 65a). It locates at the central part of the GS1 unit. Top to NEE sense of shear was indicated by stretched recrystallized quartz vein (Figure 64d) and phengite+quartz along the schistosity and shear plane (Figure 65a).

#102 is a moderately to strongly schistosed pelitic metavolcanoclastic rock (Figure 55g) from the south margin of GS1, close to the UH unit with Act-Ep-Chl-Ph-Qz±Ab±Ttn±Carb assemblage (Figure 65b). Top to N sense of shear was indicated by sigmoidal (Figure 55g) and chlorite+phengite+quartz along the schistosity and shear plane (Figure 65b). Only microprobe analyses were performed for this sample.

#22 is a weakly schistosed metavolcanoclastic rock located in the GS1 unit adjacent to the north margin of the UH unit, with Grt-Ph-Bi-Chl-Qz±relict Gln/Brs assemblage (Figure 56h). Relictual glaucophane/barroisite hints to BS facies metamorphism prior to the regional GS facies. No clear sense of shear can be found on outcrop/sample-scale, therefore phengite grains were picked up only for 40 Ar-39 Ar stepheating radiometric analysis.

#146 is a strongly schistosed pelitic rock from the northern margin of GS2, close to the GT unit (Figure 55h), with Chl-Ph-Qz±Ab±Ttn assemblage (Figure 65j). Top to S sense of shear was indicated by stretched recrystallized quartz vein (Figure 55h) and chlorite+phengite+quartz along the schistosity and shear plane (Figure 65j).

Mineral habits, textural relationships and microstructural location were used to select minerals for multiequilibrium calculations. In general, the following deformation-crystallization relationships were observed:

-In the schistosed garnet-bearing metavolcanoclastic samples (e.g., samples 135,26,117,32,148), relative euhedral or relictual garnet appears as millimeter to centimetersized 𝜎-type porphyroblast in textural equilibrium with recrystallized blue amphibolephengite-quartz tails (Figure 55d, 56a-c, 65c, h-i).

-In the schistosed garnet-free metavolcanoclastic samples (e.g., samples J2, 102, 157, 71, 146), biotite/phengite-chlorite±green amphibole±epidote appear as matrix minerals in textural equilibrium around albite/quartz porphyroblasts constituting synkinematic structures with clear shear senses along millimeter-sized shear bands (Figure 55f-h, 56i, 64d-e, 65a-b, d, j).

-In the weakly schistosed metavolcanoclastic and metavolcanics samples (e.g., samples 22, 147, 148), although garnet is significantly replaced by chloritebiotite/phengite and displays irregular rims, textural equilibrium with matrix phengitequartz/albite±chlorite±relict blue amphibole is preserved in places (Figure 56h, 65g-i).

-In the undeformed metavolcanics sample (sample, 158), a complex metamorphic history is recorded by multistage green/greenish blue/blue amphibole growth together with garnet±epidote±omphacite±phengite±albite (Figure 56e-f).

Minerals involved in the same microstructural domain (e.g., S-C structures, Figs.

60b, 66) and in close contact were considered to have crystallized coevally. In parageneses involving garnet, mineral inclusions (e.g., Figure 56a-c, e, 65c) were assumed to be in equilibrium with the corresponding garnet core/mantle compositions.

Minerals recrystallized as tails around 𝜎-type porphyroblast were assumed to be in equilibrium with the garnet rim compositions. Detail of selected mineral assemblages for P-T estimates is listed in Figure 59c and Table 17. 19.

Mineral Chemistry

Mineral analysis was performed on key minerals preserved from retrogression, as inclusions within garnet and/or in the matrix, using a CAMECA SX FIVE electron probe at ISTeP, Sorbonne Université (15Kv, 10nA, WDS), France using Fe2O3 (Fe), MnTiO3 (Mn, Ti), diopside (Mg, Si), Cr2O3 (Cr), orthoclase (Al, K), anorthite (Ca) and albite (Na) as standards. Data is shown in Figure 58 and representative analyses are listed in Table 16.

6.5.3. Thermobarometry

THERMOCALC average P-T

The internally consistent thermodynamic dataset (tc-ds55) and the program THERMOCALC v3.33 (Holland andPowell, 1998, 1990) were applied for multiequilibrium P-T estimates. Structural formulae and end-member activities were calculated with the AX program (ftp://www.esc.cam.ac.uk/pub/minp/AX/). Only P-T estimates passing the equilibrium test criteria (e.g., sigfit, hat; [START_REF] Holland | An internally consistent thermodynamic data set for phases of petrological interest[END_REF] have been considered in this study (Figure 59). Precision of P-T estimates is generally on the order of 0.05-0.2GPa for pressure and 10-30°C for temperature. The merely present end-members (e.g., Fe-celadonite/celadonite for some phengite, Figure 58c) yielding a large uncertainty on the results were removed during calculation (check Table 17 for detail).

Raman Spectroscopy of Carbonaceous Material Thermometry

The Raman spectroscopy of carbonaceous material (RSCM, calibrated in the range 330-650°C; [START_REF] Beyssac | Raman spectra of carbonaceous material in metasediments: A new geothermometer[END_REF] is used here to obtain peak temperature estimates independent from those of THERMOCALC. While absolute calibration is ±50°C, intersample comparison allows detecting much smaller temperature differences, around 10-15°C [START_REF] Beyssac | Thermal metamorphism in the lesser Himalaya of Nepal determined from Raman spectroscopy of carbonaceous material[END_REF]. RSCM was done on thin sections of graphite-bearing metavolcanoclastics oriented perpendicular to the foliation by focusing the laser beam beneath a transparent crystal. Raman spectra were obtained with a Renishaw INVIA Reflex Raman microspectrometer at the Laboratoire de Géologie of the Ecole Normale Supérieure, France. Spectra were excited at room temperature with the 514.5 nm line of a 20 mW Ar Spectra Physics laser through a LEICA 100X objective (NA 0.90). At least 13 spectra were collected for each sample, to take into account the CM heterogeneities, and processed with the program Peak Fit 4.0. Temperature estimates are given in Table 17.

Titanium in Biotite Thermometry

An empirical Ti-in-biotite geothermometer [START_REF] Henry | The Ti-saturation surface for lowto-medium pressure metapelitic biotites: Implications for geothermometry and Tisubstitution mechanisms[END_REF], calibrated in the range 0.4-0.6 GPa and 480-800°C, for compositions of XMg = 0.275-1.000 and Ti = 0.04-0.60 apfu, is used to derive temperature estimates for regional GS facies metamorphism recorded by biotite-bearing metavolcanoclastics (Table 17). Precision of the Ti-in-biotite thermometer is estimated to be ±24°C at the lower temperature range and improves to ±12°C at higher temperatures.

Radiochronology

Eleven samples for which P-T-kinematic constraints were collected ( § 5 and 6)

were selected from different tectonic sub-units (Figure 52d, 60a). Seven of them with syntectonic textural features (Figure 60b, 66) were dated by the 40 Ar-39 Ar in situ laser ablation technique on phengite grains from rock slices already analysed by microprobe. 18, 20 and 21.

40 Ar-39 Ar In Situ Laser Ablation Analysis

The 40 Ar-39 Ar in situ laser ablation technical procedure was first proposed by [START_REF] Schaeffer | Laser Ar-39-Ar-40 study of Apollo 17 basalts[END_REF] and modified by [START_REF] Maluski | 40Ar-39Ar laser probe multi-dating inside single biotites of a Variscan orthogeneiss (Pinet, Massif Central, France)[END_REF]. Sample preparation and analysis (procedure as in [START_REF] Agard | Exhumation of the Schistes Lustrés complex: in situ laser probe 40Ar/39Ar constraints and implications for the Western Alps[END_REF][START_REF] Agard | Transient, synobduction exhumation of Zagros blueschists inferred from P-T, deformation, time, and kinematic constraints: Implications for Neotethyan wedge dynamics[END_REF][START_REF] Augier | Exhumation, doming and slab retreat in the Betic Cordillera (SE Spain): in situ40Ar/39Ar ages and P-T-d-t paths for the Nevado-Filabride complex[END_REF] were conducted at Géosciences Montpellier, France. The laser system consists of a continuous 6W argon ion laser, a beam shutter for selection of lasering exposure time, with typically 5ms pulses separated by 40ms, and a set of lenses for beam focusing.

The number of pulses depends on the nature of the analyzed mineral, its K content and its presumed age. Argon extraction, purification and analyses are performed within three distinctive parts with the sample chamber where gas extraction is done, the purification line with hot getters and nitrogen liquid traps (cold) traps, and a MAP 215-50 noble gas mass spectrometer equipped with an electron multiplier. Rock sections 500µm thick, which had been used to make the petrographic thin sections, were double polished within 1µm tolerance. Whole section and detailed area photographs of both the rock section and corresponding thin section were taken for an accurate selection of favorable areas during lasering experiments. All samples were ultrasonically rinsed in ethanol and distilled water, wrapped in pure aluminum foils and then irradiated in the

McMaster nuclear reactor (Canada) with several aliquots of the MMHb-1 international standard (520.4 ± 1.7Ma, [START_REF] Samson | Calibration of the interlaboratory 40Ar-39Ar dating standard, MMhb-1[END_REF]. After irradiation, both the monitors and the sections were placed on a Cu holder inside the sample chamber and heated for 48h at 150-200°C.

For each age determination, argon was extracted from a 150×300µm surface corresponding to a mixture of several phengite grains, given grain size (Figure 59b, 68).

The crater is a 30-40µm approximate hemisphere surrounded by a circular wall made of melted material. Incision of the sample did not exceed 10-20µm deep depending on the three-dimensional orientation of the phengite crystals. Once the extraction was completed, about four minutes were required for gas cleaning of the line and 15 min for data acquisition by peak jumping from mass 40 to mass 36 (8 runs). For each experiment, ages have been obtained after correction with blanks, mass discrimination, radioactive decay of 37 Ar and 36 Ar and irradiation-induced mass interferences. They are reported with one sigma uncertainty (Table 18) and were evaluated assuming an atmospheric composition for the initially trapped argon (i.e., ( 40 Ar-36 Ar) i ~295.5). and the data acquisition. To measure the Ar background within the system, one blank analysis was performed every three sample analyses. ArArCalc v2.5.2 was used for data reduction and plotting. The two-sigma errors reported on plateau, isochron and total gas ages include the error on the irradiation factor J. Atmospheric 40 Ar was estimated using a value of the initial 40 Ar/ 36 Ar of 295.5.

U-Pb dating and trace element analysis of zircon by LA-ICP-MS

U-Pb dating and trace element analysis of zircon were simultaneously conducted by LA-ICP-MS at the Wuhan SampleSolution Analytical Technology Co., Ltd., China.

Detailed operating conditions for the laser ablation system and the ICP-MS instrument and data reduction are the same as in [START_REF] Zong | The assembly of Rodinia: The correlation of early Neoproterozoic (ca. 900 Ma) high-grade metamorphism and continental arc formation in the southern Beishan Orogen, southern Central Asian Orogenic Belt (CAOB)[END_REF]. Laser sampling was performed using a GeolasPro laser ablation system that consists of a COMPexPro 102 ArF excimer laser (wavelength of 193nm and maximum energy of 200mJ) and a MicroLas optical system. An Agilent 7700e ICP-MS instrument was used to acquire ion-signal intensities. Helium was applied as a carrier gas. Argon was used as the make-up gas and mixed with the carrier gas via a T-connector before entering the ICP. A "wave" signal smoothing device is included in this laser ablation system [START_REF] Hu | Wave" signal-smoothing and mercury-removing device for laser ablation quadrupole and multiple collector ICPMS analysis: Application to lead isotope analysis[END_REF]. The spot size and frequency of the laser were set to 60µm and 6Hz, respectively, in this study. Zircon 91500 and glass NIST610 were used as external standards for U-Pb dating and trace element calibration, respectively. Each analysis incorporated a background acquisition of approximately 20-30s followed by 50s of data acquisition from the sample. An Excel-based software ICPMSDataCal was used to perform off-line selection and integration of background and analyzed signals, time-drift correction and quantitative calibration for trace element analysis and U-Pb dating [START_REF] Liu | Continental and oceanic crust recycling-induced melt-peridotite interactions in the Trans-North China Orogen: U-Pb dating, Hf isotopes and trace elements in zircons from mantle xenoliths[END_REF].

Concordia diagrams and weighted mean calculations were made using Isoplot/Ex_ver3 [START_REF] Ludwig | A Geochronological Toolkit for Microsoft Excel[END_REF].

6.6. Results

Bulk chemistry of major lithologies

The protolith lithologies of samples in this study mainly correspond to metavolcanoclastics, metavolcanics and meta-ultramafic rocks.

-The metavolcanoclastic samples locally contain mud/silty/sand components that either resemble metapelite or quartz-rich metagraywacke as reflected by the main 19).

parageneses, which comprise Grt-Ph-Amp-Qz-Rt±Cpx±Ep±Chl±Ttn±Ctd±Pg±Bi (e.g., samples 22, 135, 117, 32; abbreviations after Table 15), Grt-Ph-Qz-Chl-Rt±Pg±Ab±Ttn (e.g., sample 26) and Ph-Qz-Chl-Ab±Grt±Pg±Ttn±Amp±Carb±Bi±Ep (e.g., samples J2, 102, 157, 148, 71, 146). They uniformly show significant Rb/Ba/Th/U/Pb enrichments and notable Nb-Ta depletions in primitive mantlenormalized (PM) trace element pattern and a steep negative slope ((La/Yb)N = 1.69-32.2, Table 19) in chondrite-normalized REEs pattern (Figure 57), similar to that of the average upper continental crust (UCC, Rudnick & Gao, 2003) or trench sediment [START_REF] Li | Chemical composition and mineralogy of marine sediments[END_REF][START_REF] Plank | The chemical composition of subducting sediment and its consequences for the crust and mantle[END_REF]. These lithologies are found in all sub-units, without significant differences, except in MU.

-The metavolcanics are dominantly mafic, as reflected by Grt-Amp-Ph-Ep-Rt-Ttn±Cpx±Pg±Qz±Bi±Chl±Ab±Carb parageneses (e.g., samples 158, 147). They were here only sampled in units MU and GT. Their moderate Rb/Ba/Th/U/Pb enrichments and lack of detectable Nb-Ta depletions in primitive mantle-normalized trace element pattern, and a moderately negative slope ((La/Yb)N = 5.51-5.95, Table 19) in chondritenormalized REEs pattern (Figure 57) fall into the range between that of ocean island basalt and enriched mid-ocean ridge basalt (OIB, E-MORB, [START_REF] Sun | Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes[END_REF]).

-The meta-ultramafic rocks are serpentinized and/or metasomatized with parageneses consisting of MgChl-Ttn (e.g., sample 156-1), Grs-Cpx-Chl (e.g., sample 156-2), Srp-Cpx (e.g., sample 156-3). They present Rb/Ba/Th/U/Pb comparable to PM and a slightly positive slope ((La/Yb)N = 0.27-1.53, Table 19) in chondrite-normalized REEs pattern (Figure 57). 6.6.2. Mineral compositions 6.6.2.1. Phengite White mica compositions are mostly phengitic with variations along the tschermak Si (Fe, Mg) = AlAl exchange vector between muscovite and celadonite, as shown by Figure 8c. The deviation from the purely phengitic substitution trend (Figure 58c) is observed for all samples, which suggests that a certain amount of ferric iron is present.

Phengite is the main matrix mineral in most metavolcanoclastic samples (Figure56,60b,65,66), showing several distinct generations with respect to porphyroblasts and/or C-S structures (see § 4). Microprobe images also reveal complicated multistage growth structure (e.g., Figure 68) or contamination by biotite growth (Figure 56h, 65g). The Si content of samples from the UH unit (3.38-3.66) is higher than that from the EB (3.34-3.50), MU (3.35-3.45), GS1/2 (3.07-3.45) and GT units (3.05-3.38), especially with a few crystals with high Si content in sample 26 (Si = 3.66). Larger variations of compositions are observed in samples 148 and 71 (GT), 135 (UH) and 117 (EB), and partial clusters in 157 (MU) and 148 (GT). These variations are compared below to age constraints, in particular in situ analyses.

Amphibole

Blue or blue-green amphiboles were detected either as inclusion or matrix mineral in most garnet-bearing samples (samples 22,135,117,32,158,147,65g) with compositions varying largely and ranging from glaucophane to barroisite to actinolite (Figure 58a). Barroisite replaces glaucophane in many of the high grade metavolcanoclastics (samples 135, 117, 32, Figure 56a-c), as a consequence of retrogression, but the opposite evolution is documented in sample 158, with euhedral actinolite rimmed by an anhedral glaucophane matrix (Figure 56e-g).

6.6.2.3. Clinopyroxene Omphacitic clinopyroxene (Figure 58b) is common in metavolcanic rocks and true eclogites of the UH unit (e.g., [START_REF] Gao | PT path of highpressure/low-temperature rocks and tectonic implications in the western Tianshan Mountains[END_REF][START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF]. In the selected metavolcanoclastic samples, it was only found as small crystals in garnet and/or in the matrix of samples 135 and 158 (~100 µm, Figure 56a, e-f, 68a), with average compositions between ~48% jadeite and ~6% acmite end-members (and ~46% diopside) for the former and between ~30% jadeite and ~5% acmite end-members (and ~65% diopside) for the latter, which is out of the common area of omphacite from regional eclogites (unpublished compilation). Diopside (Figure 58b) appears as a relict mineral wrapped by serpentine matrix or vein crosscutting grossular matrix in metaultramafic rocks (samples, 156-1 to -3, Figure 56d, 65e-f).

Chlorite

Chlorite compositions are mainly ferrous and range between clinochlore/daphnite and amesite along the tschermak exchange vector (Figure 58d), with XMg ~0.16-0.50.

It either appears as the main matrix mineral in the low to intermediate grade metavolcanoclastics (Figure 56i,d,j) or retrograde mineral rimming/cutting porphyroblasts (Figure 56a-c, h, 65g-i). Significantly magnesium-rich chlorite, with XMg ~0.55-0.88, is found only as prograde mineral inclusion in garnet (Figure 56b,65c) or matrix mineral in metaultramafic samples (Figure 65e-f). Deviation toward sudoite is very limited.

Garnet

Garnet is dominantly ferrous (FeO ~23.7-34.8wt%), with XMg values ranging from 0.04 to 0.24 (Figure 58e). The evolution of garnet zoning is characterized by a Mn decrease with a Ca, Fe and Mg fluctuation toward rim in samples from the UH and EB sub-units (Figure 58e), with limited reequilibration on the garnet rims. In detail, diverse patterns (Figure 58e) are encountered for metavolcanoclastic (e.g., samples 135, 32)

and metavolcanic rocks (e.g., samples 158, 147) from the different sub-units. The "-" means did not calclulate.

Figure 59: P-T plot showing the results of our P-T estimates using THERMOCALC [START_REF] Holland | An enlarged and updated internally consistent thermodynamic dataset with uncertainties and correlations: the system K2O-Na2O-CaO-MgO-MnO-FeO-Fe2O3-Al2O3-TiO2-SiO2-C-H2-O2[END_REF] together with estimates of metamorphic temperature by the Raman spectroscopy of carbonaceous material (RSCM, [START_REF] Beyssac | Raman spectra of carbonaceous material in metasediments: A new geothermometer[END_REF][START_REF] Beyssac | Thermal metamorphism in the lesser Himalaya of Nepal determined from Raman spectroscopy of carbonaceous material[END_REF] and Ti-in-biotite geothermometry [START_REF] Henry | The Ti-saturation surface for lowto-medium pressure metapelitic biotites: Implications for geothermometry and Tisubstitution mechanisms[END_REF]. Ellipses indicate confidence intervals obtained with THERMOCALC. Ellipses with nondense dash-, soild-and dense dash-lines respectively correspond to P-T estimates for pre-peak, peak and post peak metamorphism. 22), with relatively precise P-T estimates tied to comparable age constraints. Numbers in black boxes correspond those in Table 22, for the detail compilation of regional P-T-time works.

Notes that average peak P-T estimates correspond to a metamorphic P-T gradient decrease for rocks exhumation from Table 17: a THERMOCALC (version 3.3.3 [Holland andPowell, 1990, 1998]). The analyses quoted here can be found in Table 16. Mineral abbreviations are the same as for Table 16.

b End-members present only in small amounts (inducing a large uncertainty in the results) that were removed in the calculations (cel, celadonite; fcel, Fe-celadonite; ann, annite; ames, amesite; fact, Fe-actinolite; parg, paragasite; ts, tschermakite; clin, clinochlorite; phl, phlogopite; rieb, riebeckite; fgl, Fe-glaucophane; gl, glaucophane; jd, jadeite; pa, paragonite; daph, daphnite; gr, grossular; spss, spessartite; an, anorthite; mnctd, Mn-chloritoid; east, eastonite; py, pyrope; hed, hedenbergite; andr, andradite).

c Fit corresponds to a threshold value: results of the calculations (column Fit) should be lower than this value to ensure reliability (see [START_REF] Holland | An internally consistent thermodynamic data set for phases of petrological interest[END_REF] for further details).

d Samples with too simply minearl assemblage (e.g., qz + chl + ph) to give a potential avPT fit.

Thermobarometric results

P-T estimates were obtained with THERMOCALC for 13 samples (Figure 59a; see and EB units (sample, 32).

RSCM temperature estimates for metavolcanoclastics from the UH unit range between 506 ± 15°C (n=29) and 523 ± 20°C (n=19) with an average value of 515 ± 9°C. Similar temperatures are found for the EB unit, between 497 ± 19°C (n=26) and 527 ± 19°C (n=24) with an average value of 512 ± 15°C. RSCM temperature for rocks from the GS1, GS2 and GT units clusters between 521 ± 36°C (n=15), 518 ± 34°C (n=17), 547 ± 29°C (n=21), 501 ± 35°C (n=25), 528 ± 33°C (n=19), 522 ± 27°C (n=22), 500 ± 20°C (n=13) and 535 ± 15°C (n=17) with an average value of 522 ± 16°C. Those RSCM temperatures are somewhat lower/higher than T estimated with THERMOCALC for some individual samples, but the discrepancy remains within the bounds of the RSCM calibration (± 50°C, [START_REF] Beyssac | Raman spectra of carbonaceous material in metasediments: A new geothermometer[END_REF]. Overall, good fits exist samples for which both the RSCM temperature and the peak P-T estimates are available (samples,102,22,26,117,32,148,Figure 59a). The RSCM temperature estimates in this study are also consistent with previous works which propose 500-600°C maximum peak temperature for the AMC [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF]Meyer et al., 2016).

Titanium-in-biotite thermometry on biotite-bearing samples J2, 22, 147 (GS1 and GT units) and 32 (EB unit) yields estimates between 588 ± 19°C (n=10), 588 ± 10°C (n=12), 502 ± 26°C (n=7) and 585 ± 21°C (n=11) with a slightly higher average value than THERMOCALC and RSCM estimates (i.e., 566 ± 43°C; Figure 59a). This estimate is nevertheless in agreement with the recent Zr-in-titanite temperature constraints at ~569-608°C for retrograde eclogite in the AMC (Zhang et al., 2018). We identified major contacts across domains with slightly different lithologies and/or tectonic patterns (as illustrated on the cross-section of Figure 52d), that we regard as distinct km-scale tectonic sub-units. Overall, asymmetric shearing is more pronounced in UH, while upright symmetrical folding is typical of EB. Mafic boudins are also more numerous in UH. The lateral extension of these sub-units is shown in Figure 54a, but was limited by the presence of glaciers to the east. For example, the more mafic EB unit likely corresponds to the pillow unit described by [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF]. As discussed below, the metamorphic evolution and ages tend to support the view that there are indeed distinct sub-units.

Our observations (Figure 52-54) highlight the following deformation patterns:

-BS facies asymmetric shear senses with a northward component prevail for all lithologies and sub-units (except in the MU unit, where kinematic indicators are rare and not statistically significant). This points to the importance of simple shear under retrograde conditions, hence during exhumation (also see [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF]. No indication of dominant syn-eclogite pure shear deformation was found at the outcrop scale, and is possibly only preserved in boudins (e.g., LPO measurements of Soldner et al., 2017).

-top to NEE and a few top to N/S GS facies shear senses are restricted to the GS1, GS2, GT units and the north margin of the MU.

We propose that the top to NNW shear senses (mostly BS facies, and more rarely transitional EC/BS or BS/GS) correspond to exhumation dynamics following northward subduction [START_REF] Scheltens | Northward subduction-related orogenesis of the southern Altaids: Constraints from structural and metamorphic analysis of the HP/UHP accretionary complex in Chinese southwestern Tianshan, NW China[END_REF], while regional dextral strike-slip deformation is marked by the dominance of top to NEE GS facies shear sense.

P-T estimates inferred from average P-T calculations suggest contrasting peak burial for the sub-units. Care in selecting potentially co-stable minerals/analyses and statistical fits obtained make these estimates relatively robust. In the UHP/HP complex (UH, Figure 59a), maximum burial P-T estimates cluster around 480-560°C, 2.75GPa (±0.1), similar to most recent estimates [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF][START_REF] Lü | The coherent ultrahigh-pressure terrane of the Tianshan meta ophiolite belt[END_REF], and consistent with the range of 480-580°C, 2.2-3.0GPa obtained by earlier studies (e.g., Du et al., 2014;Lü & Zhang, 2016;[START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF][START_REF] Yang | Petrology and U-Pb zircon dating of coesite-bearing metapelite from the Kebuerte Valley, Western Tianshan, China[END_REF]Zhang et al., 2018) and the widespread occurrence of coesite ( Figure 50c, 51a, d;[START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF][START_REF] Lü | Petrology of coesite-bearing eclogite from Habutengsu Valley, western Tianshan, NW China and its tectonometamorphic implication[END_REF]Lü & Zhang, 2012;[START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF][START_REF] Yang | Petrology and U-Pb zircon dating of coesite-bearing metapelite from the Kebuerte Valley, Western Tianshan, China[END_REF]. In contrast, somewhat lower peak pressure of ~2.1GPa (± 0.15), 505°C (±15) were obtained for the EB unit, with moderately to highly substituted phengite and in general lesser amounts of omphacite than in UH (Figure 59a), in agreement with the preliminary P-T estimates for blueschists close to the EB unit [START_REF] Beinlich | Trace-element mobilization during Ca-metasomatism along a major fluid conduit: Eclogitization of blueschist as a consequence of fluid-rock interaction[END_REF]. We regard the possibility of having 'missed' UHP samples and/or that retrogression was so pervasive that all hints of UHP metamorphism was removed as fairly unlikely but still possible. This unit resembles the pillow-basalt bearing unit (Figure 51d, 52e) of [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF], for which P-T conditions were unfortunately not determined. Different conditions were also obtained for the MU ultramafic/mafic unit equilibrated at ~1.46GPa (±0.16), 484°C (±29). Rocks from the northern-and southernmost units (GS1, GS2 and GT, Figure 59a) yield GS to lower-BS facies P-T conditions around 0.4-1.0GPa, 470-570°C.

The GT unit shows evidence for an earlier, higher pressure blueschist facies episode whose P-T conditions could not be determined. Similar GS to lower-BS facies conditions around 0.90-1.10GPa, 460-500°C (using moderately substituted phengite)

were determined for the retrograde overprint of the UH and EB samples (135,26,32).

Different age clusters (discussed further below) also emerge for peak burial of the sub-units from the data obtained in this study: schematically ~320 Ma for UH, ~330

Ma for EB, ~360 Ma for MU (from metamorphic zircon overgrowth). A similar age of 360 Ma was in fact obtained by Ar-Ar dating on the MU unit (Figure 61c, Table 22).

Similar ages around 300-310 Ma are found, in contrast, for early exhumation of these units and for GS facies metamorphism (Figure 59b, 61b-e).

These observations and field mapping (e.g., cross-section of Figure 52d) therefore suggest that the Akeyasi metamorphic complex, at least in the surroundings of the Kebuerte valley, is a metamorphic dome made of a stack of individual sub-units or nappes. This rules out the view that the AMC might be a subduction mélange in the sense of Cloos & Shreve (1988a, 1988b) or Meyer et al. (2016). That the exposed core of the metamorphic dome (i.e., the EB unit) does not correspond to the most deeply buried slice requires thrusting at some point of the tectonic history. The contrasting ages for the different sub-units also indicate diachronous detachment from the subducting slab.

P-T-t trajectories, exhumation rates and tectonic stacking

The successive detachment of sub-units (MU, EB then finally UH), if confirmed, reveals a change in metamorphic gradient with time, from an intermediate to cold subduction regime (i.e., from ~12 to 5-7°C/km; Figure 59b; also see [START_REF] Agard | The subduction plate interface: Rock record and mechanical coupling (from long to short time scales)[END_REF] and [START_REF] Angiboust | Zagros blueschists: Episodic underplating and long-lived cooling of a subduction zone[END_REF]). The accuracy and significance of Ar-Ar ages (i.e., whether they are 'real' tectonic episodes or 'blended' ages with excess argon) is therefore critical and more thoroughly discussed here.

As outlined above ( § 6.4), a key observation is that most radiometric ages respect the chronological relationship inferred from mineral textures, i.e. phengite in shear bands cutting across the schistosity are effectively younger (e.g., as visible in samples 135 or 32, Figure 60b, 66). Ages obtained from highly substituted phengite in the UH unit, at ~320 ± 1 Ma, also match the results of previous geochronological studies (mostly focused on the UH unit in adjacent valleys), i.e. peak metamorphic conditions at 315 ± 5 Ma ( Figure 61b-c, e, 69, Table 22; also see the compilation of Tan et al.

( Our observations confirm that recrystallization enhanced by deformation and fluid circulation is commonly more effective than volume diffusion [START_REF] Agard | Exhumation of the Schistes Lustrés complex: in situ laser probe 40Ar/39Ar constraints and implications for the Western Alps[END_REF][START_REF] Augier | Exhumation, doming and slab retreat in the Betic Cordillera (SE Spain): in situ40Ar/39Ar ages and P-T-d-t paths for the Nevado-Filabride complex[END_REF][START_REF] Laurent | Extraneous argon in high-pressure metamorphic rocks: Distribution, origin and transport in the Cycladic Blueschist Unit (Greece)[END_REF], and that the 'closure temperature' for phengite is at least 550°C (as in Syros: [START_REF] Laurent | Extraneous argon in high-pressure metamorphic rocks: Distribution, origin and transport in the Cycladic Blueschist Unit (Greece)[END_REF], since all ages within a given sample should be the same otherwise. We therefore conclude that i) the radiometric ages obtained here mainly result from phengite recrystallization in deformation sites and/or deformation-controlled reequilibrations, with only minor effects of excess argon (and/or contamination by minerals adjacent to phengite) and ii) that the sub-units UH and EB reached peak conditions diachronously at ~320 and ~330 Ma, respectively. The metamorphic zircon rim overgrowth constrains peak burial of the MU unit at ~360 Ma (whereas the magmatic core is ~450 Ma). This evolution reflects a change in metamorphic gradient and possibly of the subduction thermal regime with time (Figure 59b).

Peak burial for the EB unit at ~330 Ma is reminiscent of ages ~328 ± 26 Ma obtained on 'blueschists' from the Atantayi/Akesayi valleys that closely paralleled to EB (Figure 61b-c, e, 69; Table 22) and the Kekesu valley (although located ~60km to the East;

Figure 50c, 69), mostly with the Ar-Ar step-heating technique [START_REF] Gao | but not systematically[END_REF]Gao et al., 2000[START_REF] Gao | South Tianshan: Late Paleozoic or Triassic collision orogenic belt?[END_REF][START_REF] Klemd | New Age Constraints on the Metamorphic Evolution of the High-Pressure/Low-Temperature Belt in the Western Tianshan Mountains, NW China[END_REF]. Although this age dispersion was previously interpreted as reflecting some excess Ar (by us; e.g., [START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF], or the prograde growth of an eclogite facies mineral assemblage [START_REF] Klemd | Changes in dip of subducted slabs at depth: Petrological and geochronological evidence from HP-UHP rocks (Tianshan, NW-China)[END_REF], these ages may be a further indication of the existence of a distinct metamorphic episode around 330

Ma in the AMC (Figure 61c,e).

For the MU unit, only two previous phengite/glaucophane Ar-Ar ages around ~364-370 Ma (Figure 61c, e; Table 22) were reported from samples immediately to the west of the MU unit (Gao et al., 2000). Some ultramafic lithologies were reported in the Changawuzi valley (~40 km to the west, Figure 50c, 69), with an age of 308 ± 5 Ma for blackwall formation [START_REF] Shen | In-situ U-Pb dating and Nd isotopic analysis of perovskite from a rodingite blackwall associated with UHP serpentinite from southwestern Tianshan, China[END_REF], but no eclogite boudins or Ti-chondrodite/clinohumite were found in the MU unit contrary to the Changawuzi samples.

Rocks from the GS facies sub-units (GS1, GS2 and GT, Figure 60a) yield ages around ~275-318 Ma matching i) retrogression ages (Figure 60, 66) found for the UH and EB sub-units, ii) the ~293-316 Ma phengite Ar-Ar plateau ages of regional GS facies rocks at the Kekesu valley (Wang et al., 2010;[START_REF] Xia | Late Palaeozoic40Ar/39Ar ages of the HP-LT metamorphic rocks from the Kekesu Valley, Chinese southwestern Tianshan: New constraints on exhumation tectonics[END_REF], iii) the ca. 304

Ma titanite U-Pb age of retrograde eclogite (Zhang et al., 2018) along the western part of SCTSZ, and iv) the ~280-290 Ma mica Ar-Ar plateau ages of GS facies rocks related to dextral strike-slip shearing along the eastern part of SCTSZ [START_REF] Laurent-Charvet | Late Paleozoic strike-slip shear zones in eastern central Asia (NW China): New structural and geochronological data[END_REF].

The juxtaposition of the four sub-units preserving a HP-LT history (namely the UH, EB, MU and GT) and making the center of the AMC metamorphic dome could therefore take place around 280-300 Ma at ~20km (Figure 59-61), since ages from moderately substituted, recrystallized phengite were detected in all these samples (Figure 60b, 66). As for prograde paths, exhumation P-T paths is slightly different, with some moderate heating for the MU and GT units and an isothermal to cooling return path for the UH and EB units (Figure 59b, 62b-e).

Exhumation velocities could not be calculated for individual samples but a first-order constraint can be inferred: assuming that ages for samples 135 and 26 are representative of the average UHP to GS history (from ~320 to 280-300 Ma, Figure 59a, 60) the decrease from ~ 2.75GPa to ~0.65GPa in approximately 20-40 Ma yields ~1.8-3.5 mm/yr for the UH unit, consistent with our previous independent estimate for a coesite- Final tectonic stacking of the UH, EB, MU and GT units around 280-300 Ma at ~20km Ma also suggests, contrary to some interpretations (e.g., [START_REF] Gao | Large-scale porphyry-type mineralization in the Central Asian metallogenic domain: A review[END_REF][START_REF] Wang | Final Assembly of the Southwestern Central Asian Orogenic Belt as Constrained by the Evolution of the South Tianshan Orogen: Links with Gondwana and Pangea[END_REF]Zhang et al., 2018), that the peak burial of the UHP does not mark oceanic closure (and/or does not relate to continental collision). In particular, the ~300 Ma phengite 40 Ar-39 Ar step-heating ages (Figure 60a, 67) from both the glaucophanebearing GT and GS1 units suggest that subduction was still active around the Late Carboniferous (i.e., ~300 Ma). This inference is further supported by the following This study

Previous works

Table 22: a Letters and numbers here correspond to data quoted in Figure 59b, 61 and 69.

b Amongst our compilation, there are only [this study], [START_REF] Klemd | Changes in dip of subducted slabs at depth: Petrological and geochronological evidence from HP-UHP rocks (Tianshan, NW-China)[END_REF] and [START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF] 7. Discussion and Perspective 7.1. Insight from regional P-T-time-lithologies review

Two decades have elapsed since eclogites were firstly reported from the STMB [START_REF] Gao | The discovery of eclogites and its tectonic implication, Southwest Tianshan[END_REF]. Fruitful investigations on field occurrences, protoliths, petrological characteristics, peak metamorphic P-T conditions and ages, metamorphic fluids have been obtained ( §2, also see [START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF] for comprehasive review). The STMB has been interpreted as an accretionary mélange associated with the subduction of the South Tianshan Ocean (Gao et al., 1998;[START_REF] Gao | Eclogite Occurrences in the Southern Tianshan High-Pressure Belt, Xinjiang[END_REF]Li et al., 2016a). In that sense it would represent the largest oceanic-type UHP belt in the world [START_REF] Zhang | A huge oceanic-type UHP metamorphic belt in southwestern Tianshan, China: Peak metamorphic age and P-T path[END_REF]Zhang et al., 2007;Zhang et al., 2018), though not in the sense of an oceanic lithosphere: it is essentially made of metavolcanoclastics and lacks thick mafic and ultramafic horizons. An opposite interpretation considers the SMTB as the result of continental subduction [START_REF] Loury | Tectonometamorphic evolution of the Atbashi highpressure units (Kyrgyz CAOB, Tien Shan): implications for the closure of the Turkestan Ocean and continental subduction-exhumation of the South Kazakh continental margin[END_REF].

Although the metamorphic evolution of eclogites and host micaschists has been studied in detail ( §2), controversy on the exhumation mechanism of these rocks still exist: i) some early studies suggested that the exhumation of HP-UHP rocks underwent an early syn-subduction wedge extrusion stage and a later thrust stage [START_REF] Gao | The mineralogy, petrology, metamorphic PTDt trajectory and exhumation mechanism of blueschists, south Tianshan, northwestern China[END_REF][START_REF] Gao | Formation of HP-LT rocks and their tectonic implications in the western Tianshan Orogen, NW China: Geochemical and age constraints[END_REF]; ii) Lü et al. (2012) divided the metamorphic terrane into a northern "UHP unit" and a southern "HP unit" (separated by a somewhat cryptic contact) juxtaposed from different depths; iii) Li et al. (2016aLi et al. ( , 2016b) ) tentatively proposed a subduction channel model, considering eclogites as discrete blocks within a buoyant micaschist matrix facilitating their exhumation; iv) a surprisingly long exhumation period (>70 Myr) was tentatively proposed for the UHP terrane by [START_REF] Zhang | A huge oceanic-type UHP metamorphic belt in southwestern Tianshan, China: Peak metamorphic age and P-T path[END_REF].

Two questions are therefore of particular interest, prior to answering how the AMC can be recovered (i.e., [START_REF] Agard | The subduction plate interface: Rock record and mechanical coupling (from long to short time scales)[END_REF]:

1) does the STMB behave like an oceanic-type fossil subduction remnant (e.g., with respect to W. Alpine and/or Franciscan remnants)?

2) Can we clarify exhumation mechanisms?

A tentative estimate of the abundance (vol%) of the different lithologies exposed in the STMB (Figure 52) can be made based on our field investigations ( §2 and 6) and literature data (e.g., [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF][START_REF] Gao | PT path of highpressure/low-temperature rocks and tectonic implications in the western Tianshan Mountains[END_REF][START_REF] Gao | The mineralogy, petrology, metamorphic PTDt trajectory and exhumation mechanism of blueschists, south Tianshan, northwestern China[END_REF]Z. Lü et al., 2012;Meyer et al., 2016;Soldner et al., 2017).

Exposures of meta-ultramafic rocks are limited (<5 vol%) in the STMB, with rare occurrences only reported at present in the adjacent Muzaerte-Changawuzi [START_REF] Gao | PT path of highpressure/low-temperature rocks and tectonic implications in the western Tianshan Mountains[END_REF][START_REF] Li | Petrology of rodingite derived from eclogite in western Tianshan[END_REF] and Kebuerte-Akesayi valley ( §6). Metavolcanic blocks or boudins/lenses/slices of various scales are commonly found within the STMB (not only limited to the AMC) but amount to ≤10-15 vol% (Figure 52).

Potential buoyancy contrasts for the various rock types are assessed below using P-T-density pseudosections. Previous P-T estimates are used (Figure 72) to identify whether the average exhumed eclogite, blueschist, and ultramafic rocks are buoyant or not (Figure 71). Eclogitic metavolcanics with pervasive dehydrated dense phases (e.g., omphacite, garnet) are essentially too dense (~3.28-3.46 g/cm 3 ; Figure 72a), whether at HP or UHP conditions, compared with mantle peridotite (>3.3 g/cm 3 ). Blueschists, in contrast, are less dense (~3.10-3.25 g/cm 3 ; Figure 72b), even when Tpeak reach ~600˚C.

Serpentinites (containing ~80 vol% antigorite at UHP peak in the area) are obviously lighter than the mantle, with estimated density ranging from 2.70 to 2.90 g/cm 3 , almost independent of pressure if T < 500˚C (Figure 72c). In contrast, pseudosections performed for the average composition of regional metavolcanoclastics as well as for common felsic (sandstone & graywacke) and pelitic lithologies (Figure 73) shows that the metasedimentary matrix host rocks of the STMB are buoyant enough (i.e., < 3.3 g/cm 3 ) even at UHP conditions.

Considering the compositional diversity of the entire STMB (e.g., assuming felsic:pelitic:mafic EC/BS:serpentinite ~35:50:10:5; according to our field investigations and those of [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF]; Figure 52), the bulk density will be ~3.02 g/cm 3 at 2.75 GPa and 520˚C. Computated densities are ~2.88 g/cm 3 for a completely serpentinized mantle and ~3.33 g/cm 3 for a dry mantle [START_REF] Angiboust | Initial water budget: The key to detaching large volumes of eclogitized oceanic crust along the subduction channel?[END_REF]. Even considering 30% of serpentinization (i.e. density~3.09 g/cm 3 ), for both the slab and upper plate mantle, the buoyancy contrast at peak conditions between the STMB slices and the surrounding mantle will be relatively small yet still positive (~+0.05 g/cm 3 ). While changes in boundary conditions (e.g., transient mechanical coupling; [START_REF] Agard | Exhumation of oceanic blueschists and eclogites in subduction zones: timing and mechanisms[END_REF][START_REF] Agard | The subduction plate interface: Rock record and mechanical coupling (from long to short time scales)[END_REF] are probably required at depth to detach the various sub-units (see §7.2), a continental buoy is thus not inherently needed to explain their preservation. Continental subduction [START_REF] Loury | Tectonometamorphic evolution of the Atbashi highpressure units (Kyrgyz CAOB, Tien Shan): implications for the closure of the Turkestan Ocean and continental subduction-exhumation of the South Kazakh continental margin[END_REF] would be an additional help, but seems unlikely for now in the absence of key lithologies such as gneisses and/or felsic amphibolitic rocks (± garnet-bearing peridotites with mafic lenses as in Dora Maira, Dabie-Sulu or Kokchetav; Guillot et al. (2009)). Moreover, several internal contact and mass thick metasedimentary slices stacking had been proposed for the AMC, with pervasive coesite findings and EC/BS facies senses of shear ( §2) observed in both metavolcanics and metavolcanoclastics (Figure 52; [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF]. This essentially rule out the possibility of 'long exhumation period (>70 Ma) of the UHP terrane in the AMC' since the pervasive preservation of coesite and/or lawsonite (although less reported in the AMC, §2) imply the exhumation of the UHP terrane should be relatively fast enough before the 'refrigerator' condition could be broke by retrograde metamorphism and/or fluid-rock interaction during exhumation, while the so-called 'long exhumation period (>70 Ma)' is too long compared with that of worldwide fossil oceanic subduction remnants (~15 Ma; [START_REF] Agard | The subduction plate interface: Rock record and mechanical coupling (from long to short time scales)[END_REF][START_REF] Agard | Exhumation of oceanic blueschists and eclogites in subduction zones: timing and mechanisms[END_REF]Guillot et al., 2009). Hence, the recovery puzzle of the STMB is then located on how can rocks/slices detached from down-going slab through space and time, and how fast it should be for preserving some key minerological 'information'. (Figure 52a-c), pointing to the importance of simple shear during exhumation (also see [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF], following northward subduction [START_REF] Scheltens | Northward subduction-related orogenesis of the southern Altaids: Constraints from structural and metamorphic analysis of the HP/UHP accretionary complex in Chinese southwestern Tianshan, NW China[END_REF]. The dominance of top to NEE GS facies shear senses might relate, by contrast, to later regional dextral strike-slip deformation.

Contacts between domains with slightly different lithologies and/or tectonic patterns (e.g., asymmetric shearing and abundance of mafic boudins in UH, Figure 52d) are interpreted to mark distinct km-scale tectonic sub-units: from north to south the GS1, UH, EB, MU, GT, and GS2 units (e.g., Figure 74d). Our observations and field mapping (e.g., cross-section of Figure 52d) thus suggest that the Akeyasi metamorphic complex, at least in the surroundings of the Kebuerte valley, is a metamorphic dome made of a stack of individual sub-units or nappes. This contradicts the view that the AMC might be a subduction mélange in the sense of Cloos & Shreve (1988a, 1988b) or Meyer et al. (2016). The lateral extension of the contacts can in places only be inferred, unfortunately, due the presence of glaciers (but the more mafic EB unit seems to correspond to the pillow unit described by [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF]). This identification of distinct sub-units is nevertheless strengthened by our results on the patterns and timing of their metamorphic evolutions: the exposed core of the metamorphic dome (i.e., the EB unit) does not correspond to the most deeply buried slice (indicating thrusting at some point of the tectonic history) and contrasting ages were obtained for the different sub-units, suggesting diachronous detachment from the subducting slab.

P-T constraints

P-T conditions were estimated by thermodynamic modelling for the coesitebearing oceanic eclogite (in the UH unit, §4). This yields UHP peak burial ~ 2.95 ± 0.2

GPa, 510 ± 20 ℃, with later reequilibration stages at ~ 2.45 ± 0.2 GPa, 540 ± 20 ℃ and ~ 2.0 ± 0.15 GPa, 525 ± 25 ℃. These results are consistent with the P-T estimates of previous UHP reports (Lü et al., 2012;Wei et al., 2009;[START_REF] Yang | Petrology and U-Pb zircon dating of coesite-bearing metapelite from the Kebuerte Valley, Western Tianshan, China[END_REF]. P-T estimates were also obtained using the THERMOCALC multi-equilibrium average PT approach for 13 samples along the Kebuerte transect. Metavolcanoclastics from the UH sub-unit (similar to the coesite-bearing oceanic eclogite sample), yield UHP peak burial P-T conditions around 480-560°C and 2.75GPa (±0.1) on average. Samples from the EC/BS EB unit (Figure 56b-c) record a prograde increase in pressure and temperature from 1.8 GPa (±0.10), 490°C (±15), to peak burial ~2.1 GPa (±0.15), 505°C (±15). The meta-mafic/-ultramafic unit experienced a much lower pressure from prograde ~0.95 GPa (±0.18) and 464°C (±28) to peak burial ~1.46 GPa (±0.16), 484°C (±29) and postpeak ~0.93 GPa (±0.06), 556°C (±13). P-T estimates for samples located to the north and south of the AMC (GS1 and GS2 sub-units) and from the transitional GT sub-unit reveal broadly comparable GS to lower-BS facies P-T histories, with peak burial around 0.7-1.0 GPa, 470-520°C and post-peak conditions of ~0.4-0.6 GPa, 520-570°C.

Similar GS to lower-BS facies conditions around 0.90-1.10GPa, 460-500°C were identified as retrograde overprint on metavolcanoclastics from the UH and EB units

Figure 75 The compilation of regional Pmax-T estimates and P-T paths. Numbers in black box corresponds to the detail of previous works in Table 1. Letters in white box marks the P-T estimates from this PhD thesis (mainly §6), listed in Table 22.

(sample, 32). Ages (recalled below) support a change in metamorphic gradient with time, from an intermediate to cold subduction regime (i.e., from ~12 to 5-7°C/km; Figure 59b; also see [START_REF] Agard | The subduction plate interface: Rock record and mechanical coupling (from long to short time scales)[END_REF] and [START_REF] Angiboust | Zagros blueschists: Episodic underplating and long-lived cooling of a subduction zone[END_REF]).

Previous P-T estimates (i.e., until this year, whether with conventional thermobarometry or pseudosection modeling; see §2 for the compilation) mainly focused on individual key samples in the UH unit with results clustering between HP and UHP conditions (i.e., 2.2 to 3.0 GPa, with ~70% located within the HP field, Figure 75). Homogeneous distribution of UHP conditions ≥2.5 GPa, however, has recently been argued based on Raman Quartz elastic barometry mapping results [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF]. This conclusion is in fact supported by the recent study, by means of pseudosection modeling, of [START_REF] Lü | The coherent ultrahigh-pressure terrane of the Tianshan meta ophiolite belt[END_REF]. Altogether, claims of 'only' HP slices/blocks/boudins in the UH unit, as previously indicated (Du et al., 2014;[START_REF] Li | A common high-pressure metamorphic evolution of interlayered eclogites and metasediments from the "ultrahigh-pressure unit" of the Tianshan metamorphic belt in China[END_REF]Meyer et al., 2016), are probably to be taken with caution.

Radiometric age constraints Implication for Late Carboniferous cold subduction dynamics

Our P-T-time study (e.g., Figure 76) was performed:

-for one representative coesite-bearing UHP eclogitic slice ( §4) with informative zircon textures/inclusions, using U-Pb, Sm-Nd minerals-bulk rock radiometry.

-for samples from the different sub-units with reasonable texture control ( §6), using in situ Ar-Ar probing on thin-sections (together with additional zircon U-Pb for the MU unit, and step-heating Ar-Ar radiometric dating for the GS facies units).

Ma, so that the most likely timing for the juxtaposition of the four sub-units preserving a HP-LT history (namely the UH, EB, MU and partly GT), and making the center of the AMC metamorphic dome, could be around 280-300 Ma (Figure 59-61).

P-T-time results suggest the diachronous recovery of different sub-units (Figure 59b), from ~45 km (MU; 360 Ma), ~65 km (EB; 330 Ma) and ~85 km depth (UH; 320 Ma), highlighting discrete, transient episodes of detachment from the slab, in particular with respect to long-lived South Tianshan ocean subduction duration of ~120 Myr [START_REF] Scheltens | Northward subduction-related orogenesis of the southern Altaids: Constraints from structural and metamorphic analysis of the HP/UHP accretionary complex in Chinese southwestern Tianshan, NW China[END_REF]. This punctuated recovery likely results from changes in mechanical coupling [START_REF] Agard | The subduction plate interface: Rock record and mechanical coupling (from long to short time scales)[END_REF], whose origin could be i) a change in slab geometry (e.g., slab rollback: [START_REF] Brun | Exhumation of high-pressure rocks driven by slab rollback[END_REF]slab kink: Klemd et al., 2011) (Figure 62b-c) and/or ii) a modification of the physical properties along the plate interface (i.e., mantle rheology, fluid regime, etc; [START_REF] Agard | The subduction plate interface: Rock record and mechanical coupling (from long to short time scales)[END_REF].

Final tectonic stacking of the UH, EB, MU and GT units around 280-300 Ma at ~20km Ma suggests, contrary to some interpretations (e.g., [START_REF] Gao | Large-scale porphyry-type mineralization in the Central Asian metallogenic domain: A review[END_REF]Wang et al., 2018;Zhang et al., 2018), that the peak burial of the UHP does not mark oceanic closure (and/or does not relate to continental collision). In particular, the ~300 Ma phengite 40 Ar-39 Ar step-heating ages (Figure 60a, 67) from both the glaucophanebearing GT and GS1 units suggest that subduction was still active around the Late Carboniferous (i.e., ~300 Ma). This inference is further supported by the regional magmatic indications (Figure 70). Overall, available magmatic and/or metamorphic constraints (e.g., this study) tend to show that the subduction of the Paleo South Tianshan ocean basin and relevant deposition were probably still active during the Late Carboniferous (Figure 62a). Final emplacement of the AMC complex could take place around early Permian-late carboniferous (i.e., ~280-300 Ma, Figure 62e), prior to the collision of the Paleo Kazakhstan Continent and the Tarim Craton (+STB, Figure 62a).

A witness of transient rock dynamics

One striking feature of the STMB is the pervasive preservation of coesite both in the metavolcanics blocks and the metavolcanoclastics matrix host rocks (e.g, Figure 11) (and lawsonite, but only rarely reported as inclusions in robust phases). This further implies the existence of short-lived detachment of tectonic slices maintaining relatively refrigerating conditions. Luckily, detailed petrological investigations on major and trace elements geochemistry of garnet highlight an unusual garnet zoning with concordant, annular enrichment in Mn, HREEs and Y (Figure 38a-c), but not in other major (Fe, Ca, Mg) or key trace elements (L/MREEs, Ti, Sr, Zr, Sc, Rb and P; Figure 38). This is visible at the outcrop-and probably km-scale, in a nearby representative i) The present-day geometry of the AMC is that of a metamorphic dome preserving evidence for internal nappe stacking.

ii) In situ laser probe 40 Ar-39 Ar radiometric dating of phengite and zircon U-Pb dating yield peak burial ages of 320 ± 1, 332 ± 2, 359 ± 2 Ma and ~280-310 Ma, respectively, for the UH, EB, MU and regional GS facies units (GS1, GS2 and GT), with recrystallization enhanced by fluid circulation and deformation.

iii) Juxtaposition and exhumation of the UH, EB, MU and GT units to mid-crustal depth (~20 km) was accomplished around 290-300 Ma, at rates on the order of 1-3 mm/yr.

iv) The existence of ~300 Ma glaucophane-bearing BS/GS facies metavolcanoclastic units (i.e., the GT and part of GS1 units) suggests that the subduction of the Paleo South Tianshan ocean basin was probably still active during late Carboniferous.

Figure 1 :

 1 Figure 1:(a) Global seismicity distribution pattern(M≥4, depth<70 Km, 1964(M≥4, depth<70 Km, -1998) ) with locations presented as black dots; (b) The surface subdivision with the major tectonic plates of earth.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 2: Schematic illustration of the Plate tectonics theory. •••••••••••••••••••••• --Figure 3: (a)Structure of subducted slabs as inferred from mantle tomography(Engdahl et al., 1998). •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 4:The global distribution pattern of fossil subduction remnants along plates sutured boundaries.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 5: Sketch of subduction accretion versus erosion, indicating variations in material incorporation in the subduction zone.••••••••••••••••••••••••••••••••••••••••• --Figure 6: Schematic sketch of the plate interface in subduction setting, according to present understanding. ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 7: Compilation of the Pmax-T condition of global HP/UHP remnants . •• --Figure 8: Tectonic sketch showing the middle to western segments of the Central Asian metallogenic domain.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure9: Simple sketch showing the relationship between main contacts and tectonic units in the South Tianshan Orogen and adjacent region.••••••••••••••••••••••••••••• --Figure 10: Geological map of the Southwestern Tianshan HP/UHP metamorphic belt (STMB). . •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure11: Brief geological map of the AMC, with emphasizing the finding of key lithologies and coesite.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 12:The collection of the protolith feature of samples of previous works. --Figure13: The compilation of previous P-T estimates for diverse lithologies in the STMB.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 14: The compilation of regional age reports. •••••••••••••••••••••••••••••••••• --Figure 15: Sampling location of this thesis in the AMC. ••••••••••••••••••••••••••••• --Figure 16: Simplified geological map of (a) the Chinese Western Tianshan and (b) close-up map for the area.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 17: Compilation of age data (a) as a function of estimated Pmax and (b) shown as a histogram.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 18: (a) Schematic outline of the studied outcrop; (b) field view of the sampling and (c) location of the samples in the layered eclogite.••••••••••••••••••••••••••••••• --Figure 19: Whole-rock discrimination diagrams for the samples. •••••••••••••••••• --Figure 20: Mineral assemblages and microstructures of the studied coesite-bearing eclogites..••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 21: Thin-section scale shear senses in eclogite and greenschist facies for the UHP eclogite and its meta-volcano-sedimentary host-rock, respectively. ••••••••• --

Figure 5 :

 5 Figure 1:(a) Global seismicity distribution pattern(M≥4, depth<70 Km, 1964(M≥4, depth<70 Km, -1998) ) with locations presented as black dots; (b) The surface subdivision with the major tectonic plates of earth.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 2: Schematic illustration of the Plate tectonics theory. •••••••••••••••••••••• --Figure 3: (a)Structure of subducted slabs as inferred from mantle tomography(Engdahl et al., 1998). •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 4:The global distribution pattern of fossil subduction remnants along plates sutured boundaries.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 5: Sketch of subduction accretion versus erosion, indicating variations in material incorporation in the subduction zone.••••••••••••••••••••••••••••••••••••••••• --Figure 6: Schematic sketch of the plate interface in subduction setting, according to present understanding. ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 7: Compilation of the Pmax-T condition of global HP/UHP remnants . •• --Figure 8: Tectonic sketch showing the middle to western segments of the Central Asian metallogenic domain.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure9: Simple sketch showing the relationship between main contacts and tectonic units in the South Tianshan Orogen and adjacent region.••••••••••••••••••••••••••••• --Figure 10: Geological map of the Southwestern Tianshan HP/UHP metamorphic belt (STMB). . •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure11: Brief geological map of the AMC, with emphasizing the finding of key lithologies and coesite.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 12:The collection of the protolith feature of samples of previous works. --Figure13: The compilation of previous P-T estimates for diverse lithologies in the STMB.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 14: The compilation of regional age reports. •••••••••••••••••••••••••••••••••• --Figure 15: Sampling location of this thesis in the AMC. ••••••••••••••••••••••••••••• --Figure 16: Simplified geological map of (a) the Chinese Western Tianshan and (b) close-up map for the area.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 17: Compilation of age data (a) as a function of estimated Pmax and (b) shown as a histogram.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 18: (a) Schematic outline of the studied outcrop; (b) field view of the sampling and (c) location of the samples in the layered eclogite.••••••••••••••••••••••••••••••• --Figure 19: Whole-rock discrimination diagrams for the samples. •••••••••••••••••• --Figure 20: Mineral assemblages and microstructures of the studied coesite-bearing eclogites..••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 21: Thin-section scale shear senses in eclogite and greenschist facies for the UHP eclogite and its meta-volcano-sedimentary host-rock, respectively. ••••••••• --

Figure 7 :Figure 8 :

 78 Figure 1:(a) Global seismicity distribution pattern(M≥4, depth<70 Km, 1964(M≥4, depth<70 Km, -1998) ) with locations presented as black dots; (b) The surface subdivision with the major tectonic plates of earth.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 2: Schematic illustration of the Plate tectonics theory. •••••••••••••••••••••• --Figure 3: (a)Structure of subducted slabs as inferred from mantle tomography(Engdahl et al., 1998). •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 4:The global distribution pattern of fossil subduction remnants along plates sutured boundaries.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 5: Sketch of subduction accretion versus erosion, indicating variations in material incorporation in the subduction zone.••••••••••••••••••••••••••••••••••••••••• --Figure 6: Schematic sketch of the plate interface in subduction setting, according to present understanding. ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 7: Compilation of the Pmax-T condition of global HP/UHP remnants . •• --Figure 8: Tectonic sketch showing the middle to western segments of the Central Asian metallogenic domain.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure9: Simple sketch showing the relationship between main contacts and tectonic units in the South Tianshan Orogen and adjacent region.••••••••••••••••••••••••••••• --Figure 10: Geological map of the Southwestern Tianshan HP/UHP metamorphic belt (STMB). . •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure11: Brief geological map of the AMC, with emphasizing the finding of key lithologies and coesite.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 12:The collection of the protolith feature of samples of previous works. --Figure13: The compilation of previous P-T estimates for diverse lithologies in the STMB.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 14: The compilation of regional age reports. •••••••••••••••••••••••••••••••••• --Figure 15: Sampling location of this thesis in the AMC. ••••••••••••••••••••••••••••• --Figure 16: Simplified geological map of (a) the Chinese Western Tianshan and (b) close-up map for the area.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 17: Compilation of age data (a) as a function of estimated Pmax and (b) shown as a histogram.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 18: (a) Schematic outline of the studied outcrop; (b) field view of the sampling and (c) location of the samples in the layered eclogite.••••••••••••••••••••••••••••••• --Figure 19: Whole-rock discrimination diagrams for the samples. •••••••••••••••••• --Figure 20: Mineral assemblages and microstructures of the studied coesite-bearing eclogites..••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 21: Thin-section scale shear senses in eclogite and greenschist facies for the UHP eclogite and its meta-volcano-sedimentary host-rock, respectively. ••••••••• --

Figure 17 :

 17 Figure 1:(a) Global seismicity distribution pattern(M≥4, depth<70 Km, 1964(M≥4, depth<70 Km, -1998) ) with locations presented as black dots; (b) The surface subdivision with the major tectonic plates of earth.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 2: Schematic illustration of the Plate tectonics theory. •••••••••••••••••••••• --Figure 3: (a)Structure of subducted slabs as inferred from mantle tomography(Engdahl et al., 1998). •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 4:The global distribution pattern of fossil subduction remnants along plates sutured boundaries.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 5: Sketch of subduction accretion versus erosion, indicating variations in material incorporation in the subduction zone.••••••••••••••••••••••••••••••••••••••••• --Figure 6: Schematic sketch of the plate interface in subduction setting, according to present understanding. ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 7: Compilation of the Pmax-T condition of global HP/UHP remnants . •• --Figure 8: Tectonic sketch showing the middle to western segments of the Central Asian metallogenic domain.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure9: Simple sketch showing the relationship between main contacts and tectonic units in the South Tianshan Orogen and adjacent region.••••••••••••••••••••••••••••• --Figure 10: Geological map of the Southwestern Tianshan HP/UHP metamorphic belt (STMB). . •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure11: Brief geological map of the AMC, with emphasizing the finding of key lithologies and coesite.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 12:The collection of the protolith feature of samples of previous works. --Figure13: The compilation of previous P-T estimates for diverse lithologies in the STMB.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 14: The compilation of regional age reports. •••••••••••••••••••••••••••••••••• --Figure 15: Sampling location of this thesis in the AMC. ••••••••••••••••••••••••••••• --Figure 16: Simplified geological map of (a) the Chinese Western Tianshan and (b) close-up map for the area.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 17: Compilation of age data (a) as a function of estimated Pmax and (b) shown as a histogram.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 18: (a) Schematic outline of the studied outcrop; (b) field view of the sampling and (c) location of the samples in the layered eclogite.••••••••••••••••••••••••••••••• --Figure 19: Whole-rock discrimination diagrams for the samples. •••••••••••••••••• --Figure 20: Mineral assemblages and microstructures of the studied coesite-bearing eclogites..••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 21: Thin-section scale shear senses in eclogite and greenschist facies for the UHP eclogite and its meta-volcano-sedimentary host-rock, respectively. ••••••••• --

Figure 18 :

 18 Figure 1:(a) Global seismicity distribution pattern(M≥4, depth<70 Km, 1964(M≥4, depth<70 Km, -1998) ) with locations presented as black dots; (b) The surface subdivision with the major tectonic plates of earth.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 2: Schematic illustration of the Plate tectonics theory. •••••••••••••••••••••• --Figure 3: (a)Structure of subducted slabs as inferred from mantle tomography(Engdahl et al., 1998). •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 4:The global distribution pattern of fossil subduction remnants along plates sutured boundaries.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 5: Sketch of subduction accretion versus erosion, indicating variations in material incorporation in the subduction zone.••••••••••••••••••••••••••••••••••••••••• --Figure 6: Schematic sketch of the plate interface in subduction setting, according to present understanding. ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 7: Compilation of the Pmax-T condition of global HP/UHP remnants . •• --Figure 8: Tectonic sketch showing the middle to western segments of the Central Asian metallogenic domain.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure9: Simple sketch showing the relationship between main contacts and tectonic units in the South Tianshan Orogen and adjacent region.••••••••••••••••••••••••••••• --Figure 10: Geological map of the Southwestern Tianshan HP/UHP metamorphic belt (STMB). . •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure11: Brief geological map of the AMC, with emphasizing the finding of key lithologies and coesite.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 12:The collection of the protolith feature of samples of previous works. --Figure13: The compilation of previous P-T estimates for diverse lithologies in the STMB.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 14: The compilation of regional age reports. •••••••••••••••••••••••••••••••••• --Figure 15: Sampling location of this thesis in the AMC. ••••••••••••••••••••••••••••• --Figure 16: Simplified geological map of (a) the Chinese Western Tianshan and (b) close-up map for the area.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 17: Compilation of age data (a) as a function of estimated Pmax and (b) shown as a histogram.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 18: (a) Schematic outline of the studied outcrop; (b) field view of the sampling and (c) location of the samples in the layered eclogite.••••••••••••••••••••••••••••••• --Figure 19: Whole-rock discrimination diagrams for the samples. •••••••••••••••••• --Figure 20: Mineral assemblages and microstructures of the studied coesite-bearing eclogites..••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 21: Thin-section scale shear senses in eclogite and greenschist facies for the UHP eclogite and its meta-volcano-sedimentary host-rock, respectively. ••••••••• --

Figure 20 :

 20 Figure 1:(a) Global seismicity distribution pattern(M≥4, depth<70 Km, 1964(M≥4, depth<70 Km, -1998) ) with locations presented as black dots; (b) The surface subdivision with the major tectonic plates of earth.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 2: Schematic illustration of the Plate tectonics theory. •••••••••••••••••••••• --Figure 3: (a)Structure of subducted slabs as inferred from mantle tomography(Engdahl et al., 1998). •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 4:The global distribution pattern of fossil subduction remnants along plates sutured boundaries.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 5: Sketch of subduction accretion versus erosion, indicating variations in material incorporation in the subduction zone.••••••••••••••••••••••••••••••••••••••••• --Figure 6: Schematic sketch of the plate interface in subduction setting, according to present understanding. ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 7: Compilation of the Pmax-T condition of global HP/UHP remnants . •• --Figure 8: Tectonic sketch showing the middle to western segments of the Central Asian metallogenic domain.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure9: Simple sketch showing the relationship between main contacts and tectonic units in the South Tianshan Orogen and adjacent region.••••••••••••••••••••••••••••• --Figure 10: Geological map of the Southwestern Tianshan HP/UHP metamorphic belt (STMB). . •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure11: Brief geological map of the AMC, with emphasizing the finding of key lithologies and coesite.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 12:The collection of the protolith feature of samples of previous works. --Figure13: The compilation of previous P-T estimates for diverse lithologies in the STMB.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 14: The compilation of regional age reports. •••••••••••••••••••••••••••••••••• --Figure 15: Sampling location of this thesis in the AMC. ••••••••••••••••••••••••••••• --Figure 16: Simplified geological map of (a) the Chinese Western Tianshan and (b) close-up map for the area.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 17: Compilation of age data (a) as a function of estimated Pmax and (b) shown as a histogram.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 18: (a) Schematic outline of the studied outcrop; (b) field view of the sampling and (c) location of the samples in the layered eclogite.••••••••••••••••••••••••••••••• --Figure 19: Whole-rock discrimination diagrams for the samples. •••••••••••••••••• --Figure 20: Mineral assemblages and microstructures of the studied coesite-bearing eclogites..••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 21: Thin-section scale shear senses in eclogite and greenschist facies for the UHP eclogite and its meta-volcano-sedimentary host-rock, respectively. ••••••••• --

Figure 22 :

 22 Figure 22: selected garnet porphyroblast and relevant mineral inclusions information.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -70 -Figure 23: Cathodoluminescence imaging and sketches of analyzed zircon grains, showing multistage growth features.••••••••••••••••••••••••••••••••••••••••••••••••••••• -75 -Figure 24: Chondrite-normalized[START_REF] Sun | Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes[END_REF]) REE abundances of the various zircon (a) and garnet domains (b).•••••••••••••••••••••••••••••••••••••••••••••• -78 -Figure 25: Results of SIMS U-Pb isotopic dating and δ 18 O compositions for various zircon domains.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -79 -Figure 26: WR-garnet-omphacite Sm-Nd isochron age for the oriented sample. -82 -Figure 27: P-T estimates for the studied UHP eclogites, inferred from Perple_X pseudosection modeling and Thermocalc averagePT calculation.••••••••••••••••••• -85 -Figure 28: P-T trajectory estimates from this study (a) and previous works (b).. -87 -Figure 29: (a-b) Patterns of trace element distribution coefficients between various possibly coexisting zircon and garnet domains. (c) sketch summarizing the various growth zones observed in zircon and garnet.••••••••••••••••••••••••••••••••••••••••••• -90 -Figure30: Sketch depicting the petrologic evolution of mineral growth within metabasalts and inferred mobility of elements (mainly REEs) within the garnet-zirconmatrix metamorphic system during subduction and exhumation.••••••••••••••••••• -91 -Figure31: Previous radiometric data (see Table2) and results from this study place constraints on the main tectonic stages for the area.••••••••••••••••••••••••••••••••••• -92 -Figure32: Simplified geodynamic cartoon setting back the studied samples and the overall time constraints inferred from this study within the evolution of the Chinese Southwestern Tianshan HP-UHP/LT metamorphic belt.••••••••••••••••••••••••••••• -93 -Figure 33: BSE imaging of mineral inclusion distribution in the studied garnet porphyroblast. •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -103 -Figure 34: Rutile armored by sphene in both omphacite matrix (a, b) and later stage retrograde-growth quartz (c, d).•••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -103 -Figure35: Rb vs K, Nb/U vs U, K/Th vs Ba/Th and Ba/Nb vs U/Nb diagrams[START_REF] Bebout | Metamorphic chemical geodynamics of subduction zones[END_REF][START_REF] Bebout | Metasomatism in Subduction Zones of Subducted Oceanic Slabs, Mantle Wedges, and the Slab-Mantle Interface[END_REF] for discriminating between LILE enrichment by metamorphism and seafloor alteration.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -104 -Figure 36: Continued from Figure 23: (a-i): cathodoluminescence images of other studied zircon grains; (m-n): typical HP (or UHP) metamorphic minerals (omphacite and rutile) revealed from Raman analyses.•••••••••••••••••••••••••••••••••••••••••••• -104 -Figure 37: Geological background of the SW-Tianshan LT-HP/UHP metamorphic complex. (a) Location of the research area with respect to other key UHP reports in China; (b) Close-up view showing the regional geological setting and sampling location: previous UHP reports based on coesite inclusions in garnet are highlighted by red stars.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -107 -Figure 38: Key features of the specific garnet zoning investigated here, examplified by garnet A1.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -109 -

Figure 23 :

 23 Figure 22: selected garnet porphyroblast and relevant mineral inclusions information.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -70 -Figure 23: Cathodoluminescence imaging and sketches of analyzed zircon grains, showing multistage growth features.••••••••••••••••••••••••••••••••••••••••••••••••••••• -75 -Figure 24: Chondrite-normalized[START_REF] Sun | Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes[END_REF]) REE abundances of the various zircon (a) and garnet domains (b).•••••••••••••••••••••••••••••••••••••••••••••• -78 -Figure 25: Results of SIMS U-Pb isotopic dating and δ 18 O compositions for various zircon domains.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -79 -Figure 26: WR-garnet-omphacite Sm-Nd isochron age for the oriented sample. -82 -Figure 27: P-T estimates for the studied UHP eclogites, inferred from Perple_X pseudosection modeling and Thermocalc averagePT calculation.••••••••••••••••••• -85 -Figure 28: P-T trajectory estimates from this study (a) and previous works (b).. -87 -Figure 29: (a-b) Patterns of trace element distribution coefficients between various possibly coexisting zircon and garnet domains. (c) sketch summarizing the various growth zones observed in zircon and garnet.••••••••••••••••••••••••••••••••••••••••••• -90 -Figure30: Sketch depicting the petrologic evolution of mineral growth within metabasalts and inferred mobility of elements (mainly REEs) within the garnet-zirconmatrix metamorphic system during subduction and exhumation.••••••••••••••••••• -91 -Figure31: Previous radiometric data (see Table2) and results from this study place constraints on the main tectonic stages for the area.••••••••••••••••••••••••••••••••••• -92 -Figure32: Simplified geodynamic cartoon setting back the studied samples and the overall time constraints inferred from this study within the evolution of the Chinese Southwestern Tianshan HP-UHP/LT metamorphic belt.••••••••••••••••••••••••••••• -93 -Figure 33: BSE imaging of mineral inclusion distribution in the studied garnet porphyroblast. •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -103 -Figure 34: Rutile armored by sphene in both omphacite matrix (a, b) and later stage retrograde-growth quartz (c, d).•••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -103 -Figure35: Rb vs K, Nb/U vs U, K/Th vs Ba/Th and Ba/Nb vs U/Nb diagrams[START_REF] Bebout | Metamorphic chemical geodynamics of subduction zones[END_REF][START_REF] Bebout | Metasomatism in Subduction Zones of Subducted Oceanic Slabs, Mantle Wedges, and the Slab-Mantle Interface[END_REF] for discriminating between LILE enrichment by metamorphism and seafloor alteration.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -104 -Figure 36: Continued from Figure 23: (a-i): cathodoluminescence images of other studied zircon grains; (m-n): typical HP (or UHP) metamorphic minerals (omphacite and rutile) revealed from Raman analyses.•••••••••••••••••••••••••••••••••••••••••••• -104 -Figure 37: Geological background of the SW-Tianshan LT-HP/UHP metamorphic complex. (a) Location of the research area with respect to other key UHP reports in China; (b) Close-up view showing the regional geological setting and sampling location: previous UHP reports based on coesite inclusions in garnet are highlighted by red stars.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -107 -Figure 38: Key features of the specific garnet zoning investigated here, examplified by garnet A1.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -109 -

Figure 25 :

 25 Figure 22: selected garnet porphyroblast and relevant mineral inclusions information.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -70 -Figure 23: Cathodoluminescence imaging and sketches of analyzed zircon grains, showing multistage growth features.••••••••••••••••••••••••••••••••••••••••••••••••••••• -75 -Figure 24: Chondrite-normalized[START_REF] Sun | Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes[END_REF]) REE abundances of the various zircon (a) and garnet domains (b).•••••••••••••••••••••••••••••••••••••••••••••• -78 -Figure 25: Results of SIMS U-Pb isotopic dating and δ 18 O compositions for various zircon domains.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -79 -Figure 26: WR-garnet-omphacite Sm-Nd isochron age for the oriented sample. -82 -Figure 27: P-T estimates for the studied UHP eclogites, inferred from Perple_X pseudosection modeling and Thermocalc averagePT calculation.••••••••••••••••••• -85 -Figure 28: P-T trajectory estimates from this study (a) and previous works (b).. -87 -Figure 29: (a-b) Patterns of trace element distribution coefficients between various possibly coexisting zircon and garnet domains. (c) sketch summarizing the various growth zones observed in zircon and garnet.••••••••••••••••••••••••••••••••••••••••••• -90 -Figure30: Sketch depicting the petrologic evolution of mineral growth within metabasalts and inferred mobility of elements (mainly REEs) within the garnet-zirconmatrix metamorphic system during subduction and exhumation.••••••••••••••••••• -91 -Figure31: Previous radiometric data (see Table2) and results from this study place constraints on the main tectonic stages for the area.••••••••••••••••••••••••••••••••••• -92 -Figure32: Simplified geodynamic cartoon setting back the studied samples and the overall time constraints inferred from this study within the evolution of the Chinese Southwestern Tianshan HP-UHP/LT metamorphic belt.••••••••••••••••••••••••••••• -93 -Figure 33: BSE imaging of mineral inclusion distribution in the studied garnet porphyroblast. •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -103 -Figure 34: Rutile armored by sphene in both omphacite matrix (a, b) and later stage retrograde-growth quartz (c, d).•••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -103 -Figure35: Rb vs K, Nb/U vs U, K/Th vs Ba/Th and Ba/Nb vs U/Nb diagrams[START_REF] Bebout | Metamorphic chemical geodynamics of subduction zones[END_REF][START_REF] Bebout | Metasomatism in Subduction Zones of Subducted Oceanic Slabs, Mantle Wedges, and the Slab-Mantle Interface[END_REF] for discriminating between LILE enrichment by metamorphism and seafloor alteration.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -104 -Figure 36: Continued from Figure 23: (a-i): cathodoluminescence images of other studied zircon grains; (m-n): typical HP (or UHP) metamorphic minerals (omphacite and rutile) revealed from Raman analyses.•••••••••••••••••••••••••••••••••••••••••••• -104 -Figure 37: Geological background of the SW-Tianshan LT-HP/UHP metamorphic complex. (a) Location of the research area with respect to other key UHP reports in China; (b) Close-up view showing the regional geological setting and sampling location: previous UHP reports based on coesite inclusions in garnet are highlighted by red stars.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -107 -Figure 38: Key features of the specific garnet zoning investigated here, examplified by garnet A1.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -109 -

Figure 26 :

 26 Figure 22: selected garnet porphyroblast and relevant mineral inclusions information.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -70 -Figure 23: Cathodoluminescence imaging and sketches of analyzed zircon grains, showing multistage growth features.••••••••••••••••••••••••••••••••••••••••••••••••••••• -75 -Figure 24: Chondrite-normalized[START_REF] Sun | Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes[END_REF]) REE abundances of the various zircon (a) and garnet domains (b).•••••••••••••••••••••••••••••••••••••••••••••• -78 -Figure 25: Results of SIMS U-Pb isotopic dating and δ 18 O compositions for various zircon domains.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -79 -Figure 26: WR-garnet-omphacite Sm-Nd isochron age for the oriented sample. -82 -Figure 27: P-T estimates for the studied UHP eclogites, inferred from Perple_X pseudosection modeling and Thermocalc averagePT calculation.••••••••••••••••••• -85 -Figure 28: P-T trajectory estimates from this study (a) and previous works (b).. -87 -Figure 29: (a-b) Patterns of trace element distribution coefficients between various possibly coexisting zircon and garnet domains. (c) sketch summarizing the various growth zones observed in zircon and garnet.••••••••••••••••••••••••••••••••••••••••••• -90 -Figure30: Sketch depicting the petrologic evolution of mineral growth within metabasalts and inferred mobility of elements (mainly REEs) within the garnet-zirconmatrix metamorphic system during subduction and exhumation.••••••••••••••••••• -91 -Figure31: Previous radiometric data (see Table2) and results from this study place constraints on the main tectonic stages for the area.••••••••••••••••••••••••••••••••••• -92 -Figure32: Simplified geodynamic cartoon setting back the studied samples and the overall time constraints inferred from this study within the evolution of the Chinese Southwestern Tianshan HP-UHP/LT metamorphic belt.••••••••••••••••••••••••••••• -93 -Figure 33: BSE imaging of mineral inclusion distribution in the studied garnet porphyroblast. •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -103 -Figure 34: Rutile armored by sphene in both omphacite matrix (a, b) and later stage retrograde-growth quartz (c, d).•••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -103 -Figure35: Rb vs K, Nb/U vs U, K/Th vs Ba/Th and Ba/Nb vs U/Nb diagrams[START_REF] Bebout | Metamorphic chemical geodynamics of subduction zones[END_REF][START_REF] Bebout | Metasomatism in Subduction Zones of Subducted Oceanic Slabs, Mantle Wedges, and the Slab-Mantle Interface[END_REF] for discriminating between LILE enrichment by metamorphism and seafloor alteration.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -104 -Figure 36: Continued from Figure 23: (a-i): cathodoluminescence images of other studied zircon grains; (m-n): typical HP (or UHP) metamorphic minerals (omphacite and rutile) revealed from Raman analyses.•••••••••••••••••••••••••••••••••••••••••••• -104 -Figure 37: Geological background of the SW-Tianshan LT-HP/UHP metamorphic complex. (a) Location of the research area with respect to other key UHP reports in China; (b) Close-up view showing the regional geological setting and sampling location: previous UHP reports based on coesite inclusions in garnet are highlighted by red stars.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -107 -Figure 38: Key features of the specific garnet zoning investigated here, examplified by garnet A1.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -109 -

Figure 36 :

 36 Figure 22: selected garnet porphyroblast and relevant mineral inclusions information.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -70 -Figure 23: Cathodoluminescence imaging and sketches of analyzed zircon grains, showing multistage growth features.••••••••••••••••••••••••••••••••••••••••••••••••••••• -75 -Figure 24: Chondrite-normalized[START_REF] Sun | Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes[END_REF]) REE abundances of the various zircon (a) and garnet domains (b).•••••••••••••••••••••••••••••••••••••••••••••• -78 -Figure 25: Results of SIMS U-Pb isotopic dating and δ 18 O compositions for various zircon domains.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -79 -Figure 26: WR-garnet-omphacite Sm-Nd isochron age for the oriented sample. -82 -Figure 27: P-T estimates for the studied UHP eclogites, inferred from Perple_X pseudosection modeling and Thermocalc averagePT calculation.••••••••••••••••••• -85 -Figure 28: P-T trajectory estimates from this study (a) and previous works (b).. -87 -Figure 29: (a-b) Patterns of trace element distribution coefficients between various possibly coexisting zircon and garnet domains. (c) sketch summarizing the various growth zones observed in zircon and garnet.••••••••••••••••••••••••••••••••••••••••••• -90 -Figure30: Sketch depicting the petrologic evolution of mineral growth within metabasalts and inferred mobility of elements (mainly REEs) within the garnet-zirconmatrix metamorphic system during subduction and exhumation.••••••••••••••••••• -91 -Figure31: Previous radiometric data (see Table2) and results from this study place constraints on the main tectonic stages for the area.••••••••••••••••••••••••••••••••••• -92 -Figure32: Simplified geodynamic cartoon setting back the studied samples and the overall time constraints inferred from this study within the evolution of the Chinese Southwestern Tianshan HP-UHP/LT metamorphic belt.••••••••••••••••••••••••••••• -93 -Figure 33: BSE imaging of mineral inclusion distribution in the studied garnet porphyroblast. •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -103 -Figure 34: Rutile armored by sphene in both omphacite matrix (a, b) and later stage retrograde-growth quartz (c, d).•••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -103 -Figure35: Rb vs K, Nb/U vs U, K/Th vs Ba/Th and Ba/Nb vs U/Nb diagrams[START_REF] Bebout | Metamorphic chemical geodynamics of subduction zones[END_REF][START_REF] Bebout | Metasomatism in Subduction Zones of Subducted Oceanic Slabs, Mantle Wedges, and the Slab-Mantle Interface[END_REF] for discriminating between LILE enrichment by metamorphism and seafloor alteration.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -104 -Figure 36: Continued from Figure 23: (a-i): cathodoluminescence images of other studied zircon grains; (m-n): typical HP (or UHP) metamorphic minerals (omphacite and rutile) revealed from Raman analyses.•••••••••••••••••••••••••••••••••••••••••••• -104 -Figure 37: Geological background of the SW-Tianshan LT-HP/UHP metamorphic complex. (a) Location of the research area with respect to other key UHP reports in China; (b) Close-up view showing the regional geological setting and sampling location: previous UHP reports based on coesite inclusions in garnet are highlighted by red stars.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -107 -Figure 38: Key features of the specific garnet zoning investigated here, examplified by garnet A1.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -109 -

Figure 37 :

 37 Figure 22: selected garnet porphyroblast and relevant mineral inclusions information.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -70 -Figure 23: Cathodoluminescence imaging and sketches of analyzed zircon grains, showing multistage growth features.••••••••••••••••••••••••••••••••••••••••••••••••••••• -75 -Figure 24: Chondrite-normalized[START_REF] Sun | Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes[END_REF]) REE abundances of the various zircon (a) and garnet domains (b).•••••••••••••••••••••••••••••••••••••••••••••• -78 -Figure 25: Results of SIMS U-Pb isotopic dating and δ 18 O compositions for various zircon domains.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -79 -Figure 26: WR-garnet-omphacite Sm-Nd isochron age for the oriented sample. -82 -Figure 27: P-T estimates for the studied UHP eclogites, inferred from Perple_X pseudosection modeling and Thermocalc averagePT calculation.••••••••••••••••••• -85 -Figure 28: P-T trajectory estimates from this study (a) and previous works (b).. -87 -Figure 29: (a-b) Patterns of trace element distribution coefficients between various possibly coexisting zircon and garnet domains. (c) sketch summarizing the various growth zones observed in zircon and garnet.••••••••••••••••••••••••••••••••••••••••••• -90 -Figure30: Sketch depicting the petrologic evolution of mineral growth within metabasalts and inferred mobility of elements (mainly REEs) within the garnet-zirconmatrix metamorphic system during subduction and exhumation.••••••••••••••••••• -91 -Figure31: Previous radiometric data (see Table2) and results from this study place constraints on the main tectonic stages for the area.••••••••••••••••••••••••••••••••••• -92 -Figure32: Simplified geodynamic cartoon setting back the studied samples and the overall time constraints inferred from this study within the evolution of the Chinese Southwestern Tianshan HP-UHP/LT metamorphic belt.••••••••••••••••••••••••••••• -93 -Figure 33: BSE imaging of mineral inclusion distribution in the studied garnet porphyroblast. •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -103 -Figure 34: Rutile armored by sphene in both omphacite matrix (a, b) and later stage retrograde-growth quartz (c, d).•••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -103 -Figure35: Rb vs K, Nb/U vs U, K/Th vs Ba/Th and Ba/Nb vs U/Nb diagrams[START_REF] Bebout | Metamorphic chemical geodynamics of subduction zones[END_REF][START_REF] Bebout | Metasomatism in Subduction Zones of Subducted Oceanic Slabs, Mantle Wedges, and the Slab-Mantle Interface[END_REF] for discriminating between LILE enrichment by metamorphism and seafloor alteration.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -104 -Figure 36: Continued from Figure 23: (a-i): cathodoluminescence images of other studied zircon grains; (m-n): typical HP (or UHP) metamorphic minerals (omphacite and rutile) revealed from Raman analyses.•••••••••••••••••••••••••••••••••••••••••••• -104 -Figure 37: Geological background of the SW-Tianshan LT-HP/UHP metamorphic complex. (a) Location of the research area with respect to other key UHP reports in China; (b) Close-up view showing the regional geological setting and sampling location: previous UHP reports based on coesite inclusions in garnet are highlighted by red stars.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -107 -Figure 38: Key features of the specific garnet zoning investigated here, examplified by garnet A1.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -109 -

Figure 39 :

 39 Figure39: Variations in the concentrations of (a) major divalent cations, (b-d) HREEs and Yttrium, (e-f) MREEs and (g-h) other key trace elements for garnet A1, along the profile shown in Figure38b. ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 40: (a-b) Mn concentration profiles for diverse sized garnets. ••••••••••••• --Figure 41: Influence of key parameters on diffusion-controlled garnet growth. • --Figure 42: Modelling of the concordant MnYHREE garnet zoning for diverse size garnets and in garnet A1.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure43: Simplified sketches depicting the impact of diffusion-controlled garnet growth (here during a transient thermal pulse). ••••••••••••••••••••••••••••••••••••••• --Figure44: Tentative interpretation of the thermal excursion in terms of rock dynamics along a cold subduction plate interface.•••••••••••••••••••••••••••••••••••••••••••••••• --Figure 45: (a) Ti, (b) P, (c) Ca and (d) Mg mapping reveal the relationships between garnet A1 and associated Ti, P, Ca, Mg-bearing inclusion/matrix minerals.•••••• --Figure 46: EMPA-BSE, transmitted light and cross-polarized light images of investigated garnet grains (A1-3, B1-4, C1), sampled from different parts of the outcrop (Figure 37d).•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 47:The Ca, Mg and Mn mapping as well as corresponding compositional profiles of the rest of investigated garnet grains.•••••••••••••••••••••••••••••••••••••• --Figure 48: Systematic garnet size survey. The three main groups and estimated mineral modes (vol %) for investigated UHP eclogite samples are shown.••••••••••••••••• --Figure49: Polynomial fitting for estimating effective bulk rock compositions during garnet growth (and uptake of major elements, HREEs and Y).••••••••••••••••••••• --Figure 50: (a) Tectonic sketch showing the middle to western segments of the Central Asian metallogenic domain.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 51: (a) Close-up views of the Akesayi metamorphic complex (AMC) showing sampling localities and reappraised tectonic sub-units & contacts. •••••••••••••••• --Figure 52: (a) Close-up view of the area along the Kebuerte valley showing sampling sites, measured shear senses and the location of field observations.••••••••••••••• --Figure53: Panoramic views of the main sub-units and contacts in the AMC, with representative sample localities.••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 54: (a)The structural sketch showing the extension on E-W of the revised AMC, with (b, c) the detail data of field structural measurements for the schistosity and lineation.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 55: Outcrop observation of representative samples in this study. The letter of sub-figures corresponds to the localities marked in Figure 52c. •••••••••••••••••••• --Figure 56: Microphotographs of samples investigated in the present study. ••••• --Figure 57: Primitive mantle-normalized spider diagram and chondrite-normalized REE pattern for samples in this study.•••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 58: Mineral plots of compositions determined with the electron probe microanalysis. •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --

Figure 40 :

 40 Figure39: Variations in the concentrations of (a) major divalent cations, (b-d) HREEs and Yttrium, (e-f) MREEs and (g-h) other key trace elements for garnet A1, along the profile shown in Figure38b. ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 40: (a-b) Mn concentration profiles for diverse sized garnets. ••••••••••••• --Figure 41: Influence of key parameters on diffusion-controlled garnet growth. • --Figure 42: Modelling of the concordant MnYHREE garnet zoning for diverse size garnets and in garnet A1.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure43: Simplified sketches depicting the impact of diffusion-controlled garnet growth (here during a transient thermal pulse). ••••••••••••••••••••••••••••••••••••••• --Figure44: Tentative interpretation of the thermal excursion in terms of rock dynamics along a cold subduction plate interface.•••••••••••••••••••••••••••••••••••••••••••••••• --Figure 45: (a) Ti, (b) P, (c) Ca and (d) Mg mapping reveal the relationships between garnet A1 and associated Ti, P, Ca, Mg-bearing inclusion/matrix minerals.•••••• --Figure 46: EMPA-BSE, transmitted light and cross-polarized light images of investigated garnet grains (A1-3, B1-4, C1), sampled from different parts of the outcrop (Figure 37d).•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 47:The Ca, Mg and Mn mapping as well as corresponding compositional profiles of the rest of investigated garnet grains.•••••••••••••••••••••••••••••••••••••• --Figure 48: Systematic garnet size survey. The three main groups and estimated mineral modes (vol %) for investigated UHP eclogite samples are shown.••••••••••••••••• --Figure49: Polynomial fitting for estimating effective bulk rock compositions during garnet growth (and uptake of major elements, HREEs and Y).••••••••••••••••••••• --Figure 50: (a) Tectonic sketch showing the middle to western segments of the Central Asian metallogenic domain.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 51: (a) Close-up views of the Akesayi metamorphic complex (AMC) showing sampling localities and reappraised tectonic sub-units & contacts. •••••••••••••••• --Figure 52: (a) Close-up view of the area along the Kebuerte valley showing sampling sites, measured shear senses and the location of field observations.••••••••••••••• --Figure53: Panoramic views of the main sub-units and contacts in the AMC, with representative sample localities.••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 54: (a)The structural sketch showing the extension on E-W of the revised AMC, with (b, c) the detail data of field structural measurements for the schistosity and lineation.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 55: Outcrop observation of representative samples in this study. The letter of sub-figures corresponds to the localities marked in Figure 52c. •••••••••••••••••••• --Figure 56: Microphotographs of samples investigated in the present study. ••••• --Figure 57: Primitive mantle-normalized spider diagram and chondrite-normalized REE pattern for samples in this study.•••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 58: Mineral plots of compositions determined with the electron probe microanalysis. •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --

Figure 45 :

 45 Figure39: Variations in the concentrations of (a) major divalent cations, (b-d) HREEs and Yttrium, (e-f) MREEs and (g-h) other key trace elements for garnet A1, along the profile shown in Figure38b. ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 40: (a-b) Mn concentration profiles for diverse sized garnets. ••••••••••••• --Figure 41: Influence of key parameters on diffusion-controlled garnet growth. • --Figure 42: Modelling of the concordant MnYHREE garnet zoning for diverse size garnets and in garnet A1.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure43: Simplified sketches depicting the impact of diffusion-controlled garnet growth (here during a transient thermal pulse). ••••••••••••••••••••••••••••••••••••••• --Figure44: Tentative interpretation of the thermal excursion in terms of rock dynamics along a cold subduction plate interface.•••••••••••••••••••••••••••••••••••••••••••••••• --Figure 45: (a) Ti, (b) P, (c) Ca and (d) Mg mapping reveal the relationships between garnet A1 and associated Ti, P, Ca, Mg-bearing inclusion/matrix minerals.•••••• --Figure 46: EMPA-BSE, transmitted light and cross-polarized light images of investigated garnet grains (A1-3, B1-4, C1), sampled from different parts of the outcrop (Figure 37d).•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 47:The Ca, Mg and Mn mapping as well as corresponding compositional profiles of the rest of investigated garnet grains.•••••••••••••••••••••••••••••••••••••• --Figure 48: Systematic garnet size survey. The three main groups and estimated mineral modes (vol %) for investigated UHP eclogite samples are shown.••••••••••••••••• --Figure49: Polynomial fitting for estimating effective bulk rock compositions during garnet growth (and uptake of major elements, HREEs and Y).••••••••••••••••••••• --Figure 50: (a) Tectonic sketch showing the middle to western segments of the Central Asian metallogenic domain.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 51: (a) Close-up views of the Akesayi metamorphic complex (AMC) showing sampling localities and reappraised tectonic sub-units & contacts. •••••••••••••••• --Figure 52: (a) Close-up view of the area along the Kebuerte valley showing sampling sites, measured shear senses and the location of field observations.••••••••••••••• --Figure53: Panoramic views of the main sub-units and contacts in the AMC, with representative sample localities.••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 54: (a)The structural sketch showing the extension on E-W of the revised AMC, with (b, c) the detail data of field structural measurements for the schistosity and lineation.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 55: Outcrop observation of representative samples in this study. The letter of sub-figures corresponds to the localities marked in Figure 52c. •••••••••••••••••••• --Figure 56: Microphotographs of samples investigated in the present study. ••••• --Figure 57: Primitive mantle-normalized spider diagram and chondrite-normalized REE pattern for samples in this study.•••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 58: Mineral plots of compositions determined with the electron probe microanalysis. •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --

Figure 50 :

 50 Figure39: Variations in the concentrations of (a) major divalent cations, (b-d) HREEs and Yttrium, (e-f) MREEs and (g-h) other key trace elements for garnet A1, along the profile shown in Figure38b. ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 40: (a-b) Mn concentration profiles for diverse sized garnets. ••••••••••••• --Figure 41: Influence of key parameters on diffusion-controlled garnet growth. • --Figure 42: Modelling of the concordant MnYHREE garnet zoning for diverse size garnets and in garnet A1.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure43: Simplified sketches depicting the impact of diffusion-controlled garnet growth (here during a transient thermal pulse). ••••••••••••••••••••••••••••••••••••••• --Figure44: Tentative interpretation of the thermal excursion in terms of rock dynamics along a cold subduction plate interface.•••••••••••••••••••••••••••••••••••••••••••••••• --Figure 45: (a) Ti, (b) P, (c) Ca and (d) Mg mapping reveal the relationships between garnet A1 and associated Ti, P, Ca, Mg-bearing inclusion/matrix minerals.•••••• --Figure 46: EMPA-BSE, transmitted light and cross-polarized light images of investigated garnet grains (A1-3, B1-4, C1), sampled from different parts of the outcrop (Figure 37d).•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 47:The Ca, Mg and Mn mapping as well as corresponding compositional profiles of the rest of investigated garnet grains.•••••••••••••••••••••••••••••••••••••• --Figure 48: Systematic garnet size survey. The three main groups and estimated mineral modes (vol %) for investigated UHP eclogite samples are shown.••••••••••••••••• --Figure49: Polynomial fitting for estimating effective bulk rock compositions during garnet growth (and uptake of major elements, HREEs and Y).••••••••••••••••••••• --Figure 50: (a) Tectonic sketch showing the middle to western segments of the Central Asian metallogenic domain.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 51: (a) Close-up views of the Akesayi metamorphic complex (AMC) showing sampling localities and reappraised tectonic sub-units & contacts. •••••••••••••••• --Figure 52: (a) Close-up view of the area along the Kebuerte valley showing sampling sites, measured shear senses and the location of field observations.••••••••••••••• --Figure53: Panoramic views of the main sub-units and contacts in the AMC, with representative sample localities.••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 54: (a)The structural sketch showing the extension on E-W of the revised AMC, with (b, c) the detail data of field structural measurements for the schistosity and lineation.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 55: Outcrop observation of representative samples in this study. The letter of sub-figures corresponds to the localities marked in Figure 52c. •••••••••••••••••••• --Figure 56: Microphotographs of samples investigated in the present study. ••••• --Figure 57: Primitive mantle-normalized spider diagram and chondrite-normalized REE pattern for samples in this study.•••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 58: Mineral plots of compositions determined with the electron probe microanalysis. •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --

Figure 51 :

 51 Figure39: Variations in the concentrations of (a) major divalent cations, (b-d) HREEs and Yttrium, (e-f) MREEs and (g-h) other key trace elements for garnet A1, along the profile shown in Figure38b. ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 40: (a-b) Mn concentration profiles for diverse sized garnets. ••••••••••••• --Figure 41: Influence of key parameters on diffusion-controlled garnet growth. • --Figure 42: Modelling of the concordant MnYHREE garnet zoning for diverse size garnets and in garnet A1.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure43: Simplified sketches depicting the impact of diffusion-controlled garnet growth (here during a transient thermal pulse). ••••••••••••••••••••••••••••••••••••••• --Figure44: Tentative interpretation of the thermal excursion in terms of rock dynamics along a cold subduction plate interface.•••••••••••••••••••••••••••••••••••••••••••••••• --Figure 45: (a) Ti, (b) P, (c) Ca and (d) Mg mapping reveal the relationships between garnet A1 and associated Ti, P, Ca, Mg-bearing inclusion/matrix minerals.•••••• --Figure 46: EMPA-BSE, transmitted light and cross-polarized light images of investigated garnet grains (A1-3, B1-4, C1), sampled from different parts of the outcrop (Figure 37d).•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 47:The Ca, Mg and Mn mapping as well as corresponding compositional profiles of the rest of investigated garnet grains.•••••••••••••••••••••••••••••••••••••• --Figure 48: Systematic garnet size survey. The three main groups and estimated mineral modes (vol %) for investigated UHP eclogite samples are shown.••••••••••••••••• --Figure49: Polynomial fitting for estimating effective bulk rock compositions during garnet growth (and uptake of major elements, HREEs and Y).••••••••••••••••••••• --Figure 50: (a) Tectonic sketch showing the middle to western segments of the Central Asian metallogenic domain.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 51: (a) Close-up views of the Akesayi metamorphic complex (AMC) showing sampling localities and reappraised tectonic sub-units & contacts. •••••••••••••••• --Figure 52: (a) Close-up view of the area along the Kebuerte valley showing sampling sites, measured shear senses and the location of field observations.••••••••••••••• --Figure53: Panoramic views of the main sub-units and contacts in the AMC, with representative sample localities.••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 54: (a)The structural sketch showing the extension on E-W of the revised AMC, with (b, c) the detail data of field structural measurements for the schistosity and lineation.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 55: Outcrop observation of representative samples in this study. The letter of sub-figures corresponds to the localities marked in Figure 52c. •••••••••••••••••••• --Figure 56: Microphotographs of samples investigated in the present study. ••••• --Figure 57: Primitive mantle-normalized spider diagram and chondrite-normalized REE pattern for samples in this study.•••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 58: Mineral plots of compositions determined with the electron probe microanalysis. •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --

Figure 55 :

 55 Figure39: Variations in the concentrations of (a) major divalent cations, (b-d) HREEs and Yttrium, (e-f) MREEs and (g-h) other key trace elements for garnet A1, along the profile shown in Figure38b. ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 40: (a-b) Mn concentration profiles for diverse sized garnets. ••••••••••••• --Figure 41: Influence of key parameters on diffusion-controlled garnet growth. • --Figure 42: Modelling of the concordant MnYHREE garnet zoning for diverse size garnets and in garnet A1.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure43: Simplified sketches depicting the impact of diffusion-controlled garnet growth (here during a transient thermal pulse). ••••••••••••••••••••••••••••••••••••••• --Figure44: Tentative interpretation of the thermal excursion in terms of rock dynamics along a cold subduction plate interface.•••••••••••••••••••••••••••••••••••••••••••••••• --Figure 45: (a) Ti, (b) P, (c) Ca and (d) Mg mapping reveal the relationships between garnet A1 and associated Ti, P, Ca, Mg-bearing inclusion/matrix minerals.•••••• --Figure 46: EMPA-BSE, transmitted light and cross-polarized light images of investigated garnet grains (A1-3, B1-4, C1), sampled from different parts of the outcrop (Figure 37d).•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 47:The Ca, Mg and Mn mapping as well as corresponding compositional profiles of the rest of investigated garnet grains.•••••••••••••••••••••••••••••••••••••• --Figure 48: Systematic garnet size survey. The three main groups and estimated mineral modes (vol %) for investigated UHP eclogite samples are shown.••••••••••••••••• --Figure49: Polynomial fitting for estimating effective bulk rock compositions during garnet growth (and uptake of major elements, HREEs and Y).••••••••••••••••••••• --Figure 50: (a) Tectonic sketch showing the middle to western segments of the Central Asian metallogenic domain.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 51: (a) Close-up views of the Akesayi metamorphic complex (AMC) showing sampling localities and reappraised tectonic sub-units & contacts. •••••••••••••••• --Figure 52: (a) Close-up view of the area along the Kebuerte valley showing sampling sites, measured shear senses and the location of field observations.••••••••••••••• --Figure53: Panoramic views of the main sub-units and contacts in the AMC, with representative sample localities.••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 54: (a)The structural sketch showing the extension on E-W of the revised AMC, with (b, c) the detail data of field structural measurements for the schistosity and lineation.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 55: Outcrop observation of representative samples in this study. The letter of sub-figures corresponds to the localities marked in Figure 52c. •••••••••••••••••••• --Figure 56: Microphotographs of samples investigated in the present study. ••••• --Figure 57: Primitive mantle-normalized spider diagram and chondrite-normalized REE pattern for samples in this study.•••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 58: Mineral plots of compositions determined with the electron probe microanalysis. •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --

Figure 56 :

 56 Figure39: Variations in the concentrations of (a) major divalent cations, (b-d) HREEs and Yttrium, (e-f) MREEs and (g-h) other key trace elements for garnet A1, along the profile shown in Figure38b. ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 40: (a-b) Mn concentration profiles for diverse sized garnets. ••••••••••••• --Figure 41: Influence of key parameters on diffusion-controlled garnet growth. • --Figure 42: Modelling of the concordant MnYHREE garnet zoning for diverse size garnets and in garnet A1.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure43: Simplified sketches depicting the impact of diffusion-controlled garnet growth (here during a transient thermal pulse). ••••••••••••••••••••••••••••••••••••••• --Figure44: Tentative interpretation of the thermal excursion in terms of rock dynamics along a cold subduction plate interface.•••••••••••••••••••••••••••••••••••••••••••••••• --Figure 45: (a) Ti, (b) P, (c) Ca and (d) Mg mapping reveal the relationships between garnet A1 and associated Ti, P, Ca, Mg-bearing inclusion/matrix minerals.•••••• --Figure 46: EMPA-BSE, transmitted light and cross-polarized light images of investigated garnet grains (A1-3, B1-4, C1), sampled from different parts of the outcrop (Figure 37d).•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 47:The Ca, Mg and Mn mapping as well as corresponding compositional profiles of the rest of investigated garnet grains.•••••••••••••••••••••••••••••••••••••• --Figure 48: Systematic garnet size survey. The three main groups and estimated mineral modes (vol %) for investigated UHP eclogite samples are shown.••••••••••••••••• --Figure49: Polynomial fitting for estimating effective bulk rock compositions during garnet growth (and uptake of major elements, HREEs and Y).••••••••••••••••••••• --Figure 50: (a) Tectonic sketch showing the middle to western segments of the Central Asian metallogenic domain.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 51: (a) Close-up views of the Akesayi metamorphic complex (AMC) showing sampling localities and reappraised tectonic sub-units & contacts. •••••••••••••••• --Figure 52: (a) Close-up view of the area along the Kebuerte valley showing sampling sites, measured shear senses and the location of field observations.••••••••••••••• --Figure53: Panoramic views of the main sub-units and contacts in the AMC, with representative sample localities.••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 54: (a)The structural sketch showing the extension on E-W of the revised AMC, with (b, c) the detail data of field structural measurements for the schistosity and lineation.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 55: Outcrop observation of representative samples in this study. The letter of sub-figures corresponds to the localities marked in Figure 52c. •••••••••••••••••••• --Figure 56: Microphotographs of samples investigated in the present study. ••••• --Figure 57: Primitive mantle-normalized spider diagram and chondrite-normalized REE pattern for samples in this study.•••••••••••••••••••••••••••••••••••••••••••••••••••••••• --Figure 58: Mineral plots of compositions determined with the electron probe microanalysis. •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• --

Figure 62 :

 62 Figure59: P-T plot showing the results of our P-T estimates using THERMOCALC[START_REF] Holland | An enlarged and updated internally consistent thermodynamic dataset with uncertainties and correlations: the system K2O-Na2O-CaO-MgO-MnO-FeO-Fe2O3-Al2O3-TiO2-SiO2-C-H2-O2[END_REF] together with estimates of metamorphic temperature by the Raman spectroscopy of carbonaceous material (RSCM,[START_REF] Beyssac | Raman spectra of carbonaceous material in metasediments: A new geothermometer[END_REF][START_REF] Beyssac | Thermal metamorphism in the lesser Himalaya of Nepal determined from Raman spectroscopy of carbonaceous material[END_REF] and Ti-in-biotite geothermometry[START_REF] Henry | The Ti-saturation surface for lowto-medium pressure metapelitic biotites: Implications for geothermometry and Tisubstitution mechanisms[END_REF].••••••••••••••• -191 -Figure60: (a) Radiometric ages obtained for all samples, with respect to respective localities on Kebuerte section.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• b, c, d) The compilation of regional age reports with respect to sampling localities (ages versus latitude). Ages reported in key valleys are listed respectively from the top to bottom.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -202 -Figure 62: (a) Paleogeographic reconstruction during the Gondwana assembly at ~510-470 Ma and Pangea assembly at ~300-280 Ma. (b) Interpretative sketches relating the formation and exhumation of the SW-Tianshan HP/UHP-LT accretionary complex during the period 360-280 Ma.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -206 -Figure63: Panoramic views of the main north and south contacts in between the AMC and the SCTSZ mylonitized shear zone (GS1, GS2).•••••••••••••••••••••••••••••••• -211 -Figure 64: Outcrop observation of representative samples in this study. ••••••••• -212 -Figure 65: Microphotographs of samples investigated in the present study. ••••• -213 -Figure 66: The rest of in situ 40 Ar-39 Ar laser probe ablation results.•••••••••••••• -214 -Figure67: The phengite 40 Ar-39 Ar step-heating results of regional GS to lower BS facies samples (J2, 22, 157 and 147), and the LA-ICP-MS zircon U-Pb radiometric results of meta-basite sample (158). •••••••••••••••••••••••••••••••••••••••••••••••••••• -215 -Figure 68: Examples of later stage phengite recrystallization in samples from distinct sub-units (UH versus GT units).••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -216 -Figure 69: Geological map with the locality of previous age reports. ••••••••••••• -217 -Figure 70: The comparison between ages from metamorphic indications (this study+ previous works) and those from magmatic indications (previous works) that related to the Paleo South Tianshan Ocean Basin subduction setting.••••••••••••••••••••••••• -219 -Figure71: Major elements composition of selected samples in this PhD thesis and those from previous works.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -221 -Figure72: P-T-density pesudosections conducted for representative compositions of metavolcanoclsatics (regional and global)••••••••••••••••••••••••••••••••••••••••••••• -224 -Figure73: P-T-density pesudosections conducted for representative compositions of regional eclogitie, blueschist and serpentinite.•••••••••••••••••••••••••••••••••••••••• -224 -Figure 74: (a) Close-up view of the area along the Kebuerte valley showing sampling sites, measured shear senses and the location of field observations. ••••••••••••••• -225 -Figure 75: The compilation of regional Pmax-T estimates and P-T paths. ••••••• -228 -Figure 76: The summary of radiometric age constraints in this PhD thesis. ••••• -230 -

Figure 64 :

 64 Figure59: P-T plot showing the results of our P-T estimates using THERMOCALC[START_REF] Holland | An enlarged and updated internally consistent thermodynamic dataset with uncertainties and correlations: the system K2O-Na2O-CaO-MgO-MnO-FeO-Fe2O3-Al2O3-TiO2-SiO2-C-H2-O2[END_REF] together with estimates of metamorphic temperature by the Raman spectroscopy of carbonaceous material (RSCM,[START_REF] Beyssac | Raman spectra of carbonaceous material in metasediments: A new geothermometer[END_REF][START_REF] Beyssac | Thermal metamorphism in the lesser Himalaya of Nepal determined from Raman spectroscopy of carbonaceous material[END_REF] and Ti-in-biotite geothermometry[START_REF] Henry | The Ti-saturation surface for lowto-medium pressure metapelitic biotites: Implications for geothermometry and Tisubstitution mechanisms[END_REF].••••••••••••••• -191 -Figure60: (a) Radiometric ages obtained for all samples, with respect to respective localities on Kebuerte section.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• b, c, d) The compilation of regional age reports with respect to sampling localities (ages versus latitude). Ages reported in key valleys are listed respectively from the top to bottom.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -202 -Figure 62: (a) Paleogeographic reconstruction during the Gondwana assembly at ~510-470 Ma and Pangea assembly at ~300-280 Ma. (b) Interpretative sketches relating the formation and exhumation of the SW-Tianshan HP/UHP-LT accretionary complex during the period 360-280 Ma.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -206 -Figure63: Panoramic views of the main north and south contacts in between the AMC and the SCTSZ mylonitized shear zone (GS1, GS2).•••••••••••••••••••••••••••••••• -211 -Figure 64: Outcrop observation of representative samples in this study. ••••••••• -212 -Figure 65: Microphotographs of samples investigated in the present study. ••••• -213 -Figure 66: The rest of in situ 40 Ar-39 Ar laser probe ablation results.•••••••••••••• -214 -Figure67: The phengite 40 Ar-39 Ar step-heating results of regional GS to lower BS facies samples (J2, 22, 157 and 147), and the LA-ICP-MS zircon U-Pb radiometric results of meta-basite sample (158). •••••••••••••••••••••••••••••••••••••••••••••••••••• -215 -Figure 68: Examples of later stage phengite recrystallization in samples from distinct sub-units (UH versus GT units).••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -216 -Figure 69: Geological map with the locality of previous age reports. ••••••••••••• -217 -Figure 70: The comparison between ages from metamorphic indications (this study+ previous works) and those from magmatic indications (previous works) that related to the Paleo South Tianshan Ocean Basin subduction setting.••••••••••••••••••••••••• -219 -Figure71: Major elements composition of selected samples in this PhD thesis and those from previous works.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -221 -Figure72: P-T-density pesudosections conducted for representative compositions of metavolcanoclsatics (regional and global)••••••••••••••••••••••••••••••••••••••••••••• -224 -Figure73: P-T-density pesudosections conducted for representative compositions of regional eclogitie, blueschist and serpentinite.•••••••••••••••••••••••••••••••••••••••• -224 -Figure 74: (a) Close-up view of the area along the Kebuerte valley showing sampling sites, measured shear senses and the location of field observations. ••••••••••••••• -225 -Figure 75: The compilation of regional Pmax-T estimates and P-T paths. ••••••• -228 -Figure 76: The summary of radiometric age constraints in this PhD thesis. ••••• -230 -

Figure 68 :

 68 Figure59: P-T plot showing the results of our P-T estimates using THERMOCALC[START_REF] Holland | An enlarged and updated internally consistent thermodynamic dataset with uncertainties and correlations: the system K2O-Na2O-CaO-MgO-MnO-FeO-Fe2O3-Al2O3-TiO2-SiO2-C-H2-O2[END_REF] together with estimates of metamorphic temperature by the Raman spectroscopy of carbonaceous material (RSCM,[START_REF] Beyssac | Raman spectra of carbonaceous material in metasediments: A new geothermometer[END_REF][START_REF] Beyssac | Thermal metamorphism in the lesser Himalaya of Nepal determined from Raman spectroscopy of carbonaceous material[END_REF] and Ti-in-biotite geothermometry[START_REF] Henry | The Ti-saturation surface for lowto-medium pressure metapelitic biotites: Implications for geothermometry and Tisubstitution mechanisms[END_REF].••••••••••••••• -191 -Figure60: (a) Radiometric ages obtained for all samples, with respect to respective localities on Kebuerte section.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• b, c, d) The compilation of regional age reports with respect to sampling localities (ages versus latitude). Ages reported in key valleys are listed respectively from the top to bottom.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -202 -Figure 62: (a) Paleogeographic reconstruction during the Gondwana assembly at ~510-470 Ma and Pangea assembly at ~300-280 Ma. (b) Interpretative sketches relating the formation and exhumation of the SW-Tianshan HP/UHP-LT accretionary complex during the period 360-280 Ma.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -206 -Figure63: Panoramic views of the main north and south contacts in between the AMC and the SCTSZ mylonitized shear zone (GS1, GS2).•••••••••••••••••••••••••••••••• -211 -Figure 64: Outcrop observation of representative samples in this study. ••••••••• -212 -Figure 65: Microphotographs of samples investigated in the present study. ••••• -213 -Figure 66: The rest of in situ 40 Ar-39 Ar laser probe ablation results.•••••••••••••• -214 -Figure67: The phengite 40 Ar-39 Ar step-heating results of regional GS to lower BS facies samples (J2, 22, 157 and 147), and the LA-ICP-MS zircon U-Pb radiometric results of meta-basite sample (158). •••••••••••••••••••••••••••••••••••••••••••••••••••• -215 -Figure 68: Examples of later stage phengite recrystallization in samples from distinct sub-units (UH versus GT units).••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -216 -Figure 69: Geological map with the locality of previous age reports. ••••••••••••• -217 -Figure 70: The comparison between ages from metamorphic indications (this study+ previous works) and those from magmatic indications (previous works) that related to the Paleo South Tianshan Ocean Basin subduction setting.••••••••••••••••••••••••• -219 -Figure71: Major elements composition of selected samples in this PhD thesis and those from previous works.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -221 -Figure72: P-T-density pesudosections conducted for representative compositions of metavolcanoclsatics (regional and global)••••••••••••••••••••••••••••••••••••••••••••• -224 -Figure73: P-T-density pesudosections conducted for representative compositions of regional eclogitie, blueschist and serpentinite.•••••••••••••••••••••••••••••••••••••••• -224 -Figure 74: (a) Close-up view of the area along the Kebuerte valley showing sampling sites, measured shear senses and the location of field observations. ••••••••••••••• -225 -Figure 75: The compilation of regional Pmax-T estimates and P-T paths. ••••••• -228 -Figure 76: The summary of radiometric age constraints in this PhD thesis. ••••• -230 -

Figure 69 :

 69 Figure59: P-T plot showing the results of our P-T estimates using THERMOCALC[START_REF] Holland | An enlarged and updated internally consistent thermodynamic dataset with uncertainties and correlations: the system K2O-Na2O-CaO-MgO-MnO-FeO-Fe2O3-Al2O3-TiO2-SiO2-C-H2-O2[END_REF] together with estimates of metamorphic temperature by the Raman spectroscopy of carbonaceous material (RSCM,[START_REF] Beyssac | Raman spectra of carbonaceous material in metasediments: A new geothermometer[END_REF][START_REF] Beyssac | Thermal metamorphism in the lesser Himalaya of Nepal determined from Raman spectroscopy of carbonaceous material[END_REF] and Ti-in-biotite geothermometry[START_REF] Henry | The Ti-saturation surface for lowto-medium pressure metapelitic biotites: Implications for geothermometry and Tisubstitution mechanisms[END_REF].••••••••••••••• -191 -Figure60: (a) Radiometric ages obtained for all samples, with respect to respective localities on Kebuerte section.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• b, c, d) The compilation of regional age reports with respect to sampling localities (ages versus latitude). Ages reported in key valleys are listed respectively from the top to bottom.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -202 -Figure 62: (a) Paleogeographic reconstruction during the Gondwana assembly at ~510-470 Ma and Pangea assembly at ~300-280 Ma. (b) Interpretative sketches relating the formation and exhumation of the SW-Tianshan HP/UHP-LT accretionary complex during the period 360-280 Ma.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -206 -Figure63: Panoramic views of the main north and south contacts in between the AMC and the SCTSZ mylonitized shear zone (GS1, GS2).•••••••••••••••••••••••••••••••• -211 -Figure 64: Outcrop observation of representative samples in this study. ••••••••• -212 -Figure 65: Microphotographs of samples investigated in the present study. ••••• -213 -Figure 66: The rest of in situ 40 Ar-39 Ar laser probe ablation results.•••••••••••••• -214 -Figure67: The phengite 40 Ar-39 Ar step-heating results of regional GS to lower BS facies samples (J2, 22, 157 and 147), and the LA-ICP-MS zircon U-Pb radiometric results of meta-basite sample (158). •••••••••••••••••••••••••••••••••••••••••••••••••••• -215 -Figure 68: Examples of later stage phengite recrystallization in samples from distinct sub-units (UH versus GT units).••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -216 -Figure 69: Geological map with the locality of previous age reports. ••••••••••••• -217 -Figure 70: The comparison between ages from metamorphic indications (this study+ previous works) and those from magmatic indications (previous works) that related to the Paleo South Tianshan Ocean Basin subduction setting.••••••••••••••••••••••••• -219 -Figure71: Major elements composition of selected samples in this PhD thesis and those from previous works.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -221 -Figure72: P-T-density pesudosections conducted for representative compositions of metavolcanoclsatics (regional and global)••••••••••••••••••••••••••••••••••••••••••••• -224 -Figure73: P-T-density pesudosections conducted for representative compositions of regional eclogitie, blueschist and serpentinite.•••••••••••••••••••••••••••••••••••••••• -224 -Figure 74: (a) Close-up view of the area along the Kebuerte valley showing sampling sites, measured shear senses and the location of field observations. ••••••••••••••• -225 -Figure 75: The compilation of regional Pmax-T estimates and P-T paths. ••••••• -228 -Figure 76: The summary of radiometric age constraints in this PhD thesis. ••••• -230 -

Figure 74 :Figure 1 :

 741 Figure59: P-T plot showing the results of our P-T estimates using THERMOCALC[START_REF] Holland | An enlarged and updated internally consistent thermodynamic dataset with uncertainties and correlations: the system K2O-Na2O-CaO-MgO-MnO-FeO-Fe2O3-Al2O3-TiO2-SiO2-C-H2-O2[END_REF] together with estimates of metamorphic temperature by the Raman spectroscopy of carbonaceous material (RSCM,[START_REF] Beyssac | Raman spectra of carbonaceous material in metasediments: A new geothermometer[END_REF][START_REF] Beyssac | Thermal metamorphism in the lesser Himalaya of Nepal determined from Raman spectroscopy of carbonaceous material[END_REF] and Ti-in-biotite geothermometry[START_REF] Henry | The Ti-saturation surface for lowto-medium pressure metapelitic biotites: Implications for geothermometry and Tisubstitution mechanisms[END_REF].••••••••••••••• -191 -Figure60: (a) Radiometric ages obtained for all samples, with respect to respective localities on Kebuerte section.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• b, c, d) The compilation of regional age reports with respect to sampling localities (ages versus latitude). Ages reported in key valleys are listed respectively from the top to bottom.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -202 -Figure 62: (a) Paleogeographic reconstruction during the Gondwana assembly at ~510-470 Ma and Pangea assembly at ~300-280 Ma. (b) Interpretative sketches relating the formation and exhumation of the SW-Tianshan HP/UHP-LT accretionary complex during the period 360-280 Ma.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -206 -Figure63: Panoramic views of the main north and south contacts in between the AMC and the SCTSZ mylonitized shear zone (GS1, GS2).•••••••••••••••••••••••••••••••• -211 -Figure 64: Outcrop observation of representative samples in this study. ••••••••• -212 -Figure 65: Microphotographs of samples investigated in the present study. ••••• -213 -Figure 66: The rest of in situ 40 Ar-39 Ar laser probe ablation results.•••••••••••••• -214 -Figure67: The phengite 40 Ar-39 Ar step-heating results of regional GS to lower BS facies samples (J2, 22, 157 and 147), and the LA-ICP-MS zircon U-Pb radiometric results of meta-basite sample (158). •••••••••••••••••••••••••••••••••••••••••••••••••••• -215 -Figure 68: Examples of later stage phengite recrystallization in samples from distinct sub-units (UH versus GT units).••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -216 -Figure 69: Geological map with the locality of previous age reports. ••••••••••••• -217 -Figure 70: The comparison between ages from metamorphic indications (this study+ previous works) and those from magmatic indications (previous works) that related to the Paleo South Tianshan Ocean Basin subduction setting.••••••••••••••••••••••••• -219 -Figure71: Major elements composition of selected samples in this PhD thesis and those from previous works.••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• -221 -Figure72: P-T-density pesudosections conducted for representative compositions of metavolcanoclsatics (regional and global)••••••••••••••••••••••••••••••••••••••••••••• -224 -Figure73: P-T-density pesudosections conducted for representative compositions of regional eclogitie, blueschist and serpentinite.•••••••••••••••••••••••••••••••••••••••• -224 -Figure 74: (a) Close-up view of the area along the Kebuerte valley showing sampling sites, measured shear senses and the location of field observations. ••••••••••••••• -225 -Figure 75: The compilation of regional Pmax-T estimates and P-T paths. ••••••• -228 -Figure 76: The summary of radiometric age constraints in this PhD thesis. ••••• -230 -

Figure 2 :

 2 Figure 2: Schematic illustration of the Plate tectonics theory.

Figure 3 :

 3 Figure 3: (a) Structure of subducted slabs as inferred from mantle tomography (Engdahl et al., 1998). Red lines

Figure 4 :

 4 Figure 4: The global distribution pattern of fossil subduction remnants along plates sutured boundaries. Modified from Karason and Van Der Hilst (2000) and Stern (2002).

Figure 5 :

 5 Figure 5: Sketch of subduction accretion versus erosion, indicating variations in material incorporation in the subduction zone (after Cloos and Shreve, 1996, 1988b). (a) Model of subduction accretion, with the Marianas subduction as an example. (b) Model of subduction erosion, with the Chilean subduction as an example.

Figure 6 :

 6 Figure 6: Schematic sketch of the plate interface in subduction setting, according to present understanding (modified after Bassett and Watts (2015).

Figure 7 :

 7 Figure 7: Compilation of the Pmax-T condition of global HP/UHP remnants (according to the data collection from Guillot et al. (2009)). Grey box represents HP rocks recovered within accretionary wedge; Purple box marks exhumed HP/UHP oceanic rocks wrapped in serpentinite mélange; Brown box indicates UHP crustal rocks associated with continental subduction. Abbreviation: KO, Kokchetav; N/SQDS: North/South Qinling-Dabie; DM: Dora Maira; ZS: Zermatt Saas; VO: Voltri Italy; SI: Sistan Iran; ZA: Zagros Iran; FC: Franciscan Complex; SLC/A: Schistes Lustrés Corsica/W.Alps.

A

  systematic review of previous works is presented in 'Chapter 2-Geological Setting of the STMB'. This chapter provides the geological background for the STMB and our studied area, the Akeyazi metamorphic complex (AMC), and reviews previous P-T(-time-lithologies) investigations on individual samples. Relevant methods for geochemical & radiometric experimental measurements and P-T estimates are briefly introduced in 'Chapter 3-Methods'. Three manuscripts written during this PhD thesis, either published or submitted, are presented respectively in 'Chapter 4. P-T-timeisotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan' (Lithos, 2017), 'Chapter 5. Concordant pulse in Mn, Y and HREEs concentrations during UHP eclogitic garnet growth: transient rock dynamics along a cold subduction plate interface' (EPSL, under review) and 'Chapter 6. Contrasting P-T-deformation-time evolutions in the SW-Tianshan (Akeyasi HP/UHP complex, China): implications for Late Carboniferous subduction dynamics' (prepare to submit to Lithos). 'Chapter 7-Discussion and Perspective' and 'Chapter 8-Conclusions' provide

Figure 8 :

 8 Figure 8: Tectonic sketch showing the middle to western segments of the Central Asian metallogenic domain, modified after Gao et al. (2017), Soldner et al. (2017) and Xiao et al. (2015). Colored stars with number marked the occurrence of high (ltra-high) pressure/low temperature metamorphic rocks (see Gao et al. (2017) and references therein): 1. Akesayi, ~320 Ma; 2. Atbashi, ~320 Ma; 3. Chatkal, ~301 Ma; 4. FanpKarategin, ?; 5. Beishan, ~465 Ma; 6. Chara Zone, ~445 Ma; 7. SW Mongolia, ~540 Ma; 8. Gony Altai, ~630 Ma; 9. Aktyuz, ~460-470 Ma; 10. Chu-Yili, ~490 Ma; 11. Makbal, ~475-500 Ma; 12. Barleik, ~492-504 Ma; 13. Central inner Mongolia, <235 Ma; 14. Toudaoqiao, ~490-510 Ma; 15. Yilan, ~180~210 Ma; 16. Kokchetav, ~524-537 Ma.

Figure 9 :

 9 Figure 9: Simple sketch showing the relationship between main contacts and tectonic units in the South Tianshan Orogen and adjacent region. CTB = Central Tianshan Block, KNTB = Kyrgyzstan North Tianshan Block, NTSZ = North Tianshan Suture Zone, TNNSZ = Terskey-North Nalati Suture Zone, SCTSZ = South Central Tianshan Suture Zone, DNSZ = Djalair-Naiman Suture Zone, NTF = North Tarim Fault, TTF = Talas-Fergana Fault.

Figure 10 :

 10 Figure 10: Geological map of the Southwestern Tianshan HP/UHP metamorphic belt (STMB). The structural data was plotted according to the measurement from this study, Bayet et al. (2018), Gao et al. (1998), Lin et al. (2008) and Soldner et al. (2017). The location of coesite reports follows the compilation of Tan et al. (2017) and Bayet et al. (2018).

Figure 11 :

 11 Figure 11: Brief geological map of the AMC, with emphasizing the finding of key lithologies and coesite. The location of coesite reports were marked as red stars after the compilation of Tan et al. (2017) and Bayet et al. (2018). The location of lawsonite reports were presented as light blue according to Du et al. (2011), Du et al. (2014) and Li et al. (2013). (a) mafic block wrapped by metavolcanoclastics matrix. (b) massive eclogite block in metavolcanoclastics matrix. (c) eclogitic facies pillow-shape metabasalt block (not in place). (e) The first coesite inclusion found in the metavolcanoclastics[START_REF] Lü | Coesite inclusions in garnet from eclogitic rocks in western Tianshan, northwest China: convincing proof of UHP metamorphism[END_REF].

Figure 12 :

 12 Figure 12: The collection of the protolith feature of samples from previous works. The legend follows those of Figure 11. Colors in the protolith boxes correspond to the lithology: Green, eclogite; Blue, blueschist; Grey, metavolcanoclastics. Abbreviation: N/E-MORB: Normal-/Enriched-middle ocean ridge basalt; OIB: Oceanic island basalt; UCC: Upper continental crust.

Figure 13 :

 13 Figure 13: The compilation of previous P-T estimates for diverse lithologies in the STMB. (a) The plot of Pmax-T conditions of regional diverse lithologies. (b,c) Corresponding localities of previous P-T estimates. Relevant numbers correspond to those in Table1. Legends in b&c follow those in Figures10 and 11d.

Figure 14 :

 14 Figure14: The compilation of regional age reports.Letters on the lower-left corner of the age boxes refer to lithology: "M" for mafic (typical eclogite), "m" for matrix (mainly meta-volcanic sediment with abundant amphibole) and "m" for micaschist (mainly felsic). Numbers on the upper-right corner of the boxes correspond to publications listed in Table. S2. #1: blueschist (used to be eclogite), Grt-Gln-WR Lu-Hf & Grt-Gln-WR Sm-Nd isochron ages, Soldner et al. (2016); #2: granitoids, zircon SHRIMP age, (Pu et al., 2011); #3: calc-Alkaline granite and granodiorite, Zircon LA-ICP-MS and SHRIMP age, Gao et al. (2009); #4: eclogite, rutile SIMS U-Pb age, Li et al. (2011); #5: eclogite, Grt-Omp-WR Sm-Nd isochron age, (Du et al., 2014); #6: Metapelite, Phengite Ar-Ar plateau ages, Lv and Zhang (2016); #7: eclogite, Grt-Omp-WR Lu-Hf isochron age, Klemd et al. (2011); #8: eclogite, zircon SHRIMP U-Pb age, Zhang et al. (2007); #9: blueschist, crosstie & phengite Ar-Ar plateau age, Gao and Klemd (2003); #10: eclogite, zircon SHRIMP U-Pb age, Zhang et al. (2007); #11: eclogite & micaschist, whitemica Ar-Ar plateau& Rb-Sr isochron age, Klemd et al. (2005); #12: eclogite, zircon SHRIMP U-Pb age, Zhang et al. (2007); #13: eclogite, glaucophane & white-mica Ar-Ar plateau age, Gao et al. (2000); #14: blueschist, whitemica Ar-Ar plateau age, Gao et al. (2000); #15: blueschist, glaucophane Ar-Ar plateau age, Gao et al. (2000); #16: Blueschist, white-mica & glaucophane Ar-Ar plateau age, (Gao et al., 2006); #17: eclogite, Grt-Gln Sm-Nd isochron age, Gao and Klemd (2003); #18: eclogite, zircon SHRIMP U-Pb age, Zhang et al. (2007); #19: micaschist, zircon SHRIMP U-Pb age, Yang et al. (2013); #20:eclogite, zircon SHRIMP U-Pb age, Su et al. (2010); #21: eclogite (Terrigenous detrital material), zircon SIMS U-Pb age, Liu et al. (2014a);

  Notes: Exhaustive collection of regional Pmax-T estimates and their relevant data was done above, mainly focusing on the collection of locality, lithology, protolith, P-T estimate method and result, whether did age dating or not, and relevant detail of thermodynamic modeling presetting if present. "n.m." in Coordinates column means not mention; "n.c." in Protolith and Age column means not conducted; "Px-, Tc-, DtPs" in Pmax-T column represent pseudosection calculation, respectively, by Perple_x, Thermocalc and Domino. PG, CTB, avPT respectively represent petrological grid, conventional thermobarometer (e.g., grt-cpx thermometer) and Thermocalc average PT multi equilibrium calculation; "n.c. and not int." in solid solution mode column respectively means not considered and not international (i.e., can not be found in solid solution mode databases of both Perple_x and Thermocalc); * marked solid solution modes only existed in Thermocalc database, and

  Three rounds of field trip were undertaken in 2013, 2014 and 2015 to i) identify deformation features at outcrop-/handsample-/microscope-scales, ii) ensure a systematic mapping of structures and lithologies, and iii) sample representative rocks for further analyses. The study area mainly follows a ~30km-long N-S transect along the Kebuerte valley (Figure 15) crosscuting from the North (South Central Tianshan Suture Zone, SCTSZ) to the South contacts (North Haerkeshan Peak Fault, NHF) of the AMC. Extending the study area to further West/East was unfortunately difficult, due to the presence of large glaciers and the difficulty to cross the Kebuerte river. About 200 samples from ~120 samping localities have been investigated at the microscopic scale to facilitate further selection for subsequent analyses. Amongst those, i) several representative samples were chosen for petrologcial, mineralogical and

Figure 15 :

 15 Figure 15: Sampling location of this thesis in the AMC. Detail of coordinates, lithology, mineral assemblage, analysis strategy of each sample is listed in TableS1.

  5-3.0 nA in intensity. The 16 O and18 O ions are detected simultaneously by two Faraday cups, and the currents are amplified by 1010 ohms and 1011 ohms resistors, respectively. Each spot analysis consists of pre-sputtering, beam centering in apertures, and a signal collecting process.A single spot analysis lasts 3 mins, including 2 mins for pre-sputtering and centering the secondary beam, and 1 min to collect 16 cycles of 16 O and 18 O signals. Oxygen isotopes were measured using the multi-collection mode. The instrumental mass fractionation (IMF) was corrected using an in-house zircon standard Penglai with δ 18 OVSMOW = 5.31 ± 0.10‰ (Q.-L.Li et al., 2010). The measured 18 O/ 16 O ratios were normalized to the VSMOW composition, then corrected for IMF as described in(Li et al., 2010b): IMF =δ 18 OM δ 18 OStandard, and δ 18 OSample = δ 18 OM + IMF, where δ 18 OM = [( 18 O/ 16 O)M/0.0020052-1] ×1000 (‰) and δ 18 O Standard is the recommended δ 18 O value for the zircon standard on the VSMOW scale. Corrected δ 18 O values are reported in the standard per mil notation with 2σ errors. Analytical conditions, instrumentation and operation conditions are similar to Li et al. (2010) and Tang et al. (2015).

1 .

 1 The Chinese Southwestern Tianshan HP-UHP/LT metamprphic complex

Figure 16 :

 16 Figure 16: Simplified geological map of (a) the Chinese Western Tianshan and (b) close-up map for the area (modified after Gao et al. (1999) with tagged locality distribution of previous radio-chronological data. Red stars mark the location of UHP reports (the finding of coesite). Green overlays indicate the inferred distribution of eclogites based on literature data. The dashed blue box marks the sample location (Fig. 3) of this study. Letters on the lower-left

Figure 17 :

 17 Figure 17: Compilation of age data (a) as a function of estimated Pmax and (b) shown as a histogram (detail see

Figure 18 :

 18 Figure 18: (a) Schematic outline of the studied outcrop; (b) field view of the sampling and (c) location of the samples in the layered eclogite.

Figure 19 :

 19 Figure 19: Whole-rock discrimination diagrams for the samples: (a) chondrite-normalized REE patterns, (b) primitive mantle-normalized spider diagram and (c) Th/Yb versus Nb/Yb diagram[START_REF] Pearce | Geochemical fingerprinting of oceanic basalts with applications to ophiolite classification and the search for Archean oceanic crust[END_REF]. Reference curves for average N-MORB and OIB from[START_REF] Sun | Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes[END_REF], and fromRudnick and Gao (2003) for upper continental crust.

Figure 20 :

 20 Figure 20: Mineral assemblages and microstructures of the studied eclogites. (a,b) Typical eclogitic facies mineral assemblages in sample 11AT06: subhedral-anhedral omphacite matrix grains (partially replaced by euhedralsubeuhedral amphibole porphyroblasts and subeuhedral paragonite grains), idioblastic garnet porphyroblasts and minor rutile grains in the omphacite matrix (cross-polar view). (c,d) Idioblastic garnet porphyroblasts partially replaced by subhedral epidote group minerals. (e) typical texture of studied garnet porphyroblast (same as in Figure 22a, d), with abundant mineral inclusions (showed both in cross polar and plane polar view) within the core-mantle domain and slightly replaced by chlorite. (f) Moderately foliated omphacite matrix in the oriented sample of the studied layered eclogite (cross polars). (g) Occurrence of rutile inclusions in paragonite porphyroblast. Note the amphibole with a glaucophane core (pale blue) and a more barroisitic greenish rim. (h) Glaucophane inclusions in the core of a garnet porphyroblast. (i) Omphacite inclusions in a paragonite porphyroblast. Mineral abbreviations: grt, garnet; omp, omphacite; brs, barroisite; gln, glaucophane; ph, phengite; pg, paragonite; ep, epidote; zo, zoisite; qz, quartz; rt, rutile; pyr, pyrite; chl, chlorite.

Figure 21 :

 21 Figure 21: Thin-section scale shear senses in eclogite and greenschist facies for the UHP eclogite and its metavolcano-sedimentary host-rock, respectively. (a, b) Foliated omphacite matrix and σ-type garnet porphyroclasts with epidote, omphacite and phengite recrystallized tails. (c) Foliated albite and amphibole matrix, and σ-type fractured porphyroclasts of garnet with quartz, albite, paragonite and amphibole recrystallized tails. Gray solidcircles show the location of EMPA analyses for Thermocalc averagePT calculations (see Table10). Mineral

  abbreviations as for Figure20.

Figure 22 :

 22 Figure 22: Garnet porphyroblast and mineral inclusions: (a) BSE imaging and location of mineral inclusions in the garnet core-mantle domain (dashed blue boxes shown in Fig. S2); (b) Raman spectrum of the analysed coesite inclusion; (c) Close-up view of the coesite inclusion in the garnet mantle domain; (d) Sketch of mineral inclusion distribution and location of analyses. Black dashed circles: laser-ICP-MS spots (see Fig. 9b); thick dashed line: EMPA profile (see Figure 22e; Table 5); red dashed rectangles: region with coexisting mineral inclusions chosen for thermocalc averagePT calculations; (e) Composition profile across the center of the studied garnet porphyroblast (Figure 22a, d); (f) composition of sodic clinopyroxene(Morimoto, 1988)

4. 5 . 4 .

 54 White micaParagonite and minor phengite appear as matrix mineral and as inclusions in garnet. Paragonite flakes occur as subhedral fine grains (~0.05 mm across) or occasionally as porphyroblasts in the matrix (~0.5 to 2 mm across, Figure20f-g, i).They are parallel or subparallel to the foliation (Figure20f-g), contain omphacite and rutile inclusions (Figure20g, i), and are interpreted to result from post-peak retrograde metamorphism. Phengite mainly occurs as subhedral fine grains in the matrix (~0.02 mm across) or as inclusions in garnet porphyroblasts (Figure34). Both of them exhibit a similar Si content (~3.43 p.f.u.).

Figure 23 :

 23 Figure 23: Cathodoluminescence imaging and sketches of analyzed zircon grains, showing multistage growth features. The location of U-Pb, REEs, δ 18 O analyses is shown by red solid-ellipse (10 × 15 um 2 beam-size via SIMS), orange dash-circle (with 40 × 40 um 2 beam-size via Laser-ICP-MS) and blue solid-circle (with 20 × 20 um 2 beamsize via SIMS) respectively (see Table7). Other zircon grains are shown in Figure35.

  Some of the zircon cores show HREE contents 2-3 times higher ((Lu/Sm)N ~ 51.72; (Lu/Tb)N ~ 2.71; Y ~ 230 ppm; Figure 24a, 35i-l; Table

Figure 24 :

 24 Figure 24: Chondrite-normalized (Sun and McDonough, 1989) REE abundances of the various zircon (a) and garnet domains (b) (Table6). Overlays outline the compositional range of the various generations observed (taking into account the 1-σ uncertainty). For a better comparison of REEs patterns, average patterns of core, core with high HREEs, mantle and rim domains of zircon are labelled 1, 2, 3, 4. Circled numbers 1, 2, 3 in Figure24bcorrespond to REE patterns of the core, mantle and rim of garnet (e.g. marked as grt-c, R, 02), identified as potentially coexisting with metamorphic zircon domain (rim), in the eclogite-facies micaschist of[START_REF] Rubatto | Zircon trace element geochemistry: partitioning with garnet and the link between U-Pb ages and metamorphism[END_REF].

4. 8 .

 8 Pressure-Temperature estimates 4.8.1. Multi-equilibrium thermobarometry P-T estimates for prograde equilibrium stages (using mineral inclusion pairs within garnet porphyroblast cores of sample 11AT06-1; Figure22d), peak eclogiticfacies and retrograde blueschist-to greenschist-facies recrystallizations (e.g., recrystallized tails of σ-type porphyroclasts in oriented samples 11AT06-2, GJ01-6 and GJ01-1; Figure21a, b, c), are constrained using THERMOCALC average PT multi-

Table 9 :

 9 NOTES: WR means the whole rock, the absolute errors of 143 Nd/ 144 Nd and isochron ages are given in 2σ; λ = 6.54 ×10-12 year-1; 147 Sm/ 144 NdCHUR = 0.1967, 147 Sm/ 144 NdDM = 0.2137, 143 Nd/ 144 NdCHUR(0) = 0.512638, 143 Nd/ 144 NdDM(0) = 0.513151 are used for the calculation.

Figure 26 :

 26 Figure 26: WR-garnet-omphacite Sm-Nd isochron

  and water activity was set to 1.0. Lowering the water activity (e.g. aH2O = 0.8) only results in a minor decrease in temperature (≤ 15 ℃) and pressure (≤ 0.05 GPa). P-T estimates obtained for the garnet rim, omphacite-amphibole-epidote± phengite assemblage marking the foliation of both sheared eclogitic samples (Figure21a-b; GJ01-6 and 11AT06-2) are 525 ± 25 ℃ & 2.0 ± 0.15 GPa. P-T conditions for the retrograde, blueschist-to (or) greenschist-facies equilibration stages associated with top-to-NNE shear senses (Fig.6c, GJ01-1) were estimated from the mineral assemblage amphibole + paragonite + epidote + chlorite + feldspar (albite) at 380 ± 50 ℃ and 1.0 ± 0.2 GPa, and 420 ± 25 ℃ & 0.9 ± 0.1 GPa.

Figure 27 :

 27 Figure 27: P-T estimates for the studied UHP eclogites, inferred from Perple_X pseudosection modeling and Thermocalc averagePT calculation: (a) compilation of Thermocalc averagePT results (Table 10); the pink arrow features the estimated trajectory, taking into account the uncertainties from avPT calculations. (b) P-T pseudosection in the system NMnCKFMASHTO for the studied UHP eclogite (effective bulk composition in Table

  5 %-calculated uncertainties. White arrow: estimated P-T trajectory from pseudosection modelling; dashed box: estimation of retrograde P-T conditions from the (Na)M4 content of matrix amphibole. Mineral abbreviations as in Figure 20.P, from 2.55~2.70 GPa and 495~505℃ to 2.95~3.30 GPa and 500~520℃. Peak pressure (Pmax) is constrained by using the garnet mantle compositions (corresponding to Grt-M2 to Grt-M4) which have the lowest Xgrs content, and coincide with the location of coesite inclusions (Figure22a-d).

1 .

 1 Nature of the protolith and P-T-(fluid) constraints

  The δ 18 O values of the various zircon domains are remarkably constant despite considerable multistage growth from ca. ~ 318 to 280 Ma. This suggests that the rock system remained essentially closed over ~ca. 40 Ma, during metamorphic reequilibration, with respective to potential external fluid infiltration, at both the cm-and m-scale (zircon grains were collected from rock fragments from different parts of the outcrop), and/or that fluids were derived from (or equilibrated with) a similar source.

Figure 28

 28 Figure 28: P-T trajectory estimates from this study (a) and previous works (b). See text for details. Brown boxes mark: estimates of peak metamorphism for UHP mica schist (Wei et al. (2009) Yang et al. (2013). Light-green box:peak metamorphic UHP conditions for metabasite from[START_REF] Tian | Metamorphism of ultrahigh-pressure eclogites from the Kebuerte Valley, South Tianshan, NW China: phase equilibria and P-T path[END_REF]. Ages shown in Figure28aare discussed in §4.9.3.

Figure 29 :

 29 Figure 29: (a-b) Patterns of trace element distribution coefficients between various possibly coexisting zircon and garnet domains. (c) sketch summarizing the various growth zones observed in zircon and garnet.

Figure 30 :

 30 Figure 30: Sketch depicting the petrologic evolution of mineral growth within metabasalts and inferred mobility of elements (mainly REEs) within the garnet-zircon-matrix metamorphic system during subduction and exhumation.

Figure 31 :

 31 Figure 31: Previous radiometric data (see Table2) and results from this study place constraints on the main tectonic

Figure 32 :

 32 Figure 32: Simplified geodynamic cartoon setting back the studied samples and the overall time constraints inferred from this study within the evolution of the Chinese Southwestern Tianshan HP-UHP/LT metamorphic belt.

  respectively.Mineral trace elementsIn situ trace element analyses of zoned garnet and zircon were performed by LA-ICP-MS at the IGGCAS with a single collector quadrupole Agilent 7500a ICM-MS, equipped with an UP193Fx argon fluoride New Wave Research Excimer laser ablation system. The glass reference material NIST SRM 610 and NIST SRM 612 were used as standards for external calibration. LA-ICP-MS measurements were conducted using a spot size diameter of 40 to 60 μm, a laser frequency of 15 Hz and 0.63 GW/cm2 and a fluence of 3.32 J/cm2. Acquisition time was 20 s for the background and 120 s for the mineral analyses. The Ca-content of garnet determined by EMP analyses and the Sicontent of zircon constrained by standard zircon 91500 were used as internal standards.

  eclogite were sampled from outcrop (detailed sampling locations are shown in Figure18a, c.11AT06-1, ca. 40 kg, sampled in 2011; 11AT06-2, ca. 60 kg, sampled in 2013), and approximately 500 zircon grains were collected and mounted in three different epoxy mounts. Fifty point analyses on different zircon domains from grains selected via CL images were chosen for investigating the U-Pb isotopic chronology and Oxygen isotopic composition of the potential multistage growth of zircon.Zircon grains of sample 11AT06 were prepared by conventional crushing techniques and were hand-picked, mounted onto epoxy resin disks and polished with 0.25 μm diamond paste. The zircon grains and zircon standards (Plesovice, Peng Lai and Qing Hu zircon were used here as standards) were mounted in epoxy mounts and then polished to section the crystals in half. Assessment of zircon grains and the choice of analytical sites were based on the transmitted and reflected light microscopy and cathodoluminescence (CL) images. CL imaging was processed on the LEO145VP scabbubg electron microscope with a Mini detector at the Institute of Geology and Geophysics, Chinese Academy of Sciences in Beijing (IGGCAS). The mount was vacuum-coated with high-purity gold prior to secondary ion mass spectrometry (SIMS)

  processed with the use of the Cameca IMS-1280 SIMS at IGGCAS. After U-Pb dating, the mount was carefully repolished for the O isotope analyses. The Gaussian focused Cs+ ions are used as a primary beam to sputter zircon for O-isotope analyses. The primary beam size is ~10 um in diameter, and 2.5-3 nA in intensity. The 16 O and 18 O ions are detected simultaneously by two Faraday cups, and the currents are amplified by 10 10 ohms and 10 11 ohms resistors, respectively. Each spot analysis consists of presputtering, beam centering in apertures, and a signal collecting process. A single spot analysis lasts 3 mins, including 2 mins for pre-sputtering and centering the secondary beam, and 1 min to collect 16 cycles of 16 O and 18 O signals. Oxygen isotopes were measured using the multi-collection mode. The instrumental mass fractionation (IMF) was corrected using an in-house zircon standard Penglai with δ 18 OVSMOW = 5.31 ± 0.10‰(Li et al., 2010d). The measured 18 O/ 16 O ratios were normalized to the VSMOW composition, then corrected for IMF as described in(Li et al., 2010b): IMF =δ 18 OM δ 18 OStandard, and δ 18 OSample = δ18OM + IMF, where δ 18 OM = [( 18 O/ 16 O)M/0.0020052-1] ×1000 (‰) and δ 18 OStandard is the recommended δ 18 O value for the zircon standard on the VSMOW scale. Corrected δ 18 O values are reported in the standard per mil notation with 2σ errors. Analytical conditions, instrumentation and operation conditions are similar toLi et al. (2010d);Tang et al. (2015), and the results of oxygen isotope for zircon in sample 11AT06 are listed in Table

Figure 36 :

 36 Figure 36: Continued from Figure 23: (a-i): cathodoluminescence images of other studied zircon grains; (mn): typical HP (or UHP) metamorphic minerals (omphacite and rutile) revealed from Raman analyses.

Figure 35 :

 35 Figure 35: Rb vs K, Nb/U vs U, K/Th vs Ba/Th and Ba/Nb vs U/Nb diagrams[START_REF] Bebout | Metamorphic chemical geodynamics of subduction zones[END_REF][START_REF] Bebout | Metasomatism in Subduction Zones of Subducted Oceanic Slabs, Mantle Wedges, and the Slab-Mantle Interface[END_REF] for

  .2 5.72 -10.38 0.16 -0.00175 0.516 -0.359 0.458 3) 21.9 5.09 -76.11 4.11 -0.02594 7.780 -11.552 6.129 4) 24.3 5.82 185.58 0.87 -0.15400 -1.701 -3.925 1.534 5) 27.5 8.48 186.52 2.14 -0.22413 0.998 -6.223 1.274 T = 493℃, sd = 22, P = 27.5 kbars, sd = 0.4, cor = 0.233, sigfit = 1

Figure 37 :

 37 Figure 37: Geological background of the SW-Tianshan LT-HP/UHP metamorphic complex. (a) Location of the research area with respect to other key UHP reports in China; (b) Close-up view showing the regional geological setting and sampling location: previous UHP reports based on coesite inclusions in garnet are highlighted by red stars (modified after Tan et al., 2017). SCTSZ: South Central Tianshan Suture Zone; (c) Comparison of the P-T conditions experienced by SW-Tianshan metavolcanics with those of exhumed oceanic rocks worldwide (modified after[START_REF] Agard | Exhumation of oceanic blueschists and eclogites in subduction zones: timing and mechanisms[END_REF][START_REF] Plunder | Accretion, underplating and exhumation along a subduction interface: From subduction initiation to continental subduction (Tavşanlı zone, W. Turkey)[END_REF] highlighting the provenance of these rocks from a deep, cold subduction zone (i.e., ~100 km, ~5 ˚C/km); (d) Location of samples on the outcrop.

Figure 38 :

 38 Figure 38: Key features of the specific garnet zoning investigated here, examplified by garnet A1: (a) Manganese mapping reveals a euhedral annular Mn-rich zone in the mantle of garnet A1, which hosts coesite in its outer rim (Tan et al., 2017); (b) Yttrium laser-ICP-MS points and profile (superimposed on Y mapping, fogged by microprobe detect limitation); (c) Superimposed microprobe and laser-ICP-MS profiles of garnet A1 reveal concordant concentration pulses in Mn, Y and HREEs; (d) Spatial variations of Zr content in rutile grains located within different garnet domains (i.e., inclusions in the core, annular pulse, rim or in the matrix). Skeleton map exported from matrix data of Mn, Y, Ti and P mapping via XMapTools (Lanari et al., 2014); (e) Results of Zr-in-rutile thermometry (Table13) using four different calibrations, pointing to a ~80 ˚C thermal pulse.

5. 4 . 1 .

 41 Garnet compositional profile and mappingMicroprobe major element composition profiles and mapping were conducted for eight garnet porphyroblasts representative of the size distribution in the studied eclogites. Additional high-resolution mapping for key elements (Mn, Y, Ti and P; Figure38a-b, 46) and LA-ICP-MS trace element profiles were performed on one coesite-bearing garnet grain (i.e., A1, Figure38).

4. 1 . 1 .

 11 Concordant, annular zoning in Mn, Y and HREEsGarnet growth zoning reveals a concordant pulse in Mn, Y and HREEs concentrations, as shown for garnet porphyroblast A1 in Figure38, 46, 48. This similarity between Mn, Y and HREEs compositional profiles (Figure38c, 39) is not observed, however, for the rest of major and trace elements (Figure39a, e-h).

4. 1 . 2 .

 12 Concordant Mn pulse among diverse size garnets Eight representative garnet grains from samples A-B-C were selected for detailed compositional investigations (garnets A1-2-3, B1-2-3-4, C1, ranging from 0.35 to 1.58 mm in radius), based on an extensive garnet size survey (Figure 48). Mn profiles vary with respect to garnet radius (Figure 40a-b): (i) large garnet grains (A1 ~1.22mm; A2 ~1.11mm; B1: ~1.58mm; B2: ~0.90mm; C1: ~1.12mm) show marked central peaks and symmetrical secondary peaks; (ii) middle-size garnet grains of (A3: ~0.42mm; B3: ~0.51mm) show depleted cores with moderate secondary peaks yet Mn concentrations comparable to the large ones (cMn ~0.66 to 0.72 wt%); (iii) the small garnet B4 (R ~0.35mm) shows a central peak with Mn concentration comparable to secondary peaks of larger garnets (cMn ~0.75 wt%). Corepeak-secondarypeak distances are remarkably similar among large garnets at ~0.77 ± 0.04 mm (n=7, 1𝜎). Mn secondary peaks coincide with a euhedral garnet growth zone (Figure 38a, 47).

Figure 40 :

 40 Figure 40: (a-b) Mn concentration profiles for diverse sized garnets. Large garnet grains display a variably high Mn core peak and an annular secondary peak (except B2), with similar corepeak-annularpeak distance (Rp ~0.77 ± 0.04 mm; n=7, 1𝜎). Middle size garnet grains (A3, B3) display an annular peak with depleted core, and small garnet grains (e.g., B4) only a core peak. These patterns are more readily observed in element maps (Figure 47); (c) Map of inclusions hosted in garnet A1; (d-e) MnO concentrations and REEs patterns of key mineral inclusions in garnet A1, showing that chlorite and lawsonite represent potential budgets of Mn and HREEs; (f) Evolution of mineral modes predicted by Perple_X thermodynamic modeling on stepwise fractionated effective bulk rock compositions (EBCs, Figure 49, Table11) along different activity and/or temperature paths. Modelling shows that garnet growth coincides with a certain amount of chlorite and/or lawsonite breakdown. Major and trace elements composition of lawsonite were cited from literature[START_REF] Spandler | Redistribution of trace elements during prograde metamorphism from lawsonite blueschist to eclogite facies; implications for deep subduction-zone processes[END_REF] Vitale Brovarone et al., 2014).

Figure 41 :

 41 Figure 41: Influence of key parameters on diffusion-controlled garnet growth. (a) Sketch depicting the spherical geometry, finite system size and diffusion in both the crystal and matrix considered by Hesse (2012), after which modelling is performed (see App. B for details). (b) Linear (black) or pulse-like (color) T-time paths with variable Tfinal. (c-f) Tests exploring the range of plausible pre-exponential D0m values needed to match the Mn garnet concentration profile. (g-j) Influence of key parameters on the possibility to produce secondary concentration pulse (Y is here taken as example), along a linear T-time path (black line in Figure 42b). (k-l) Modelled Mn concentration profiles for different T-time paths and durations for fixed D0m (~1012 cm2/yrs). The best-fit is obtained for a transient thermal excursion of ~0.3 Myrs (out of 5 Myrs; red-line). Parameters and details are given in Table14.

Figure 42 :

 42 Figure 42: Modelling of the concordant MnYHREE garnet zoning for diverse size garnets and in garnet A1 (Runs 30, 34-36 for a-b; Runs 37-43 for c-I; Table14). See text for details.

  -b. Noteworthily, the similar distance to the annular Mn pulse in the different large garnets (i.e., ~0.77 mm; Figure 40a, 42a') and timing (i.e., ≈ 4.65 Myrs, based on garnet A1 radius and a 5 Myrs growth duration) logically implies slight different growth durations of diverse size garnets (Figure 42a'; Table

5. 7 . 1 .

 71 Interpretation of petrological patternsGarnet with secondary peak zoning in Mn and/or HREEs (± Y) was previously reported in a few studies: 1) partial correlation (with asymmetric peaks) of Mn, Ca, Sc, Zr, Y and M/HREEs attributed to Mn-rich epidote breakdown and/or resorption of garnet (W-Labrador metapelite;[START_REF] Yang | The origin of Mn and Y annuli in garnet and the thermal dependence of P in garnet and Y in apatite in calc-pelite and pelite, Gagnon terrane, western Labrador[END_REF]; 2) correlated Y, HREEs and Hf peaks in Cignana UHP eclogite attributed to clinozoisite + titanite breakdown[START_REF] King | Ultrahigh-pressure metabasaltic garnets as probes into deep subduction zone chemical cycling[END_REF]; 3) positive or negative Ca, Fe and Mg anomalies coincident with (disordered) secondary peaks of MREEs, attributed to element sequestration into garnet cores combined with changes in major garnet-forming reactions (UHP eclogites, WGR Norway;Konrad-Schmolke et al., 2008); 4) oscillatory zoning of Mn decoupled from Fe due to slight fluctuations in decompression rate and P-T path[START_REF] Schumacher | Subtle oscillatory zoning in garnet from regional metamorphic phyllites and mica schists, western Erzgebirge, Germany[END_REF]; 5) Mn, Y and REEs multi-secondary peaks possibly linked to externally derived fluids (Franciscan blueschist;[START_REF] Moore | Origins of yttrium and rare earth element distributions in metamorphic garnet[END_REF].[START_REF] Skora | Diffusion-limited REE uptake by eclogite garnets and its consequences for Lu-Hf and Sm-Nd geochronology[END_REF] interpreted their discordant MREE/HREEs mantle maxima garnet zoning in Zermatt-Sass Fee eclogites D 0 m as reflecting the interplay between growth and intergranular diffusion rates, hence departing from Rayleigh fractionation.Yet, none of the specific Mn, HREEs and Y garnet patterns shown here, namely (i) concordant annular zoning in Mn, HREEs & Y (e.g., garnet A1; Figure38, 39) and (ii) similar Mn zoning amongst diverse sized garnets (Figure40, 47), was reported so far. Whether this zoning results from a change in source (fluid-mediated or not) and/or in P-T conditions (i.e., a change in diffusion or incorporation properties) needs to be assessed.

Figure 43 :

 43 Figure 43: Simplified sketches depicting the impact of diffusion-controlled garnet growth (here during a transient thermal pulse). Left column: growth of diverse size garnets at thin-section scale. The concordant MnYHREE pulse is highlighted as the red-zone. Grey overlays indicate the respective sizes of diffusion halos. Right column: evolution of concentrations as a function of time (or garnet radius).

  We herein show that this zoning can nevertheless develop if a specific T-time pulse modifies the rate of intergranular diffusion. T-time paths with a transient ∆T of ~80°C (Run 16 to 27, Table14) indeed allow to satisfactorily model Mn profiles (color lines in Figure41c-f) at moderate (8.0×10 11 cm 2 /yrs). Tests were performed for different values of grain size ( ), growth ( ) and T pulse durations ( ) with constant concentration pulse position ( =0.77mm), range of temperatures ( ) and preexponential diffusion factors ( ) for intergranular diffusivity. Tests evaluating the interplay of and (Figure 41k-l) argue for the necessity of a transient T pulse with duration ~300 Kyrs (~1/20 of set as 5 Myrs) to best-fit the observed Mn profile of garnet A1 (Run 30, Table

Figure 44 :

 44 Figure 44: Tentative interpretation of the thermal excursion recorded by the UHP volcanoclastics in terms of rock dynamics along a deep cold subduction plate interface.

scale: 7 .

 7 55 ± 0.52 Myrs for a single 2.7 cm radius garnet grain by Sm-Nd dating (Austrian Alps;[START_REF] Pollington | High resolution Sm-Nd garnet geochronology reveals the uneven pace of tectonometamorphic processes[END_REF] and ca. 7 Myrs for a millimeter-scale garnet in HP rocks by combined Sm-Nd and Lu-Hf geochronology (Dabie orogen,[START_REF] Cheng | Coupled Lu-Hf and Sm-Nd geochronology constrains garnet growth in ultra-high-pressure eclogites from the Dabie orogen[END_REF] SW-Tianshan, Soldner et al., 2016), although a geologically surprising 30-40 Myrs duration for UHP eclogitic garnet growth (Lago di Cignana, W-Alps) was inferred by[START_REF] Skora | The duration of prograde garnet crystallization in the UHP eclogites at Lago di Cignana, Italy[END_REF]. A transient 1-5 cm/yr movement of UHP eclogitic slices exceeds the average exhumation rate of (U)HP oceanic rocks worldwide (~1-5mm/yr,[START_REF] Agard | Exhumation of oceanic blueschists and eclogites in subduction zones: timing and mechanisms[END_REF] but resembles that of (U)HP continental rocks (≥cm/yr,

  Detailed petrological investigations on major and trace elements geochemistry of garnet highlight a concordant annular Mn, Y and HREEs zoning, visible at the outcropand probably km-scale, in a representative UHP oceanic eclogitic slice in SW-Tianshan. This pattern coincides with a transient ~80 °C increase in temperature revealed by Zr-in-rutile thermometry. Mineral compositions together with thermodynamic modeling indicate that mineral breakdown cannot account alone for this unusual garnet zonation. Diffusion-controlled garnet growth modeling supports the necessity of a ~300 kyr transient thermal excursion to reproduce the observed garnet zonation (assuming a 5 Myr duration for the overall garnet growth). Such a transient thermal excursion is tentatively tied to the fast movement of detached UHP oceanic slices towards the hotter mantle wedge. This study also highlights the necessity of considering diffusion-controlled garnet growth whenever assigning major element zoning to specific P-T conditions.Labrousse, Y. Chen, J-J. Yang, J-L. Li, M. Locatelli and G. Bonnet. We further thank Y. Chen for the support of microprobe mapping in IGGCAS and M. Fialin & N. Rividi for the help of rutile trace elements microprobe analyses in ISTeP.

Figure

  Figure 40a-b, 48) are used to infer approximate volume proportions for EBC

  of element , respectively, in effective bulk rock composition and corresponding position from garnet profiles with respect to the representative Mn, Y and HREEs annular zoning of garnet A1

( 4 )

 4 At the moving internal boundary during modeling, the diffusive flux across the porphyroblast interface is continuous while the concentration profile is discontinuous because of the partitioning of trace elements, controlled by the effective partition coefficient (also see App. A. for the definition and estimates of ). The conditions at the interface are therefore descripted as: power-laws functions with preset exponential factors by[START_REF] Hesse | A finite volume method for trace element diffusion and partitioning during crystal growth[END_REF], these were modified here to test the impact of a thermal pulse on MnYHREE garnet zoning. is therefore computed as:

  , 39) analyses of zoned garnet and associated matrix mineral were performed by LA-ICP-MS at IGGCAS with a single collector quadrupole Agilent 7500a ICM-MS, equipped with an UP193Fx argon fluoride New Wave Research Excimer laser ablation system. Glass reference material NIST SRM 610 and NIST SRM 612 were used as standards for external calibration.

Figure 46 :

 46 Figure 46: EMPA-BSE, transmitted light and cross-polarized light images of investigated garnet grains (A1-3, B1-4, C1), sampled from different parts of the outcrop (Figure 37d).

Figure 48 :

 48 Figure 48: Systematic garnet size survey. The three main groups and estimated mineral modes (vol %) for investigated UHP eclogite samples are shown. See main text for details.

Figure 47 :

 47 Figure 47: The Ca, Mg and Mn mapping as well as corresponding compositional profiles of the rest of investigated garnet grains (except garnet A1, shown in Figure 38).

Figure 49 :

 49 Figure 49: Polynomial fitting for estimating effective bulk rock compositions during garnet growth (and uptake of major elements, HREEs and Y). See Appendix A.

6 .

 6 Figure 50: (a) Tectonic sketch showing the middle to western segments of the Central Asian metallogenic domain, modified after Gao et al. (2017), Soldner et al. (2017) and Xiao et al. (2015). Colored stars with number marked the occurrence of high (ltra-high) pressure/low temperature metamorphic rocks (see Gao et al. (2017) and references therein): 1. Akesayi, ~320 Ma; 2. Atbashi, ~320 Ma; 3. Chatkal, ~301 Ma; 4. FanpKarategin, ?; 5. Beishan, ~465 Ma; 6. Chara Zone, ~445 Ma; 7. SW Mongolia, ~540 Ma; 8. Gony Altai, ~630 Ma; 9. Aktyuz, ~460-470 Ma; 10. Chu-Yili, ~490 Ma; 11. Makbal, ~475-500 Ma; 12. Barleik, ~492-504 Ma; 13. Central inner Mongolia, <235 Ma; 14. Toudaoqiao, ~490-510 Ma; 15. Yilan, ~180~210 Ma; 16. Kokchetav, ~524-537 Ma. (b) Simple sketch showing the relationship between main contacts and tectonic units in the South Tianshan Orogen and adjacent region. CTB = Central Tianshan Block, KNTB = Kyrgyzstan North Tianshan Block, NTSZ = North Tianshan Suture Zone, TNNSZ = Terskey-North Nalati Suture Zone, SCTSZ = South Central Tianshan Suture Zone, DNSZ = Djalair-Naiman Suture Zone, NTF = North Tarim Fault, TTF = Talas-Fergana Fault. (c) Geological map of the Southwestern Tianshan HP/UHP metamorphic belt (STMB). The structural data was plotted according to the measurement from this study, Bayet et al. (2018), Gao et al. (1998), Lin et al. (2008) and Soldner et al. (2017). The location of coesite reports follows the compilation of Tan et al. (2017) and Bayet et al. (2018).

Figure 51 :

 51 Figure 51: (a) Close-up views of the Akesayi metamorphic complex (AMC) showing sampling localities and reappraised tectonic sub-units & contacts. The location of coesite reports follows the compilation of Tan et al.(2017) and[START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF]. The location of lawsonite reports were cited from[START_REF] Li | Fluid-mediated metal transport in subduction zones and its link to arc-related giant ore deposits: Constraints from a sulfide-bearing HP vein in lawsonite eclogite (Tianshan, China)[END_REF],[START_REF] Du | Lawsonite-bearing chloritoidglaucophane schist from SW Tianshan, China: Phase equilibria and P-T path[END_REF]

Figure 52 :

 52 Figure 52: (a) Close-up view of the area along the Kebuerte valley showing sampling sites, measured shear senses and the location of field observations (Figure 53). (b) The summary of the pattern of regional schistosity and lineation. Detail data with respect to measurement location are presented in Figure 54. (c) Simple map with the plots of structural element showing the location of field observations corresponding to those in Figures 55, 64 and 65. (d) Approximately N-S ~30km-long section constructed, along the Kebuerte valley, across the previous socalled HP/UHP mélange (e.g.,[START_REF] Klemd | Changes in dip of subducted slabs at depth: Petrological and geochronological evidence from HP-UHP rocks (Tianshan, NW-China)[END_REF] Li et al., 2016) and further touch to the South margin of the STMB around the Northern Haerkeshan Fault (NHF), with detailed sample sites and analysis strategy. (e) The Akesayi section from recent work[START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF] was also cited for comparison.

Figure 53 :

 53 Figure 53: Panoramic views of the main sub-units and contacts in the AMC, with representative sample localities.

  facies blueschist horizon (EB) Meta-ultramafic/mafic unit (MU) Table 15: Notes: Abbreviation for Data column, P: petrological investigation (e.g., microprobe); R: RSCM thermometer; Dst, Din and Dzu respectatively mean age dating via phengite/biotite Ar-Ar step-heating, in situ phengite Ar-Ar probing and zircon U-Pb technology. Mineral abbreviations: Qz, quartz; Grt, garnet; Ph, phengite; Pg, paragonite; Bi, biotite; Cpx, clinopyroxene; Amp, amphibole; Ep/Czo, epidote/clinozoisite; Chl, chlorite; Ctd, chloritoid; Rt, rutile; Ttn, titanite; Fsp/Ab, feldspar/albite; Carb, carbonate; Srp, serpentine. The x means that the mineral is present. The x* marks the samples with special mineral composition compared with the others: Grt in sample 156-2 is grossular (Grs); Cpx in samples 135 and 158 is omphacite (Omp), but in samples 156-2 and 156-3 is diopside; Chl in samples 156-1 and 156-2 is Mg-rich chlorite (MgChl).

  55h, 63c, 65j) and phengite-biotite quartz schists (Figure52a, d, 53d). It is bounded to the south by a major EW-trending fault, the North Haerkeshan Peak Fault (NHF; Figure52a, d, 53d, 63b, d).

Figure 54 :

 54 Figure 54: (a) The structural sketch showing the extension on E-W of the revised AMC, with (b, c) the detail data of field structural measurements for the schistosity and lineation.

Figure 56 :

 56 Figure 56: Microphotographs of some of the samples investigated in the present study. Mineral abbreviations are Qz, quartz; Grt, garnet; Ph, phengite; Pg, paragonite; Bi, biotite; Di, diopside; Omp, Omphacite; Gln, Glaucophane; Brs, barroisite; Act, Actinolite; Ep/Czo, epidote/clinozoisite; Chl, chlorite; Ctd, chloritoid; Rt, rutile; Ttn, titanite; Fsp/Ab, feldspar/albite; Carb, carbonate; Srp, serpentine. (a, b, c) Grt-Ph-Amp-Qz-Rt±Cpx±Ep±Chl±Ttn±Ctd±Pg±Bi assemblages and relevant garnet inclusion patterns in metavolcanoclastics from the UH and EB units. (d) Serpentinized ultra-mafic rock (sample, 156-3) with relict diopside. (e) Grt-Act-Gln-Brs-Ep-Ttn±Cpx±Pg±Qz ±Chl±Ab±Carb assemblage and relevant garnet inclusion pattern in metamafic sample 158 from the MU unit. (f, g) The pattern of the appearance of amphiboles, with euhedral actinolite columnar crystals rounded by anhedral glaucophane matrix then both partly replaced by barroisite rim, in sample 158 is distinct compared with those in samples from the UH and EB units (normally gln replaced by brs rim), further indicating contrasting P-T (-time) experiences. (h) Strongly retrograded metavolcanoclast (sample, 22) located in the GS1 unit with relict glaucophane and garnet replaced by chlorite+biotite assemblage. (i) S-C structure constructed by chlorite+phengite+quartz assemblage in GS facies metavolcanoclast (sample, 71) from the GT unit indicating a top to E shear sense. Also check Table15for the detail of mineral assemblage of each sample and Figure65for the rest of microphotographs.

  Figure 57 and listed in Table19.

  Figure 60b, 66 and 67, and data are listed in Table18, 20 and 21.

5. 4 . 2 40

 42 Ar-39 Ar Step-Heating Analysis Selected samples were crushed and sieved. Single grains of phengite were handpicked under binocular microscope and cleaned in ultrasonic bath with acetone and distilled water. They were packaged in Al foils and irradiated for 40h in the core of the Triga Mark II nuclear reactor of Pavia (Italia) with several aliquots of the Fish Canyon sanidine standard (28.03 ± 0.08 Ma, Jourdan & Renne, 2007) as flux monitor. Argon isotopic interferences on K and Ca were determined by irradiation of KF and CaF2 pure salts from which the following correction factors were obtained. Argon analyses were performed at Géosciences Montpellier, France with two analytical devices that each consist of: (a) an IR-CO2 laser of 100kHz used at 5-15% during 60s, (b) a lenses system for beam focusing, (c) a steel chamber, kept at 10 -8 -10 -9 bar, with a drilled copper plate, (d) an inlet line for purification of gases including two Zr-Al getters, (e) a multi-collector mass spectrometer (Argus VI from Thermo-Fisher). A custom-made software controls the laser intensity, the timing of extraction/purification

Figure 57 :

 57 Figure 57: Primitive mantle-normalized spider diagram and chondrite-normalized REE pattern for samples in this study (Table19).

Figure 58 :

 58 Figure 58: Mineral plots of compositions determined with the electron probe microanalysis (check Table 16 for detail data). XMg is herein after taken as Mg/(Mg+Fe 2+ ). (a) Na (site B) versus Si content in all the AMC amphiboles analyzed in this study. Compositions mainly cluster in the glaucophane field and around a composition intermediate between actinolite and barroisite but almost span the entire range. Terminology is after Hawthorne & Oberti (2006). (b) Composition of sodic and calcic clinopyroxenes (Morimoto, 1988). (c) Phengite composition variations, which are mostly parallel to the muscovite-celadonite (Ms-Cel) joint. The variations are dominated by the tschermak substitution exchange vector Si(Mg, Fe)-2Al as for most metavolcanoclastics and metavolcanics. Note that phengite in sample 135 and 26 from the UH unit reach exceptionally high tschermak values (Si 4+ >3.6, Table 16). (d) Chlorite plot mostly along the amesiteclinochlore (Ames-Clin) joint as a result of the tschermak substitution. (e) Triangular plot for garnet composition expressed as a function of their grossular, pyrope and almandine (+spessartite) content. Thick gray arrows indicate core to rim evolution of the composition observed in the garnet profiles of each sample. Garnet profile patterns of representative samples from different sub-units are also present as examples.

6. 6

 6 .2.6. Others No fresh lawsonite was found but only box-shaped pseudomorphs (epidote +albite/paragonite±chlorite assemblages, Figure 56a, c, 65c) in the garnet of samples 135, 26, 32. Coesite was assumed to appear at or near the metamorphic peak of UH samples since i) sampling locations (i.e., samples 135, 26, Figure 51a, 52a) are very close to previous UHP reports of coesite, ii) the UH unit was confirmed as a UHP unit with ubiquitous coesite (Figure 50c, 51a, d; Bayet et al., 2018). Epidote appears as matrix mineral (Figure 56e-g, 66b, g) and inclusion (occasionally within the boxshaped lawsonite pseudomorphs; Figure 56a, c), with a pistacite composition varying between 0.12 and 0.58 but broadly constant in each sample. Biotite either appears as the main mineral making up the schistosity in sample J2 (Figure 66a) or replaces garnet/phengite (Figure 56h, 66g) in samples 22, 32 and 147. Its composition lies along the tschermak substitution trend between eastonite and phlogopite/annite with Si ~2.75-2.91, XMg ~0.34-0.58 and Ti ~0.06-0.10apfu. Plagioclase is purely albitic in composition in all relevant samples.

  of the Main Mineral Groups Found in Samples from Different Sub-units in the Akesayi Metamorphic Complex

  (a) Results without further interpretations. (b) Results plotted with synthetic P-T paths, radiometric indications and geodynamic implications (e.g., exhumation velocities) for different sub-units. Colored rectangles (solid-line: metavolcanics, dash-line: metavolcanoclastics) showing previous works, which belong/close to the same sub-units as redefined in this study Figure 69, Table

  different depths: the UH ~5, Eb ~7, MU ~10 and GT ~12°C/km. The maximum burial conditions of each sub-units were reached at the timing broadly as their index minerals (i.e., phengite or zircon) recorded and revealed by in situ Ar-Ar or U-Pb technique (Figure 60, 66): the UH ~320, EB ~330, MU ~360 and GT ~ 310 Ma. The final juxtaposition of these sub-units could take place around 280-300 Ma, as echoed by the dominance of ages within this range probed from moderately substituted phengite in samples amongst all those four sub-units (Figure 60, 66). (c) List of selected mineral assemblages of each sample for the THERMOCALC average P-T calculation. Also checkTable 16 for corresponding mineral compositions.

Figure 56a ,

 56a Figure56a, 65c) yield UHP peak burial P-T conditions around 480-560°C and 2.75GPa

Figure 60 :

 60 Figure 60: (a) Radiometric ages obtained for all samples, with respect to respective localities on Kebuerte section. Check Table 18, 20 and 21 for detailed isotopic results. (b) Examples of in situ 40 Ar-39 Ar laser probe ablation result. Overlays show surface areas from which argon was extracted during measurement, and numbers correspond to ages obtained. Phengite grains following the schistosity are marked as white overlays, while light blue overlays represent those encountered along late shear bands. The in situ Ar-Ar probling ages (e.g., used in Figure 59b, 60a, 61 and text) for constraining the deformation around peak metamorphism of each samples are calculated from the average of absolute ages obtained from phengite grains following the schistosity and shear bands. Orange overlays indicate phengite grains with ambiguous old age that probably results from excess Ar or imply early growth of phengite. Green overlays locate phengite grains with relative younger age which could indicate later stage recrystallization. Colored sketch, which exported from the combined microprobe mapping matrix data via Xmaptools (https://www.xmaptools.com, Lanari et al., 2014), clearly show the mineral assemblage with respect to deformation. Detail of the rest of in situ Ar-Ar probing results are illustrated in Figure 66 (Table18).

Figure 61 :

 61 Figure61: (a, b, c, d) The compilation of regional age reports with respect to sampling localities (ages versus latitude). Ages reported in key valleys (Kekesu, Akeyazi-Akesayi/-Habutengsu/-Kebuerte/-Atantayi, Muzaerte-Changawuzi; Figure50c, 69), are listed respectively from the top to bottom. Bars with bold letters marked results from this study, while those with grey numbers represent previous works. Dashline rectangles mark previous works without precise P-T constraints (i.e., roughly tied to lithologies) or did not tie dated ages to metamorphism. The bar colors indicate the P-T estimates linked to ages (whatever roughly or precisely), and black bar marks ages with metasomatic or magmatic origins. Check Table22for the detail of exhaustive compilation of regional age reports and associated P-T estimates. (e) The age histogram of sub-units in the AMC from this study. Black dash-line spectrum represents age pattern of previous works from adjacent areas with respect to respective sub-units. Other major geological constraints are also recalled for comparison: i) discrete hydrothermal zircon ages obtained from regional rodingite(Li et al., 2010) probably witness the fate of SW-Tianshan ocean basin; ii) The range of formation age of regional igneous rocks and ophiolites are cited from Jiang et al. (2014) and Wang et al. (2018). iii) Metamorphic ages of (U)HP rocks from the Kyrgyz SW-Tianshan are cited from Loury et al. (2016), Loury et al. (2018) and Mühlberg et al. (2016).

  )). Another argument in favor of the absence of random excess argon is that the dispersion of in situ ages (Figure60, 66) increases with a greater dispersion in mineral chemistry (Figure58c; e.g., notably in samples 135, 117, 148-1, 71).

6. 7 . 3

 73 Implications for subduction dynamics and Late Carboniferous subduction history Importantly, our P-T-time results suggest the diachronous recovery of different subunits (Figure59b), from ~45 km (MU; 360 Ma), ~65 km (EB; 330 Ma) and ~85 km depth (UH; 320 Ma). This rock record highlights discrete, transient episodes of detachment from the slab, in particular with respect to long-lived South Tianshan ocean subduction duration of ~120 Myr[START_REF] Scheltens | Northward subduction-related orogenesis of the southern Altaids: Constraints from structural and metamorphic analysis of the HP/UHP accretionary complex in Chinese southwestern Tianshan, NW China[END_REF][START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF]. This punctuated recovery likely results from changes in mechanical coupling[START_REF] Agard | The subduction plate interface: Rock record and mechanical coupling (from long to short time scales)[END_REF], whose origin could be i) a change in slab geometry (e.g., slab rollback:[START_REF] Brun | Exhumation of high-pressure rocks driven by slab rollback[END_REF] slab kink: Klemd et al., 2011) (Figure62b-c) and/or ii) a modification of the physical properties along the plate interface (i.e., mantle rheology, fluid regime, etc;[START_REF] Agard | The subduction plate interface: Rock record and mechanical coupling (from long to short time scales)[END_REF]. Incidentally, whole-rock analyses (Figure57) reveal that there was in first approximation no drastic change in volcanoclastic content throughout this subduction history.

Figure 63 :

 63 Figure 63: Panoramic views of the main north and south contacts in between the AMC and the SCTSZ mylonitized shear zone (GS1, GS2).

Figure 64 :

 64 Figure 64: Outcrop observation of representative samples in this study. The letter of sub-figures corresponds to the localities marked in Figure 52c. (a) A fresh eclogite outcrop shows clear omphacite-stretching lineation. (b, c) Recumbent folds in the EC/BS facies blueschist horizon (EB unit). (d) Outcrop of sample J2 from the SCTSZ mylonitized shear zone, indicating asymmetrical folding over shear movement. (e) Relative ambiguous shear sense shown by complicated refolding and schistosity on the outcrop of sample 157. (f) Outcrop of the moderately schistosed serpentinized ultra-mafic rock. (g) A top to NEE sense of shear found on the outcrop of sample 148-1 from the GT unit. (f) A top to NNW sense of shear found on the outcrop of sample 148-2 from the GT unit.

Figure 67 :

 67 Figure 67: The phengite 40 Ar-39 Ar step-heating results of regional GS to lower BS facies samples (J2, 22, 157 and 147), and the LA-ICP-MS zircon U-Pb radiometric results of meta-basite sample (158) (Table 20, 21).

Figure 68 :

 68 Figure 68: Examples of later stage phengite recrystallization in samples from distinct sub-units (UH versus GT units), which could account for the accordant appearance of relative younger in situ phengite Ar-Ar probed ages ~280-300 Ma in most of samples from all sub-units (Figure 60a).

Figure 69 :

 69 Figure 69: Geological map with the locality of previous age reports. Number corresponds to the detail of each previous works compiled in Table22.

  indeed present the GPS data of samples. The rest of sample coordinates are therefore induced by roughly estimation via Google Earth plotting that based on the geological map of each previous work. c In this column, various abbreviation represent different methods used for P-T estimate: avPT, THERMOCALC average P-T; REaL, Roughly Estimated according to Lithology (corresponding P-T values in the coming columns are cited from the general P-T area of GS/BS/EC facies definited by [Bucher Kurt and Rodney Grapes, Petrogenesis of Metamorphic Rocks. Springer, 2011]; Ps mineral isopleth, Pseudosection mineral isopleth thermobarometer; CTB, conventional thermobarometer (e.g., grt-cpx Fe 2+ -Mg exchange thermometer); ZiR, Zirconium in Rutile thermometer; ZiT, Zirconium in Titanite thermometer. d In this column, various abbreviation represent different way or logic for tying dated age to metamorphism: SRtPTh., simply related to estimated rock P-T history; RTP., roughly tied to protolith; RTL., roughly tied to lithology. e The interpretation of age strictly follows what authors proposed in relevant previous works.

Figure 70 :

 70 Figure 70: The comparison between ages from metamorphic indications (this study+ previous works) and those from magmatic indications (previous works) that related to the Paleo South Tianshan Ocean Basin subduction setting (i.e., upper plate: the Paleo Kazakhstan Continent at the North, and the STB+Tarim craton at the South; lower plate: the subducting ocean basin). Check compilation Tables in Wang et al. (2018) for the detail of regional magmatic ages.

Figure 71 :

 71 Figure 71: Major elements composition of selected samples in this PhD thesis and those from previous works.

Figure 73 :

 73 Figure 73: P-T-density pesudosections conducted for representative compositions of regional eclogitie, blueschist and serpentinite.

Figure 72 :

 72 Figure 72: P-T-density pesudosections conducted for representative compositions of metavolcanoclsatics (regional and global)

  UHP oceanic eclogitic slice. This pattern coincides with a transient ~80 °C increase in temperature revealed by Zr-in-rutile thermometry. Mineral compositions together with thermodynamic modeling indicate that mineral breakdown cannot account alone for this unusual garnet zonation. Based on Zr-in-rutile thermometry and detailed petrology, geochemical diffusion and thermodynamic modeling (Figure42), we show that this ~80°C short-lived thermal pulse (~300 kyrs assuming a 5 Myr overall garnet growth duration) is tentatively tied to the fast movement of detached UHP oceanic slices towards the hotter mantle wedge (Figure44).

7. 6 .

 6 PerspectiveBased on detailed geochemical, lithological, tectonic/structural, metamorphic and chronological investigations for samples along the Kebuerte valley of the Akeyazi metamorphic complex (AMC), this PhD thesis provides answers to some of the questions raised up the introduction ( §1.4). We also propose a comprehensive geodynamic model for the tectonic-metamorphic evolution of the AMC-STMB through space and time.Major controversies and/or questions are nevertheless still pending: i) Is the N-S tectonic organization observed in the Kebuerte transect also visible laterally, along the SCTSZ? Only ambiguous answers exist for now, with the ultramafic unit reported in Muzhaerte-Changawuzi valley (~40km to the west of the AMC, which may have reached UHP conditions around ~310Ma).ii) What is the duration of fluid-rock interactions and/or of the transient thermal excursion revealed by garnet zoning? iii) Opposite subduction polarity of the Paleo South Tianshan ocean basin was proposed in the literature on the basis of structural and magmatic data.

  focuses on the structure and evolution of the Akeyazi metamorphic complex of the STMB, through a N-S ~30km-long transect along the Kebuerte valley. Contrasting P-T-time-deformation histories of key representative samples from diverse sub-units have been found. What was previously proposed as a HP/UHP "mélange" should be subdivided into several coherent, kilometre-scale, metavolcanoclastic units bearing contrasting P-T-time-deformation histories. At least four of the six sub-units identified here, namely the UH (480-560°C and 2.75 GPa), EB (~2.1 GPa and 505°C), MU (~1.45 GPa and 485°C) and GT units (>~0.7-1.0 GPa and 470-520°C) experienced subduction and were buried to depths of ~85, 65, 45 and 30km respectively. The discovery of an unusual zonation in a UHP eclogitic garnet reveals the existence of a transient episode of heating at ~80km. More precisely results indicate that:

Table

Table

Table 2 :

 2

The compilation of previous age reports with relevant P-T estimates.

Table 1

 1

	. Mafic samples are true
	eclogites with > 70 vol. % of
	garnet and omphacite (Carswell,
	1990). Mineral constituents of
	eclogite samples are garnet,
	omphacite,	epodite-group
	minerals,	paragonite,	blue
	amphibole (rimmed in places by
	blue-green amphibole), quartz, as
	well as rutile/titanite, calcite and
	phengite (Figure 20a-f) in
	subordinate	amounts.	The
	fraction of hydrous minerals
	(especially amphibole) increases
	in the vicinity of the host-rock.

Table 4 :

 4 NOTES: "-" means do not detect or calculate; EBC means calculated effective bulk composition for pseudosection modeling;

  Ph-in-grt Ph-matrix Pg-in-grt Pg-martix

	Ttn	29.82	37.86	2.11	0.03	0.00	1.07	0.02	0.01	29.11	0.05	0.01	100.08	5	0.978	0.934	0.081	0.000	0.000	0.029	0.000	0.000	1.023	0.003	0.001	-	-
	Rt	0.03	99.32	0.02	0.19	0.00	0.46	0.00	0.01	0.08	0.01	0.00	100.12	2	0.000	0.995	0.000	0.000	0.005	0.000	0.000	0.000	0.001	0.000	0.000	-	-
	Chl-matrix	25.63	0.02	19.26	0.06	0.00	25.31	0.21	14.75	0.13	0.15	0.15	85.67	14	2.903	0.003	2.407	0.010	0.000	2.088	0.023	2.408	0.014	0.036	0.022	0.464	-
	Ep	38.30	0.13	26.87	0.00	8.84	0.00	0.09	0.01	23.00	0.00	0.00	97.23	13	3.011	0.007	2.490	0.000	0.523	0.000	0.006	0.001	1.937	0.000	0.000	-	0.174
	Czo	39.51	0.16	30.65	0.00	4.49	0.00	0.04	0.04	23.03	0.01	0.00	97.92	13	3.025	0.009	2.766	0.000	0.259	0.000	0.003	0.004	1.889	0.001	0.000	-	0.086
		48.87	0.06	39.44	0.07	0.00	0.24	0.00	0.11	0.29	7.37	0.33	96.79	11	3.060	0.003	2.911	0.004	0.000	0.013	0.000	0.000	0.020	0.894	0.027	0.000	-
		46.39	0.02	38.62	0.09	0.00	1.12	0.04	0.12	0.29	7.10	0.47	94.26	11	3.004	0.001	2.949	0.005	0.000	0.061	0.002	0.012	0.020	0.892	0.038	0.012	-
		51.92	0.27	27.71	0.04	0.00	1.83	0.01	3.37	0.01	0.80	9.15	95.11	11	3.431	0.013	2.158	0.002	0.000	0.101	0.001	0.332	0.001	0.102	0.771	0.332	-
		51.44	0.33	27.64	0.05	0.00	3.58	0.03	2.38	0.10	0.42	9.37	95.34	11	3.421	0.017	2.167	0.003	0.000	0.199	0.002	0.236	0.007	0.054	0.696	0.236	-
		56.58	0.04	10.38	0.00	2.09	1.97	0.03	9.29	13.58	6.83	0.00	100.79	6	1.989	0.001	0.431	0.000	0.054	0.059	0.001	0.487	0.512	0.466	0.000	0.420	0.476
		56.80	0.12	12.47	0.02	1.62	1.50	0.04	8.28	12.51	7.69	0.00	101.05	6	1.980	0.003	0.512	0.000	0.041	0.045	0.001	0.430	0.467	0.520	0.000	0.480	0.527
		58.48	0.04	10.19	0.08	0.00	4.34	0.05	8.20	11.62	6.28	0.11	99.39	6	2.069	0.001	0.425	0.002	0.000	0.128	0.001	0.432	0.440	0.431	0.005	0.420	0.495
		55.00	0.07	8.12	0.02	4.48	4.78	0.08	7.50	13.32	6.57	0.03	99.97	6	1.995	0.002	0.347	0.001	0.122	0.145	0.002	0.406	0.518	0.462	0.001	0.340	0.471
		49.90	0.41	11.85	0.04	0.55	11.14	0.02	11.77	7.95	4.20	0.27	98.10	23	7.099	0.043	1.988	0.005	0.058	1.326	0.003	2.495	1.212	1.159	0.049	0.347	1.159
		46.62	0.23	13.96	0.08	2.00	14.22	0.15	8.78	7.15	5.06	0.06	98.31	23	6.773	0.025	2.390	0.009	0.219	1.728	0.018	1.901	1.113	1.425	0.011	0.476	1.425
		57.83	0.03	12.21	0.05	0.54	7.53	0.04	11.33	1.14	7.27	0.03	98.00	23	7.849	0.003	1.953	0.005	0.055	0.854	0.004	2.291	0.166	1.912	0.005	0.272	0.027
		57.17	0.18	10.27	0.02	1.78	11.52	0.10	9.75	1.51	6.96	0.02	99.28	23	7.854	0.019	1.663	0.002	0.184	1.323	0.011	1.996	0.222	1.853	0.003	0.399	0.100
		38.09	0.10	21.93	0.01	0.92	25.92	0.21	5.28	7.76	0.03	0.01	100.26	12	2.964	0.006	2.011	0.000	0.054	1.687	0.014	0.612	0.647	0.004	0.001	0.207	0.219
		38.02	0.06	21.76	0.09	1.02	27.66	0.39	5.15	6.25	0.06	0.00	100.46	12	2.967	0.004	2.002	0.006	0.060	1.805	0.026	0.599	0.523	0.009	0.000	0.203	0.177
		38.10	0.01	21.65	0.03	0.39	29.93	0.48	4.47	5.44	0.04	0.01	100.55	12	2.989	0.001	2.003	0.002	0.023	1.964	0.032	0.523	0.457	0.006	0.001	0.176	0.154
		37.86	0.02	21.39	0.06	0.83	30.89	0.52	3.86	5.42	0.01	0.00	100.86	12	2.980	0.001	1.985	0.004	0.049	2.034	0.035	0.453	0.457	0.002	0.000	0.152	0.153
		37.33	0.06	21.47	0.04	1.31	30.91	0.81	3.20	5.41	0.07	0.00	100.61	12	2.958	0.004	2.006	0.003	0.078	2.049	0.054	0.378	0.459	0.011	0.000	0.129	0.156
		38.24	0.16	20.94	0.21	0.00	31.89	0.70	2.56	6.09	0.11	0.02	100.92	12	3.024	0.010	1.953	0.013	0.000	2.109	0.047	0.302	0.516	0.017	0.002	0.102	0.174
		SiO2 37.52	TiO2 0.15	Al2O3 21.15	Cr2O3 0.03	Fe2O3 0.73	FeO 30.20	MnO 1.48	MgO 2.46	CaO 6.88	Na2O 0.02	K2O 0.00	Total 100.62	O 12	Si 2.979	Ti 0.009	Al 1.981	Cr 0.002	Fe 3+ 0.044	Fe 2+ 2.006	Mn 0.100	Mg 0.292	Ca 0.585	Na 0.003	K 0.000	X(phase) 0.098	Y(phase) 0.196

Table 5 :

 5

NOTES: Microprobe data presented here are calculated from RAW data via AX_2 program (Holland; http://www.esc.cam.ac.uk/research/research-groups/holland/ax); X (grt) = Xpy = Mg (Fe 2+

  Average Laser-ICP-MS trace-element compositions of various garnet and zircon domains.

				Garnet						Zircon
		Core	Mantle	Rim		Core		Core high HREEs	Mantle	Rim
	Element Average	Std(N=8)	Average	Std(N=9)	Average Std(N=10)	Average Std(N=30)	Average Std(N=5)	Average	Std(N=4)	Average Std(N=15)
	P	53.5	31.9	117	155	13.9	2.84	27.2	9.92	34.6	10.4	-	-	21.2	6.27
	Ti	681	152	1661	979	106	17.5	2.89	1.04	10.6	3.77	1.55	0.140	1.93	0.930
	Nb	bd	bd	1.43	1.74	bd	bd	5.75	1.22	6.27	1.20	5.27	0.979	5.62	1.04
	Y	81.2	17.6	47.4	11.5	49.8	5.42	89.1	17.2	231	57.7	44.6	8.57	47.6	19.3
	La	bd	bd	0.471	0.356	bd	bd	bd	bd	bd	bd	bd	bd	bd	bd
	Ce	0.181	0.204	1.63	1.35	bd	bd	0.121	0.060	0.123	0.064	bd	bd	bd	bd
	Pr	0.042	0.015	0.314	0.214	bd	bd	bd	bd	bd	bd	bd	bd	bd	bd
	Nd	0.308	0.249	2.38	1.16	bd	bd	bd	bd	bd	bd	bd	bd	bd	bd
	Sm	0.746	0.245	1.77	0.590	bd	bd	0.336	0.051	0.420	0.269	bd	bd	bd	bd
	Eu	0.882	0.281	1.13	0.360	0.278	0.060	0.284	0.115	0.294	0.137	0.325	0.248	bd	bd
	Gd	5.14	1.38	5.18	1.63	1.83	0.401	2.81	0.905	2.87	0.873	2.34	1.09	0.648	0.135
	Tb	1.69	0.301	1.24	0.328	0.926	0.125	1.23	0.299	1.96	0.578	0.705	0.291	0.192	0.093
	Dy	13.9	2.74	8.91	1.95	8.46	0.772	10.5	2.14	24.0	6.72	4.91	1.80	2.03	1.32
	Ho	3.38	0.788	1.89	0.458	1.89	0.208	2.40	0.539	6.70	1.86	1.01	0.411	0.913	0.603
	Er	10.0	2.64	5.23	1.37	4.87	0.614	6.63	1.62	20.37	5.64	2.69	0.853	5.48	3.38
	Tm	1.56	0.455	0.703	0.193	0.646	0.096	1.03	0.271	3.18	0.791	0.351	0.096	1.65	0.994
	Yb	11.2	3.58	4.72	1.29	4.19	0.660	8.00	2.00	23.72	5.80	3.00	1.13	20.2	10.9
	Lu	1.54	0.535	0.654	0.187	0.654	0.098	1.28	0.331	3.61	1.01	0.450	0.190	4.42	2.47
	Ta	bd	bd	bd	bd	bd	bd	0.071	0.044	0.077	0.026	0.095	0.042	0.099	0.054
	Hf	bd	bd	bd	bd	bd	bd	10127	366	10306	359	10553	317	10341	671
	Th	bd	bd	bd	bd	bd	bd	3.59	3.00	5.39	5.27	2.86	1.57	0.174	0.107
	U	bd	bd	bd	bd	bd	bd	982	660	982	657	740	255	30.6	34.9
	Pb	bd	bd	bd	bd	bd	bd	232	158	229	141	170	60.6	16.3	12.8
	(Lu/Sm)N	12.4		2.23		-		22.9		51.7		-		-
	(Lu/Eu)N	3.99		1.33		5.37		10.3		28.0		3.17		-
	(Lu/Tb)N	1.35		0.779		1.04		1.53		2.71		0.940		33.9

  broadly similar (and comparable to the REE distributions within zircon), with relatively high and flat HREE content and relative depletion in MREE and LREE.

	Zircon core (n=31)	(ug/g)	(ug/g)	Th/U	f 206 (%)	207 Pb 235 U	±1s %	206 Pb 238 U	±1s %		207 Pb 235 U	±1s	206 Pb 238 U	±1s
	11AT06-1a @10		1.69	0.003	0.33	0.36991	2.56	0.0505	1.50	0.5882	319.6	7.0	317.4	4.7
	11AT06-1a @14		2.44	0.004	0.13	0.36494	2.68	0.0495	1.50	0.5614	315.9	7.3	311.2	4.6
	11AT06-1a @15		2.94	0.004	0.23	0.36427	2.73	0.0496	1.50	0.5500	315.4	7.4	311.8	4.6
	11AT06-1a @18		1.29	0.002	0.43	0.36714	2.53	0.0500	1.50	0.5956	317.5	6.9	314.7	4.6
	11AT06-1a @2		1.94	0.003	0.03	0.36225	2.07	0.0507	1.50	0.7258	313.9	5.6	318.7	4.7
	11AT06-1a @20		2.69	0.003	0.23	0.35596	2.91	0.0493	1.51	0.5199	309.2	7.8	310.0	4.6
	11AT06-1a @28		1.57	0.002	0.09	0.37086	2.39	0.0509	1.54	0.6442	320.3	6.6	320.1	4.8
	11AT06-1a @29		4.02	0.004	0.11	0.37306	1.96	0.0506	1.50	0.7682	321.9	5.4	318.2	4.7
	11AT06-1a @32		1.16	0.002	0.29	0.35594	2.25	0.0499	1.50	0.6686	309.2	6.0	313.9	4.6
	11AT06-1a @36		4.55	0.005	0.22	0.37544	2.29	0.0505	1.50	0.6566	323.7	6.4	317.8	4.7
	11AT06-1a @38		3.46	0.003	0.21	0.36159	2.69	0.0493	1.51	0.5630	313.4	7.3	310.4	4.6
	11AT06-1a @39		2.03	0.003	0.11	0.37371	2.64	0.0497	1.51	0.5699	322.4	7.3	313.0	4.6
	11AT06-1a @6		3.47	0.005	0.19	0.37025	2.14	0.0509	1.51	0.7046	319.8	5.9	320.1	4.7
	11AT06-1b @6		3.08	0.003	0.09	0.36843	1.82	0.0506	1.50	0.8259	318.5	5.0	318.4	4.7
	11AT06-1c @2		2.00	0.003	0.00	0.35589	1.82	0.0496	1.55	0.8485	309.1	4.9	312.1	4.7
	11AT06-1c @6		3.93	0.004	0.48	0.37138	2.05	0.0506	1.67	0.8115	320.7	5.7	318.2	5.2
	11AT06-1d @1		1.77	0.003	0.00	0.36228	1.86	0.0496	1.53	0.8221	313.9	5.0	312.0	4.7
	11AT06-1d @33		0.45	0.003	0.82	0.36347	3.96	0.0499	1.51	0.3817	314.8	10.8	314.0	4.6
	11AT06-1d @22		1.29	0.002	0.04	0.37170	1.86	0.0499	1.50	0.8071	320.9	5.1	314.1	4.6
	11AT06-1d @6		4.00	0.004	0.00	0.36469	1.72	0.0500	1.56	0.9084	315.7	4.7	314.4	4.8
	11AT06-1d @19		0.65	0.001	0.06	0.36804	2.00	0.0506	1.50	0.7510	318.2	5.5	318.1	4.7
	11AT06-1d @30		3.54	0.005	0.02	0.37868	2.13	0.0510	1.52	0.7131	326.1	6.0	320.6	4.8
	11AT06-1d @7		1.19	0.003	0.20	0.37550	2.12	0.0516	1.50	0.7079	323.7	5.9	324.3	4.8
	11AT06-1a @23		3.37	0.002	0.03	0.37595	1.85	0.0514	1.50	0.8098	324.1	5.2	323.4	4.7
	11AT06-1d @10		6.57	0.003	0.01	0.37210	1.60	0.0505	1.52	0.9451	321.2	4.4	317.8	4.7
	11AT06-1a @35		4.76	0.005	0.04	0.37629	2.00	0.0505	1.50	0.7528	324.3	5.6	317.5	4.7
	11AT06-1b @34		25.69	0.008	0.15	0.37570	1.59	0.0509	1.51	0.9441	323.9	4.4	320.2	4.7
	11AT06-1d @13		11.91	0.004	0.24	0.37897	1.92	0.0515	1.53	0.8000	326.3	5.4	323.8	4.8
	11AT06-1a @33		1.39	0.002	0.10	0.36444	2.48	0.0501	1.53	0.6188	315.5	6.7	315.0	4.7
	11AT06-1d @14		1.72	0.003	0.00	0.37136	1.97	0.0503	1.51	0.7661	320.7	5.4	316.4	4.7
	11AT06-1e @2		4.64	0.004	1.60	0.37476	3.16	0.0496	1.51	0.4790	323.2	8.8	312.1	4.6
	Zircon core with high HREEs (n=4)
	11AT06-1b @1		2.23	0.002	0.06	0.36720	1.71	0.0502	1.50	0.8780	317.6	4.7	315.9	4.6
	11AT06-1d @29		1.01	0.002	0.02	0.38270	1.96	0.0506	1.50	0.7666	329.0	5.5	318.1	4.7
	11AT06-1a @42		14.14	0.004	0.03	0.37221	1.79	0.0510	1.50	0.8395	321.3	4.9	320.4	4.7
	11AT06-1b @5		1.62	0.003	0.18	0.36372	1.79	0.0501	1.51	0.8451	315.0	4.9	315.3	4.7
	Zircon mantle (n=7)
	11AT06-1a @1		4.00	0.004	{0.28}	0.35010	2.32	0.0480	1.52	0.6532	304.8	6.1	302.4	4.5
	11AT06-1a @11		4.00	0.004	{0.30}	0.34716	2.98	0.0477	1.54	0.5181	302.6	7.8	300.2	4.5
	11AT06-1a @21		2.00	0.003	{0.13}	0.35383	2.70	0.0482	1.52	0.5613	307.6	7.2	303.4	4.5
	11AT06-1a @9		3.00	0.003	{0.19}	0.34857	3.15	0.0485	1.52	0.4813	303.6	8.3	305.4	4.5
	11AT06-1a @37		3.00	0.004	{0.50}	0.35923	3.12	0.0488	1.50	0.4823	311.6	8.4	307.1	4.5
	11AT06-1c @1		0.06	0.002	{0.00}	0.35326	6.18	0.0472	1.56	0.2519	307.2	16.5	297.2	4.5
	11AT06-1d @8		0.58	0.003	{1.43}	0.31633	10.20	0.0486	1.51	0.1480	279.1	25.2	305.6	4.5
	continued
	Zircon rim (n=8)	U (ug/g)	Th (ug/g)	Th/U	f 206 (%)	238 U* 206 Pb	±1s %	207 Pb* 206 Pb	±1s %	206 Pb 238 U	±1s
	11AT06-1a @13		1.64	0.002	{1.32}	22.149	1.58	0.05735	1.90	281.0	4.4
	11AT06-1a @31		1.66	0.006	{0.09}	22.896	1.51	0.05207	2.69	275.6	4.1
	11AT06-1a @7		0.66	0.004	{0.00}	22.241	1.57	0.05238	4.20	283.5	4.3
	11AT06-1d @31		0.03	0.004	{9.84}	19.487	9.29	0.14442	9.81	291.6	11.1
	11AT06-1e @3		0.02	0.004	{10.30}	19.625	9.667	0.10951	15.34	288.1	10.5
	11AT06-1e @4		0.01	0.009	{14.43}	19.656	10.210	0.08647	20.06	274.7	20.7
	11AT06-1d @9		0.15	0.003	{34.21}	15.081	3.06	0.29376	3.04	275.3	7.9
	11AT06-1d @34		0.05	0.009	{24.88}	16.306	5.14	0.20910	6.17	290.3	13.7

Garnet cores show the highest HREE enrichment with (Lu/Sm)N ~ 12, compared to the mantle domain ((Lu/Sm)N ~ 2). Garnet mantle shows the highest LREE and a slightly SIMS zircon U-Pb isotopic data. U Th r Table 7: NOTES: f 206 (%) is the percentage of common 206 Pb in total 206 Pb, calculated by 207 Pb-based; t 206 / 238 is 206 Pb-238 U age calculated by 207 Pb-based common-lead correction; "*" means that the ratios are common Pb uncorrected;

  206 Pb/ 238 U ages from 310.0 to 324.[START_REF]Sample selection and whole-rock composition[END_REF] Ma, a mean Concordia age of 316.8 ± 0.83 Ma (MSWD = 1.01, n = 31) and a weighted mean age of 316.3 ± 1.6 Ma (MSWD = 0.71, n = 31) (Figure 25e). Similar results are found for the HREE enriched cores, with apparent 206 Pb/ 238 U ages varying from 315.3 to 320.4 Ma, a mean Concordia age of

318.0 ± 2.3 Ma (MSWD = 2.7, n = 4) and a weighted mean age of 317.4 ± 4.6 Ma (MSWD = 0.25, n = 4) (Figure 25d). The mantle domain gives younger apparent 206 Pb/ 238 U ages, from 297.2 to 307.1 Ma, a mean Concordia age of 303.1 ± 1.7 Ma (MSWD = 0.49, n = 7) and a weighted mean age of 303.1 ± 3.3 Ma (MSWD = 0.58, n = 7) (Figure

Table 9

 9

	Sample	δ 18 O(‰) a 2σ(‰)	Sample	δ 18 O(‰) a 2σ(‰)
	zircon core			zircon rim
	11AT06-1a @10	9.49	0.22	11AT06-1a @13	9.25	0.26
	11AT06-1a @14	9.23	0.30	11AT06-1a @31	8.10	0.33
	11AT06-1a @15	9.52	0.32	11AT06-1a @7	9.09	0.29
	11AT06-1a @18	9.34	0.27	11AT06-1d @31	9.35	0.49
	11AT06-1a @2	9.46	0.48	11AT06-1e @3	9.00	0.28
	11AT06-1a @20	8.99	0.35	11AT06-1e @4	8.99	0.30
	11AT06-1a @28	9.20	0.37	11AT06-1d @9	9.17	0.27
	11AT06-1a @29	9.82	0.46	11AT06-1d @34	9.19	0.21
	11AT06-1a @32	9.60	0.23	11AT06-1e @6	9.19	0.20
	11AT06-1a @36	9.08	0.24	11AT06-1e @7	8.06	0.29
	11AT06-1a @38	9.19	0.25	11AT06-1e @8	8.93	0.15
	11AT06-1a @39	9.61	0.36	11AT06-1e @9	9.02	0.33
	11AT06-1a @6	9.26	0.28	11AT06-1e @10	9.43	0.28
	11AT06-1b @6	9.29	0.31	11AT06-1e @11	8.88	0.28
	11AT06-1c @2	9.74	0.38	11AT06-1e @12	9.16	0.40
	11AT06-1c @6	9.10	0.22	11AT06-1e @13	9.22	0.28
	11AT06-1d @1	9.24	0.44	11AT06-1e @14	9.10	0.35
	11AT06-1d @33	9.40	0.36	11AT06-1e @15	8.94	0.24
	11AT06-1d @22	9.11	0.46	11AT06-1e @16	9.27	0.29
	11AT06-1d @6	9.04	0.31	11AT06-1e @17	9.22	0.36
	11AT06-1d @19	9.19	0.22	11AT06-1e @18	8.55	0.22
	11AT06-1d @30	8.90	0.23	11AT06-1e @19	8.91	0.44
				11AT06-1e @20	8.66	0.22
	zircon mantle
	11AT06-1a @1	9.71	0.25	zircon high HREEs
	11AT06-1a @11	9.44	0.37	11AT06-1b @1	9.49	0.22
	11AT06-1a @21	8.87	0.20	11AT06-1a @42	9.45	0.46
	11AT06-1a @9	8.35	0.39	11AT06-1b @7	8.98	0.47
	11AT06-1a @37	9.36	0.31	11AT06-1d @29	9.44	0.38
	11AT06-1c @1	9.41	0.35	11AT06-1e @5	9.08	0.32
	Modeled results	δ 18 O(‰)	Assumed mode in P peak (vol %)	assumed end-member
	zircon	9.0000	1.00	zircon100%
	garnet	9.0995	20.00	alm60%,grs20%,prp20%
	omphacite	9.1144	70.00	Di50%,Jd50%
	coesite	9.1534	2.00	Stishovite100%
	bulk-rcok	8.47	-	-

. Sm and Nd concentrations of whole rock powder separates

(1.68 and 4.

26 ppm respectively) are in SIMS zircon oxygen isotopic data and modeled mineral & bulk-rock oxygen isotopic data at peak pressure conditions.

  . Additional support was provided by project "Zooming in between plates" (Marie Curie International Training Network) to Prof. Philippe Agard. We would like to thank the editor Prof. Marco Scambelluri and anonymous reviewers for their constructive comments that greatly helped in improving the article. We further thank He Li and Bingyu Gao for helping the major and trace elements analysis, Qian Mao and Reiner Klemd for helps and data processing during

microprobe analyses, Qiuli, Li, Yu Liu, Guoqiang Tang and Jiao Li for helps during SIMS zircon U-Pb dating and oxygen analyse, Yueheng Yang for help during zircon and garnet in situ trace elements analyse, and Zhuyin Chu for help during Sm-Nd isotope analyse.

Table 10 :

 10 NOTES: All the EMPA data are re-calculated by AX program under conditions with T=530℃ & P=2 GPa except data for GS/BS deformation (with T=400℃ & P=1.2 GPa); The entire avPT calculations are processing with setting x(H2O)=1.0.

  activation energy ( ) results in larger shifts around 0.60-0.65 mm (1/2 of fixed

	garnet radius, Table 14), for		 [4.0×10 11 to 4.0×10 14 cm 2 /yrs] or	 [320 to
	280 kJ/mol].
	More importantly, these diagrams illustrate the large shifts in peak location
	predicted from linearly T ~time path (with linear R ~time growth law; i.e., n=1 for Eq.
	(7a) in App. B.), depend on modeled system/crystal scales (i.e.,	and	) and
	intrinsic differences of	and	thermodynamic properties among elements (e.g.

Mn, HREEs+Y). As a result, chances of producing spatially concordant pulses in Mn, Y and HREEs among diverse size garnets and distinct samples are very limited (Figure

38

, 39).

5.6.2. Parameter space and boundary conditions

Diffusion-controlled garnet growth modeling was performed with the following assumptions and boundary conditions (see Appendix B for further details):

  Trace element data of rutile analysed in garnet and in the matrix. Calculated temperatures via different calibrations are indicated

	Occurrence		Close to core	Within annular peak	As inclusions in garnet Within annular peak	Close to rim	Close to rim	In matrix
	Elements (µg/g)		Av. (n=7) Std.	Av. (n=17)	Std.	Av. (n=6)	Std.	Av. (n=7) Std.	Av. (n=13) Std.	Av. (n=23) Std.
	Zr		22.7	8.96	66.4	6.71	63.7	10.5	20.3	4.25	21.1	5.93	21.4	6.19
	V		1579	535	1825	382	2054	185	1539	533	1896	321	1886	335
	Cr		690	390	1116	576	1274	385	696	446	858	307	1118	535
	Nb		75.4	41.5	64.2	23.0	68.2	17.6	76.3	39.6	65.1	21.5	65.3	20.0
	Si		99.6	43.0	114	50.7	95.2	54.2	119	46.5	126	34.3	130	61.3
	Fe		2931	634	2444	879	1993	439.0	3237	778	3769	1106	2784	996
	Al		134	86.1	97.7	54.4	176	97.7	102	60.1	199	108	174	118
	T estimates
	Zack et al. (2004)		389	53.4	526	13.2	521	23.6	375	28.2	379	39.0	381	40.9
	Watson et al. (2006)	*	472	22.2	534	6.51	532	11.4	466	11.6	467	16.0	468	16.7
	Tomkins et al. (2007)	540	24.2	608	7.08	605	12.4	533	12.6	535	17.4	536	18.2
	Ferry and Watson (2007) *	474	22.1	536	6.45	534	11.3	468	11.5	470	15.9	471	16.6

Table 14 :

 14 Notes: * marked calibrations with specfic preassumed parameters, e.g., activity of SiO2 or pressure value input. Check figure. 2c-d and relevant context for detail.

Table 13 :

 13

Notes: * marked estimated initial KD for garnet grains whose concentration central peak of givin elements were probably missed during EMPA. Check App. A for detail estimate strategy.

Table 16 :

 16 Notes: Mineral abbreviations with No. in "Analysis" row correspond to EMPA data that used in average P-T and Ti-in-biotite T. calculation (Table17). nOx is the amount of oxygen anion used in the calculation of mineral structural formula. Mineral abbreviations are grt, garnet; grs, grossular; ph, phengite; bi, biotite; cpx, clinopyroxene; omp, omphacite; di, diopside; gln, glaucophane; brs, barroisite; act, actinolite; ep/czo, epidote/clinozoisite; chl, chlorite; ctd, chloritoid; serp, serpentine;

Table 17

 17

	for details on calculations and Table 16 for corresponding analyses), except
	for three GS facies samples whose mineral assemblage are too high-variant to ensure a
	satisfactory fit. Metavolcanoclastics from the UH sub-unit, with Grtcore/mantle/rim-
	Qz(Coe)-Lws(Pseudomorph)±Ph±Gln±Omp±Tlc assemblages (samples 135, 26,

  Table 18).

	~9.2-14.4, Table 21) in chondrite-
	normalized REEs diagram, with	Th/U
	~0.52-0.99 and a weighted mean age (if
	exclude discordant, older inherited core) of
	448.5 ± 4.7 Ma (MSWD=0.56, n=9). These
	observations support a magmatic origin
	(e.g., Corfu et al., 2003; Schaltegger &
	Davies, 2017). The bright zircon rims yield
	a weighted mean age of 359.2 ± 3.6 Ma
	(MSWD=1.14, n=8), with relatively gentle
	slope from LREEs to HREEs ((Lu/La)N
	~13.7-141.0) and obvious HREEs plateau
	((Lu/Tb)N ~1.3-2.2, Table 21) but no
	detectable Ce/Pr/Eu anomalies in chondrite-
	normalized REEs diagram. The REEs
	pattern of bright zircon rims and their
	smaller Th/U ~0.09-0.26 could suggest a
	metamorphic origin equilibrated with the
	growth of relatively L/MREEs-poor &
	HREEs-rich phase (e.g., garnet; see Rubatto,
	2017; Tan et al., 2017).

Table 18 :

 18

	6.7. Discussions
	6.7.1. Distinct metamorphic sub-units?

a Average age value calculated from the results of in situ Ar-Ar dating on phengite flakes that following the major shearing deformation (i.e., S-C structure) around peak metamorphism. b Standard deviation in 2 sigma error.

Table 19 :

 19 Results of bulk rock trace element compositions.

Table 20 :

 20 Results of PhengiteStep-Heating 40 Ar-39 Ar Radiometric Data

Table 21 :

 21

Results of LA-ICP-MS Zircon U-Pb Radiometric Data of meta-basite sample.

Table 22 .

 22 Exhaustive compilation of previous age reports and associated P-T estimates in Chinese SW-Tianshan HP/UHP-LT accretionary complexCoordinates b

	No. a	Lithology	Location			Dating method	Age (Ma) 2σ-error	PT E. method c	Tie age to metamorphism d	P (GPa)	dP	T (˚C)	dT	Interpretation of age e	Reference
	a (J2)	chl-ph-bi-qz schist	Akeyazi-kebuerte	42.5531	81.1816	Phengite Ar-Ar step-heating	277	1.8	avPT	SRtPTh.	0.51	0.24	578	56	Dated the SCTSZ strike-slip deformation	-
	b (22)	grt-bearing chl-ph-bi-qz schist	Akeyazi-kebuerte	42.5385	81.1969	Phengite Ar-Ar step-heating	300	3.8	avPT	SRtPTh.	0.85	0.35	518	19	Constrainted the later stage GS-facies deformation during doming and/or final juxtaposition	-
	c (135)	UHP meta-pelite	Akeyazi-kebuerte	42.5319	81.2035	Phengite in situ Ar-Ar	319	3.6	avPT	Directly in situ probing on kinematic structure	2.77	0.03	562	11 Dated the major shearing deformation around UHP peak metamorphism of UH unit	-
	d (26)	UHP meta-graywack	Akeyazi-kebuerte	42.5132	81.2029	Phengite in situ Ar-Ar	321	2.5	avPT	Directly in situ probing on kinematic structure	2.75	0.05	507	32 Dated the major shearing deformation around UHP peak metamorphism of UH unit	-
	e (117)	blueschist	Akeyazi-kebuerte	42.4839	81.2003	Phengite in situ Ar-Ar	334	7.8	avPT	Directly in situ probing on kinematic structure	2.08	0.11	514	14 Dated the major shearing deformation around HP BS/EC facies peak metamorphism of EB unit	-
	f (32)	blueschist	Akeyazi-kebuerte	42.4739	81.1989	Phengite in situ Ar-Ar	330	7.7	avPT	Directly in situ probing on kinematic structure	1.99	0.15	519	12 Dated the major shearing deformation around UHP peak metamorphism of UH unit	-
	g (157)	chl-ph-qz-ab schist	Akeyazi-kebuerte	42.4690	81.2076	Phengite in situ Ar-Ar	276	5.2	REaL.	Directly in situ probing on kinematic structure	0.50	0.40	400	100	Echoed the SCTSZ strike-slip deformation	-
	h (157)	chl-ph-qz-ab schist	Akeyazi-kebuerte	42.4690	81.2076	Phengite Ar-Ar step-heating	326	2.6	REaL.	RTP.	0.50	0.40	400	100	Troubled by excess Ar or dated early stage ph growth	-
	I (158)	grt-gln-ep meta-basite	Akeyazi-kebuerte	42.4589	81.2246	Zircon U-Pb	359	3.6	avPT	tie zircon to garnet grwth via REEs pattern	1.46	0.16	484	29	Constrainted the major garnet growth event around lower BS facies peak metamorphism of MU unit	-
	j (158)	grt-gln-ep meta-basite	Akeyazi-kebuerte	42.4589	81.2246	Zircon U-Pb	449	4.7	avPT	SRtPTh.	0.50	0.40	400	100	Protolith age	-
	k (147)	retrograde blueschist	Akeyazi-kebuerte	42.4477	81.1899	Phengite Ar-Ar step-heating	304	2	avPT	SRtPTh.	0.92	0.08	473	21	Constrainted the later stage GS-facies deformation during doming and/or final juxtaposition	-
	l (148-1)	meta-graywack	Akeyazi-kebuerte	42.4447	81.1908	Phengite in situ Ar-Ar	313	0.9	avPT	Directly in situ probing on kinematic structure	0.81	0.10	516	15 Dated the major shearing deformation around GS-facies peak metamorphism of GT unit	-
	m (148-2)	meta-graywack	Akeyazi-kebuerte	42.4447	81.1908	Phengite in situ Ar-Ar	313	1.1	avPT	Directly in situ probing on kinematic structure	0.81	0.10	516	15 Dated the major shearing deformation around GS-facies peak metamorphism of GT unit	-
	n (71)	meta-graywack	Akeyazi-kebuerte	42.4358	81.1878	Phengite in situ Ar-Ar	284	1.5	REaL.	Directly in situ probing on kinematic structure	0.50	0.40	400	100	Echoed the SCTSZ strike-slip deformation	-
	1	blueschist	Akeyazi-kebuerte	42.4515	81.1983	White-mica Ar-Ar	364	1	REaL.	RTL.	1.40	0.60	325	175	GS facies overprint	Gao et al., Chinese Science Bulletin (in CN), 2000
	2	blueschist	Akeyazi-kebuerte	42.4654	81.1981	Gln Ar-Ar	370	1	REaL.	RTL.	1.40	0.60	325	175	BS facies overprint	Gao et al., Chinese Science Bulletin (in CN), 2000
	3	eclogite	Akeyazi-kebuerte	42.4808	81.2003	Grt-gln Sm-Nd	346	3	CTB.	SRtPTh.	1.90	0.10	525	25	(HP/UHP?) EC facies metamorphism	Gao et al., Lithos, 2003
	4	UHP mica shcist	Akeyazi-kebuerte	42.5200	81.1916	Zircon U-Pb	320.4	3.7	Ps grt isopleth	SRtPTh.	2.70	0.20	560	15	UHP EC facies metamorphism	Yang et al., JAES, 2013
	5	blueschist (used to be EC)	Akeyazi-kebuerte	42.5181	81.1950	Grt-gln-WR Sm-Nd	318.4	3.9	Ps grt isopleth	SRtPTh.	2.55	0.05	463	38	HP EC facies metamorphism	Soldner et al., GR, 2016
	6	eclogite	Akeyazi-kebuerte	42.5367	81.2092	White-mica Ar-Ar	316.9	1	Ps grt isopleth	tie phengite to garnet growth via thermodynamic modelling	2.20	0.20	505	25	HP EC facies prograde metamorphism	Tan et al., IGR, 2018
	7	eclogite	Akeyazi-atantayi	42.5325	81.2103	Zircon U-Pb	318	2.3	Ps grt isopleth + CTB. tie zircon to garnet grwth via REEs pattern	2.95	0.20	510	15	UHP EC facies metamorphism	Tan et al., Lithos, 2017
	7	eclogite	Akeyazi-atantayi	42.5325	81.2103	Zircon U-Pb	316.8	0.83	Ps grt isopleth + CTB. tie zircon to garnet grwth via REEs pattern	2.40	0.30	550	30	HP EC facies metamorphism	Tan et al., Lithos, 2017
	7	eclogite	Akeyazi-atantayi	42.5325	81.2103	Zircon U-Pb	303.1	1.7	Ps grt isopleth + CTB.	SRtPTh.	0.90	0.30	400	110	GS/BS facies overprinting & deformation	Tan et al., Lithos, 2017
	7	eclogite	Akeyazi-atantayi	42.5325	81.2103	Zircon U-Pb	280.8	4.9	Ps grt isopleth + CTB.	SRtPTh.	0.50	0.40	400	100	Near surface	Tan et al., Lithos, 2017
	7	eclogite	Akeyazi-atantayi	42.5325	81.2103	Grt-gln-WR Sm-Nd	312.1	2.4	Ps grt isopleth + CTB.	tie to deformation via observation	1.90	0.13	530	25	EC facies deformation	Tan et al., Lithos, 2017
	8	eclogite	Akeyazi-atantayi	42.5139	81.2475	Zircon U-Pb	318	2	REaL.	RTL.	2.20	1.00	600	200	(HP/UHP?) EC facies metamorphism	Liu et al.,Lithos, 2014
	9	eclogite	Akeyazi-atantayi	42.5125	81.2477	Zircon U-Pb	319.8	3.1	REaL.	RTL.	2.20	1.00	600	200	(HP/UHP?) EC facies metamorphism	Su et al., EJM, 2010
	10	eclogite	Akeyazi-atantayi	42.4955	81.2766	Zircon U-Pb	234	6	REaL.	RTL.	2.20	1.00	600	200	(HP/UHP?) EC facies metamorphism	Zhang et al.,Lithos, 2007
	11	blueschist	Akeyazi-atantayi	42.4949	81.2608	White-mica Ar-Ar	311.6	0.5	REaL.	RTL.	1.40	0.60	325	175	cooling or recrystallization	Klemd et al., AMG, 2005
	11	blueschist	Akeyazi-atantayi	42.4949	81.2608	White-mica Ar-Ar	311.6	0.4	REaL.	RTL.	1.40	0.60	325	175	cooling or recrystallization	Klemd et al., AMG, 2005
	11	blueschist	Akeyazi-atantayi	42.4949	81.2608	White-mica Ar-Ar	327.8	0.5	REaL.	RTL.	1.40	0.60	325	175	cooling or recrystallization	Klemd et al., AMG, 2005
	11	blueschist	Akeyazi-atantayi	42.4949	81.2608	White-mica Ar-Ar	321	0.5	REaL.	RTL.	1.40	0.60	325	175	cooling or recrystallization	Klemd et al., AMG, 2005
	11	blueschist	Akeyazi-atantayi	42.4949	81.2608	White-mica Ar-Ar	322.9	0.8	REaL.	RTL.	1.40	0.60	325	175	cooling or recrystallization	Klemd et al., AMG, 2005
	11	blueschist	Akeyazi-atantayi	42.4949	81.2608	White-mica Rb-Sr	313	3.8	REaL.	RTL.	1.40	0.60	325	175	cooling or recrystallization	Klemd et al., AMG, 2005
	11	blueschist	Akeyazi-atantayi	42.4949	81.2608	White-mica Rb-Sr	301.6	3.4	REaL.	RTL.	1.40	0.60	325	175	cooling or recrystallization	Klemd et al., AMG, 2005
	11	blueschist	Akeyazi-atantayi	42.4949	81.2608	White-mica Rb-Sr	309.4	2.3	REaL.	RTL.	1.40	0.60	325	175	cooling or recrystallization	Klemd et al., AMG, 2005
	11	blueschist	Akeyazi-atantayi	42.4949	81.2608	White-mica Rb-Sr	309	3	REaL.	RTL.	1.40	0.60	325	175	cooling or recrystallization	Klemd et al., AMG, 2005
	11	blueschist	Akeyazi-atantayi	42.4949	81.2608	White-mica Rb-Sr	310.7	3.2	REaL.	RTL.	1.40	0.60	325	175	cooling or recrystallization	Klemd et al., AMG, 2005
	11	blueschist	Akeyazi-atantayi	42.4949	81.2608	White-mica Rb-Sr	310.1	3.1	REaL.	RTL.	1.40	0.60	325	175	cooling or recrystallization	Klemd et al., AMG, 2005
	12	blueschist	Akeyazi-atantayi	42.4902	81.2694	Gln Ar-Ar	345.4	0.7	REaL.	RTL.	1.40	0.60	325	175	(HP/UHP?) EC facies metamorphism	Gao et al., Acta Petrologica Sinica (in CN), 2006
	12	grt-gln mica schist	Akeyazi-atantayi	42.4902	81.2694	White-mica Ar-Ar	334.7	0.9	REaL.	RTL.	1.40	0.60	325	175	cooling or recrystallization	Gao et al., Acta Petrologica Sinica (in CN), 2006
	12	grt-gln mica schist	Akeyazi-atantayi	42.4902	81.2694	White-mica Ar-Ar	317.1	0.2	REaL.	RTL.	1.40	0.60	325	175	cooling or recrystallization	Gao et al., Acta Petrologica Sinica (in CN), 2006
	12	blueschist	Akeyazi-atantayi	42.4902	81.2694	White-mica Ar-Ar	310.3	0.3	REaL.	RTL.	1.40	0.60	325	175	cooling or recrystallization	Gao et al., Acta Petrologica Sinica (in CN), 2006
	13	eclogite	Akeyazi-atantayi	42.4885	81.2806	Crs Ar-Ar	344	1	CTB.	SRtPTh.	1.9	0.1	525	25	cooling or recrystallization	Gao et al., Lithos, 2003
	13	eclogite	Akeyazi-atantayi	42.4885	81.2806	White-mica Ar-Ar	331	2	CTB.	SRtPTh.	1.9	0.1	525	25	GS facies overprint	Gao et al., Lithos, 2003
	14	eclogite	Akeyazi-atantayi	42.4848	81.2697	Gln Ar-Ar	401	1	REaL.	RTL.	2.20	1.00	600	200	(HP/UHP?) EC facies metamorphism	Gao et al., Chinese Science Bulletin (in CN), 2000
	14	eclogite	Akeyazi-atantayi	42.4848	81.2697	White-mica Ar-Ar	381	1	REaL.	RTL.	2.20	1.00	600	200	(HP/UHP?) EC facies metamorphism	Gao et al., Chinese Science Bulletin (in CN), 2000
	15	eclogite	Akeyazi-akesayi	42.5439	81.3044	Rutile U-Pb	318	7	REaL.	RTL.	2.20	1.00	600	200	(HP/UHP?) EC facies metamorphism	Li et al., Lithos, 2011
	16	eclogite	Akeyazi-akesayi	42.5248	81.2908	Zircon U-Pb	320.4	0.84	Ps grt isopleth + ZiR.	SRtPTh.	2.85	0.15	550	20	UHP EC facies metamorphism	Zhang et al., JMG, 2018
	16	eclogite	Akeyazi-akesayi	42.5248	81.2908	Zircon U-Pb	306	6.2	ZiT.	SRtPTh.	1.23	0.23	560	60	GS/BS facies overprinting	Zhang et al., JMG, 2018
	16	eclogite	Akeyazi-akesayi	42.5248	81.2908	Titanite U-Pb	305.5	6.4	ZiT.	SRtPTh.	1.23	0.23	560	60	GS/BS facies overprinting	Zhang et al., JMG, 2018
	17	mafic rock	Akeyazi-akesayi	42.5166	81.3138	Micro-scale mutli-points grt sampling Lu-Hf	313	12	CTB.	SRtPTh.	2.10	0.20	570	30	(HP/UHP?) EC facies metamorphism	Klemd et al., EPSL, 2011
	17	mafic schist	Akeyazi-akesayi	42.5166	81.3138	Micro-scale mutli-points grt sampling Lu-Hf	313.9	4.8	CTB.	SRtPTh.	1.80	0.20	540	40	(HP/UHP?) EC facies metamorphism	Klemd et al., EPSL, 2011
	18	eclogite	Akeyazi-akesayi	42.5030	81.2938	Zircon U-Pb	226.3	4.6	REaL.	RTL.	2.20	1.00	600	200	(HP/UHP?) EC facies metamorphism	Zhang et al.,Lithos, 2007
	19	eclogite	Akeyazi-akesayi	42.5012	81.3206	Zircon U-Pb	310	6	REaL.	RTL.	2.20	1.00	600	200	Formation of ocean crust	Zhang et al.,Lithos, 2007
	20	metapelite	Akeyazi-habutengsu	42.5353	81.3245	White-mica Ar-Ar	315.3	1.6	Ps grt isopleth	SRtPTh.	3.00	0.18	530	15	recrystallization age of UHP phengite	Lv and Zhang., 2016
	21	eclogite	Akeyazi-habutengsu	42.5159	81.3371	Grt-omp-WR Sm-Nd	306	15	Ps grt isopleth	SRtPTh.	2.30	0.20	560	15	HP EC facies metamorphism	Du et al., Lithos, 2014
	22	UHP metapelite	Akeyazi-habutengsu	42.5113	81.3482	White-mica Ar-Ar	315.3	1.7	Ps grt isopleth	SRtPTh.	2.45	0.20	535	35	recrystallization age of HP phengite	Lv and Zhang., 2016
	23	eclogite	Akeyazi-habutengsu	42.4973	81.3461	Grt-omp-WR Sm-Nd	305	11	Ps grt isopleth	SRtPTh.	2.40	0.20	550	20	HP EC facies metamorphism	Du et al., Lithos, 2014
	24	eclogite	Akeyazi-habutengsu	42.4819	81.3544	Grt-omp-WR Sm-Nd	309.8	4.6	Ps grt isopleth	SRtPTh.	2.50	0.20	550	20	HP EC facies metamorphism	Du et al., Lithos, 2014
	25	mafic schist	Akesayi-muzisayi	42.5373	81.4523	Micro-scale mutli-points grt sampling Lu-Hf	315.2	1.6	CTB.	SRtPTh.	1.70	0.20	380	50	(HP/UHP?) EC facies metamorphism	Klemd et al., EPSL, 2011
	26	epidote mica schist	Kekesu	42.7135	81.9249	White-mica Ar-Ar	293.3	1.5	REaL.	RTL.	0.50	0.40	400	100	GS facies overprint	Xia et al., IGR, 2015
	27	retrograde mica-quart schist	Kekesu	42.7016	81.9323	White-mica Ar-Ar	323	1	REaL.	RTL.	1.40	0.60	325	175	cooling or recrystallization	Wang et a., JG, 2010
	28	retrograde blueschist	Kekesu	42.6696	81.9430	White-mica Ar-Ar	316	2	REaL.	RTL.	1.40	0.60	325	175	cooling or recrystallization	Wang et a., JG, 2010
	29	retrograde blueschist	Kekesu	42.6692	81.9455	White-mica Ar-Ar	331	1	REaL.	RTL.	1.40	0.60	325	175	cooling or recrystallization	Wang et a., JG, 2010
	30	grt-gln mica schist	Kekesu	42.6661	81.9471	White-mica Ar-Ar	321.4	1.6	REaL.	RTL.	1.40	0.60	325	175	BS facies overprint	Xia et al., IGR, 2015
	31	grt-phn schist	Kekesu	42.6622	81.9523	White-mica Ar-Ar	318.6	1.6	REaL.	RTL.	1.40	0.60	325	175	BS facies overprint	Xia et al., IGR, 2015
	32	eclogite	Kekesu	42.6266	82.0048	White-mica Ar-Ar	345.4	6.5	REaL.	RTL.	1.40	0.60	325	175	Retrograde GS facies metamorphism	Gao et al., TP, 1995
	33	rodingite	Changawuzi	42.4738	80.9354	Zircon U-Pb	291	15	CTB.	SRtPTh.	0.50	0.40	400	100	rodingitization after exhumated to near-surface	Li et al., Lithos, 2010
	33	rodingite	Changawuzi	42.4738	80.9354	Zircon U-Pb	422	10	CTB.	SRtPTh.	0.50	0.40	400	100	seafloor metamorphism before subducted	Li et al., Lithos, 2010
	34	rodingite blackwall	Changawuzi	42.4728	80.9333	Perovskite U-Pb	308	5	Ps atg isopleth	SRtPTh.	2.50	1.50	500	50	GS/BS/HP/UHP?	Shen et al., CG, 2016

Acknowledgements Acknowledgements

This study was essentially funded by the National Natural Science Foundation of China (No. 41390440, 41390445, 41025008) to Prof. Jun Gao and the International Training Network ZIP (Marie Curie Actions, Zooming In-between Plates, REA grant agreement No. 604713) to Prof. Philippe Agard. We would like to thank the editor Prof.

Michael James Bickle and anonymous reviewers for their constructive comments that greatly helped in improving the article. We greatly benefitted from discussions with L.

Acknowledgements

This study was funded through projects of the National Natural Science Foundation of China to Prof. Gao Jun (No. 41390440, 41390445, 41025008) and by the International Training Network ZIP (Marie Curie Actions, Zooming In-between Plates, REA grant agreement No. 604713) to Prof. Philippe Agard. Additional supports were provided by programs of the Chinese Academy of Sciences of China (No. GJHZ1776, 2013047) to Prof. Wan Bo. We greatly benefitted from discussions with Labrousse L., Yang J-J., Chen Y., Li J-L., Locatelli M. and Bonnet G. We also thank Fialin M. and Rividi N. (CAMPARIS), Boudouma O. (ISTeP), Arnaud N. (Géosciences Montpellier) and Deldicque D. (ENS Paris, France) for analytical support, Delairis E. and Devaux D. (ISTeP) for the preparation of thin sections. We further thank the meticulous help of Prof. Klemd Reiner and Li J-L during field work.

The results of SIMS U-Pb age and δ 18 O composition of ,respectively, (d, number "1" with square in Figure 24b) zircon core domain with high HREEs content (corresponding to green contour in Figure 24a), (e, number "2" with square in Figure 25b) zircon core domain (corresponding to red contour in Figure 24a), (f, number "3" with square in Figure 25b) zircon mantle domain (corresponding to blue contour in Figure 24a) and (g, number "4" with square in Figure 25b) zircon rim domain (corresponding to yellow contour in Figure 24a) are listed in Table 7 and8. than most exhumed HP/UHP oceanic units [START_REF] Agard | Exhumation of oceanic blueschists and eclogites in subduction zones: timing and mechanisms[END_REF][START_REF] Plunder | Accretion, underplating and exhumation along a subduction interface: From subduction initiation to continental subduction (Tavşanlı zone, W. Turkey)[END_REF] Figure 37c). Several possible explanations can be envisioned for such a thermal transient during deep cold oceanic subduction (~5°C/km, peak T <500-600°C, [START_REF] Bayet | Massive sediment accretion at ~80 km depth along the subduction interface: Evidence from the southern Chinese Tianshan[END_REF][START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF]: (i) heat advection from pervasive fluid flow [START_REF] Ague | Brief thermal pulses during mountain building recorded by Sr diffusion in apatite and multicomponent diffusion in garnet[END_REF][START_REF] Baxter | Prograde temperature-time evolution in the Barrovian type-locality constrained by Sm/Nd garnet ages from Glen Clova, Scotland[END_REF] but magmas are relatively rare during the fate of SW-Tianshan ocean from ca. 320 to 300 Myrs; Gao et al., 2009;[START_REF] Gao | South Tianshan: Late Paleozoic or Triassic collision orogenic belt?[END_REF][START_REF] Long | Geochemical and geochronological studies of granitoid rocks from the Western Tianshan Orogen: Implications for continental growth in the southwestern Central Asian Orogenic Belt[END_REF] and/or radioactive decay could in principle modify thermal patterns along the subduction interface but are likely <30°C [START_REF] Penniston-Dorland | The global range of subduction zone thermal structures from exhumed blueschists and eclogites: Rocks are hotter than models[END_REF][START_REF] Royden | The steady state thermal structure of eroding orogenic belts and accretionary prisms[END_REF]; (ii) metamorphic hydration reactions may supply additional energy [START_REF] Lyubetskaya | Effect of metamorphic reactions on thermal evolution in collisional orogens[END_REF][START_REF] Penniston-Dorland | The global range of subduction zone thermal structures from exhumed blueschists and eclogites: Rocks are hotter than models[END_REF], but dehydration reactions (of lawsonite and chlorite) are instead predicted across the temperature range (i.e., 490 to 570°C); (iii) shear heating, which is proportional to velocity times rock strength, could in principle modify the thermal budget along the subduction thrust by up to ~200°C [START_REF] Mako | Magnitudes of Shear Heating in Metamorphic Systems With Temperature Dependent Rheology[END_REF]; see discussion in [START_REF] Penniston-Dorland | The global range of subduction zone thermal structures from exhumed blueschists and eclogites: Rocks are hotter than models[END_REF] but will be small in fluid-rich environments. Furthermore, no mylonites/ultramylonites advocating for high strain are observed (but only fine-grained omphacite at the margin of the studied UHP eclogitic slices. [START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF] and lattice prefered orientations of omphacite in strained eclogites from exposures ~1 km away (Soldner et al., 2016) advocate for maximum strain around peak to early exhumation, hence rather after peak garnet growth. The duration of shear heating would also probably exceed that of the modeled thermal pulse (i.e., ~300 Kyrs across 5 Myrs).

Supplementary Figures and Tables:

Convective motion of subducted material along the plate interface has been proposed based on thermomechanical numerical modeling (e.g., [START_REF] Gerya | Exhumation of high-pressure metamorphic rocks in a subduction channel: A numerical simulation[END_REF] and 45a) hosted in garnet A1 (e) and in matrix (f). These images indicate that measured rutile grains are mainly host by Zr-free phases (i.e., garnet and omphacite, Table 12), and that no Zr-rich phase can be found rimming rutile (e.g., no zircon, which would be very bright in the BSE image). is likely in sample 117; Fig. S4), or both. Similar age patterns with deformationcontrolled phengite recrystallization can be observed for the rest of the metavolcanoclastics dated by in situ 40 Ar-39 Ar (Figure 60b, 66), except sample 157 whose rare phengite grains along a weak schistosity yield ages ~270-281 Ma.

Supplementary figures and tables

Weighted plateau ages of phengite in samples J2, 22, 157 and 147, from regional GS facies units (GS1, GS2 and GT, Figure 52a,d 66), which is a bit puzzling but may reflect local recrystallization and/or fluid circulation [START_REF] De | Excess argon incorporation in phengite of the Mulhacen Complex: submicroscopic illitization and fluid ingress during late Miocene extension in the Betic[END_REF][START_REF] Vincenzo | 40Ar-39Ar laser dating of ductile shear zones from central Corsica (France): Evidence of Alpine (middle to late Eocene) syn-burial shearing in Variscan granitoids[END_REF].

Zircon grains of the metamafic sample 158 from the MU unit present core-rim texture in CL image (Figure 67) with apparent 206 Pb/ 238 U ages varying from 351 to 2075 Ma (Th/U ~0.09-0.99, Table 21). Dark/grey oscillatory zircon cores (Figure 67)

were characterized by typically Ce positive and Pr & Eu negative anomalies, steep positive slope from LREEs to HREEs ((Lu/La)N ~1984-248266), significant enrichment in HREEs ((Lu/Sm)N ~50.9-147.4) and inclined HREEs pattern ((Lu/Tb)N bearing oceanic eclogite in the same sub-unit [START_REF] Tan | P-T-time-isotopic evolution of coesite-bearing eclogites: Implications for exhumation processes in SW Tianshan[END_REF]. The same approach yields ~0.8-1.3 mm/yr for the EB unit, showing that both units have exhumation velocities comparable to most oceanic blueschists and eclogites (i.e., ~1-5 mm/yr; [START_REF] Agard | Exhumation of oceanic blueschists and eclogites in subduction zones: timing and mechanisms[END_REF]. regional magmatic indications (Figure 70): i) the histogram of the crystallization ages of regional igneous rocks from tectonic plates to the north (i.e., PKC: the Paleo Kazakhstan Continent) and south (i.e., STB + Tarim Craton) of the Paleo South Tianshan ocean show a broadly consistent peak around ~280-300 Ma; ii) Detrital zircon U-Pb ages of (meta-) sediments from both the north/south plates and the accretionary complex (including the AMC and Atbashi metamorphic complex at the western part of SCTSZ, and the Wuwamen complex at the eastern part of SCTSZ, Figure 50b)

uniformly show either youngest detrital zircon ages of ~300 Ma or peaks around ~280-300 Ma; iii) ~285 Ma leucogranites cut across the STMB (Gao et al., 2011b). Overall, available magmatic and/or metamorphic constraints (e.g., this study) tend to show that the subduction of the Paleo South Tianshan ocean basin and relevant deposition were probably still active during the Late Carboniferous (Figure 62a). Final emplacement of the AMC complex could take place around early Permian-late carboniferous (i.e., ~280-300 Ma, Figure 62e), prior to the collision of the Paleo Kazakhstan Continent and the Tarim Craton (+STB, Figure 62a).

Conclusions

The main results of our study of the Akesayi metamorphic complex, in the Chinese Southwestern Tianshan metamorphic belt (i.e., a portion of the South Central Tianshan Suture Zone, which also comprises the Atbashi, Chatkal and Fan-Karategin (U)HP metamorphic complexes), can be summarized as follows:

 What was previously proposed as a HP/UHP "melange" should be subdivided into several coherent, kilometre-scale, essentially metavolcanoclastic tectonic units bearing contrasting P-T-time-D histories (and to some extent lithologies).

 The present-day geometry of the AMC is that of a metamorphic dome preserving evidence for internal nappe stacking.

 Pervasive deformation following eclogite and/or blueschist-eclogite peak burial is marked by pervasive BS facies, exhumation-related shear senses with a top to the north component.

 At least four of the six sub-units identified here, namely the UH (480-560°C and 2.75 Ma).



The tectono-metamorphic evolution records a progressive change of metamorphic gradients from ~12°C/km to ~5-7 °C/km, which could reflect a cooling of the subduction system with time.

 Juxtaposition and exhumation of the UH, EB, MU and GT units to mid-crustal depth (~20 km) was accomplished around 290-300 Ma, at rates on the order of 1-3 mm/yr.

 The existence of ~300 Ma glaucophane-bearing BS/GS facies metavolcanoclastic units (i.e., the GT and part of GS1 units) suggests that the subduction of the Paleo South Tianshan ocean basin was probably still active during late Carboniferous.

 Final juxtaposition of the diverse sub-units making the metamorphic dome could have occurred at around ~280-290 Ma, and been broadly coeval with dextral strike-slip movements along the STCSZ. 18).

Supplementary figures and tables

Structure and Deformation Pattern

Structure and deformation pattern investigations have been performed both on moderately schistosed coesite-bearing oceanic eclogite slices ( §4) and regional scale P-T-time-deformation mapping along the Kebuerte transect ( §6), crossing through peak metamorphic conditions at 315 ± 5 Ma).

The other HP-LT sub-units reached peak conditions diachronously (EB: ~330 Ma;

MU: ~360 Ma), reflecting a change in metamorphic gradient and possibly of the subduction thermal regime with time (Figure 59b). Overall, exhumation velocities estimate yields ~1.8-3.5 mm/yr for the UH unit, whether by U/Pb or Ar/Ar dating, and ~0.8-1.3 mm/yr for the EB unit, showing that both units have exhumation velocities comparable to most oceanic blueschists and eclogites [START_REF] Agard | Exhumation of oceanic blueschists and eclogites in subduction zones: timing and mechanisms[END_REF]. Rocks from the GS facies sub-units (GS1, GS2 and GT, Figure 60a) yield ages around ~275-318 v) Final juxtaposition of the diverse sub-units making the metamorphic dome could have occurred at around ~280-290 Ma, and been broadly coeval with dextral strike-slip movements along the STCSZ.