A Verlaguet
email: anne.verlaguet@sorbonne-universite.fr

D Bonnemains

C Mével

J Escartín

M Andreani

F Bourdelle

M-C Boiron

V Chavagnac

Fluid circulation along an oceanic detachment fault: insights from fluid inclusions in silicified brecciated fault rocks (Mid-Atlantic Ridge at 13°20'N)

Keywords: MAR 13°20'N, silicified detachment, fluid inclusions, mafic breccias, phase separation, hangingwall overplating

Keypoints

• MAR 13°20'N corrugated detachment fault is composed of pervasively silicified mafic breccias overplated from hangingwall diabases • Quartz fluid inclusions record mixing of hangingwall silica-rich brines with footwall serpentinite-derived fluids (H2+CH4) in detachment • This heterogeneous fluid circulation in shallow detachment fault is inconsistent with models of detachments channeling deep fluid flow

Plain language summary

Here we present constraints on fluid circulation along the 13°20′N oceanic detachment fault along the Mid-Atlantic Ridge. Rocks recovered in situ with a deep-sea robot yield mafic breccias, instead of serpentinized mantle rocks commonly found at other detachments. They likely originate from the base of the hangingwall dyke complex, brecciated during fault exhumation. These rocks are intensely silicified (quartz mineralization), resulting from upflow circulation of silica-rich fluids derived from reactions with mafic rocks in a reaction zone. Fluid inclusion (micrometric cavities in quartz crystals that trapped circulating fluid) analyses reveal highly-saline fluids likely formed by phase separation, while traces of hydrogen and methane likely record serpentinization.

We thus propose that seawater infiltrated the crust down to a reaction zone at its base (2 km depth), where it became silica-rich by rock hydrothermal alteration. Upon brecciation, these silica-rich brines were released in the detachment where they mixed with fluids coming from footwall rock alteration. Temperature and pressure drops during fluid upflow promoted intense quartz crystallization. The active Irinovskoe hydrothermal site, sitting on the detachment fault ~5 km offaxis, is unrelated to fluid circulation in the detachment plane, and likely linked to a heat source within the footwall and directly below it.

Introduction

Low-angle detachment faults are common along slow-and ultra-slow spreading ridges, forming primarily at ridge sections with reduced melt supply [START_REF] Buck | Modes of faulting at mid-ocean ridges[END_REF][START_REF] Cannat | Modes of seafloor generation at a melt-poor ultraslow-spreading ridge[END_REF][START_REF] Escartín | Central role of detachment faults in accretion of slow-spreading oceanic lithosphere[END_REF][START_REF] Tucholke | Role of melt supply in oceanic detachment faulting and formation of megamullions[END_REF]. Rooting deep below the rift valley floor, detachments can operate over long periods of time (up to a few Myrs), exhume deep-seated materials from the oceanic lithosphere, and lead to the formation of oceanic core complexes (OCCs). OCCs are often capped by a fault surface displaying corrugations parallel to spreading. Ridge sections hosting OCCs tend to be associated with high seismicity rates relative to magma-rich, symmetrical ridge sections, and often display active hydrothermal venting [START_REF] Escartín | Central role of detachment faults in accretion of slow-spreading oceanic lithosphere[END_REF][START_REF] Son | Tectonic and magmatic control of hydrothermal activity along the slow-spreading Central Indian Ridge, 8°S-17°S[END_REF].

The microseismicity along the Northern Atlantic and the Southwest Indian Ridge detachments [START_REF] Demartin | Kinematics and geometry of active detachment faulting beneath the Trans-Atlantic Geotraverse (TAG) hydrothermal field on the Mid-Atlantic Ridge[END_REF][START_REF] Parnell-Turner | Causes and Consequences of Diachronous V-Shaped Ridges in the North Atlantic Ocean[END_REF][START_REF] Tao | Deep high-temperature hydrothermal circulation in a detachment faulting system on the ultra-slow spreading ridge[END_REF] reaches sub-Moho depths (between ~8 and ~13 km bsf). These results suggest that detachments are associated to a thick lithosphere, and that brittle deformation may provide potential pathways for fluid circulation reaching deep levels. Indeed, fault zone rocks from various OCCs along the MAR display evidence for fluid-rock interactions coeval with deformation. In most cases, the fault zone is characterized by deformed ultramafics and gabbros recrystallized into talcschists and amphibolites, respectively [START_REF] Boschi | Mass transfer and fluid flow during detachment faulting and development of an oceanic core complex, Atlantic Massif (MAR 30°N)[END_REF][START_REF] Escartín | Constraints on deformation conditions and the origin of oceanic detachments: The Mid-Atlantic Ridge core complex at 15°45[END_REF][START_REF] Escartín | Tectonic structure, evolution, and the nature of oceanic core complexes and their detachment fault zones (13°20′N and 13°30′N[END_REF][START_REF] Karson | Detachment shear zone of the Atlantis Massif core complex[END_REF][START_REF] Macleod | Direct geological evidence for oceanic detachment fauling: The Mid-Atlantic Ridge, 15°45[END_REF][START_REF] Mccaig | Oceanic deachment faults focus very large volumes of black smoker fluids[END_REF][START_REF] Schroeder | Strain localization on an oceanic detachment fault system[END_REF]. Moreover, active hydrothermal fields are often found on the OCC surface, with hydrothermal circulation crosscutting pre-existing and/or inactive fault zones, as observed at Rainbow [START_REF] Andreani | Tectonic structure, lithology, and hydrothermal signature of the Rainbow massif (Mid-Atlantic Ridge 36°14′N)[END_REF], Ashadze [START_REF] Ondréas | Geological context and vents morphology of the ultramafic-hosted Ashadze hydrothermal areas (Mid-Atlantic Ridge 13°N)[END_REF], Logatchev [START_REF] Petersen | The geological setting of the ultramafic-hosted Logatchev hydrothermal field (14°45'N, Mid-Atlantic Ridge) and its influence on massive sulfide formation[END_REF], Lost City (Fruh-Green et al., 2003) or Von Damm (Hogkinson et al., 2015).

To date, however, there is still limited information regarding fluid sources and pathways along the detachment fault zone at depth, the location and nature of heat sources animating this hydrothermal circulation, and the possible links between the hydrothermal activity observed at the surface of these OCCs and the flow along the detachment.

The 13°20'N detachment fault, located on the western flank of the Mid-Atlantic Ridge (MAR), exposes a structurally continuous and corrugated detachment fault surface (e.g, [START_REF] Escartín | Tectonic structure, evolution, and the nature of oceanic core complexes and their detachment fault zones (13°20′N and 13°30′N[END_REF][START_REF] Macleod | Life cycle of oceanic core complexes[END_REF][START_REF] Smith | Widespread active detachment faulting and core complex formation near 13° N on the Mid-Atlantic Ridge[END_REF]. While morphology is similar to OCCs elsewhere [START_REF] Parnell-Turner | Genesis of corrugated fault surfaces by strain localization recorded at oceanic detachments[END_REF], sampling of the detachment fault zone reveals unique characteristics. Indeed, while other detachment faults are composed of deformed and hydrated footwall ultramafics and gabbros [START_REF] Boschi | Mass transfer and fluid flow during detachment faulting and development of an oceanic core complex, Atlantic Massif (MAR 30°N)[END_REF][START_REF] Escartín | Constraints on deformation conditions and the origin of oceanic detachments: The Mid-Atlantic Ridge core complex at 15°45[END_REF]Escartín et al., , 2016;;[START_REF] Karson | Detachment shear zone of the Atlantis Massif core complex[END_REF][START_REF] Macleod | Direct geological evidence for oceanic detachment fauling: The Mid-Atlantic Ridge, 15°45[END_REF][START_REF] Mccaig | Oceanic deachment faults focus very large volumes of black smoker fluids[END_REF][START_REF] Schroeder | Strain localization on an oceanic detachment fault system[END_REF], the well-preserved and corrugated 13°20'N detachment fault zone is composed essentially of highly silicified mafic cataclastic breccias [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF][START_REF] Escartín | Tectonic structure, evolution, and the nature of oceanic core complexes and their detachment fault zones (13°20′N and 13°30′N[END_REF]. These silicified fault breccias likely result from the overplating of mafic material from the base of the hangingwall dyke complex into the footwall during fault exhumation [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF]; these rock types have not been reported from any other studied OCC. The silicified fault zone is ~70 m or thicker, and the mechanisms of strain localization and fault development leading to a corrugated structure seem to operate independently of lithologies within the fault zone (e.g., [START_REF] Parnell-Turner | Genesis of corrugated fault surfaces by strain localization recorded at oceanic detachments[END_REF]. Fault zone silicification is evidenced by massive quartz precipitation that may result from elevated fluxes of silica-rich fluids, possibly syntectonic [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF]. This detachment fault surface also hosts the active Irinovskoe hydrothermal site, where several black smokers discharge high temperature fluids [START_REF] Escartín | Tectonic structure, evolution, and the nature of oceanic core complexes and their detachment fault zones (13°20′N and 13°30′N[END_REF][START_REF] Macleod | Life cycle of oceanic core complexes[END_REF].

The 13°20'N silicified fault rocks, and the fluid inclusions trapped in quartz crystals, provide a unique opportunity to investigate the nature, sources and pathways of fluids circulating within an active detachment fault zone, and to compare them to fluid circulation feeding the active footwall Irinovskoe hydrothermal site. Indeed, to date geochemical and fluid inclusion studies have been conducted on hydrothermally altered rocks from both hangingwall (e.g., [START_REF] Delaney | Quartz-cemented breccias from the Mid-Atlantic Ridge: Samples of a high-salinity hydrothermal upflow zone[END_REF][START_REF] Humphris | Geochemical changes during hydrothermal alteration of basement in the stockwork beneath the active TAG hydrothermal mound[END_REF][START_REF] Mccaig | Oceanic deachment faults focus very large volumes of black smoker fluids[END_REF][START_REF] Mccaig | Detachment fault control on hydrothermal circulation systems: Interpreting the subsurface beneath the TAG hydrothermal field using the isotopic and geological evolution of oceanic core complexes in the Atlantic[END_REF][START_REF] Tivey | Temperature and salinity of fluid inclusions in anhydrite as indicators of seawater entrainment and heating in the TAG active mound[END_REF][START_REF] Vanko | Fluid inclusion evidence for subsurface phase separation and variable fluid mixing regimes beneath the deepsea PACMANUS hydrothermal field, Manus Basin back arc rift, Papua New Guinea[END_REF] and footwall of detachments (e.g., [START_REF] Andreani | Tectonic structure, lithology, and hydrothermal signature of the Rainbow massif (Mid-Atlantic Ridge 36°14′N)[END_REF][START_REF] Boschi | Mass transfer and fluid flow during detachment faulting and development of an oceanic core complex, Atlantic Massif (MAR 30°N)[END_REF][START_REF] Castelain | Fluid evolution in an Oceanic Core Complex: A fluid inclusion study from IODP hole U1309 D-Atlantis Massif[END_REF].

However, in these either the link to detachment fault deformation is not established, or the associated hydrothermal systems post-date detachment activity, as in active and inactive systems preserved at the footwall of oceanic detachments (e.g., [START_REF] Andreani | Tectonic structure, lithology, and hydrothermal signature of the Rainbow massif (Mid-Atlantic Ridge 36°14′N)[END_REF][START_REF] Escartín | Tectonic structure, evolution, and the nature of oceanic core complexes and their detachment fault zones (13°20′N and 13°30′N[END_REF][START_REF] Hodgkinson | Talc-dominated seafloor deposits reveal a new class of hydrothermal system[END_REF][START_REF] Ondréas | Geological context and vents morphology of the ultramafic-hosted Ashadze hydrothermal areas (Mid-Atlantic Ridge 13°N)[END_REF]. Thus, studies addressing syntectonic fluid flow at detachments are scarce, and rely on geochemical data from rock samples, (e.g., [START_REF] Mccaig | Oceanic deachment faults focus very large volumes of black smoker fluids[END_REF][START_REF] Mccaig | Detachment fault control on hydrothermal circulation systems: Interpreting the subsurface beneath the TAG hydrothermal field using the isotopic and geological evolution of oceanic core complexes in the Atlantic[END_REF], not from fluids.

To constrain fluid-rock interactions within an active detachment fault zone, here we present a study of fluid inclusions trapped in quartz crystals from silicified fault rocks of the 13°20'N OCC.

A microthermometric study was conducted on >100 fluid inclusions from four representative fault rock samples collected in situ at different outcrops throughout the 13°20'N fault zone, and with varying degrees of silicification. Fluid inclusion composition was also investigated by Raman spectroscopy. Whole-rock geochemical analyses were performed to constrain nature and composition of the host rocks, and chlorite analyses to constrain the temperature of quartz-chlorite crystallization. With these results and available geological constraints, we propose a model of hydrothermal fluid circulation within an active oceanic detachment fault.

Geological background of 13°20'N OCC and sampling

Geological setting

The 13°20'N oceanic detachment displays a structurally continuous fault surface with prominent extension-parallel corrugations, exposed at the seafloor, and that roots at the rift valley floor. This OCC develops on the western flank of the MAR, which spreads at a full rate of 24.6 mm/yr [START_REF] Macleod | Life cycle of oceanic core complexes[END_REF][START_REF] Smith | Fault rotation and core complex formation: Significant processes in seafloor formation at slow-spreading mid-ocean ridges (Mid-Atlantic Ridge, 13 -15° N)[END_REF], and is likely active based on its morphology, the absence of late tectonic disruption [START_REF] Escartín | Tectonic structure, evolution, and the nature of oceanic core complexes and their detachment fault zones (13°20′N and 13°30′N[END_REF][START_REF] Macleod | Life cycle of oceanic core complexes[END_REF][START_REF] Mallows | A geophysical study of oceanic core complexes and surrounding terrain, Mid-Atlantic Ridge 13°N-14[END_REF], and seismic activity. Microseismicity defines a curved fault plane reaching >10 km below the ridge axis [START_REF] Parnell-Turner | Causes and Consequences of Diachronous V-Shaped Ridges in the North Atlantic Ocean[END_REF], reminiscent of that of other detachments such as TAG [START_REF] Demartin | Kinematics and geometry of active detachment faulting beneath the Trans-Atlantic Geotraverse (TAG) hydrothermal field on the Mid-Atlantic Ridge[END_REF] or Longqi [START_REF] Tao | Deep high-temperature hydrothermal circulation in a detachment faulting system on the ultra-slow spreading ridge[END_REF]. This OCC and its detachment fault were extensively investigated and sampled during the ODEMAR cruise, using deep-sea vehicles (http://www.doi.org/10.17600/13030070). Main cruise results, geological context, details of fault rocks are provided elsewhere [START_REF] Escartín | Tectonic structure, evolution, and the nature of oceanic core complexes and their detachment fault zones (13°20′N and 13°30′N[END_REF][START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF].

The exposed, corrugated detachment fault extends ~7 km in the spreading direction (East-West), and ~5.5 km perpendicular to the extension (North-South), respectively (Figure 1a; [START_REF] Olive | Controls on the seafloor exposure of detachment fault surfaces[END_REF]. The microbathymetric corrugations (Figure 1b) have a relief of up to ~10-20 m, and alongextension lengths of a few hundred meters to a maximum of 2 km [START_REF] Parnell-Turner | Genesis of corrugated fault surfaces by strain localization recorded at oceanic detachments[END_REF].

While the detachment fault surface is heavily blanketed by sediment and rubble, fault planes crop out on the flank of these corrugations, showing subhorizontal striations parallel to extension [START_REF] Escartín | Tectonic structure, evolution, and the nature of oceanic core complexes and their detachment fault zones (13°20′N and 13°30′N[END_REF]. During the ODEMAR cruise, in situ fault rocks were sampled at seven outcrops distributed both along-and across-extension throughout the corrugated detachment fault surface (see numbered circles in Figure 1b). Among these outcrops, Outcrop #1 (Figure 1b) was in a ~70 m deep structural low within the detachment fault surface, which shows corrugations throughout. From these observations it was inferred that the fault zone is composed of anastomosing fault planes developing over a thickness of ~70 m or more [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF][START_REF] Escartín | Tectonic structure, evolution, and the nature of oceanic core complexes and their detachment fault zones (13°20′N and 13°30′N[END_REF][START_REF] Parnell-Turner | Genesis of corrugated fault surfaces by strain localization recorded at oceanic detachments[END_REF].

The activity of the Irinovskoe hydrothermal field was confirmed during the ODEMAR cruise [START_REF] Escartín | Tectonic structure, evolution, and the nature of oceanic core complexes and their detachment fault zones (13°20′N and 13°30′N[END_REF], ~1.8 km from the footwall cutoff (black circle in Figure 1b), at a location where samples of sulfides indicated recent or active hydrothermalism [START_REF] Cherkashev | Massive sulfide ores of the northern equatorial Mid Atlantic Ridge[END_REF][START_REF] Macleod | Life cycle of oceanic core complexes[END_REF][START_REF] Pertsev | Recent massive sulfide deposits of the Semenov ore district, Mid-Atlantic Ridge, 13°31′ N: Associated rocks of the oceanic core complex and their hydrothermal alteration[END_REF]. This site displays two black smoker vents at the summit of hydrothermal mounds (Active Pot and Pinnacle Ridge) venting fluids at ~365°C, in addition to several inactive mounds and chimneys [START_REF] Escartín | Tectonic structure, evolution, and the nature of oceanic core complexes and their detachment fault zones (13°20′N and 13°30′N[END_REF].

Detachment fault rocks: lithology and silicification

A total of 36 fault rocks were recovered in situ from the seven outcrops throughout the 13°20'N corrugated detachment fault using ROV Victor 6000, and are described in detail by Bonnemains et al. (2017). All the rocks are cataclastic breccias, with significant heterogeneity in clast abundance and size, and clast/matrix ratios, even at sample-scale (Figure 2). Most breccias contain solely mafic clasts (basalt/diabase; Figure 2a-d), and only 2 of the 36 samples display a mixed lithology, with coexisting mafic and ultramafic clasts (see Figures 1b and2e-f). Several fault rock samples display highly localized deformation with striated slip plane surfaces (Figures 2c-e), as well as complex internal deformation textures, with cataclastic slip zones. Textures record, at the sample scale, several phases of both localized and distributed, penetrative deformation [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF].

Fault rocks are variably silicified indicating that (1) silica-rich fluids percolated through the fault rocks, and that (2) this silicification (and associated fluid flow) was likely heterogeneous at small spatial (outcrop) scale [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF]. Moderately silicified mafic samples are clastsupported breccias, and contain clasts of hydrothermally altered mafic rocks with still identifiable magmatic textures. Most clasts display a relatively coarse doleritic texture underlined by fresh plagioclase laths (Figure 3b; see [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF] for additional micrographs) indicating a diabase protolith. We have identified a single sample with a clast showing vesicular texture, corresponding to extrusive basalt (Figure 3a). Hence, the bulk of the fault material is incorporated from a dyke complex [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF], with limited reworking of shallow basalts, and consistent with an efficient exhumation [START_REF] Olive | Controls on the seafloor exposure of detachment fault surfaces[END_REF].

The least silicified diabase clasts show rare relict clinopyroxene, largely replaced by amphibole of hornblende composition, associated to fresh plagioclase of labradorite composition, and no associated chlorite (detailed mineral compositions in [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF]. This secondary mineral assemblage thus records hydrothermal recrystallization initiated under amphibolite facies conditions (≥ 500 °C). With increasing silicification, amphibole in clasts turns to actinolite, plagioclase becomes more albitic while chlorite crystallizes in clasts too, indicating greenschist facies conditions (~300°-500 °C). Clasts in these low to moderately silicified samples are surrounded by a matrix of finely crushed material, with newly formed chlorite and scattered quartz grains (<10 vol.% quartz). Highly silicified mafic samples are matrix-supported breccias with highly recrystallized clasts whose primary texture is largely obliterated. These breccia clasts are made up almost exclusively of chlorite and quartz, and are surrounded by a quartz-dominated (>90 vol.% quartz) matrix that also contains chlorite. Of the two samples bearing ultramafic clasts, only one has been silicificied. Abundant sulfides associated with quartz are found in three silicified fault rocks.

Cathodoluminescence imaging of selected samples also shows that quartz grains record successive fracturing and recrystallization episodes [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF], thus consistent with syntectonic quartz crystallization. Silicification and chloritization are closely associated during the alteration of the 13°20'N detachment fault mafic breccias. Indeed, chlorite is absent from the freshest diabase clasts [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF], chlorite content is low in moderately silicified samples and increases significantly with degree of silicification. Chlorite crystals imbricate quartz ones, or are included within quartz crystals, demonstrating co-crystallization in both clasts and matrix. Coeval quartz and chlorite crystallization is also unequivocal within late chlorite-filled veins crosscutting mafic samples. Thus, these microtextures record coeval formation of both minerals during detachment exhumation, and indicate that silicification occurred at greenschistfacies conditions [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF].

Samples selected for fluid inclusion and geochemical study

This study is based on a set of 6 representative detachment fault rocks that have been selected in order to (1) obtain a spatial coverage throughout the 13°20'N corrugated surface, and (2) cover various degrees of alteration and silicification (Table 1; Figure 1). These rocks were sampled in situ from five fault surface outcrops that are described in detail by [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF]Figure 1b). All silicified samples contain abundant albeit very small fluid inclusions in quartz crystals.

Fluid inclusions suitable for this study were identified in 4 samples: three variably silicified breccias with only mafic clasts (ODM195, ODM155 and ODM218), and one silicified breccia with mixed mafic-ultramafic clasts (ODM173). We benchmarked geochemical analyses with two additional unsilicified samples of mafic and mixed mafic-ultramafic material (ODM115 and ODM217, respectively). Sample texture and mineralogy are summarized in Table 1. These samples are heterogeneous, showing a complex history with several deformation phases (Bonnemains et al., 2017), thus subsamples were also taken in some cases at varying distances from slip surfaces, as indicated below. Furthermore, to obtain representative whole-rock chemical analyses, larger subsamples were taken for three samples (i.e., ODM218, ODM173 and ODM217), labeled wr (whole rock) in Tables 2 andS1.

ODM115 is a basaltic clast from an unsilicified breccia (Figure 2a). It displays a typical pillow lava microtexture, with skeletal olivine microphenocrysts, radiating dendritic plagioclase, very fine-grained clinopyroxene crystals and vesicles (Figure 3a). Vesicles are filled with chlorite, veins with epidote, and the ground mass contains chlorite and pumpellyite. This quartz-free clast of extrusive basalt is considered as a reference for mafic material incorporated into the fault zone. It is the sole unsilicified mafic sample recovered from the fault outcrops.

ODM195 is a moderately silicified clast-supported breccia (Figure 2b) with clasts composed of either chlorite only, or actinolite + plagioclase ± chlorite displaying relict doleritic textures (Figure 3b). The matrix contains crushed sub-millimetric clast fragments surrounded by newly formed chlorite and 5-10 vol.% of quartz (Figure 3b). Anhedral quartz crystals, typically ~100 µm in length, are either scattered or in local aggregates in the matrix.

ODM155 and ODM218 are two highly silicified, matrix-supported fault breccias (Figures 2cd). Both display a striated surface (slip plane) and an underlying well-developed slip zone (penetrative deformation). No primary mineral is preserved in any of the clasts, which contain either chlorite + titanite or chlorite + quartz (Figures 3c-d). Rare clasts preserve a primary doleritic texture (Figure 3c) despite pervasive alteration and mineral replacement, thus indicating a diabase protolith. Anhedral and subhedral quartz grains surrounded by interstitial chlorite represent >90 vol.% of the matrix. Both samples contain abundant sulfides, ODM155 containing only pyrite, whereas ODM218 contains pyrite with minor pyrrhotite and chalcopyrite. Three subsamples were taken from ODM218, at varying distance from the slip surface, to investigate relationships between sample geochemistry and distance to slip planes, which may act as preferential fluid flow zones. ODM218a is located within 1 cm from the striated slip surface (Figure 2d), and contains only rare and submillimetric sulfide grains and clasts embedded in a quartz-rich matrix. When present, clasts are mostly silicified. ODM218b is ~4-5 cm away from the slip plane, and displays clasts either silicified or quartz-free up to 1 cm in size, in addition to disseminated quartz grains in the matrix. ODM218c is a fragment dislodged from the lower surface of the sample and away (~12 cm) from the slip plane, and contains quartz-free clasts surrounded by a silicified matrix with sulfides. In this set of samples, matrix quartz grain sizes increase with the distance to the slip plane, and thus ODM218c contains the largest matrix quartz grains.

ODM217 is a quartz-free, brecciated talc-amphibole schist displaying a slip surface on one side and several internal slip zones (Figure 2e). Clasts are either made up of talc and amphibole or chlorite ± titanite (Figure 3e). Matrix mineralogy varies among slip zones, and is made of talc, serpentine or chlorite (Figure 3e), with disseminated spinels. To account for sample heterogeneity, two subsamples were taken (Figure 2e). Subsample ODM217a is a chlorite-rich slip zone adjacent to a striated slip surface, whereas subsample ODM217b is a talc-rich zone a few cm away from this same slip surface. For whole-rock geochemical analyses, we thus consider the unsilicified breccia ODM217 as a reference, as it contains both ultramafic and mafic clasts.

ODM173 is a matrix-supported breccia (Figure 2f) containing both mafic and ultramafic clasts, made of talc or chlorite ± titanite (Figure 3f). The matrix is made of chlorite and talc, with variable amounts of quartz at the sample scale, and scattered spinel and sulfides (chalcopyrite + pyrite; Figure 3f). As for ODM217, we selected two sub-samples to investigate this heterogeneity.

ODM173a displays few small clasts (< 1 mm) surrounded by a silicified matrix made of chlorite and talc associated with anhedral quartz crystals (<60 vol.% quartz, Figure 3f), whereas clasts in ODM173b are more abundant and larger (up to 1-2 cm), with only rare quartz grains and minor chlorite in the matrix. Sulfides are more abundant in ODM173b than in ODM173a.

Methods

To investigate the composition of fluids circulating through the detachment fault zone, and that are responsible for pervasive silicification, a study of fluid inclusions trapped in quartz crystals was coupled to whole-rock and mineral geochemical analyses (major and trace element). Fluid inclusion analyses included microthermometry, Raman spectroscopy, and LA-ICP-MS. We also used SEM-cathodoluminescence to study the growth history of quartz crystals hosting fluid inclusions. Microthermometric measurements of fluid inclusions determined isochoric relationships that, coupled with geologically constrained pressure intervals, provided estimates of fluid inclusion entrapment temperatures. These temperatures were then compared to silicification temperatures inferred from the composition of chlorite co-crystallized with quartz, using the geothermometer of [START_REF] Bourdelle | A new chlorite geothermometer for diagenetic to low-grade metamorphic conditions[END_REF].

Whole-rock and mineral chemical analyses

Whole rock chemical analyses were performed at the SARM-CRPG (Nancy, France). Major elements were analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES) after fusion with LiBO3 and dissolution in HNO3. Trace elements were quantified by inductively coupled plasma mass spectrometry (ICP-MS) following the procedure described by [START_REF] Carignan | Routine analyses of trace elements in geological samples using flow injection and low pressure on-line liquid chromatography coupled to ICP-MS: a study of geochemical reference materials BR, DR-N, UB-N, AN-G and GH[END_REF]. To account for sample heterogeneity, subsamples were analyzed for ODM218, ODM173 and ODM217 (see section 2.3).

Major element composition of chlorite was analyzed by EPMA (CAMECA SX-FIVE, CAMPARIS, Sorbonne Université, Paris, France). Analytical conditions were 15 kV-10 nA in WDS mode, for analysis of major elements. Fe2O3 (Fe), MnTiO3 (Mn, Ti), diopside (Mg, Si), Cr2O3 (Cr), orthoclase (Al, K), anorthite (Ca) and albite (Na) were used as standards for elements in parentheses. Only chlorite analysis with oxide sum in the 86-89 wt.% range and Na2O + K2O + CaO < 1 wt.% were considered. Structural formulas were derived on a 14-oxygen basis. Chlorite analyses with Si ≤ 4 atoms per formula unit, cation sum ≤ 10.1 apfu and vacancies >0.01 pfu were considered. In situ trace element analyses were carried out on 22 chlorites at GeoRessources (Nancy, France) using LA-ICP-MS. Technical details can be found with results in Table S3.

Fluid inclusion analyses

Fluid inclusions analyses were performed on 100 µm thick double-polished sections. Successive generations of fluid inclusions trapped during quartz crystal growth were first characterized using an Olympus BX-50 transmitted light microscope at IPGP. Inclusions either isolated or clustered (i.e., distant less than five times their length; Figure 4a) are considered as primary according to the criteria of [START_REF] Roedder | Fluid Inclusions[END_REF] and [START_REF] Van Den Kerkhof | Fluid inclusion petrography[END_REF], whereas those located along trails crosscutting quartz grains are considered as secondary (Figure 4b). The location of the different generations of fluid inclusions within individual quartz crystals was compared to crystal growth history as revealed by SEM-cathodoluminescence observations (as in [START_REF] Boiron | Identification of fluid inclusions in relation to their host microstructural domains in quartz by cathodoluminescence[END_REF], conducted at ISTeP -Sorbonne Université (Paris, France) on a Scanning Electron Microscope Zeiss Supra 55 equipped with an EDS system and an Oxford Instruments cathodoluminescence system.

Microthermometric fluid inclusion measurements were carried out at ISTeP -Sorbonne Université under an optical microscope equipped with a Linkam THMSG 600 heating-freezing stage with temperatures ranging from -196 °C to +600 °C. The stage is controlled by a Linkam TMS 93 programmer via LinkSys software v.2.15.

Cycles of repeated homogenization and ice melting temperature measurements were conducted on 176 individual inclusions to measure the temperature of phase changes for the gas-to-liquid homogenization (temperature of homogenization, Th) and for the ice melting point (temperature of final ice melting, Tmice), respectively. Several cycles performed to test reproducibility show that ice melting and homogenization temperatures were reproducible within 0.1 °C (~0.2 wt.% eq. NaCl) and 1 °C, respectively. Inclusions yielding non-reproducible measurements systematically showed complex morphologies and were thus discarded, yielding 119 fluid inclusions for this study. We performed temperature cycles in the potential range of hydrate melting temperatures, following [START_REF] Raimbourg | A new method of reconstituting the P-T conditions of fluid circulation in an accretionary prism (Shimanto, Japan) from microthermometry of methane-bearing aqueous inclusions[END_REF], but no gas hydrate was detected. Salinity was estimated from Tmice using the equation in [START_REF] Bodnar | Revised equation and table for determining the freezing point depression of H 2 O-NaCl solutions[END_REF], assuming that the entrapped fluid is a pure H2O-NaCl solution. Isochoric P-T relationships followed by fluid inclusions were derived from Th and NaCl molality, following the equation of [START_REF] Zhang | Determination of the homogenization temperatures and densities of supercritical fluids in the system NaCl-KCl-CaCl2-H2O using synthetic fluid inclusions[END_REF], suitable for our P-T and salinity range.

Gas content of fluid inclusions was analyzed with a Dilor-Labram Raman microspectrometer at GeoRessources (Nancy, France) on a representative set of 83 inclusions. As all studied inclusions are two-phase, we focused the laser on the gas bubble to determine gas proportions. In these dominantly aqueous inclusions, H2O vapor is by far the dominant gaseous phase. The relative molar proportions of the remaining minor gases (H2, CO2, CH4, H2S) were calculated with accuracy better than 5% [START_REF] Pasteris | Practical aspects of quantitative laser Raman microprobe spectroscopy for the study of fluid inclusions[END_REF] following the procedure described in [START_REF] Dubessy | Advances in C-O-H-N-S fluid geochemistry based on micro-Raman spectrometric analysis of fluid inclusions[END_REF]. This involves band area integration at wavenumbers of each gas and gas specific volume, i.e., Raman scattering cross-section for each gas and instrument efficiency at the specific wavenumbers [START_REF] Frezzotti | Water content and nature of solutes in shallow-mantle fluids from fluid inclusions[END_REF]. To subtract the air signal for N2, we conducted blank analyses in the quartz immediately adjacent to each inclusion.

Fluid inclusion chemical composition was analyzed on all inclusions larger than 8 µm (i.e., 24 inclusions) with a LA-ICP-MS at GeoRessources (Nancy, France; see technical details in Table S3). We analyzed Na, K, Li, Mg, Fe, Mn, Cr, Co, Ni, and calculated absolute concentrations and limits of detection following [START_REF] Leisen | Determination of Cl and Br concentrations in individual fluid inclusions by combining microthermometry and LA-ICPMS analysis: Implications for the origin of salinity in crustal fluids[END_REF], using Na content derived from microthermometric Tmice measurements (and calculated salinity) as internal standard. However, due to the low signal intensity for most measured elements, it was impossible to calculate accurate fluid inclusion element concentrations; these fluid inclusions were very small, with fluid released after 1-2 laser shots, and contained low salinity fluids that are therefore very diluted in metallic elements. While Na is likely the most concentrated cation, it was systematically difficult to detect by LA-ICP-MS due to ionization problems.

Results

Chemistry

Whole rock analyses

Major element compositions and selected trace element contents for samples described in Section 2.3 are presented in Table 2 (see Table S1 for full trace element analysis). Chemical data are compared with published data of mafic and ultramafic rocks recovered at the 13°20'N OCC [START_REF] Wilson | Mantle composition controls the development of an Oceanic Core Complex[END_REF], and at the 15°20'N Fracture Zone [START_REF] Godard | Geochemistry of the highly depleted peridotites drilled at ODP Sites 1272 and 1274 (Fifteen-Twenty Fracture Zone, Mid-Atlantic Ridge): Implications for mantle dynamics beneath a slow spreading ridge[END_REF][START_REF] Paulick | Geochemistry of abyssal peridotites (Mid-Atlantic Ridge, 15°20'N, ODP Leg 209): implications for fluidrock interaction in slow spreading environments[END_REF], although such comparison must be done with care as 13°20'N fault rocks are breccias, and differ from those at other sites, as presented above.

The unsilicified basaltic fault rock clast fragment (ODM115) has a composition similar to that of MAR basalts. In silicified mafic samples, the concentration of alkalis, Ca and Al (CaO in Figure 5a; Na2O and Al2O3 in Figures S1a-b) decreases sharply with increasing Si content, with almost complete depletion in the highly-silicified samples ODM155 and ODM218. Mg# for basaltic ODM115 and moderately silicified diabase ODM195 are in the range of MAR basalt and diabase values (Figure 5b). In contrast, Mg# clearly decreases in highly silicified samples ODM155 and ODM218 (Mg# < 45). Mixed mafic-ultramafic breccias show compositions that are intermediate between MAR mafic and ultramafic compositions, resulting from mafic and ultramafic material mixed in variable amounts . As in mafic samples, CaO, Na2O and Al2O3 contents, as well as Mg#, are significantly lower in the silicified sample ODM173 compared to unsilicified ODM217 (Figures 5a-b andS1a-b). Their SiO2 content is higher than that of ultramafic rocks for both the silicified ODM173 and the unsilicified ODM217, which is talc-rich.

Cr and Ni concentrations (Figure 5c) in most mafic samples are similar to those of MAR basalts and diabases, with subsample ODM218b showing slightly higher contents in both Cr and Ni. For the two samples with both mafic and ultramafic clasts, Cr and Ni contents are intermediate between those of MAR mafic and ultramafic compositions, reflecting again their mixed lithologies. The REE patterns (Figure S1c) for all mafic breccias are flat, as observed for MAR basalt and diabase patterns [START_REF] Wilson | Mantle composition controls the development of an Oceanic Core Complex[END_REF]. While the unsilicified basaltic clast ODM115 displays REEnormalized values consistent with those of MAR mafic rocks, REE concentrations progressively decrease as silicification increases, but without any pattern modification, likely due to dilution by quartz crystallization. The two mafic-ultramafic fault rocks display REE patterns between those of mafic and ultramafic signatures, reflecting their mixed lithologies (Figure S1c).

Hence, bulk rock analyses reflect significant heterogeneity of breccia samples, controlled by both the degree of silicification and the nature of the clasts. However, such analysis only reveals relative elemental enrichment or depletion. We combine these chemical analyses to textural and mineralogical observations to constrain effective mass transfer, and to determine if silicification resulted from significant silica enrichment only, or was associated to efficient leaching of other elements. Several arguments indicate massive silica influx rather than an important leaching: (1) dilution effect observed for most trace elements (Figure S1c), (2) preferential preservation of initial textures with well-defined clast borders, which would have been erased by massive leaching, (3) the fact that the most silicified breccias are matrix supported (while less silicified ones are clastsupported), and (4) the preferential crystallization of quartz in the matrix. However, calcium and alkalis (and part of the aluminum) were almost completely leached from silicified mafic and mixed mafic-ultramafic samples, and this important decrease with increasing silicification cannot be explained solely by passive depletion due to quartz crystallization (grey arrows, Figures 5a andS1a-b). Almost complete alkali leaching is also supported by mineralogical composition of all mafic fault rocks from the seven outcrops [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF]. Indeed, highly silicified samples contain mainly chlorite and quartz, lacking mineral phases able to host alkalis (i.e., no plagioclase or amphibole in highly silicified samples ODM218 and ODM155). The decrease in Mg# for silicified samples (ODM155, ODM218 and ODM173) compared to unsilicified ones likely reflects iron enrichment, as Mg# would be unaffected by quartz crystallization (Figure 5b). This is supported by the growth of iron-rich sulfides, essentially pyrite, as confirmed by the low Cu and Zn content (Table 2).

Chlorite composition

Microprobe analyses show that chlorites from both mafic and mixed mafic-ultramafic samples contain 40-50 wt.% of FeO+MgO, 30-40 wt.% SiO2 and 15-25 wt.% Al2O3 (Figure 6a). There is no systematic difference in chlorite composition between clasts and matrix for each sample (Figure 6a). Chlorites in moderately silicified ODM195 show slightly lower FeO+MgO and higher SiO2 contents than highly silicified ODM218, while chlorite composition of highly silicified ODM155 overlaps both samples.

Chlorites contain Si apfu in the range 2.7-3.5, Al apfu is 1.5-2.6 and Mg# between 43 and 85 (Table S2). While Si and Al contents are clearly anticorrelated for all chlorites, Si content and Mg# are roughly correlated in each sample, although more scattered (Figure 6b). The unsilicified basalt sample (ODM115) has chlorite compositions similar to those from MAR basalts [START_REF] Alt | Alteration of the upper oceanic crust: mineralogy and processes in Deep Sea Drilling Project Hole 504B[END_REF]Gillis & Thompson, 1993;[START_REF] Humphris | Hydrothermal alteration of oceanic basalts by seawater[END_REF]. Chlorite composition in moderately silicified breccia (ODM195), in both clast and matrix, is comparable to that in diabases (amphibolite facies; [START_REF] Castelain | Fluid evolution in an Oceanic Core Complex: A fluid inclusion study from IODP hole U1309 D-Atlantis Massif[END_REF][START_REF] Escartín | Constraints on deformation conditions and the origin of oceanic detachments: The Mid-Atlantic Ridge core complex at 15°45[END_REF]Figure 6b). For highly silicified samples (ODM155 and ODM218), chlorites clearly have a lower Mg# compared to ODM195, with a wider range (about 80-40), although most of them remain comparable to oceanic basalt chlorites (Figure 6b). Increasing silicification is obviously associated with iron enrichment and silica depletion in chlorites, a trend also observed by [START_REF] Saccocia | Hydrothermal upflow zones in the oceanic crust[END_REF] and [START_REF] Delaney | Quartz-cemented breccias from the Mid-Atlantic Ridge: Samples of a high-salinity hydrothermal upflow zone[END_REF] in the MARK area, and by [START_REF] Castelain | Fluid evolution in an Oceanic Core Complex: A fluid inclusion study from IODP hole U1309 D-Atlantis Massif[END_REF] in diabase chlorite-quartz veins at the footwall of the Atlantis Massif detachment (Figure 6b). Indeed, iron-rich chlorites have been described in oceanic hydrothermal breccias and quartz veins associated with the dyke complex or the dyke-lava transition [START_REF] Alt | Alteration of the upper oceanic crust: mineralogy and processes in Deep Sea Drilling Project Hole 504B[END_REF][START_REF] Delaney | Quartz-cemented breccias from the Mid-Atlantic Ridge: Samples of a high-salinity hydrothermal upflow zone[END_REF]Honorez et al., 1998;[START_REF] Humphris | Geochemical changes during hydrothermal alteration of basement in the stockwork beneath the active TAG hydrothermal mound[END_REF][START_REF] Mottl | Metabasalts, axial hot springs, and the structure of hydrothermal systems at mid-ocean ridges[END_REF][START_REF] Saccocia | Hydrothermal upflow zones in the oceanic crust[END_REF].

Concerning mixed mafic-ultramafic breccias, chlorites from the unsilicified sample ODM217 show the highest Mg# at ~80. This is expected in rocks containing fragments of ultramafic rocks, and are mostly comparable to chlorites from other oceanic detachment talcschits and amphibolite schists (e.g., 15°45'N, [START_REF] Escartín | Constraints on deformation conditions and the origin of oceanic detachments: The Mid-Atlantic Ridge core complex at 15°45[END_REF]South Atlantis massif, Boschi et al., 2006; Figure 6b).

Mg# for chlorites in the silicified mixed breccia (ODM173) presents a broader range and lower values (Mg#~50-80) than those of talcschists (Mg#~80, Figure 6b), similar to the decrease in Mg# and Si with increasing silicification observed for mafic samples.

Concerning trace elements, chlorites from mixed mafic-ultramafic fault rocks are generally enriched in Cr, Ni, Co, but depleted in Ti, V, Mn compared to chlorites from mafic breccias (Tables S2 andS3), in line with literature data (e.g., chlorites from diabases and talcschists, [START_REF] Boschi | Mass transfer and fluid flow during detachment faulting and development of an oceanic core complex, Atlantic Massif (MAR 30°N)[END_REF][START_REF] Escartín | Constraints on deformation conditions and the origin of oceanic detachments: The Mid-Atlantic Ridge core complex at 15°45[END_REF]. We note that a few chlorites from highly silicified mafic samples (ODM155 and ODM218) also show enrichments in Cr, Co, and slight enrichments in Ni (Tables S2 andS3).

Calculated temperature of chlorite formation

Several chlorite thermometers exist in the literature, based on empirical, semi-empirical, or thermodynamic approaches. Empirical thermometers cannot be used here as their application is restricted to the chlorite compositional space used for their calibration [START_REF] Bourdelle | Low-temperature chlorite geothermometry: a graphical representation based on a T-R 2+ -Si diagram[END_REF]. Furthermore, their applicability is questionable as they only consider one substitution, do not take into account the bulk rock composition, and have no thermodynamic basis [START_REF] Bourdelle | Low-temperature chlorite geothermometry: a graphical representation based on a T-R 2+ -Si diagram[END_REF]. Thermobarometric models (e.g., [START_REF] Vidal | Exhumation paths of high-pressure metapelites obtained from local equilibria for chlorite-phengite assemblages[END_REF][START_REF] Vidal | A thermodynamic model for Fe-Mg aluminous chlorite using data from phase equilibrium experiments and natural pelitic assemblages in the 100-600 °C, 1-25 kb range[END_REF][START_REF] Vidal | Thermodynamic properties of the Tschermak solid solution in Fe-chlorite: application to natural examples and possible role of oxidation[END_REF][START_REF] Vidal | P-Tdeformation-Fe3+/Fe2+ mapping at the thin section scale and comparison with XANES mapping: application to a garnet-bearing metapelite from the Sambagawa metamorphic belt (Japan)[END_REF][START_REF] Walshe | A six-component chlorite solid solution model and the conditions of chlorite formation in hydrothermal and geothermal systems[END_REF], widely used in metamorphic environments, lack of thermodynamic data for the Si-rich Al-free chlorite end-member (Figure 6c), therefore precluding their use for our samples. Indeed, chlorites formed in the fault breccias (Figures 6b-c) have a relatively high Si content (2.7-3.5 apfu) and some chlorites plot in the clinochlore-sudoite-Al-free chlorite field (Figure 6c). We thus used the semi-empirical geothermometer of [START_REF] Bourdelle | A new chlorite geothermometer for diagenetic to low-grade metamorphic conditions[END_REF], suitable for all compositions of chlorite in equilibrium with quartz. This choice is also comforted by the quartz and chlorite co-crystallization in both matrix and clasts during silicification (see 2.2 and [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF].

The geothermometer of [START_REF] Bourdelle | A new chlorite geothermometer for diagenetic to low-grade metamorphic conditions[END_REF] is specifically calibrated for low-temperature contexts (i.e., T < 350 °C), through a linear equation linking the chlorite + quartz equilibrium constant to the temperature of crystallization, taking into account cationic substitutions involving Si and R 2+ contents. For higher-grade contexts, several thermodynamic parameters (as the nonideal contribution of the site mixing) cannot be linearized, and a quadratic correction (Bourdelle et al., 2013) is proposed instead ("Tcorrected" in Table S2). While these "Tcorrected" results should be cautiously considered [START_REF] Bourdelle | A new chlorite geothermometer for diagenetic to low-grade metamorphic conditions[END_REF], this involves a small portion of our analyses.

Temperatures obtained with this thermometer mostly span the 150-400 °C range (except for a few outliers which are not considered). We find median temperatures of ~250 °C for the moderately silicified samples ODM173 and ODM195, and ~275 and ~300 °C for the highly silicified samples ODM155 and ODM218 respectively (Figure 6d; Tables S2 andS4).

Fluid inclusion results

Distribution and morphology of fluid inclusions

Fluid inclusions are common in quartz from the 13°20'N detachment fault rocks. Those in quartz crystals from clasts in highly silicified breccias are bigger and better preserved than those in quartz grains within the matrix, which shows abundant decrepitated inclusions. All inclusions contain aqueous fluid that is two-phase (liquid-vapor; Figure 4) at room temperature, with a vapor to total volume ratio ranging from 0.1 to 0.5 (Figure S2). In quartz grains distant from slip planes (>1 cm), fluid inclusions are abundant and mostly range in size from 8 to 12 µm (Figure 4a). The contour of primary fluid inclusions is spherical to elongated, sometimes approaching negative crystal shapes (Figures 4a,d,e,i). No sign of decrepitation (e.g., [START_REF] Roedder | Fluid Inclusions[END_REF][START_REF] Touret | Fluids in metamorphic rocks[END_REF] is noticeable, except in samples within ~1 cm from a slip plane (sample ODM218a), in which inclusions are small (<5 µm), very irregular in shape, and often empty and probably decrepitated (e.g., [START_REF] Roedder | Fluid Inclusions[END_REF]. Inclusions in this sub-sample ODM218a were therefore discarded for microthermometric measurements.

Small and elongated fluid inclusions, a few microns thick and a few tens of micron long, are regularly distributed, defining trails. Their elongation is often slightly oblique to the trail direction (Figures 4b,c,f,g,h), but their vapor ratio is similar to that of primary inclusions (Figure S2).

These correspond to recrystallized microfractures, and thus postdate primary ones described above (e.g., [START_REF] Roedder | Fluid Inclusions[END_REF]. These trails do not show any distinct orientation, neither relative to each other nor at the sample scale (Figures 4f,g). Most of them are intra-grain trails, as they remain within the limits of quartz grains (Van den [START_REF] Van Den Kerkhof | Fluid inclusion petrography[END_REF], with few occurrences crosscutting grain boundaries (Figures 4f,g). These trails are thus related to quartz fracturing between successive quartz crystallization episodes as revealed by SEM cathodoluminescence (Figures 7 and S3;[START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF]. Therefore, this second set of inclusions can be classified as "pseudo-secondary", following the criteria of [START_REF] Roedder | Fluid Inclusions[END_REF].

Microthermometry

Ice melting temperature (Tmice) measurements indicate that all inclusions, primary and secondary, contain moderately saline aqueous fluids. Tmice ranges from -6°C to -1.5 °C (Figure S4), yielding equivalent salinities ranging from 2.1 to ~10 wt.% eq. NaCl. Most fluid inclusions studied here thus have a salinity higher than that of seawater (3.2 wt.% eq. NaCl, blue line in Figure 8a; Table 3) with salinity restricted to the 4-6 wt.% eq. NaCl range for all samples but ODM218, which displays a wider salinity range (2.1-10 wt.% eq. NaCl). We note that the salinity is higher for subsample ODM218b (from 6.3 to 10 wt.% eq. NaCl) than for subsample ODM218c (from 2.1 to 6.1 wt.% eq. NaCl; Figure 8a).

Highly silicified mafic breccias (ODM155, ODM218) present higher homogenization temperatures (180-350 °C) than moderately silicified ones, either mafic (ODM195) or mixed mafic-ultramafic (ODM173; 150-220 °C; Figure 8a; Table 3). The highly-silicified sample ODM155 shows a wide range of Th values, spreading over ~130 °C, whereas the Th for all other samples show more restricted ranges of up to 90 °C. We do not observe any systematic difference in Tmice and Th between primary and secondary fluid inclusions in any of the samples (Figure 8a).

Intra-grain variations of fluid inclusion Th and salinities are shown in Figure 8b, where sets of inclusions from different quartz grains are shown with different colors. The strong variation of Th and salinity observed respectively for ODM155 and subsamples OM218b and ODM218c (highly silicified mafic breccias) is thus observed not only at the sample scale, but also at the quartz grain scale (Figure 8b). SEM-cathodoluminescence observations reveal core-to-rim variations in quartz luminescence (Figures 7 andS3) that record successive steps of quartz crystallization [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF]. The location of fluid inclusions displaying scattered microthermometric values on cathodoluminescence images (Figure 7b,d and S3b,e) suggests that fluid inclusions were trapped in quartz of varying luminescence, and thus during different quartz grain crystallization phases, between successive quartz fracturing episodes.

Composition of fluid inclusions

Fluid inclusions from the 4 fault rock samples studied here are mostly aqueous (i.e., H2O-NaCl), as shown by the absence of gas hydrate detection. Raman spectroscopy analyses of the vapor phase (i.e., gas bubble) of aqueous fluid inclusions detected minor amounts of H2, CO2, CH4 and H2S (in addition to H2O) in the highly silicified mafic breccias (ODM155 and ODM218; Table 3; Figure 9). Conversely, only H2O vapor was detected in the moderately silicified samples ODM173 and ODM195, although the high fluorescence observed during Raman analyzes for the latter could have hidden small gas signal.

In sample ODM155, only two out of 17 fluid inclusions (Table 3) were not purely aqueous and contained traces of CO2. On the other hand, 15 out of 28 inclusions from subsample ODM218b, and the 21 analyzed inclusions of ODM218c, contained traces of gases (other than H2O), and dominated by H2 (up to 100 mol.% of the H2-CO2-CH4-H2S content in 18 inclusions) in addition to variable proportions of CO2 (up to 80 mol.% of the H2-CO2-CH4-H2S content), CH4 (up to 12 mol.% of the H2-CO2-CH4-H2S content) and H2S (up to 12 mol.% of the H2-CO2-CH4-H2S content, in 4 inclusions from ODM218c; Figure 9a). All inclusions display very low H2S/H2 ratios (Figure 9b), similar to those measured in ultramafic-derived hydrothermal vent fluids [START_REF] Fouquet | Geodiversity of Hydrothermal Processes Along the Mid-Atlantic Ridge and Ultramafic-Hosted Mineralization: a New Type Of Oceanic Cu-Zn-Co-Au Volcanogenic Massive Sulfide Deposit[END_REF], while mafic hosted vents rather show high H2S/H2 ratios. We do not observe any correlation between gas compositions and microthermometric data (Figure S5).

LA-ICP-MS analyses were performed on a set of 24 fluid inclusions, but their small size precludes calculating reliable concentrations (see 3.2). K +/-Na and Li were detected in 10 inclusions, and associated to the presence of Cr +/-Ni, Co, Mn, Fe, Mg in 7 of them. Despite these limitations due to inclusion sizes, inclusion fluids in the 13°20'N detachment fault rocks appear to be very diluted fluids. They can thus be assimilated to fluids in the H2O-NaCl system, and hence their salinity can be estimated from the ice melting temperature [START_REF] Bodnar | Revised equation and table for determining the freezing point depression of H 2 O-NaCl solutions[END_REF].

Interpretation and discussion

Pressure and temperature conditions of silicification

Pressure range deduced from the geological context

Silicification occurred in the detachment plane, affecting cataclastic breccias of mainly mafic composition. Preserved doleritic textures in moderately silicified breccias indicate that these diabase rocks were part of the base of Layer 2 (dyke complex) at the hangingwall, underlying the rift valley floor, and mechanically accreted into the fault zone [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF].

Geophysical observations along slow-spreading ridges suggest that Layer 2 thickness may vary between 1 and 2 km (see discussion in Bonnemains et al., 2017 and references therein), while a recent seismic experiment in this study area reports a Layer 2A thickness on-axis of ~2 km [START_REF] Simão | 3-D P-wave velocity structure of oceanic core complexes at 13°N on the Mid-Atlantic Ridge[END_REF]. Assuming a rift valley floor depth of ~3000 m, and considering seawater and crustal rocks densities of 1025 and 3000 kg.m -3 respectively, the pressure ranges for the base of Layer 2 can be estimated to 600-890 bars for lithostatic pressure, and 400-500 bars for hydrostatic pressure.

Therefore, silicification and coeval fluid entrapment in quartz crystals in the detachment fault zone necessarily took place between the base of Layer 2 (400-890 bars) and the seafloor (300 bars; Figure 10).

Temperature of fluid inclusion trapping during silicification

Fluid inclusion isochores derived from microthermometric data (equation of [START_REF] Zhang | Determination of the homogenization temperatures and densities of supercritical fluids in the system NaCl-KCl-CaCl2-H2O using synthetic fluid inclusions[END_REF] represent the P-T relationship along which fluid inclusions were trapped (Figure 10), while the measured homogenization temperature Th (Figure 8) indicates the rooting temperature of the isochore on the liquid-vapor curve (from [START_REF] Sourirajan | The system H 2 O-NaCl at elevated temperatures and pressures[END_REF]. Intersection of fluid pressure ranges (see above) with isochores provides an estimate of the temperature range of silicification and subsequent fluid entrapment in quartz crystals (Figure 10). For samples ODM195 and ODM173, temperatures of fluid entrapment are in the 160-280 °C range, while for highly silicified samples ODM155 and ODM218, entrapment temperatures are in the 200-400 °C and 275-425 °C ranges respectively (Figure 10). As these fluid inclusions were trapped at various stages of quartz syntectonic crystallization (Figures 7 andS3), fluid entrapment temperatures do represent the temperature interval over which silicification occurred.

Significant scatter in isochores for ODM155 reflect Th variability. Indeed, ODM155 (and to a lesser extent ODM195) exhibits a broad range of homogenization temperatures (~130 °C) at both sample-and grain-scale, associated to homogeneous salinities (4-6 wt.% eq. NaCl; Figure 8). This pattern is typical of post-entrapment deformation of fluid inclusions [START_REF] Roedder | Fluid Inclusions[END_REF], and is common in most hydrothermal systems [START_REF] Delaney | Quartz-cemented breccias from the Mid-Atlantic Ridge: Samples of a high-salinity hydrothermal upflow zone[END_REF][START_REF] Kelley | Fluid evolution in submarine magmahydrothermal systems at the Mid-Atlantic Ridge[END_REF][START_REF] Petersen | Fluid inclusion studies as a guide to the temperature regime within the TAG hydrothermal mound[END_REF]. This result suggests that some inclusion cavities (and therefore fluid density) underwent later re-equilibration during penetrative deformation phases (i.e., slip zones and planes in both samples), slightly modifying P-T isochoric relationships [START_REF] Diamond | Modification of fluid inclusions in quartz by deviatoric stress II: experimentally induced changes in inclusion volume and composition[END_REF]Tarantola et al., 2010;2012;[START_REF] Vityk | Textural evolution of synthetic fluid inclusions in quartz during reequilibration, with applications to tectonic reconstruction[END_REF]. In contrast, ODM218 shows a very restricted Th range, thus the isochore fan rather reflects its high variation in salinity (2-10 wt.% NaCl, Figure 8) and thus in fluid density.

Comparison with the temperature of chlorite formation

The formation temperature of chlorite, which coevally crystallized with quartz in both matrix and clasts during silicification (see 2.2 and [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF], is calculated from chlorite composition (see 4.1.3; Figure 6d; Tables S2 andS4), and is thus an independent estimate of silicification temperature. The large range of chlorite crystallization temperatures (~150-400 °C, Figure 6d) reflects continuous crystallization with quartz during breccia infiltration by hydrothermal fluids and exhumation towards progressively lower P-T conditions in the detachment plane. The temperature range of chlorite formation is coherent with the estimated trapping temperatures for fluid inclusions, intersecting in all cases the isochores at realistic pressures (Figure 10). Interestingly, the chlorite temperature range intersects the isochores at higher pressures, corresponding to lithostatic fluid pressures, for the moderately silicified samples (ODM173 in particular), than for highly silicified samples (ODM218 in particular) for which the median chlorite temperatures intersect the isochores at hydrostatic fluid pressures instead. Near hydrostatic fluid pressures are coherent with the significant fluid amount required to explain pervasive silicification, thus associated with an open system. In contrast, moderately silicified samples submitted to more restricted fluid circulation may instead correspond to a system only transiently open. Silicification is both static and linked to deformation episodes, as demonstrated by successive steps of quartz growth-hydrofracturing-overgrowth (Figures 7 andS3). This complex system witnessed both spatial and temporal fluid pressure variations, bounded by end-member lithostatic to hydrostatic pressures, and linked to variations in rock permeability and fault zone connectivity, likely modulated by both silica sealing and hydrofracturing episodes [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF].

We thus interpret this silicification as a long-lived, complex process along the detachment plane during exhumation of the hangingwall-derived breccias ( [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF], consistent with the large temperature ranges of both chlorite crystallization and fluid entrapment in quartz.

We also infer that silicification occurred mostly in the temperature range ~200 -400 °C, the highest temperatures corresponding to the highly silicified sample spanning the largest salinity variations (2-10 wt.% NaCl, ODM218).

Fluid compositions and potential fluid sources

Insights from fluid inclusion salinity: phase separation

Fluid inclusions contain an aqueous fluid with salinities generally higher than that of seawater.

Fluid inclusions from most samples (ODM155, ODM195, ODM173) present restricted salinity ranges (4-6 wt.% eq. NaCl) corresponding to ~115 to 170% of seawater salinity (3.2 wt.% eq. NaCl). This range is comparable to ranges of salinity (and Th) measured in fluid inclusions (Figure 8a) in rocks associated with hydrothermal fields both of mafic (TAG: [START_REF] Petersen | Fluid inclusion studies as a guide to the temperature regime within the TAG hydrothermal mound[END_REF]MARK: Delaney et al., 1987;[START_REF] Saccocia | Hydrothermal upflow zones in the oceanic crust[END_REF] and ultramafic nature (Rainbow, Logatchev, Ashadze, Semenov, Irinovskoe; [START_REF] Bortnikov | The physicochemical conditions of hydrothermal ore-forming systems of "black smokers" associated with mantle ultrabasites in the Central Atlantic region[END_REF][START_REF] Bortnikov | Anomalously high concentrations of metals in fluid of the Semenov Modern Hydrothermal System (Mid-Atlantic Ridge, 13°31"N): LA-ICP-MS study of fluid inclusions in minerals[END_REF][START_REF] Bortnikov | The metalliferous fluid of the hydrothermal sulfide system associated with the oceanic core complex 13°20´N, The Mid-Atlantic Ridge (LA-ICP-MS and fluid inclusions)[END_REF][START_REF] Simonov | LA-ICP-MS evidence for high concentrations of metals in fluid from modern sea-floor hydrothermal systems: a case study of fluid inclusions in minerals from Semenov, Ashadze, and Logatchev sulfide edifices (Mid-Atlantic Ridge)[END_REF]. Fluid inclusions from the highly silicified sample ODM218 display a large salinity range (2.1 to 10 wt.% eq. NaCl, Figure 8a). At the grain scale, core-to-rim salinity variations are associated to luminescence variations (Figures 7b,d, S3b, e and 8b) but do not show any systematic pattern, rather suggesting that the fault zone witnessed pulses of fluids with variable salinity during deformation.

Salinity in fluid inclusions from subsample ODM218b reaches up to 3 times seawater salinity (i.e., 10 wt.% equiv. NaCl, Figure 8a). Similar values are also reported for MARK silicified breccias [START_REF] Delaney | Quartz-cemented breccias from the Mid-Atlantic Ridge: Samples of a high-salinity hydrothermal upflow zone[END_REF]. In contrast, many fluid inclusions of subsample ODM218c cluster at seawater-like salinities, while others in the same sample have salinities below that of seawater (2.1 wt.% eq. NaCl, Figure 8a), as reported from TAG [START_REF] Petersen | Fluid inclusion studies as a guide to the temperature regime within the TAG hydrothermal mound[END_REF]. At least three mechanisms have been proposed to explain salinities of fluid inclusions differing from that of seawater: hydration reactions, chloride retention in secondary minerals, and phase separation:

(1) Hydration reactions consume water and, consequently, residual fluids may be enriched in dissolved elements. These reactions increase salinity modestly, with +15% for basalt-seawater equilibration at 350 °C [START_REF] Wetzel | Distinguishing ultramafic-from basalt-hosted submarine hydrothermal vent fluid compositions[END_REF], therefore clearly insufficient to explain the high salinities recorded in sample ODM218b. This process is only efficient at low water-rock ratio conditions and closed systems [START_REF] Delaney | Quartz-cemented breccias from the Mid-Atlantic Ridge: Samples of a high-salinity hydrothermal upflow zone[END_REF]. However, important fluid fluxes are required to attain the observed high levels of silicification (up to ~90 vol.% quartz) in these matrix-supported breccias (see 5.2.2). This precludes that hydration reactions alone may significantly change salinities to values consistent with those observed here (Figure 8a).

(2) Chloride storage in transient phases (such as amphiboles, up to 4 wt.% chlorine ;[START_REF] Vanko | Temperature, pressure, and composition of hydrothermal fluids with their bearing on the magnitude of tectonic uplift at mid-ocean ridges, inferred from fluid inclusions in oceanic layer 3 rocks[END_REF] can also modulate the salinity of the circulating hydrothermal fluids [START_REF] Kelley | Development of a brine-dominated hydrothermal system at temperatures of 400-500 °C in the upper level plutonic sequence, Troodos ophiolite, Cyprus[END_REF][START_REF] Kelley | Processes of brine generation and circulation in the oceanic crust: Fluid inclusion evidence from the Troodos Ophiolite, Cyprus[END_REF]. At 13°20'N OCC, hydrothermal amphiboles formed under amphibolite facies conditions (i.e., in clasts, pre-dating silicification) are progressively replaced by chlorite during silicification at lower temperatures (greenschist facies), and could therefore increase fluid salinity. However, the low chloride content of these amphiboles (<0.29 wt.%; [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF] suggests that dissolution of these phases during silicification cannot account by itself for salinities of fluid inclusions within mafic fault breccias, which are three times higher than those of seawater.

(3) The only efficient mechanism to generate both high and low salinity fluids is the formation of brine and vapor phases by supercritical phase separation of either seawater or magmatic fluids, as invoked for high-temperature hydrothermal systems (e.g., [START_REF] Alt | Subsurface structure of a submarine hydrothermal system in ocean crust formed at the East Pacific Rise, ODP/IODP Site 1256[END_REF][START_REF] Castelain | Fluid evolution in an Oceanic Core Complex: A fluid inclusion study from IODP hole U1309 D-Atlantis Massif[END_REF][START_REF] Delaney | Quartz-cemented breccias from the Mid-Atlantic Ridge: Samples of a high-salinity hydrothermal upflow zone[END_REF][START_REF] Kelley | Two-phase separation and fracturing in mid-ocean ridge gabbros at temperatures greater than 700 °C[END_REF][START_REF] Kelley | Processes of brine generation and circulation in the oceanic crust: Fluid inclusion evidence from the Troodos Ophiolite, Cyprus[END_REF][START_REF] Vanko | Temperature, pressure, and composition of hydrothermal fluids with their bearing on the magnitude of tectonic uplift at mid-ocean ridges, inferred from fluid inclusions in oceanic layer 3 rocks[END_REF]. At the 13°20'N detachment fault, the minimum temperature for supercritical phase separation at the seafloor (~3000 m, 300 bars, see 5.1) is ~400 °C (Figure 11), and would form high salinity brines and a vapor phase. However, we do not have any direct evidence for in-situ phase separation during silicification as we lack fluid inclusions with pure brines (up to ~40-50 wt.% eq. NaCl), as observed in diabases [START_REF] Kelley | Two-phase separation and fracturing in mid-ocean ridge gabbros at temperatures greater than 700 °C[END_REF] or trondhjemite [START_REF] Castelain | Fluid evolution in an Oceanic Core Complex: A fluid inclusion study from IODP hole U1309 D-Atlantis Massif[END_REF]Figure 8a), or inclusions with pure vapor phase (vapor to total volume of 0.1-0.5 in our study). This suggests that phase separation occurred earlier, at deeper levels. Vapor and brine were likely segregated and migrated upwards separately, similarly to the two-stage model proposed by [START_REF] Delaney | Quartz-cemented breccias from the Mid-Atlantic Ridge: Samples of a high-salinity hydrothermal upflow zone[END_REF] for the MARK hydrothermal field. The wide range of salinities (i.e., from lower-to three times higher-than-seawater) reported in 13°20'N silicified fault rocks may be accounted for by either rehomogenization of variable amounts of brines and vapor phases once released in the detachment fault (in the one-phase field, Figure 11), or their mixing with fluids of different salinity, prior to fluid entrapment in quartz.

Although we have no direct constraints, we hypothesize that phase separation may have occurred in the brecciation zone or its immediate vicinity. Indeed, most of the breccia clasts from 13°20'N fault zone are originally diabase, suggesting that they were initially part of the hangingwall dyke complex adjacent to the detachment fault (see 2.2 and 5. 1 and Bonnemains et al., 2017). With a fully developed amphibolite facies paragenesis (hornblende + labradorite), these rocks experienced hydrothermal alteration at temperatures higher than 500 °C (see review in [START_REF] Alt | Subseafloor processes in mid-ocean ridge hydrothermal systems[END_REF], likely at the base of the upper crust (root of the dyke complex), therefore acting as a reaction zone. Fluid pressures in this reaction zone may be between hydrostatic and lithostatic, even close to hydrostatic for high fluid fluxes. Figure 11 shows that cold seawater infiltrating the hangingwall towards the base of the crust would undergo phase separation between 440 °C and 570 °C, depending on the fluid pressure gradient. It is thus plausible that phase separation occurred in the reaction zone where brecciation is inferred to take place (e.g., [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF]. Diabase brecciation along the detachment fault zone may even enhance phase separation, promoting sudden fluid pressure drops leading to the crossing of the liquid-vapor curve (Figure 11).

Insights from bulk-rock and chlorite compositions: a mafic-rock derived fluid

Textural and mineralogical observations, coupled to bulk-rock analyses, document that diabase breccias underwent variable silicification during exhumation within the detachment zone (see 4.1.1), reaching up to ~90 vol.% of quartz in matrix-supported breccias (Figure 5; Tables 2 andS1). Such degrees of silicification require both circulation of a silica-rich fluid and high fluid-rock ratios along the detachment fault zone. Indeed, experiments suggest that water-rock ratios >50 are required for basalt replacement by quartz-chlorite assemblages at 300 °C [START_REF] Mottl | Metabasalts, axial hot springs, and the structure of hydrothermal systems at mid-ocean ridges[END_REF]. Elevated fluid fluxes are also supported by the enhanced leaching of alkalis and calcium (Figures 5a andS1a-b) from diabase clasts with increasing silicification [START_REF] Bach | Metasomatism within the oceanic crust[END_REF][START_REF] Cann | Spilites from the Carlsberg Ridge, Indian Ocean[END_REF].

Chlorite crystallization in both clasts and matrix is associated to silicification, as showed by chlorite and quartz co-crystallization textures, increasing amount of chlorite with silicification, and similar chlorite composition in both clasts and matrix (Figure 6a). The decrease of bulk-rock and chlorite Mg# with increasing silicification (Figures 5b and6b), correlated to pyrite crystallization in the highly silicified breccias, suggests interaction with iron-rich fluids. The association iron-rich chlorites, quartz and pyrite has been observed in silicified oceanic hydrothermal breccias associated with mafic-rock hosted vents such as TAG [START_REF] Alt | Alteration of the upper oceanic crust: mineralogy and processes in Deep Sea Drilling Project Hole 504B[END_REF][START_REF] Honnorez | Vivesection and autopsy of active and fossil hydrothermal alteration of basalts beneath and whitin the TAG hydrothermal mound[END_REF]Humphris et al., 1998) or at the MARK area [START_REF] Delaney | Quartz-cemented breccias from the Mid-Atlantic Ridge: Samples of a high-salinity hydrothermal upflow zone[END_REF][START_REF] Saccocia | Hydrothermal upflow zones in the oceanic crust[END_REF]. For [START_REF] Saccocia | Hydrothermal upflow zones in the oceanic crust[END_REF], these minerals result from interactions with high salinity, silica-and iron-rich fluids, depleted in H2S. This is in agreement with the high salinity (Figure 8) and low H2S content (only recorded in 4 fluid inclusions from ODM218, Figure 9a) in our fluid inclusions. Hence, almost all H2S was likely stored into pyrite, leading to iron-enriched fluids from which Fe-rich chlorites crystallized (type I breccias from [START_REF] Saccocia | Hydrothermal upflow zones in the oceanic crust[END_REF]. A low H2S content in fluids is also consistent with the small amount of metallic trace elements recorded in our fluid inclusions (i.e., diluted fluids, see 4.2.3). Such fluid composition is characteristic of highly evolved hydrothermal fluids sampled in upflow zones of hydrothermal cells, and recording mafic rock-hosted reaction zones [START_REF] Bach | Metasomatism within the oceanic crust[END_REF][START_REF] Saccocia | Hydrothermal upflow zones in the oceanic crust[END_REF].

The significant amounts of silica precipitated in detachment fault breccias also suggest the leaching of a deep mafic source. Indeed, high-temperature hydrothermal fluids from the reaction zone at the base of the mafic upper crust may be quartz-saturated (or close to) according to Wetzel and Shock (2000; ~20 mmolal of aqueous silica at 400°C for seawater-basalt equilibrium). This is in agreement with fluid composition from basalt-hosted hydrothermal vents at >300 °C [START_REF] Fouquet | Geodiversity of Hydrothermal Processes Along the Mid-Atlantic Ridge and Ultramafic-Hosted Mineralization: a New Type Of Oceanic Cu-Zn-Co-Au Volcanogenic Massive Sulfide Deposit[END_REF][START_REF] Schmidt | Fluid elemental and stable isotope composition of the Nibelungen hydrothermal field (8°18 ' S, Mid-Atlantic Ridge): constraints on fluid-rock interaction in heterogeneous lithosphere[END_REF][START_REF] Mcdermott | Geochemistry of fluids from Earth's deepest ridge-crest hot-springs: Piccard hydrothermal field, Mid-Cayman Rise[END_REF]. Fluids circulating upwards along the detachment fault zone may witness both a significant temperature reduction (to 200-300 °C) and pressure drops, promoting fluid supersaturation and quartz precipitation. On the contrary, hydrothermal fluids equilibrated with peridotite should be largely undersaturated with respect to quartz (0.5 mmolal of aqueous silica at 400°, [START_REF] Wetzel | Distinguishing ultramafic-from basalt-hosted submarine hydrothermal vent fluid compositions[END_REF], and vent fluids from ultramafic-hosted hydrothermal systems generally record 6-8 mmol/L of aqueous silica [START_REF] Fouquet | Geodiversity of Hydrothermal Processes Along the Mid-Atlantic Ridge and Ultramafic-Hosted Mineralization: a New Type Of Oceanic Cu-Zn-Co-Au Volcanogenic Massive Sulfide Deposit[END_REF]. Under these conditions, a temperature drop of 200 °C will not be sufficient to trigger quartz crystallization. Hence, silica may only be provided by fluids reacting with mafic rocks. Moreover, the high amount of silica crystallized in the breccia matrix (up to 90 vol% of quartz) requires circulation of extremely Si-rich fluids: phase separation and brine formation in the reaction zone may have enhanced aqueous silica concentration, as quartz solubility is about one order of magnitude higher in NaCl-rich brines than in pure H2O [START_REF] Scheuermann | Quartz solubility in the two-phase region of the NaCl-H2O system: an experimental study with application to the Piccard hydrothermal field, Mid-Cayman Rise[END_REF][START_REF] Schmidt | Fluid elemental and stable isotope composition of the Nibelungen hydrothermal field (8°18 ' S, Mid-Atlantic Ridge): constraints on fluid-rock interaction in heterogeneous lithosphere[END_REF][START_REF] Steele-Macinnis | Numerical model to determine the composition of H2O-NaCl-CaCl2 fluid inclusions based on microthermometric and microanalytical data[END_REF], promoting efficient silica transport towards the upflow zone along the detachment fault.

Therefore, significant amounts of highly evolved hydrothermal fluids from a reaction zone at the base of the hangingwall dyke complex flowed up along the detachment fault zone, transporting leached aqueous silica. This syntectonic circulation resulted in intense and pervasive silicification of mafic detachment fault breccias (with crystallization of Fe-rich chlorite and pyrite).

Insights from fluid inclusion gas content: mix with an ultramafic-derived fluid

While most fluid inclusions are purely aqueous (H2O-NaCl), some contain small amounts of H2, CO2, CH4, and minor amounts of H2S (i.e., ODM218b and ODM218c; Figure 9; Table 3) in addition to dominant H2O (H2O-NaCl-H2±CO2±CH4±H2S). Seawater phase separation cannot produce all these gases, and other fluid sources are required. Among these minor gases, H2 is by far the most abundant in the inclusions (Figure 9; Table 3). H2 is likely produced during serpentinization reactions by oxidation of the iron contained in olivine, reactions that preferentially occur between 200 and 350 °C [START_REF] Martin | Some experimental and theoretical observations on the kinetics of hydration reactions with particular reference to serpentinization[END_REF][START_REF] Mccollom | Thermodynamic constraints on hydrogen generation during serpentinization of ultramafic rocks[END_REF][START_REF] Seyfried | Redox evolution and mass transfer during serpentinization: An experimental and theoretical study at 200 degrees C, 500 bar with implications for ultramafic-hosted hydrothermal systems at Mid-Ocean Ridges[END_REF]. At high temperatures (>400 °C), H2 may also be produced in mafic rocks by pyroxene alteration [START_REF] Allen | Compositional controls on vent fluids from ultramatichosted hydrothermal systems at mid-ocean ridges: An experimental study at 400 degrees C, 500 bars[END_REF][START_REF] Foustoukos | Redox and pH constraints in the subseafloor root zone of the TAG hydrothermal system, 26°N Mid-Atlantic Ridge[END_REF]. CO2 can be either linked to seawater, or to a magmatic source enriching nearby fluids. CH4 likely results from CO2-rich fluids reacting with H2. This reaction may occur either during serpentinization, from hydrothermal circulation in ultramafic rocks enriching fluids in both hydrogen and methane [START_REF] Berndt | Reduction of CO2 during serpentinization of olivine at 300 degrees C and 500 bar[END_REF][START_REF] Boulart | Differences in gas venting from ultramafic-hosted warm springs: the example of Oman and Ligurian Ophiolites[END_REF][START_REF] Charlou | Intense CH4 plumes generated by serpentinization of ultramafic rocks at the intersection of the 15°20'N fracture zone and the Mid-Atlantic Ridge[END_REF][START_REF] Charlou | Geochemistry of high H2 and CH4 vent fluids issuing from ultramafic rocks at the Rainbow hydrothermal field (36°14'N, MAR)[END_REF][START_REF] Holm | Initial indications of abiotic formation of hydrocarbons in the Rainbow ultramafic hydrothermal system, Mid-Atlantic Ridge[END_REF][START_REF] Monnin | The low temperature hyperalkaline hydrothermal system of the Prony Bay (New Caledonia)[END_REF][START_REF] Wetzel | Distinguishing ultramafic-from basalt-hosted submarine hydrothermal vent fluid compositions[END_REF], in H2-rich fluid inclusions hosted in footwall magmatic rocks (e.g., [START_REF] Klein | Abiotic methane synthesis and serpentinization in olivine-hosted fluid inclusions[END_REF][START_REF] Mcdermott | Pathways for abiotic organic synthesis at submarine hydrothermal fields[END_REF], or at a later time (e.g., during transport), but in any case, prior to fluid entrapment during silicification.

To discriminate the origin of fluids that circulated along the detachment fault zone, we compare the ratios of H2, CO2, CH4, H2S in our fluid inclusions to those analyzed in vent fluids (from MAR mainly). While few inclusions present a CO2-dominant gas content comparable to basalt-hosted vent fluids, most of these inclusions show high H2/CO2 and H2/CH4 ratios (Figure 9a) and very low H2S/H2 ratios (Figure 9b), signatures typical of ultramafic-hosted vent fluids (e.g., Rainbow, Logatchev, Semenov, Irinovskoe;Destringeville et al., 2015;[START_REF] Fouquet | Geodiversity of Hydrothermal Processes Along the Mid-Atlantic Ridge and Ultramafic-Hosted Mineralization: a New Type Of Oceanic Cu-Zn-Co-Au Volcanogenic Massive Sulfide Deposit[END_REF][START_REF] Schmidt | Fluid elemental and stable isotope composition of the Nibelungen hydrothermal field (8°18 ' S, Mid-Atlantic Ridge): constraints on fluid-rock interaction in heterogeneous lithosphere[END_REF], and of hydrothermal alteration of ultramafic rocks (i.e., serpentinization < 400 °C, [START_REF] Wetzel | Distinguishing ultramafic-from basalt-hosted submarine hydrothermal vent fluid compositions[END_REF]. However, fluids from the Piccard vents at the ultraslow spreading Cayman ridge show anomalously high H2 contents and H2/H2S ratios, for mafic-rock-derived vents [START_REF] Mcdermott | Geochemistry of fluids from Earth's deepest ridge-crest hot-springs: Piccard hydrothermal field, Mid-Cayman Rise[END_REF]. These fluids are interpreted as resulting from basalt alteration in a reaction zone at very high temperature (>500°C) and high fluid/rock ratios [START_REF] Mcdermott | Geochemistry of fluids from Earth's deepest ridge-crest hot-springs: Piccard hydrothermal field, Mid-Cayman Rise[END_REF][START_REF] Scheuermann | Quartz solubility in the two-phase region of the NaCl-H2O system: an experimental study with application to the Piccard hydrothermal field, Mid-Cayman Rise[END_REF]. This suggests that the high H2/H2S ratios analyzed in our fluid inclusions could derive from the hangingwall reaction zone. Lacking experimental data on basalt alteration at >500°C, reactions able to release such high H2 amounts remain unknow. The reaction invoked by [START_REF] Scheuermann | Experimental measurement of H2(aq) solubility in hydrothermal fluids: application to the Piccard hydrothermal field, Mid-Cayman Rise[END_REF], of amphibole destabilization to magnetite and quartz, is clearly incompatible with our rocks, as hornblende is fresh in the least altered clasts [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF], and no magnetite (neither quartz) was observed. Moreover, H2/H2S ratios in Piccard vent fluids remain lower than those measured in most of our fluid inclusions (Figure 9b), although there is no reason for different partitioning of H2 and H2S between brines and vapor phases after phase separation [START_REF] Mcdermott | Geochemistry of fluids from Earth's deepest ridge-crest hot-springs: Piccard hydrothermal field, Mid-Cayman Rise[END_REF][START_REF] Scheuermann | Experimental measurement of H2(aq) solubility in hydrothermal fluids: application to the Piccard hydrothermal field, Mid-Cayman Rise[END_REF]. Therefore, H2 production in the reaction zone seems to be possible, but may not account for the elevated H2/H2S ratios analyzed in our fluid inclusions, which are best explained by H2 derived from ultramafic-rock serpentinization.

Contribution of ultramafic-derived fluids is further supported by slight Cr and Ni enrichments of both sample ODM218b (Figure 5c) and some chlorites from highly silicified mafic breccias (Tables S2 andS3; [START_REF] Angiboust | Channelized Fluid Flow and Eclogite-facies Metasomatism along the Subduction Shear Zone[END_REF][START_REF] Boutoux | Fluid systems above basement shear zones during inversion of pre-orogenic sedimentary basins (External Crystalline Massifs, Western Alps)[END_REF][START_REF] Locatelli | Fluid pulses during stepwise brecciation at intermediate subduction depths (Monviso eclogites, W. Alps): first internally then externally sourced[END_REF][START_REF] Spandler | Internal and external fluid sources for eclogitefacies veins in the Monviso meta-ophiolite, Western Alps: Implications for fluid flow in subduction zones[END_REF].

While the hangingwall sampled by the fault zone likely extends only to the base of the dyke complex, the footwall below the fault zone and deep sections of the hangingwall likely contain mantle peridotites that witnessed fluid circulation. This is demonstrated by the occurrence of mixed breccias containing altered ultramafic clasts [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF], and the outcropping of ultramafic rocks throughout the area (Escartin et al., 2017;MacLeod et al., 2011). During exhumation, peridotites likely interacted with seawater-derived fluids, and progressively serpentinized. Fluids may have been subsequently channelized into and along the detachment fault zone. Mixing of such seawater-salinity fluids with silica-rich brines and vapor phases (prior to entrapment) could account for the wide salinity range observed in trapped fluids from the silicified breccias (Figure 8). This contribution of serpentinization fluids must remain limited nonetheless, as the absolute gas amounts trapped in fluid inclusions are extremely low. We also note that two thirds of the analyzed fluid inclusions from ODM218 have a gas signature very close to that analyzed for Irinovskoe vent fluids (Figure 9a), and that present-day fluid circulation within the footwall may record similar fluid-peridotite reactions at depth, even though these fluids do not exploit the detachment fault as a flow channel.

Detachment faulting, potential heat sources at the ridge axis and scenario for fluid pathways

Our results suggest that silicification was linked to flow along the detachment fault zone of silica-rich brines and minor vapor phases likely mainly formed in the hangingwall reaction zone (Figure 12a). Such a reaction zone at the base of the upper crust requires a heat source, such as a magma chamber at deeper levels and nearby the fault, or an along-axis dyke propagation [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF][START_REF] Macleod | Life cycle of oceanic core complexes[END_REF]. The conceptual model in Figure 12a builds on the detachment fault zone structure suggested by [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF] and [START_REF] Parnell-Turner | Genesis of corrugated fault surfaces by strain localization recorded at oceanic detachments[END_REF]. This model includes a) the incorporation of mafic clasts from the hangingwall upper crust into the detachment fault zone, from its base to the near-surface (brown stars in Figure 12), b) a thickening of the fault zone during exhumation, and c) an anastomosed fault zone mixing footwall-derived ultramafic material with dominant mafic material from the hangingwall. This model is also consistent with recent 3D seismic experiments revealing elevated seismic velocities at the footwall, both along the exposed detachment fault, and below its continuation eastwards below the rift valley floor [START_REF] Simão | 3-D P-wave velocity structure of oceanic core complexes at 13°N on the Mid-Atlantic Ridge[END_REF]. Elevated footwall seismic velocities are consistent with a lithosphere composed of lower crust and upper mantle rocks, juxtaposed to mafic rocks across the detachment [START_REF] Simão | 3-D P-wave velocity structure of oceanic core complexes at 13°N on the Mid-Atlantic Ridge[END_REF].

As illustrated in Figure 12b, we propose that seawater percolates downwards through the hangingwall crust, reaching a reaction zone at temperatures >500 °C, at or near the axial zone.

High-temperature fluids circulating into the reaction zone may hydrothermally alter surrounding mafic rocks, while releasing aqueous silica and potentially small amounts of H2S in the fluid phase (e.g., [START_REF] Bach | Metasomatism within the oceanic crust[END_REF][START_REF] Wetzel | Distinguishing ultramafic-from basalt-hosted submarine hydrothermal vent fluid compositions[END_REF]. At these P-T conditions, phase separation occurs and forms high-salinity brines and low-salinity vapor phases. The small number of inclusions recording lower-than-seawater salinity (Figure 8a) suggests that only limited amounts of vapor reached and circulated within the detachment zone, while most of these low-density vapor phases may have migrated upwards through the hangingwall crust (Figures 11 and12). Denser, less buoyant brines may be stored at depth in crustal porosity, within diabase units [START_REF] Fontaine | Dynamics and storage of brine in mid-ocean ridge hydrothermal systems[END_REF][START_REF] Fontaine | Physical controls on the salinity of mid-ocean ridge hydrothermal vent fluids[END_REF]. Brines may be released into the detachment fault zone upon diabase brecciation, together with minor amounts of vapor phases, locally produced H2S, and potentially CO2 either transported by seawater or exsolved from the magma lens. Diabase brecciation may enhance phase separation by causing sudden and local fluid pressure drops (Figure 11). In turn, fluid phase separation may also promote local overpressures that may favor brecciation along the fault [START_REF] André-Mayer | Boiling and vertical mineralization zoning: a case study from the Apacheta low-sulfidation epithermal gold-silver deposit, southern Peru[END_REF][START_REF] Bertelli | A fluid inclusion study of the Suicide Ridge Breccia Pipe, Cloncurry district, Australia: implication for breccia genesis and IOCG mineralization[END_REF], with possible links to seismicity along the detachment.

Varying gas content and wide salinity ranges of trapped fluids point to a complex and dynamic system. During silicification of the fault zone, upwelling silica-rich brines and minor vapors mixed in variable amounts with H2(± CH4)-rich fluids derived from serpentinization of ultramafic material from the footwall (Figures 11 and 12;[START_REF] Andreani | Tectonic structure, lithology, and hydrothermal signature of the Rainbow massif (Mid-Atlantic Ridge 36°14′N)[END_REF][START_REF] Mccaig | Detachment fault control on hydrothermal circulation systems: Interpreting the subsurface beneath the TAG hydrothermal field using the isotopic and geological evolution of oceanic core complexes in the Atlantic[END_REF][START_REF] Mccaig | Hydrothermal circulation and the dike-gabbro transition in the detachment mode of slow seafloor spreading[END_REF]. These fluids homogenized as a single fluid phase before trapping (one-phase fluid field, Figure 11). Fluid fluxes from these different sources were likely variable both in time and within the fault zone, resulting in strong variability of both gas content and salinity of fluid inclusions (Figures 8 and9). Significant variations of inclusion fluid composition at quartz grain scale (Figures 7b, d, S3b, e and8b) clearly indicate that the fluids circulating along the detachment were inherently heterogeneous at small spatial scales and short temporal scales. Yet there is no evidence for any systematic long-term evolution in fluid sources or fluid mixing processes during silicification (i.e., similarity in primary and secondary fluid inclusion salinity ranges). Moreover, the wide distribution of samples along axis and the pervasively silicified fault zone also indicate that this heterogeneous flow was maintained over long-periods of time, and was sampled by the detachment fault along most of its along-axis length.

All these fluids were preferentially channelized within the permeable fault zone, and silica precipitation was likely triggered by a combination of temperature decrease, pressure drops, and mixing of silica-rich brines with less-salted fluids. Both chlorite and fluid inclusion temperatures (Figures 10 and11) are lower than those measured at the base of the dyke complex elsewhere (Hole 1256; [START_REF] Alt | Subsurface structure of a submarine hydrothermal system in ocean crust formed at the East Pacific Rise, ODP/IODP Site 1256[END_REF], documenting a significant temperature drop and silicification occurring under greenschist facies conditions. Upflow silica-rich brines were likely cooled either continuously or episodically, during transient circulation in a complex, anastomosing fault zone, and coeval with deformation leading to quartz fracturing-sealing episodes (i.e., fluid pressure varying between hydrostatic and lithostatic; Figures 7 and10), but also by fluid mixing with cooler fluids from the footwall serpentinization and potentially seawater percolating from the seafloor.

Fluids trapped in detachment fault rocks vs. seafloor hydrothermal venting

Models of fluid flow and detachment faulting often assume a permeable fault zone efficiently channeling fluids to the seafloor or the shallow crust (e.g., [START_REF] Andersen | Fault geometry and permeability contrast control vent temperatures at the Logatchev 1 hydrothermal field, Mid-Atlantic Ridge[END_REF][START_REF] Mccaig | Hydrothermal circulation and the dike-gabbro transition in the detachment mode of slow seafloor spreading[END_REF][START_REF] Tao | Deep high-temperature hydrothermal circulation in a detachment faulting system on the ultra-slow spreading ridge[END_REF]. In these models, fluid flow through the detachment fault feeds hydrothermal systems found both at the footwall (e.g., Logatchev; [START_REF] Andersen | Fault geometry and permeability contrast control vent temperatures at the Logatchev 1 hydrothermal field, Mid-Atlantic Ridge[END_REF]Longqi: Tao et al., 2020) and hangingwall (TAG; [START_REF] Mccaig | Hydrothermal circulation and the dike-gabbro transition in the detachment mode of slow seafloor spreading[END_REF]. The heat source animating this circulation is often located in the upper mantle, at the base of the detachment microseismicity.

Our data and results from the 13°20'N detachment are not consistent with these deep-rooted hydrothermal systems along detachment fault zones. First, the present-day Irinovskoe hydrothermal site is located on the striated surface. As the detachment fault emerges at <20° at the hangingwall cutoff and the detachment is capped by a highly fractured and deformed fault zone (e.g., [START_REF] Escartín | Tectonic structure, evolution, and the nature of oceanic core complexes and their detachment fault zones (13°20′N and 13°30′N[END_REF][START_REF] Parnell-Turner | Genesis of corrugated fault surfaces by strain localization recorded at oceanic detachments[END_REF], no plausible mechanism can channel fluids from the active detachment fault zone below the rift valley floor (below the hangingwall cutoff) to the Irinovskoe site, over a horizontal distance of ~2 km. The footwall also displays both a highvelocity seismic anomaly underlying Irinovskoe, restricted to the shallower 2 km, and a broad low velocity zone at 7-10 km depth [START_REF] Simão | 3-D P-wave velocity structure of oceanic core complexes at 13°N on the Mid-Atlantic Ridge[END_REF]. Owing to seismic resolution limitations, the presence of magma chambers or heat sources of sizes below the seismic resolution (1 to 3 km in size, depending on the depth) cannot be excluded. We propose that the fluid circulation system underlying Irinovskoe is unrelated to the active detachment, and instead is fully hosted within the footwall, probably reaching depths >2 km. While we lack direct seismic evidence here, this model is similar to that of Rainbow, a hydrothermal field at the top of a detachment massif that is underlain by seismic reflectors identified as active and fossil magma chambers at depths >3 km (Canales et al., 2017;[START_REF] Dunn | Three-Dimensional Seismic Structure of the Mid-Atlantic Ridge: An Investigation of Tectonic, Magmatic, and Hydrothermal Processes in the Rainbow Area[END_REF].

Silicified fault rocks are distributed throughout the detachment, displaying similar fluid compositions in quartz inclusions. This observation points to a flow organization along the detachment that has not been recognized before. Geological observations demonstrate that syntectonic silicification and associated fluid circulation occurred along the whole length (alongaxis, Figure 1) of the active detachment, and that it operated continuously over time (across-axis; [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF]. Fluid inclusions further indicate that similar fluid sources (similar primary and secondary inclusions) mixed within the detachment plane (see 5.2.1 and Figure 8a). This type of distributed and pervasive hydrothermal circulation, extending laterally over several km and sustained over long periods of time, contrasts with the extremely localized outflow observed at the seafloor over relatively small surfaces (spatial scales of a few hundreds of m at most). Assuming that similar fluid circulation linked to deformation operates along the presentday, active detachment fault and at depth, this would require an extreme fluid flow localization on a short vertical distance (~2 km), in addition to implausible fluid transport within the footwall.

In our preferred interpretation, the fault zone and the fluids within cool down efficiently during exhumation at the shallower levels of the fault. This cooling can effectively suppress convection and any active circulation in shallow parts of the system, precluding discharge of high-temperature fluids at the seafloor. We suggest that the observed present-day hydrothermal activity observed on the surface of footwall of detachments (e.g., Rainbow, Semenov, Irinovskoe, Mount Den, Mount Fuji) is most likely due to heat sources underlying these sites and located within the detachment footwall, rather than fluids steered along the detachment fault and with significant lateral flow. The hydrothermal system that we document here may be indeed active at depth at 13°20'N, and be widespread at other systems. Indeed, many active detachments rooting near-axis (e.g., TAG, Dragon Horn) may be active in close proximity to nearby heat sources (melt lenses or dykes propagating along-axis), sampling fluids from the associated reaction zone at depth. As these systems may be restricted to deep lithospheric levels (>1 km) and lack a seafloor expression, they may only be identifiable studying in situ detachment fault rocks.

Conclusions

The 13°20'N detachment fault zone displays pervasive, syntectonic silicification of fault breccia that is originally mostly of mafic origin (diabase). Quartz crystals in breccia matrix and clasts preserve fluid inclusions. Their analyses, coupled to both bulk-rock and chlorite geochemical compositions, allow us to constrain hydrothermal fluid flow during deformation, and propose a conceptual model of detachment deformation and fluid flow.

First, we document the mixing of two fluid sources based on fluid inclusion salinity and gas content: 1) primarily brines and minor amounts of vapor phases resulting from phase separation at high temperature (T >410 °C), and likely occurring in the hangingwall reaction zone at the base of the dyke complex; and 2) minor amounts of fluids that interacted with ultramafic rocks, likely recording serpentinization reactions at temperatures of 200-350 °C, associated with H2 (and CH4) production. The lack of correlation between salinity and gas content, as well as quartz grain-scale variations of fluid composition, suggests syntectonic mixing in variable proportions of compositionally heterogeneous flows at small spatial and short temporal scales.

The hydrothermal circulation we document along the detachment fault zone reaches the base of the hangingwall dyke complex, i.e., 2 km depth, as constrained by seismic refraction data. Fault zone rocks are brecciated and incorporated into the detachment, together with the silica-rich brines emanating from a nearby reaction zone. A significant temperature drop is recorded by chlorite thermometry, from amphibolite facies (~500 °C) to quartz/chlorite equilibrium temperatures as low as ~200 °C. This temperature drop likely occurs both over small spatial distances and over short periods of time, with transients, promoting syntectonic silica precipitation in the fault zone. The hydrothermal circulation documented here is decoupled from present day hydrothermal activity at the seafloor. We suggest that detachment-related hydrothermal flow, which is widespread, is likely hosted within the footwall of detachments, passively cross-cuts inactive detachment faults, and is unrelated to the active detachment fault operating at depth. Table 1. Characteristics of the six fault rocks considered for this study. The outcrop numbers refer to Figure 1b and to Bonnemains et al. (2017). with the ROV are shown by a circle (see [START_REF] Bonnemains | Pervasive silicification and hanging wall overplating along the 13°20′N oceanic detachment fault (Mid-Atlantic Ridge)[END_REF]. Samples used for this study come from five of them (black numbered circles and associated red symbols, see Table 1 for details). other oceanic chlorites from ultramafic rocks (talcschists from 15°45'N: [START_REF] Escartín | Constraints on deformation conditions and the origin of oceanic detachments: The Mid-Atlantic Ridge core complex at 15°45[END_REF]south of Atlantis Massif: Boschi et al., 2006); mixed mafic-ultramafic amphibolite schists [START_REF] Escartín | Constraints on deformation conditions and the origin of oceanic detachments: The Mid-Atlantic Ridge core complex at 15°45[END_REF]; mafic rocks (diabases: [START_REF] Escartín | Constraints on deformation conditions and the origin of oceanic detachments: The Mid-Atlantic Ridge core complex at 15°45[END_REF]basalts from MAR: Humphris &[START_REF] Humphris | Hydrothermal alteration of oceanic basalts by seawater[END_REF]from MARK: Gillis andThompson, 1993); altered mafic rocks (silicified breccias from MARK: [START_REF] Delaney | Quartz-cemented breccias from the Mid-Atlantic Ridge: Samples of a high-salinity hydrothermal upflow zone[END_REF][START_REF] Saccocia | Hydrothermal upflow zones in the oceanic crust[END_REF] S2 andS4. [START_REF] Delaney | Quartz-cemented breccias from the Mid-Atlantic Ridge: Samples of a high-salinity hydrothermal upflow zone[END_REF][START_REF] Saccocia | Hydrothermal upflow zones in the oceanic crust[END_REF] and TAG [START_REF] Petersen | Fluid inclusion studies as a guide to the temperature regime within the TAG hydrothermal mound[END_REF], detachment plane (ultra)mafic rocks hosting hydrothermal vents (Rainbow, Logatchev, Ashadze, Semenov, Irinovskoe;[START_REF] Bortnikov | The physicochemical conditions of hydrothermal ore-forming systems of "black smokers" associated with mantle ultrabasites in the Central Atlantic region[END_REF][START_REF] Bortnikov | Anomalously high concentrations of metals in fluid of the Semenov Modern Hydrothermal System (Mid-Atlantic Ridge, 13°31"N): LA-ICP-MS study of fluid inclusions in minerals[END_REF][START_REF] Bortnikov | The metalliferous fluid of the hydrothermal sulfide system associated with the oceanic core complex 13°20´N, The Mid-Atlantic Ridge (LA-ICP-MS and fluid inclusions)[END_REF][START_REF] Simonov | LA-ICP-MS evidence for high concentrations of metals in fluid from modern sea-floor hydrothermal systems: a case study of fluid inclusions in minerals from Semenov, Ashadze, and Logatchev sulfide edifices (Mid-Atlantic Ridge)[END_REF]; (b) Heterogeneity of inclusion Th and salinity at the sample scale for the primary inclusions only, for clarity issues, using a similar color and symbol for inclusions in each grain. Seawater salinity is indicated with a blue line. [START_REF] Fouquet | Geodiversity of Hydrothermal Processes Along the Mid-Atlantic Ridge and Ultramafic-Hosted Mineralization: a New Type Of Oceanic Cu-Zn-Co-Au Volcanogenic Massive Sulfide Deposit[END_REF].

Tables

Data from Semenov and Irinovskoe ultramafic-derived vents [START_REF] Destrigneville | Thermo-chemical fluxes, reactions and mixing in hydrothermal plumes at oceanic core complexes (Mid-Atlantic Ridge, 13°30'N and 13[END_REF] (equation of [START_REF] Zhang | Determination of the homogenization temperatures and densities of supercritical fluids in the system NaCl-KCl-CaCl2-H2O using synthetic fluid inclusions[END_REF], are plotted in black plain and dashed lines for primary and secondary fluid inclusions respectively. The liquid-vapor and liquid-vapor-halite curves are from [START_REF] Sourirajan | The system H 2 O-NaCl at elevated temperatures and pressures[END_REF]. Pressure at the seafloor is indicated with a blue line, and the range of lithostatic and hydrostatic fluid pressures at the base of the hangingwall upper crust (1-2 km thick) is in grey and blue respectively (assuming seawater and rock densities of 1025 and 3000 kg/m 3 respectively). The temperature range of chlorite crystallization during silicification, calculated from chlorite composition (geothermometer of [START_REF] Bourdelle | A new chlorite geothermometer for diagenetic to low-grade metamorphic conditions[END_REF], is in green (darker green for higher number of chlorites; see Figure 6d). to data for basalts and diabases from the 13°20'N OCC [START_REF] Wilson | Mantle composition controls the development of an Oceanic Core Complex[END_REF] and for peridotites from the 15°20'N Fracture Zone [START_REF] Godard | Geochemistry of the highly depleted peridotites drilled at ODP Sites 1272 and 1274 (Fifteen-Twenty Fracture Zone, Mid-Atlantic Ridge): Implications for mantle dynamics beneath a slow spreading ridge[END_REF][START_REF] Paulick | Geochemistry of abyssal peridotites (Mid-Atlantic Ridge, 15°20'N, ODP Leg 209): implications for fluidrock interaction in slow spreading environments[END_REF]. Analyses carried out at GeoRessources (Nancy, France) with a 193 nm GeoLas Pro ArF Excimer laser (Microlas, Göttingen. Germany) coupled with beam homogenization optics. Analyzed with an Agilent 7500c Quadrupole ICP-MS (Agilent, Santa Clara, USA) equipped with an octopole reaction system with enhanced sensitivity optional lenses (Cs type; Agilent). Internal standard: 28 Si, calibrated from the mean value of several chlorite microprobe analyses.

C6 C6 C-3 C-3 C-3 C-3 C-3 C-3 C-3 C-4 C-4 C-4 C-4 C-4 C-4 C-5 C-6 C-6 C-6 C-7 C-7 C-
a Element analyzed (isotope)

b Concentrations in ppm calibrated against the NIST SRM 610 silica glass reference using values given in [START_REF] Pearce | Compilation of new and published major trace element data for NIST 610 NIST SRM 612 glass reference materials[END_REF]. Absolute concentrations (ppm) calculated from equations in [START_REF] Longerich | Laser ablation inductively coupled plasma mass spectrometric transient signal data acquisition and analyte concentration calculation[END_REF].

FiguresFigure 1 :

 1 Figures

  Figure 1: (a) Multibeam bathymetry data of the 13°20'N detachment region, showing the core complex (black box) and the ridge axis (thick black lines). (b) Shaded relief microbathymetry acquired with the AUV Abyss (GEOMAR), collected during the ODEMAR cruise (https://doi.org/10.17600/13030070) over the 13°20'N OCC, complemented with shipboard bathymetry. White lines are tracks of ten ROV dives. Fault surface outcrops identified and sampled

Figure 2 :

 2 Figure 2: Macro-photographs of the studied fault rocks. (a) Clast of metabasalt with no quartz ODM115. (b) Moderately silicified mafic breccia ODM195. (c) Highly silicified mafic breccia ODM155. (d) Highly silicified mafic breccia ODM218 that is distinguished in two parts (subsamples a and b) at different distance from the striated surface (or slip plane) and a fragment dislodged from the lower part of sample (subsample ODM218c). (e) Unsilicified mafic-ultramafic breccia ODM217. We identify two parts based on the difference in color and mineralogical

Figure 3 :

 3 Figure 3: Microphotographs of studied samples in plane polarized light. (a) Unsilicified mafic clast showing basaltic texture with radiating plagioclase (Pl) laths and dendritic olivine (Ol) crystals. (b) Moderately silicified mafic breccia contains clasts displaying a doleritic texture, made of amphibole (Amp) + plagioclase ± chlorite (Chl), surrounded by a matrix consisting of crushed clasts mixed with chlorite and quartz (Qz). (c, d) Highly silicified mafic breccias containing clasts

Figure 4 :

 4 Figure 4: Microphotographs of representative two-phase (liquid and vapor) fluid inclusions in quartz grains. Clustered fluid inclusions with similar vapor/liquid ratios are considered as primary (a, d; e; i); fluid inclusions organized in trails are considered as secondary inclusions (b, c, f, g, h).

Figure 6 :

 6 Figure 6: Chlorite composition in clasts and matrices (a) in a FeO+MgO, Al2O3, SiO2 ternary diagram; (b) Mg# versus Si (atoms per formula unit); chlorite compositions are compared to

  chlorite-quartz vein in diabase, Atlantis Massif: Castelain et al., 2014); (c) Si versus R 2+ diagram with chlorite endmembers; (d) Histogram of chlorite crystallization temperatures estimated using the semiempirical geothermometer of Bourdelle et al. (2013). Chlorite analyses and calculated temperatures are available in Tables

Figure 7 :

 7 Figure 7: Distribution of measured fluid inclusions in quartz grains from ODM218b (a and b, orange dots) and ODM218c (c and d, green dots). Microphotographs under parallel nicols showing

Figure 8 :

 8 Figure 8: Homogenization temperatures (Th) against salinity for (a) all primary and secondary fluid inclusions; data are compared to Th and salinity ranges measured in fluid inclusions from oceanic gabbros (MARK: Kelley and Delaney, 1987), diabases (Atlantis Massif: Castelain et al., 2014), mafic silicified breccias from MARK[START_REF] Delaney | Quartz-cemented breccias from the Mid-Atlantic Ridge: Samples of a high-salinity hydrothermal upflow zone[END_REF][START_REF] Saccocia | Hydrothermal upflow zones in the oceanic crust[END_REF]

Figure 9 :

 9 Figure 9: Molar proportion of gases (other than H2O) analyzed by Raman spectroscopy in the vapor phase of two-phase fluid inclusions for the two highly silicified mafic breccias ODM155 and ODM218. All fluid inclusions are dominantly aqueous, and H2O vapor is the dominant gas phase. (a) Relative molar proportions of CH4, CO2 and H2 in the gas phase. Gases other than H2O were analyzed in only 2 inclusions (over 17 analyzed) for ODM155 (and contain only CO2 other than H2O vapor), in 15 inclusions over 28 analyzed for ODM218b, and in the 21 fluid inclusions analyzed in ODM218c. 7 and 11 fluid inclusions contain only H2 (other than H2O vapor) in ODM218b and ODM218c, respectively. (b) H2 versus H2S content in fluid inclusions (expressed as a mol.% of CH4-CO2-H2-H2S in the vapor phase). Fluid inclusion gas compositions are compared to data from basaltic-(Menez Gwen, Broken Spur, TAG, Snake Pit, Lucky Strike) and ultramafic-(Rainbow, Logatchev, Lost City) derived hydrothermal vents[START_REF] Fouquet | Geodiversity of Hydrothermal Processes Along the Mid-Atlantic Ridge and Ultramafic-Hosted Mineralization: a New Type Of Oceanic Cu-Zn-Co-Au Volcanogenic Massive Sulfide Deposit[END_REF].

Figure 10 :

 10 Figure 10: Range of P-T conditions for silicification of brecciated rocks within the detachment plane. P-T isochoric relationships for fluid inclusions, calculated from microthermometric data

Figure 11 :

 11 Figure 11: P-T-depth relationships in the NaCl-H2O system for a hydrothermal seawater-like solution (3.2 wt.% NaCl). The two-phase curve separates the one-phase liquid field from the twophase liquid+vapor field (Sourirajan & Kennedy, 1962). Temperature-depth relationship for the two-phase curve beyond the critical point (407°C, 298 bars, black dot) is calculated for both lithostatic and hydrostatic fluid pressures. Cold and hot hydrostatic pressure gradients (100 and 50 bar/km respectively) were taken from Coumou et al. (2009) and Castelain et al. (2014). Seawater (blue arrow) infiltrating the hangingwall crust (1-2 km thick) may undergo phase separation, at least when reaching the reaction zone (orange rectangle) at the base of the crust (diabase clasts suggest temperature >500 °C). While part of vapor phases can migrate upwards into the crust, higher density brines are likely released in the detachment plane upon diabase brecciation (red arrows). They are mixed in variable amounts with fluids derived from footwall serpentinization

Figure 12 :

 12 Figure 12: Schematic interpretation of fluid circulation along the 13°20'N OCC. (a) The hangingwall corresponds to a section of upper crust while the footwall progressively exhumes

Figure S1 :

 S1 Figure S1: Bulk rock geochemistry. SiO2 versus (a) Na2O and (b) Al2O3; brecciated rocks show a relative decrease in both Na2O and Al2O3 with increasing degree of silicification; grey arrows: trend of passive depletion of Na2O and Al2O3 in breccias due to silica addition. (c) Rare earth element (REE) content of brecciated rocks normalized to chondrite. Compositions are compared

Figure S2 :

 S2 Figure S2: Size distribution (left) and bubble/inclusion volumetric ratio (right) histograms for primary (top) and secondary (bottom) fluid inclusions. Vertical axis is frequency.

Figure S3 :

 S3 Figure S3: Location of analyzed fluid inclusions in quartz grains from ODM218b (a and b, orange dots in c) and ODM155 (d and e, green stars in c). Microphotographs under parallel nicols showing individual quartz crystals in ODM218b (a) and in ODM155 (d). SEM-cathodoluminescence images of the same quartz grains in ODM218b (b) and in ODM155 (e); grain boundaries are shown by the white dashed line; luminescence variations illustrate that quartz grains are composed of multiple former quartz angular clasts around which quartz recrystallized in successive generations. Quartz crystallization was unequivocally syntectonic, with successive steps of quartz growth-hydrofracturing-overgrowth. (c) Homogenization temperatures (Th) against salinity (indicated in wt.% NaCl equivalent) for primary (big symbols) and secondary (small symbols) fluid inclusions from quartz grains in ODM218b (a, b) and ODM155 (d, e). Seawater salinity is indicated with a blue line. The large salinity variation measured from fluid inclusions within individual grains indicates entrapment of fluids with varying salinities during successive quartz growth episodes. Note that the position of fluid inclusions was projected on the grain surface, while inclusions are in fact distributed at various depths within the quartz grain. In ODM218b (a, b) inclusions in red are those very close to the thick section surface.

Figure S4 :

 S4 Figure S4: Histogram showing the distribution of homogenization temperatures (Th, left) and ice melting temperatures (Tmice, right) for primary (top) and secondary (bottom) fluid inclusions. Vertical axis is frequency.

Figure S5 :

 S5 Figure S5: Gas content (mol.% of gas other than H2O in the gas bubble) versus homogenization temperature (Th) and salinity.

Table 2 .

 2 Major and selected trace element whole-rock analyses of mafic and mixed mafic-ultramafic breccias from the detachment fault surface (see TableS1for full analyses).

	Nature		Basaltic clast	Mafic	Mafic	Mafic	Mafic	Mafic	Mixed	Mixed	Mixed	Mixed	Mixed	Mixed
	Degree of silicification	Qz free	Moderately Si	Highly Si	Highly Si	Highly Si	Highly Si	Qz free	Qz free	Qz free	Moderately Si Moderately Si	Moderately Si
	Sample		ODM115	ODM195	ODM218a ODM218b ODM218 wr ODM155 ODM217a ODM217b ODM217 wr	ODM173a	ODM173b	ODM173 wr
	SiO2	wt.%	51.81	49.16	84.35	62.40	65.72	79.27	49.41	55.08	48.90	55.64	57.37	68.25
	Al2O3	wt.%	13.76	13.05	2.69	4.12	3.78	2.43	5.46	2.26	5.25	9.05	1.50	5.18
	Fe2O3	wt.%	8.16	10.76	6.30	19.97	17.09	9.47	11.25	8.07	12.50	13.79	10.04	11.07
	MnO	wt.%	0.16	0.22	0.06	0.08	0.08	0.06	0.33	0.39	0.45	0.11	0.07	0.07
	MgO	wt.%	6.08	11.88	2.43	4.33	4.08	2.10	22.70	22.93	21.30	11.24	20.49	8.18
	CaO	wt.%	11.27	4.57	0.28	0.48	0.30	0.28	4.32	6.72	5.33	0.24	0.09	0.17
	Na2O	wt.%	3.78	1.23	< D.L.	0.11	0.07	0.05	0.22	0.20	0.24	0.29	0.28	0.17
	K2O	wt.%	0.09	0.04	< D.L.	< D.L.	< D.L.	0.02	0.03	0.03	0.04	0.04	0.03	0.03
	TiO2	wt.%	1.37	0.65	0.17	0.27	0.26	0.15	0.42	0.12	0.40	0.49	< D.L.	0.26
	P2O5	wt.%	0.16	< D.L.	< D.L.	< D.L.	< D.L.	< D.L.	0.06	< D.L.	0.05	0.05	< D.L.	0.04
	PF	wt.%	3.03	7.22	3.44	7.72	7.77	6.67	6.39	4.86	6.52	9.18	10.28	6.24
	Total	wt.%	99.65	98.79	99.71	99.48	99.14	100.49	100.60	100.67	100.97	100.11	100.15	99.66
	Mg #		59.61	68.62	43.26	30.05	32.11	30.51	80.00	84.91	77.15	61.74	80.18	59.41
	FeO	wt.%	4.74	5.54	5.50	14.46	12.49	3.51	8.01	5.61	8.85	7.45	5.75	6.14
	S	wt.%	0.04	0.04	1.04	7.68	6.21	4.75	0.02	0.03	0.02	0.66	0.69	1.98
	Cr	ppm

Table S1 .

 S1 Full chemical analyses of the selected samples. 1603 1604

	Nb	ppm	6.84	0.57	1.08	1.46	1.47	0.89	3.90	0.88	2.96	2.07	< D.L.	1.16
	Nd	ppm	10.30	3.43	1.28	1.60	1.52	0.89	3.45	1.01	2.69	2.59	0.21	1.20
	Ni	ppm	112.80	126.40	140.40	492.70	385.90	190.70	1080.00	1180.00	1064.00	429.50	1609.00	710.70
	Nature Pb	ppm	Basaltic clast 0.90	Mafic < D.L.	Mafic < D.L.	Mafic 1.23	Mafic 1.17	Mafic 1.08	Mixed < D.L.	Mixed < D.L.	Mixed < D.L.	Mixed < D.L.	Mixed 2.24	Mixed 1.22
	Degree of silicification Pr ppm	Qz free 2.05	Moderately Si 0.58	Highly Si 0.26	Highly Si 0.31	Highly Si 0.29	Highly Si 0.18	Qz free 0.75	Qz free 0.21	Qz free 0.56	Moderately Si Moderately Si 0.49 0.04	Moderately Si 0.20
	Sample Rb	ppm	ODM115 0.79	ODM195 < D.L.	ODM218a < D.L.	ODM218b < D.L.	ODM218 wr < D.L.	ODM155 < D.L.	ODM217a < D.L.	ODM217b < D.L.	ODM217 wr < D.L.	ODM173a < D.L.	ODM173b < D.L.	ODM173 wr < D.L.
	SiO2 Sc	wt.% ppm	51.81 38.58	49.16 32.40	84.35 5.40	62.40 8.67	65.72 8.67	79.27 5.12	49.41 15.97	55.08 9.30	48.90 16.01	55.64 22.31	57.37 9.47	68.25 12.85
	Al2O3 Sb	wt.% ppm	13.76 < D.L.	13.05 < D.L.	2.69 < D.L.	4.12 < D.L.	3.78 < D.L.	2.43 < D.L.	5.46 < D.L.	2.26 < D.L.	5.25 < D.L.	9.05 < D.L.	1.50 0.25	5.18 < D.L.
	Fe2O3 Sm	wt.% ppm	8.16 3.30	10.76 1.36	6.30 0.37	19.97 0.51	17.09 0.50	9.47 0.28	11.25 1.03	8.07 0.31	12.50 0.90	13.79 0.95	10.04 0.10	11.07 0.50
	MnO Sn	wt.% ppm	0.16 1.55	0.22 0.64	0.06 3.80	0.08 0.48	0.08 0.52	0.06 9.66	0.33 < D.L.	0.39 < D.L.	0.45 0.54	0.11 0.79	0.07 0.83	0.07 1.09
	MgO Sr	wt.% ppm	6.08 145.50	11.88 32.01	2.43 < D.L.	4.33 4.17	4.08 < D.L.	2.10 3.86	22.70 5.94	22.93 4.84	21.30 6.93	11.24 9.61	20.49 4.48	8.18 6.18
	CaO Ta	wt.% ppm	11.27 0.52	4.57 0.05	0.28 0.09	0.48 0.11	0.30 0.11	0.28 0.07	4.32 0.28	6.72 0.06	5.33 0.21	0.24 0.16	0.09 < D.L.	0.17 0.08
	Na2O Tb	wt.% ppm	3.78 0.69	1.23 0.35	< D.L. 0.07	0.11 0.11	0.07 0.11	0.05 0.04	0.22 0.21	0.20 0.06	0.24 0.20	0.29 0.24	0.28 0.02	0.17 0.14
	K2O Th	wt.% ppm	0.09 0.55	0.04 < D.L.	< D.L. < D.L.	< D.L. 0.12	< D.L. 0.11	0.02 0.07	0.03 0.29	0.03 0.07	0.04 0.23	0.04 0.16	0.03 < D.L.	0.03 0.08
	TiO2 Tm	wt.% ppm	1.37 0.41	0.65 0.24	0.17 0.04	0.27 0.07	0.26 0.06	0.15 0.03	0.42 0.12	0.12 0.04	0.40 0.12	0.49 0.15	< D.L. 0.01	0.26 0.08
	P2O5 U	wt.% ppm	0.16 0.19	< D.L. < D.L.	< D.L. 0.07	< D.L. 0.07	< D.L. 0.06	< D.L. 0.05	0.06 0.13	< D.L. 0.07	0.05 0.15	0.05 0.14	< D.L. 0.45	0.04 0.14
	PF V	wt.% ppm	3.03 266.50	7.22 180.50	3.44 35.06	7.72 58.83	7.77 54.12	6.67 34.71	6.39 99.12	4.86 49.06	6.52 99.92	9.18 115.90	10.28 42.02	6.24 68.29
	Total W	wt.% ppm	99.65 0.32	98.79 < D.L.	99.71 0.72	99.48 < D.L.	99.14 < D.L.	100.49 0.55	100.60 0.32	100.67 < D.L.	100.97 0.41	100.11 1.28	100.15 < D.L.	99.66 1.21
	Mg # Y	ppm	59.61 26.89	68.62 14.83	43.26 2.43	30.05 4.39	32.11 4.12	30.51 1.91	80.00 7.95	84.91 2.65	77.15 7.71	61.74 10.34	80.18 0.61	59.41 5.87
	FeO Yb	wt.% ppm	4.74 2.80	5.54 1.63	5.50 0.23	14.46 0.45	12.49 0.43	3.51 0.24	8.01 0.79	5.61 0.28	8.85 0.80	7.45 1.01	5.75 0.08	6.14 0.57
	H2O total Zn	wt.% ppm	3.22 60.02	8.13 105.60	2.49 45.73	4.20 56.51	4.32 64.18	2.62 33.78	7.05 139.50	5.55 115.00	6.95 161.80	8.93 237.90	< D.L. 2947.00	5.32 379.70
	S total Zr	wt.% ppm	0.04 84.25	0.04 29.36	1.04 10.77	7.68 17.07	6.21 16.19	4.75 10.14	0.02 27.35	0.03 7.70	0.02 24.15	0.66 24.61	0.69 < D.L.	1.98 14.00
	B <D.L.: lower than detection limit. Qz: quartz. Highly/moderately Si: highly/moderately silicified ppm 5 2 2 <2	<2	4	11	8	14	8	10	7
	Cl	ppm	230	800	240	355	295	235	435	380	580	1 520	2 540	1 030
	Li	ppm	3.7	7.6	5.4	3.0		3.3	8.3	7.4	7.6	7.4	4.3	4.2	3.1
	As	ppm	2.29	< D.L.	< D.L.	< D.L.	< D.L.	1.80	1.88	1.75	3.25	1.68	< D.L.	< D.L.
	Ba	ppm	35.37	4.17	3.00	1.67	< D.L.	2.66	< D.L.	1.69	< D.L.	1.90	< D.L.	6.75
	Be	ppm	0.64	< D.L.	< D.L.	< D.L.	< D.L.	< D.L.	0.46	0.60	0.50	< D.L.	< D.L.	< D.L.
	Bi	ppm	0.19	< D.L.	0.21	0.69	1.30	0.32	< D.L.	< D.L.	0.10	0.12	0.52	0.20
	Cd	ppm	0.14	< D.L.	< D.L.	< D.L.	0.12	< D.L.	< D.L.	< D.L.	< D.L.	0.68	203.80	12.18
	Ce	ppm	13.19	3.13	1.81	2.03	1.98	1.20	5.26	1.38	3.77	3.17	0.20	1.35
	Co	ppm	30.87	31.10	36.76	206.20	151.30	82.21	71.51	61.76	71.78	49.51	280.50	60.67
	Cr	ppm	308.50	349.30	293.70	590.40	525.60	303.30	1826.00	1895.00	2070.00	934.30	3319.00	1214.00
	Cs	ppm	< D.L.	< D.L.	< D.L.	< D.L.	< D.L.	< D.L.	< D.L.	< D.L.	< D.L.	< D.L.	< D.L.	< D.L.
	Cu	ppm	66.84	11.68	87.36	564.10	697.30	19.05	874.20	450.80	1540.00	504.20	1609.00	605.20
	Dy	ppm	4.72	2.55	0.48	0.79	0.75	0.30	1.40	0.44	1.38	1.68	0.11	0.92
	Er	ppm	2.89	1.65	0.26	0.47	0.45	0.21	0.80	0.27	0.81	1.05	0.07	0.59
	Eu	ppm	1.09	0.48	0.12	0.14	0.13	0.04	0.23	0.18	0.19	0.10	0.02	0.05
	Ga	ppm	13.96	11.95	3.46	5.99	5.77	3.93	8.09	4.23	8.36	11.42	5.84	7.08
	Gd	ppm	3.93	1.88	0.43	0.63	0.60	0.25	1.21	0.38	1.12	1.32	0.09	0.75
	Ge	ppm	1.85	0.75	0.50	0.43	0.40	0.28	1.57	1.64	1.95	0.61	5.09	0.74
	Hf	ppm	2.45	0.97	0.27	0.48	0.45	0.28	0.75	0.22	0.68	0.75	< D.L.	0.39
	Ho	ppm	1.05	0.59	0.10	0.18	0.16	0.07	0.31	0.10	0.30	0.39	0.02	0.22
	In	ppm	< D.L.	< D.L.	< D.L.	< D.L.	< D.L.	< D.L.	0.11	< D.L.	0.18	< D.L.	< D.L.	< D.L.
	La	ppm	5.40	0.99	0.80	0.83	0.83	0.44	2.26	0.61	1.55	1.33	< D.L.	0.55
	Lu	ppm	0.43	0.25	0.04	0.07	0.07	0.04	0.12	0.04	0.12	0.15	0.01	0.09
	Mo	ppm	< D.L.	< D.L.	5.58	12.11	8.58	1.43	< D.L.	< D.L.	< D.L.	1.39	184.30	14.06

Table S2 .

 S2 Chemical analysis (wt.%) and structural formulas of chlorite, and calculated temperature of formation. temperature of chlorite formation calculated from R 2+ and Si with the thermometer of[START_REF] Bourdelle | A new chlorite geothermometer for diagenetic to low-grade metamorphic conditions[END_REF] calibrated for Tchl < 350 °C; a quadratic correction is applied for Tchl > 350 °C (Tcorrected) Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast

	Sample	155	155	155	155	155	155	155	155	155	155	155	155	155	155	155	155	155	155	155	155	155	155	155
	Clast vs matrix
	Sample Analysis # Clast vs matrix Chlorite composition a	195 14 Clast Clast Clast Clast Clast Clast Clast Clast Clast 195 195 195 195 195 195 195 195 73 / 1 75 / 1 76 / 1 77 / 1 81 / 1 82 / 1 83 / 1 41 / 1 . . . . . . . .	195 42 / 1 Mat .	195 43 / 1 Mat .	195 44 / 1 Mat .	195 45 / 1 Mat .	195 46 / 1 Mat .	195 48 / 1 Mat .	195 49 / 1 Mat .	195 50 / 1 Mat .	195 51 / 1 Mat .	195 52 / 1 Mat .	195 53 / 1 Mat .	195 54 / 1 Mat .	195 57 / 1 Mat .	58 / 1 195 Mat .
	Analysis # Chlorite composition a SiO2 TiO2 Al2O3 Cr2O3 FeO MnO MgO NiO CaO Na2O K2O total K2O+Na2O+CaO Structural formula b Si Ti Al Al IV Al VI Cr Fe Mn Mg Ni Ca Na K octaedral sum vacancies Mg# c R 2+ d octaedral sum vacancies 4.63 Sample 5 / 1 . 6 / 1 . 9 / 1 . 10 / 1 . 28.30 28.08 29.32 29.98 30.82 29.17 28.24 28.74 30.86 29.18 29.87 29.07 29.23 31.32 29.51 30.67 30.05 30.82 30.91 30.18 30.26 31.25 30.98 29 / 1 . 31 / 1 . 34 / 1 . 36 / 1 . 37 / 1 . 12 / 1 . 15 / 1 . 24 / 1 . 27 / 1 . 2 / 1 . 3 / 1 . 4 / 1 . 5 / 1 . 7 / 1 . 8 / 1 . 9 / 1 . 10 / 1 . 11 / 1 . 12 / 1 . 0.01 0.04 0.02 0.00 0.01 0.01 0.06 0.00 0.02 0.01 0.00 0.00 0.08 0.02 0.00 0.00 0.04 0.00 0.04 0.00 0.01 0.02 0.02 19.56 19.77 18.45 18.28 17.94 18.94 20.21 19.39 17.39 19.45 19.06 19.14 18.93 18.64 18.77 17.80 17.65 18.54 17.51 18.48 17.67 17.83 18.10 0.00 0.00 0.00 0.00 0.01 0.00 0.06 0.05 0.00 0.00 0.00 0.07 0.00 0.00 0.00 0.01 0.01 0.03 0.08 0.03 0.04 0.04 0.00 18.76 18.44 16.25 15.57 16.08 16.45 15.93 15.62 14.80 16.77 16.88 16.86 16.09 14.84 14.91 15.42 16.29 14.63 14.77 15.25 14.64 15.73 14.73 0.49 0.37 0.32 0.25 0.39 0.38 0.19 0.23 0.31 0.43 0.38 0.35 0.36 0.35 0.42 0.37 0.44 0.34 0.39 0.33 0.46 0.37 0.39 19.38 19.96 22.28 22.99 22.03 21.12 22.20 22.85 23.26 21.70 21.47 21.86 21.58 23.24 22.82 21.58 21.48 23.53 22.65 23.16 23.04 22.40 23.21 0.07 0.00 0.02 0.04 0.02 0.07 0.01 0.00 0.04 0.02 0.12 0.01 0.05 0.00 0.06 0.05 0.02 0.07 0.03 0.02 0.00 0.05 0.05 0.05 0.07 0.19 0.10 0.14 0.14 0.09 0.05 0.11 0.14 0.15 0.14 0.20 0.21 0.16 0.25 0.21 0.16 0.25 0.16 0.20 0.23 0.20 0.05 0.02 0.11 0.06 0.05 0.05 0.02 0.03 0.05 0.02 0.03 0.04 0.05 0.06 0.06 0.03 0.07 0.08 0.08 0.05 0.10 0.09 0.07 0.00 0.02 0.05 0.06 0.05 0.04 0.03 0.02 0.03 0.01 0.03 0.02 0.04 0.06 0.05 0.06 0.13 0.08 0.10 0.05 0.06 0.09 0.06 86.68 86.77 87.00 87.32 87.54 86.37 87.04 86.97 86.87 87.74 87.99 87.54 86.62 88.73 86.75 86.26 86.40 88.30 86.80 87.72 86.48 88.09 87.82 0.10 0.11 0.35 0.21 0.24 0.23 0.14 0.10 0.19 0.17 0.21 0.20 0.29 0.32 0.27 0.34 0.42 0.32 0.43 0.26 0.36 0.41 0.33 2.91 2.87 2.96 3.00 3.08 2.97 2.84 2.89 3.09 2.92 2.98 2.92 2.96 3.06 2.96 3.10 3.05 3.03 3.10 3.00 3.04 3.09 3.06 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 2.37 2.38 2.19 2.15 2.11 2.27 2.40 2.30 2.05 2.30 2.24 2.27 2.26 2.15 2.22 2.12 2.11 2.15 2.07 2.16 2.10 2.08 2.11 1.09 1.13 1.04 1.00 0.92 1.03 1.16 1.11 0.91 1.08 1.02 1.08 1.04 0.94 1.04 0.90 0.95 0.97 0.90 1.00 0.96 0.91 0.94 1.27 1.26 1.15 1.15 1.19 1.24 1.24 1.19 1.13 1.22 1.23 1.19 1.22 1.21 1.19 1.22 1.17 1.18 1.16 1.16 1.14 1.18 1.17 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 1.61 1.58 1.37 1.30 1.34 1.40 1.34 1.31 1.24 1.41 1.41 1.42 1.36 1.21 1.25 1.30 1.38 1.20 1.24 1.27 1.23 1.30 1.22 0.04 0.03 0.03 0.02 0.03 0.03 0.02 0.02 0.03 0.04 0.03 0.03 0.03 0.03 0.04 0.03 0.04 0.03 0.03 0.03 0.04 0.03 0.03 2.97 3.05 3.35 3.43 3.28 3.20 3.33 3.43 3.47 3.24 3.20 3.28 3.26 3.39 3.42 3.25 3.25 3.45 3.38 3.43 3.46 3.31 3.42 0.01 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.02 0.01 0.01 0.02 0.01 0.00 0.01 0.01 0.02 0.01 0.02 0.02 0.02 0.03 0.02 0.02 0.03 0.02 0.02 0.02 0.02 0.01 0.00 0.02 0.01 0.01 0.01 0.00 0.01 0.01 0.00 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.02 0.01 0.01 0.02 0.02 0.01 0.00 0.00 0.01 0.01 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.01 0.01 0.02 0.01 0.01 0.01 0.01 0.01 0.01 5.91 5.93 5.95 5.93 5.87 5.91 5.95 5.96 5.89 5.93 5.90 5.95 5.91 5.87 5.93 5.85 5.90 5.91 5.88 5.93 5.92 5.87 5.89 0.09 0.07 0.05 0.07 0.13 0.09 0.05 0.04 0.11 0.07 0.10 0.05 0.09 0.13 0.07 0.15 0.10 0.09 0.12 0.07 0.08 0.13 0.11 0.65 0.66 0.71 0.72 0.71 0.70 0.71 0.72 0.74 0.70 0.69 0.70 0.71 0.74 0.73 0.71 0.70 0.74 0.73 0.73 0.74 0.72 0.74 5.88 5.92 5.85 5.92 5.81 5.89 5.89 5.86 5.91 5.97 5.88 5.95 5.89 5.94 5.94 5.92 5.95 5.91 5.97 5.93 5.93 5.90 5.92 0.12 0.08 0.15 0.08 0.19 0.11 0.11 0.14 0.09 0.03 0.12 0.05 0.11 0.06 0.06 0.08 0.05 0.09 0.03 0.07 0.07 0.10 0.08 195 195 195 195 195 195 195 195 195 195 195 195 195 195 195 195 195 195 195 195 195 195 SiO2 28.07 31.03 30.61 30.78 30.68 29.35 27.02 29.24 27.94 28.79 26.59 26.61 25.39 28.07 29.40 29.06 28.72 27.25 29.02 28.86 29.17 27.82 26.49 195 Clast vs matrix Mat Mat Mat Mat Mat Mat Mat Mat Mat Mat Mat Mat Mat Mat Mat Mat Mat Mat Mat Mat Mat Mat TiO2 0.03 0.04 0.08 0.06 0.03 0.01 0.07 0.02 0.00 0.02 0.05 0.06 0.02 0.01 0.00 0.04 0.09 0.07 0.00 0.01 0.01 0.05 0.05 Mat Analysis # 13 / 1 . 17 / 1 . 18 / 1 . 19 / 1 . 20 / 1 . 21 / 1 . 22 / 1 . 23 / 1 . 24 / 1 . 25 / 1 . 26 / 1 . 28 / 1 . 30 / 1 . 31 / 1 . 32 / 1 . 33 / 1 . 34 / 1 . 35 / 1 . 36 / 1 . 37 / 1 . 38 / 1 . 39 / 1 . Al2O3 19.16 19.99 18.27 20.81 18.41 17.26 19.23 17.37 18.57 18.11 19.93 19.88 18.88 18.00 18.17 18.03 17.80 19.41 17.68 18.03 17.46 20.26 20.36 40 / 1 . Cr2O3 0.03 0.08 0.01 0.00 0.06 0.00 0.10 0.02 0.11 0.21 0.08 0.04 0.00 0.08 0.26 0.40 0.44 0.04 0.31 0.43 0.30 0.12 0.00 Chlorite composition a SiO2 FeO 22.98 19.31 19.62 19.95 20.75 22.31 24.31 21.62 22.64 24.05 25.12 25.55 29.02 21.98 21.13 21.07 22.37 24.60 22.35 22.81 22.68 24.06 25.08 30.06 30.55 30.97 30.15 31.84 30.68 30.56 31.26 30.86 30.25 30.44 30.43 31.32 30.78 29.48 29.68 29.70 30.14 28.72 29.06 29.12 29.76 29.65 TiO2 0.02 0.01 0.01 0.02 0.03 0.04 0.00 0.04 0.00 0.02 0.08 0.00 0.00 0.00 0.00 0.00 0.02 0.00 0.07 0.04 0.00 0.02 MnO 0.27 0.35 0.31 0.53 0.33 0.32 0.39 0.24 0.23 0.41 0.24 0.29 0.17 0.52 0.56 0.52 0.38 0.39 0.33 0.35 0.21 0.21 0.32 0.07 Al2O3 MgO 17.21 15.68 17.35 14.91 15.33 18.53 16.82 18.95 17.08 16.84 15.17 15.82 12.40 18.19 17.25 16.60 17.12 15.04 16.17 16.74 16.60 15.22 14.27 18.67 18.30 17.70 17.85 18.36 17.95 18.30 17.65 18.58 18.66 18.48 17.69 17.71 18.17 18.76 18.91 18.65 18.16 19.05 19.18 18.94 18.71 18.58 Cr2O3 0.04 0.01 0.04 0.07 0.01 0.02 0.02 0.00 0.00 0.08 0.01 0.05 0.00 0.01 0.04 0.01 0.01 0.00 0.00 0.04 0.03 0.00 NiO 0.09 0.09 0.07 0.15 0.12 0.11 0.00 0.09 0.14 0.08 0.00 0.01 0.03 0.09 0.01 0.17 0.08 0.05 0.07 0.17 0.06 0.00 0.02 0.00 FeO CaO 0.09 0.18 0.22 0.23 0.30 0.22 0.06 0.09 0.07 0.10 0.07 0.07 0.07 0.10 0.11 0.11 0.09 0.05 0.27 0.13 0.18 0.08 0.11 14.62 13.98 15.61 14.03 15.44 14.95 14.36 15.08 13.67 14.59 14.52 14.41 14.23 13.18 17.42 16.90 17.56 16.12 17.77 17.01 18.17 17.79 15.36 MnO 0.45 0.29 0.44 0.23 0.45 0.38 0.29 0.41 0.42 0.23 0.36 0.31 0.38 0.31 0.30 0.37 0.40 0.40 0.34 0.43 0.40 0.43 Na2O 0.01 0.08 0.06 0.08 0.11 0.01 0.06 0.04 0.00 0.03 0.04 0.07 0.06 0.04 0.07 0.10 0.05 0.06 0.12 0.07 0.04 0.05 0.03 0.31 MgO K2O 0.01 0.02 0.04 0.05 0.02 0.00 0.02 0.00 0.01 0.00 0.01 0.02 0.01 0.02 0.05 0.05 0.01 0.02 0.04 0.01 0.01 0.02 0.02 22.47 24.25 21.86 23.75 21.73 22.86 23.18 22.53 24.23 24.82 22.99 24.49 23.73 25.12 21.68 21.72 22.16 22.11 21.80 21.58 20.68 20.87 22.73 NiO 0.03 0.12 0.06 0.08 0.03 0.00 0.05 0.00 0.01 0.13 0.00 0.08 0.10 0.01 0.04 0.03 0.01 0.00 0.01 0.04 0.01 0.06 total 87.94 86.85 86.63 87.56 86.15 88.12 88.07 87.68 86.79 88.65 87.30 88.41 86.06 87.09 87.00 86.15 87.16 86.99 86.35 87.60 86.72 87.89 86.74 0.01 CaO 0.24 0.19 0.17 0.13 0.33 0.26 0.27 0.30 0.06 0.10 0.15 0.13 0.17 0.11 0.14 0.13 0.12 0.21 0.08 0.10 0.15 0.17 K2O+Na2O+CaO 0.10 0.28 0.32 0.36 0.43 0.23 0.14 0.12 0.08 0.14 0.12 0.15 0.14 0.17 0.22 0.26 0.15 0.13 0.43 0.21 0.23 0.15 0.16 0.14 Na2O 0.02 0.03 0.05 0.03 0.03 0.04 0.06 0.04 0.06 0.05 0.05 0.02 0.06 0.06 0.04 0.02 0.06 0.07 0.00 0.02 0.02 0.01 Structural formula b 0.05 K2O 0.05 0.01 0.06 0.03 0.09 0.04 0.04 0.06 0.05 0.02 0.02 0.05 0.06 0.05 0.02 0.04 0.03 0.07 0.03 0.02 0.04 0.06 Si 2.90 3.15 3.14 3.12 3.18 3.02 2.82 3.01 2.93 2.97 2.81 2.78 2.79 2.93 3.04 3.04 2.99 2.88 3.05 3.00 3.05 2.89 2.82 0.03 total Ti 0.00 0.00 0.01 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.00 0.00 0.00 0.00 0.00 86.68 87.73 86.96 86.39 88.34 87.22 87.13 87.36 87.95 88.96 87.09 87.67 87.75 87.79 87.93 87.81 88.71 87.29 87.86 87.51 87.54 87.87 86.95 K2O+Na2O+CaO 0.31 0.23 0.28 0.20 0.46 0.34 0.37 0.39 0.17 0.17 0.21 0.20 0.28 0.21 0.20 0.19 0.20 0.36 0.11 0.13 0.20 0.24 Al 2.34 2.40 2.21 2.48 2.25 2.09 2.37 2.11 2.29 2.20 2.48 2.45 2.45 2.21 2.22 2.22 2.19 2.42 2.19 2.21 2.15 2.48 2.55 0.22 Al IV 1.10 0.85 0.86 0.88 0.82 0.98 1.18 0.99 1.07 1.03 1.19 1.22 1.21 1.07 0.96 0.96 1.01 1.12 0.95 1.00 0.95 1.11 1.18 Structural formula b Si 3.01 3.01 3.11 3.02 3.13 3.06 3.04 3.11 3.03 2.96 3.03 3.02 3.09 3.02 2.96 2.97 2.96 3.02 2.89 2.93 2.95 2.99 Al VI 1.24 1.55 1.35 1.60 1.43 1.11 1.19 1.12 1.22 1.17 1.29 1.23 1.24 1.14 1.26 1.27 1.18 1.30 1.24 1.21 1.21 1.37 1.37 2.98 Ti 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 Cr 0.00 0.01 0.00 0.00 0.00 0.00 0.01 0.00 0.01 0.02 0.01 0.00 0.00 0.01 0.02 0.03 0.04 0.00 0.03 0.04 0.02 0.01 0.00 0.01 Al 2.21 2.13 2.09 2.11 2.13 2.11 2.15 2.07 2.15 2.15 2.17 2.07 2.06 2.10 2.22 2.23 2.19 2.15 2.26 2.28 2.26 2.22 Fe 1.99 1.64 1.68 1.69 1.80 1.92 2.12 1.86 1.98 2.08 2.22 2.24 2.67 1.92 1.83 1.84 1.95 2.17 1.96 1.98 1.99 2.09 2.23 2.20 Al IV 0.99 0.99 0.89 0.98 0.87 0.94 0.96 0.89 0.97 1.04 0.97 0.98 0.91 0.98 1.04 1.03 1.04 0.98 1.11 1.07 1.05 1.01 Mn 0.02 0.03 0.03 0.05 0.03 0.03 0.03 0.02 0.02 0.04 0.02 0.03 0.02 0.05 0.05 0.05 0.03 0.04 0.03 0.03 0.02 0.02 0.03 1.02 Al VI 1.22 1.14 1.20 1.13 1.26 1.17 1.19 1.18 1.18 1.10 1.20 1.08 1.15 1.12 1.18 1.20 1.14 1.17 1.15 1.20 1.21 1.21 Mg 2.65 2.38 2.65 2.25 2.37 2.84 2.62 2.91 2.67 2.59 2.39 2.47 2.03 2.83 2.66 2.59 2.66 2.37 2.53 2.59 2.59 2.36 2.26 1.17 Cr 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Ni 0.01 0.01 0.01 0.01 0.01 0.01 0.00 0.01 0.01 0.01 0.00 0.00 0.00 0.01 0.00 0.01 0.01 0.00 0.01 0.01 0.00 0.00 0.00 0.00 Fe 1.23 1.15 1.31 1.18 1.27 1.25 1.20 1.26 1.12 1.19 1.21 1.19 1.17 1.08 1.46 1.41 1.46 1.35 1.50 1.43 1.54 1.50 Ca 0.01 0.02 0.02 0.03 0.03 0.02 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.03 0.01 0.02 0.01 0.01 1.29 Mn 0.04 0.02 0.04 0.02 0.04 0.03 0.02 0.03 0.03 0.02 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.04 0.03 0.04 Na 0.00 0.02 0.01 0.01 0.02 0.00 0.01 0.01 0.00 0.01 0.01 0.01 0.01 0.01 0.01 0.02 0.01 0.01 0.02 0.01 0.01 0.01 0.01 0.03 Mg 3.36 3.57 3.27 3.55 3.19 3.40 3.44 3.34 3.54 3.62 3.41 3.62 3.49 3.68 3.24 3.24 3.29 3.31 3.27 3.24 3.12 3.13 K 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.00 0.00 0.01 0.00 0.00 0.00 0.00 3.40 Ni 0.00 0.01 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 octaedral sum 5.92 5.65 5.75 5.64 5.70 5.93 5.99 5.94 5.92 5.92 5.94 5.99 5.99 5.97 5.85 5.84 5.89 5.91 5.86 5.89 5.86 5.86 5.91 0.00 Ca 0.03 0.02 0.02 0.01 0.04 0.03 0.03 0.03 0.01 0.01 0.02 0.01 0.02 0.01 0.01 0.01 0.01 0.02 0.01 0.01 0.02 0.02 vacancies 0.08 0.35 0.25 0.36 0.30 0.07 0.01 0.06 0.08 0.08 0.06 0.01 0.01 0.03 0.15 0.16 0.11 0.09 0.14 0.11 0.14 0.14 0.09 0.02 Na 0.00 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.00 0.01 0.01 0.01 0.00 0.01 0.01 0.00 0.00 0.00 0.00 Mg# c 0.57 0.59 0.61 0.57 0.57 0.60 0.55 0.61 0.57 0.56 0.52 0.52 0.43 0.60 0.59 0.58 0.58 0.52 0.56 0.57 0.57 0.53 0.50 0.01 K 0.01 0.00 0.01 0.00 0.01 0.00 0.00 0.01 0.01 0.00 0.00 0.01 0.01 0.01 0.00 0.01 0.00 0.01 0.00 0.00 0.00 0.01 0.00 R 2+ d 4.67
	Mg# c	0.73	0.76	0.71	0.75	0.71	0.73	0.74	0.73	0.76	0.75	0.74	0.75	0.75	0.77	0.69	0.70	0.69	0.71	0.69	0.69	0.67	0.68	0.73
	R 2+ d	4.62	4.75	4.62	4.75	4.49	4.68	4.66	4.63	4.70	4.84	4.65	4.84	4.70	4.78	4.73	4.69	4.78	4.70	4.80	4.71	4.69	4.67	4.72
	Calculated T (°C)
	Bourdelle et al. (2013) e
	Tcorrected (>350°C) e	216	255	180	252	156	211	216	183	228	403	211	319	203	272	290	254	333	236	443	294	274	233	265

e

Table S3 .

 S3 Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast Clast SiO2 28.75 28.61 28.38 28.00 28.29 28.44 27.80 28.02 27.66 27.81 28.39 28.56 27.99 28.37 28.54 28.60 28.45 27.75 28.02 28.96 28.54 30.11 .75 19.48 19.58 19.71 19.08 19.25 18.25 19.14 19.10 19.93 18.93 19.01 19.32 19.88 19.38 19.07 19.85 19.33 19.66 19.59 18.50 FeO 19.01 18.52 17.89 16.44 17.60 19.25 20.10 20.73 19.67 18.92 18.31 19.41 19.11 19.49 19.89 19.64 20.55 18.36 19.79 19.49 20.95 13.56 MgO 20.59 20.17 21.41 22.15 21.14 19.97 19.22 19.21 18.95 19.65 19.58 19.23 19.61 18.82 19.43 19.90 18.89 20.27 18.44 19.42 18.63 24.56 .49 87.62 87.16 87.26 87.28 87.24 86.87 86.22 86.20 86.82 86.67 86.22 86.65 88.23 88.26 87.43 86.79 86.26 88.67 88.46 87.36 SiO230.66 28.34 28.78 26.99 26.58 27.52 27.14 27.31 28.80 29.88 27.78 26.30 28.12 26.37 26.72 26.72 26.64 28.14 31.06 30.62 Al2O3 19.94 20.83 19.88 19.73 20.45 19.92 20.08 19.97 18.05 17.19 19.13 19.38 19.46 20.03 20.13 20.48 20.67 19.12 16.18 15.94 FeO 21.27 17.35 15.81 23.87 26.12 22.39 24.36 22.95 23.72 21.24 25.96 27.42 24.31 28.69 28.29 24.56 26.33 17.71 17.14 16.92 MgO 14.43 20.71 22.77 15.71 15.33 17.69 15.54 16.93 17.11 16.92 14.25 14.09 14.37 12.71 13.27 14.93 13.45 21.41 22.53 22.31 .62 87.55 86.79 88.95 88.01 87.85 87.62 88.22 86.76 87.52 87.54 86.84 88.19 88.86 87.27 87.59 86.97 87.71 86.54 In situ LA-ICP-MS trace element analysis (ppm) of 22 chlorite crystals from silicified samples.

		Sample	218c 218c 218c 218c 218c 218c 218c 218c 218c 218c 218c 218c 218c 218c 218c 218c 218c 218c 218c 218c 218c 218c
		Clast vs matrix Clast vs matrix	Clast Clast Clast Clast	Mat	Mat	Mat	Mat	Mat	Mat	Mat	Mat	Mat
		Analysis # Chlorite composition a SiO2 Analysis # Sample Chlorite composition a Clast vs matrix TiO2 Al2O3 Cr2O3 FeO MnO MgO NiO CaO Na2O K2O total K2O+Na2O+CaO Structural formula b Si Ti Al Al IV Al VI Cr Fe Mn Mg Ni Ca Na K octaedral sum vacancies Mg# c R 2+ d TiO2 Al2O3 18.97 18Cr2O3 62 / 1 . 63 / 1 . 33 / 1 . 38 / 1 . 195 195 clast clast 28.23 29.35 27.75 28.58 28.20 30.04 28.31 27.60 28.93 28.98 28.65 30.16 29.44 64 / 1 . 65 / 1 . 9 / 1 . 10 / 1 . 11 / 1 . 44 / 1 . 45 / 1 . 46 / 1 . 47 / 1 . 50 / 1 . 69 / 1 . 39 / 1 . 40 / 1 . 41 / 1 . 42 / 1 . 101 / 1 . 102 / 1 . 103 / 1 . 103 / 5 . 103 / 9 . 103 / 13 . 103 / 14 . 195 195 155 155 155 155 155 155 155 218ab 218ab 218ab 218ab 218c 103 / 21 . 103 / 23 . 103 / 25 . 103 / 29 . 103 / 30 . clast clast clast clast matrix matrix clast clast matrix clast clast matrix matrix clast 0.01 0.08 0.04 0.04 0.00 0.03 0.00 0.04 0.00 0.09 0.03 0.00 0.03 19.86 18.85 20.29 20.27 18.42 17.92 17.90 18.64 18.47 19.06 19.56 18.66 18.49 0.00 0.01 0.02 0.11 0.27 0.67 0.08 0.11 0.03 0.04 0.26 0.17 0.03 17.36 17.43 18.52 18.22 22.93 22.55 21.15 23.60 19.10 14.22 18.97 17.54 14.29 0.16 0.17 0.15 0.21 0.38 0.40 0.36 0.43 0.25 0.28 0.26 0.26 0.11 21.71 21.00 20.83 19.95 18.08 15.79 18.24 16.47 20.11 23.98 19.42 20.42 23.76 0.02 0.07 0.16 0.06 0.10 0.04 0.16 0.04 0.25 0.10 0.11 0.02 0.28 0.00 0.11 0.03 0.06 0.05 0.28 0.10 0.15 0.00 0.07 0.11 0.06 0.06 0.00 0.01 0.01 0.00 0.00 0.05 0.08 0.03 0.00 0.02 0.08 0.05 0.00 0.00 0.00 0.02 0.02 0.00 0.08 0.00 0.00 0.00 0.03 0.03 0.03 0.01 87.35 87.08 87.82 87.52 88.42 87.85 86.38 87.11 87.13 86.87 87.50 87.37 86.49 0.00 0.11 0.05 0.09 0.05 0.40 0.18 0.18 0.00 0.12 0.23 0.13 0.07 2.85 2.97 2.81 2.89 2.91 3.10 2.96 2.90 2.96 2.90 2.92 3.04 2.96 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 2.36 2.25 2.42 2.42 2.24 2.18 2.21 2.31 2.23 2.25 2.35 2.22 2.19 1.15 1.03 1.19 1.11 1.09 0.90 1.04 1.10 1.04 1.10 1.08 0.96 1.04 1.21 1.22 1.23 1.31 1.14 1.28 1.17 1.21 1.18 1.15 1.26 1.25 1.14 0.00 0.00 0.00 0.01 0.02 0.05 0.01 0.01 0.00 0.00 0.02 0.01 0.00 1.47 1.48 1.57 1.54 1.98 1.94 1.85 2.07 1.63 1.19 1.61 1.48 1.20 0.01 0.01 0.01 0.02 0.03 0.03 0.03 0.04 0.02 0.02 0.02 0.02 0.01 3.27 3.17 3.14 3.01 2.78 2.43 2.84 2.58 3.07 3.58 2.95 3.07 3.56 0.00 0.01 0.01 0.00 0.01 0.00 0.01 0.00 0.02 0.01 0.01 0.00 0.02 0.00 0.01 0.00 0.01 0.01 0.03 0.01 0.02 0.00 0.01 0.01 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.01 0.02 0.01 0.00 0.00 0.02 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 5.97 5.90 5.98 5.89 5.96 5.79 5.94 5.94 5.93 5.97 5.91 5.85 5.94 0.03 0.10 0.02 0.11 0.04 0.21 0.06 0.06 0.07 0.03 0.09 0.15 0.06 0.69 0.68 0.67 0.66 0.58 0.56 0.61 0.55 0.65 0.75 0.65 0.67 0.75 4.75 4.66 4.74 4.57 4.79 4.41 4.74 4.70 4.74 4.80 4.59 4.57 4.79 0.14 0.02 0.03 0.67 0.05 0.08 0.04 0.04 0.03 0.00 0.06 0.03 0.07 0.10 0.06 0.14 0.06 0.09 0.41 0.01 0.00 0.02 0.03 0.03 0.33 0.19 0.29 0.18 0.11 0.13 0.00 0.08 0.00 0.04 0.04 0.17 MnO 0.22 0.26 0.27 0.17 0.26 0.21 0.27 0.31 0.28 0.31 0.28 0.22 0.22 0.30 0.35 0.27 0.18 0.17 NiO 0.17 0.07 0.12 0.06 0.08 0.13 0.09 0.04 0.11 0.13 0.05 0.03 0.09 0.00 0.00 0.16 0.09 0.05 CaO 0.13 0.05 0.04 0.05 0.06 0.07 0.06 0.05 0.05 0.06 0.09 0.09 0.08 0.06 0.09 0.12 0.10 0.09 Na2O 0.02 0.04 0.00 0.01 0.04 0.02 0.09 0.02 0.03 0.04 0.00 0.04 0.00 0.05 0.00 0.00 0.00 0.00 K2O 0.01 0.00 0.02 0.01 0.00 0.02 0.00 0.00 0.02 0.01 0.02 0.00 0.02 0.05 0.01 0.02 0.00 0.00 total 88.41 86K2O+Na2O+CaO 0.16 0.09 0.05 0.07 0.10 0.10 0.15 0.08 0.10 0.11 0.11 0.13 0.11 0.16 0.10 0.14 0.10 0.09 Structural formula b Si 2.90 2.94 2.87 2.83 2.87 2.91 2.86 2.91 2.88 2.88 2.90 2.94 2.90 2.92 2.89 2.90 2.92 2.84 Ti 0.01 0.00 0.00 0.05 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.00 0.01 0.00 0.01 Al 2.25 2.27 2.32 2.33 2.35 2.30 2.34 2.23 2.35 2.33 2.40 2.30 2.32 2.35 2.37 2.31 2.31 2.40 Al IV 1.10 1.06 1.13 1.17 1.13 1.09 1.14 1.09 1.12 1.12 1.10 1.06 1.10 1.08 1.11 1.10 1.08 1.16 Al VI 1.15 1.21 1.19 1.16 1.22 1.20 1.20 1.14 1.22 1.21 1.30 1.24 1.22 1.27 1.26 1.21 1.23 1.24 Cr 0.03 0.00 0.00 0.00 0.00 0.00 0.03 0.02 0.02 0.01 0.01 0.01 0.00 0.01 0.00 0.00 0.00 0.01 Fe 1.60 1.59 1.51 1.39 1.49 1.64 1.73 1.80 1.71 1.64 1.56 1.67 1.65 1.68 1.68 1.66 1.76 1.57 Mn 0.02 0.02 0.02 0.01 0.02 0.02 0.02 0.03 0.02 0.03 0.02 0.02 0.02 0.03 0.03 0.02 0.02 0.01 Mg 3.10 3.09 3.23 3.33 3.19 3.04 2.95 2.97 2.94 3.03 2.98 2.95 3.02 2.89 2.93 3.00 2.89 3.09 Ni 0.01 0.01 0.01 0.00 0.01 0.01 0.01 0.00 0.01 0.01 0.00 0.00 0.01 0.00 0.00 0.01 0.01 0.00 Ca 0.01 0.01 0.00 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 Na 0.00 0.01 0.00 0.00 0.01 0.00 0.02 0.00 0.01 0.01 0.00 0.01 0.00 0.01 0.00 0.00 0.00 0.00 K 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 octaedral sum 5.94 5.93 5.97 5.91 5.95 5.93 5.96 5.97 5.94 5.95 5.89 5.91 5.93 5.89 5.92 5.93 5.92 5.94 vacancies 0.06 0.07 0.03 0.09 0.05 0.07 0.04 0.03 0.06 0.05 0.11 0.09 0.07 0.11 0.08 0.07 0.08 0.06 Mg# c 0.66 0.66 0.68 0.71 0.68 0.65 0.63 0.62 0.63 0.65 0.66 0.64 0.65 0.63 0.64 0.64 0.62 0.66 R 2+ d Analysis # Chl1 Chl2 Chl2-1 Chl3b Chl1 Chl2 Chl3 Chl3-1 Chl4 Chl5 Chl6 Chl1 Chl2 Chl3 Chl4 Chl1 Chlorite composition a TiO2 0.05 0.08 0.06 0.00 0.07 0.02 0.00 0.00 0.10 0.07 0.04 0.03 0.10 0.02 0.00 0.19 0.06 0.04 Cr2O3 0.50 0.00 0.00 0.20 0.04 0.06 0.18 0.04 0.02 0.61 0.00 0.00 0.00 0.07 0.02 0.07 0.04 0.05 MnO 0.33 0.15 0.12 0.14 0.25 0.21 0.31 0.26 0.20 0.43 0.14 0.20 0.16 0.14 0.21 0.22 0.25 0.23 NiO 0.06 0.04 0.03 0.00 0.00 0.12 0.02 0.02 0.00 0.12 0.07 0.00 0.04 0.03 0.05 0.01 0.08 0.09 CaO 0.26 0.05 0.08 0.07 0.05 0.03 0.07 0.05 0.11 0.15 0.08 0.04 0.10 0.06 0.08 0.03 0.04 0.12 Na2O 0.05 0.04 0.02 0.06 0.04 0.06 0.09 0.06 0.08 0.12 0.04 0.06 0.09 0.05 0.08 0.04 0.01 0.03 K2O 0.04 0.02 0.00 0.01 0.01 0.00 0.05 0.04 0.02 0.03 0.03 0.04 0.09 0.02 0.01 0.01 0.02 0.03 total 87.59 87K2O+Na2O+CaO 0.36 0.12 0.10 0.15 0.10 0.09 0.21 0.14 0.22 0.30 0.14 0.13 0.27 0.13 0.17 0.08 0.07 0.18 Structural formula b Si 3.13 2.85 2.87 2.85 2.77 2.84 2.84 2.84 2.98 3.11 2.93 2.81 2.96 2.81 2.82 2.81 2.82 2.87 Ti 0.00 0.01 0.00 0.00 0.01 0.00 0.00 0.00 0.01 0.01 0.00 0.00 0.01 0.00 0.00 0.02 0.01 0.00 Al 2.40 2.47 2.34 2.45 2.51 2.42 2.47 2.45 2.20 2.10 2.38 2.44 2.42 2.51 2.50 2.54 2.58 2.30 Al IV 0.87 1.15 1.13 1.15 1.23 1.16 1.16 1.16 1.02 0.89 1.07 1.19 1.04 1.19 1.18 1.19 1.18 1.13 Al VI 1.53 1.32 1.21 1.30 1.28 1.26 1.31 1.28 1.18 1.21 1.31 1.25 1.38 1.32 1.31 1.35 1.39 1.16 Cr 0.04 0.00 0.00 0.02 0.00 0.01 0.01 0.00 0.00 0.05 0.00 0.00 0.00 0.01 0.00 0.01 0.00 0.00 Fe 1.81 1.46 1.32 2.11 2.27 1.93 2.13 1.99 2.05 1.85 2.29 2.45 2.14 2.55 2.49 2.16 2.33 1.51 Mn 0.03 0.01 0.01 0.01 0.02 0.02 0.03 0.02 0.02 0.04 0.01 0.02 0.01 0.01 0.02 0.02 0.02 0.02 Mg 2.19 3.10 3.39 2.47 2.38 2.72 2.42 2.62 2.64 2.62 2.24 2.24 2.26 2.02 2.08 2.34 2.12 3.25 Ni 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.01 0.01 Ca 0.03 0.01 0.01 0.01 0.01 0.00 0.01 0.01 0.01 0.02 0.01 0.00 0.01 0.01 0.01 0.00 0.00 0.01 Na 0.01 0.01 0.00 0.01 0.01 0.01 0.02 0.01 0.02 0.02 0.01 0.01 0.02 0.01 0.02 0.01 0.00 0.01 K 0.01 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.00 0.00 0.00 0.01 0.01 0.00 0.00 0.00 0.00 0.00 octaedral sum 5.65 5.91 5.95 5.93 5.97 5.95 5.93 5.95 5.92 5.82 5.88 5.98 5.83 5.93 5.94 5.89 5.88 5.98 vacancies 0.35 0.09 0.05 0.07 0.03 0.05 0.07 0.05 0.08 0.18 0.12 0.02 0.17 0.07 0.06 0.11 0.12 0.02 Ti (47) a 47 b 5289 49 116 188 -3816 384 144 110 218 248 13 29 28 66 Mn (55) 2837 2720 2383 1985 3340 2319 241 267 2734 2733 525 386 75 93 48 485 Cr (53) 41 311 249 108 1022 689 124 92 40 55 231 169 30 69 56 44 Co (59) 34 33 33 40 103 72 bdl bdl 150 146 36 bdl bdl bdl bdl 30 Ni (60) 183 179 180 202 549 401 28 29 482 604 83 101 25 27 12 110 Cu (63) 19 20 bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl bdl Zn (66) 207 172 159 152 225 161 16 14 198 180 40 29 bdl bdl bdl 25 4.73 . 103 / 31 . 218c clast matrix matrix matrix matrix 103 / 48 . 103 / 50 . 104 / 1 . 218c 173 173 173 0.17 0.39 0.08 0.02 0.00 0.10 0.09 0.12 0.21 0.26 0.34 0.28 0.05 0.08 0.07 0.14 0.20 0.25 0.11 0.05 0.05 0.05 0.03 0.03 0.00 0.01 0.02 0.00 0.25 0.30 0.17 0.07 2.91 2.91 2.90 2.98 0.01 0.03 0.01 0.00 2.36 2.33 2.35 2.16 1.09 1.09 1.10 1.02 1.27 1.24 1.25 1.14 0.00 0.01 0.01 0.01 1.72 1.64 1.78 1.12 0.02 0.02 0.03 0.02 2.85 2.91 2.82 3.62 0.00 0.01 0.01 0.01 0.02 0.03 0.01 0.00 0.01 0.01 0.01 0.01 0.00 0.00 0.00 0.00 5.89 5.87 5.91 5.94 0.11 0.13 0.09 0.06 0.62 0.64 0.61 0.76 Chl2 Chl3 Chl1 Chl2 Chl3 0.00 0.00 0.00 0.08 0.25 0.11 0.10 0.06 0.32 0.38 0.06 0.06 0.06 0.05 0.44 0.49 3.12 3.12 0.00 0.00 1.92 1.91 0.88 0.88 1.04 1.03 0.00 0.01 1.44 1.44 0.02 0.01 3.37 3.38 0.01 0.01 0.03 0.04 0.01 0.01 0.01 0.01 5.93 5.93 0.07 0.07 215 bdl 23 25 17 1725 45 278 317 281 746 15 720 1662 1107 93 bdl 166 69 84 368 bdl 2639 1330 1689 38 bdl 280 202 15 108 bdl 1216 865 905 V (51) 172 241 156 134 473 405 45 18 209 164 35 39 bdl bdl bdl 66 198 bdl 29 29 26
	1622	Calculated T (°C) Mg# c Bourdelle et al. (2013) e Tcorrected (>350°C) e R 2+ d Calculated T (°C) Bourdelle et al. (2013) e 116 0.55 422 343 4.04 Tcorrected (>350°C) e	0.68 236 4.58 307	0.72 494 367 4.72 352 315	0.54 245 4.59 306	0.51 393 332 4.67 509 371	0.58 152 4.68 360 318	0.53 284 4.58 312	0.57 309 4.64 335	0.56 267 4.71 259	0.59 415 4.51 340 175	0.49 246 4.55 223	0.48 188 4.71 490 365	0.51 300 4.41 186	0.44 4.59 321	0.46 4.60 326	0.52 4.52 272	0.48 4.48 251	0.68 4.79	0.70 4.84	0.70 4.84
	1623 1629

Acknowledgements

-The authors warmly acknowledge M-C. Caumon for her help with Raman Spectroscopy on fluid inclusions at GeoRessources Nancy, O. Boudouma and M. Fialin for their assistance with SEM-cathodoluminescence and EPMA respectively, M. Quintin and E. Delairis for thin and thick sections preparation respectively. We thank B. Dubacq and J. Touret for fruitful discussions on chlorite analysis and fluid inclusions, respectively. Two anonymous reviewers are acknowledged for their critical remarks, and W. Berh and Associate Editor for editorial handling. This work was funded by INSU Tellus-SYSTER program (ODEFLUIN). Data were acquired during the ODEMAR cruise (https://doi.org/10.17600/13030070) and we thank the extraordinary work of the crew, engineers, and officers that led to an extremely successful cruise. Bathymetry (shipboard and AUV) data are publicly available through www.seanoe.org (https://doi.org/10.17882/48324, https://doi.org/10.17882/48335), and samples presented here are available for further studies through the Marine Rock Repository at IPGP (see lithotheque.ipgp.fr) or contacting JE.

Note that most trails are intragrain trails, restricted to one quartz grain, while only few trails crosscut several quartz grain boundaries (g). Qtz: quartz; Chl: chlorite. brecciated rocks show a relative decrease in both CaO and Mg# with increasing degree of silicification; mixed mafic-ultramafic breccias (green symbols) tend to be higher in magnesium at a given silica content; grey arrows: trend of passive depletion of CaO in breccias due to silica addition; Mg# will not be affected by silica addition. (c) Cr vs Ni; mixed breccias tend to be enriched in nickel and chromium compared with purely mafic breccias. Data for basalts and diabases from the 13°20'N OCC [START_REF] Wilson | Mantle composition controls the development of an Oceanic Core Complex[END_REF] and for peridotites from the 15°20'N Fracture Zone [START_REF] Godard | Geochemistry of the highly depleted peridotites drilled at ODP Sites 1272 and 1274 (Fifteen-Twenty Fracture Zone, Mid-Atlantic Ridge): Implications for mantle dynamics beneath a slow spreading ridge[END_REF][START_REF] Paulick | Geochemistry of abyssal peridotites (Mid-Atlantic Ridge, 15°20'N, ODP Leg 209): implications for fluidrock interaction in slow spreading environments[END_REF]

Contents of this file

Figures S1 to S5

Tables S1 to S4 3