Martine Buatier

Delphine Charpentier

Claire Fialips

Juan Jiménez

Philippe Goncalves

Hugo Bourque

Sylvia Duprat-Oualid

Nicolas Carry

Cybèle Cholet

Sonia Loiacono

PORT VIEUX THRUST, PYRENEES). De

Ahmed Abd Elmola
email: abd_elmola.ahmed@yahoo.com

Pierre Lanari

Patrick Monié

Ahmed Abd Elmola
email: ahmed.abd_elmola@univ-fcomte.fr

Pierre Labaume

Pierre Trap

TEXTURAL-CHEMICAL CHANGES AND DEFORMATION CONDI-TIONS REGISTERED BY PHYLLOSILICATES IN A FAULT ZONE (PIC

Keywords: Muscovite/illite, Chlorite, Thrust faults, Pyrenees, 40 Ar/ 39 Ar geochronology, Kübler index, Chlorite thermometry Phyllosilicates Pyrenees Thrust fault Chlorite Phyllosilicates, Pyrenees, Thrust fault, Chlorite, K-white mica, Fluid-rock interactions 40 Ar/ 39 Ar geochronology, Muscovite, Thrust faults, Pyrenees

Pfendler for their assistance to prepare the oral presentation of my thesis defense

I can't forget Lisa Koralie, Javier Fernandez de Simon, Henri Leclère, Flavien Choulet, Thibault Moulin, and Al-ashoor Ahmad who shared the office with me for some time and with whom I had a great time. Lisa, Javi, I will never forget the nice moments that we had spent together, Gracias por todo! Heartfelt thanks to my father who always encouraged and supported me with his nice words, my mother, my brother, my sisters and all my family for their understanding and supports through this period of being away from home. i My second brother Ahmed Mahrous, thank you for supporting me during this period, I always remember your regular phone calls from Egypt, Shokran ya sadiki.

Finally, I specially extend appreciation to my beloved wife, Manar Abdelhafez for her patience, understanding, endless encouragement, and taking care of our lovely kids, Assil and Hamza. I can't find the words to express my appreciation about everything you have done for me during this period but I simply thank God because he chose you to be my life partner.

I sincerely apologize to everyone I forgot here,

Ahmed Abd Elmola

ii RÉSUMÉ L a chaîne pyrénéenne présente des structures de déformation bien exposées et des roches sédimentaires syntectoniques exceptionnellement bien conservées qui en font un objet idéal pour étudier les failles. En effet, les textures, structures, compositions chimiques et isotopiques enregistrées par le coeur de la faille chevauchante peuvent renseigner sur les conditions et mécanismes de la déformation et aussi contraindre dans le temps l'activité de la faille étudiée. Dans la présente thèse, trois chevauchements du versant sud Pyrénéen ont été étudiés pour mieux appréhender le comportement mécanique, chimique et isotopique des phyllosilicates dans des roches sédimentaires déformées. Ces roches sont d'âge éocène à triasique et sont impliquées dans de grand chevauchements (zone cisaillantes) à vergence sud. Ce travail combine observation pétrographique, analyse chimique, modélisation thermodynamique et technique de datation radiométrique 40 Ar/ 39 Ar sur des minéraux de moscovite/illite et de chlorite. La première faille étudiée est le chevauchement du Pic de Port Vieux (PPV), chevauchement de second ordre lié au chevauchement majeur de Gavarnie dans le sud-ouest de la Zone Axiale Pyrénéenne. Des mécanismes de pression-dissolution et recristallisation, accompagnés d'interactions avec un fluide très réducteur sont les principaux paramètres responsables des changements minéralogiques/chimiques observés dans la zone centrale de la faille. L'indice Kübler de la moscovite et les données thermométrique sur chlorite suggèrent des températures de 285 • C ± 28 • C pour l'activité de PPV. De plus, la datation 40 Ar/ 39 Ar de la moscovite syn-cinématique indique que la faille a fonctionné il y a 36.9 ± 0.2 Ma, ce qui coïncide avec l'âge de l'activité du chevauchement de Gavarnie. Les deux autres failles étudiées sont le chevauchement de Lakora qui est situé sur le bord sud de la zone Nord Pyrénéenne et celui de Monte Perdido (au niveau de Torla) situé dans la partie ouest de la zone Sud-Pyrénéenne. Ces deux chevauchements ont été affectés (déformés) par la mise en place de chevauchement de Gavarnie. Les observations pétrographiques et les analyses microstructurales ont démontré que la déformation est marquée par du plissement, du boudinage, par le développement d'une schistosité intense, de surfaces de cisaillement, de veines et par un enrichissement en phyllosilicates au coeur de la zone de faille des deux chevauchements. De manière similaire au chevauchement du Pic de PPV, les mécanismes de pression-dissolution et recristallisation sont les principaux mécanismes qui contrôlent la déformation et ils sont à l'origine de l'enrichissement en phyllosilicates néoformés dans les zones de failles des deux chevauchements. En se basant sur les mesures de l'indice de Kübler, il apparait que la déformation de Lakora et Torla s'est produite dans des conditions de température plus basse que celles enregistrées pour le chevauchement du PPV. Par v ailleurs, es âges les plus jeunes obtenus par la technique 40 Ar/ 39 Ar ne peuvent être rattachés à l'âge de la déformation car ils sont plus vieux que les âges des sédiments impliqués dans les zones de faille. D'autres hypothèses sont proposées à la fin de cette thèse afin de comprendre les raisons de cette incohérence dans les âges et afin de dater la déformation de Lakora et Torla.

Ainsi l'ensemble des résultats de cette thèse montrent que les minéraux phyllosilicatés peuvent être des outils thermochronologiques fiables permettant de dater avec précision l'activité des failles lorsqu'ils ont été combinés avec des préparations d'échantillons précises et caractérisation détaillée des échantillons.

Mots-clés: Moscovite/illite; Chlorite; Failles chevauchement; Pyrénées; Géochronologie 40 Ar/ 39 Ar; Indice de Kübler; Thermométrie du chlorite. vi ABSTRACT T he Pyrenees belt features well-exposed deformation structures and exceptionally well preserved syntectonic sedimentary rocks that make it ideally suited to study thrust faults. The texture, structure and chemical-isotopic compositions of synkinematic phyllosilicates are widely used to estimate the deformation conditions-mechanisms and timing of fault activities.Therefore, in the present thesis, three thrusts from the Pyrenean orogen have been studied to better understand the mechanical, chemical and isotopic behavior of phyllosilicates from deformed sediments of Eocene-Triassic age that have been involved in large south-verging shear zones. This work combined petrographic observation, chemical analyses, and thermodynamic modeling with 40 Ar/ 39 Ar geochronology on muscovite/illite and chlorite. The first studied fault is the Pic de Port Vieux thrust (PPVT), a second-order thrust related to the major Gavarnie thrust (GT) in the south-western part of the Pyrenees Axial Zone. The dissolution-recrystallization, pressure solution mechanisms, and interaction with highly reductive fluids are the main parameters responsible for the mineralogical and chemical changes in the fault core zone. The Kübler index and chlorite thermometry suggest upper-anchizone to epizone conditions with a temperature of 285 • C ± 28 • C for the PPVT activity. Moreover, the 40 Ar/ 39 Ar step-heating dating of synkinematic muscovite indicates that the fault activity occurred at 36.9 ± 0.2 Ma which coincides with the activity of the GT. The two other faults are: Lakora thrust that is located on the southern edge of the North Pyrenean Zone, and the Monte Perdido thrust (Torla location) situated on the western part of the South Pyrenean Zone. The two thrust are affected (deformed) by the emplacement of the Gavarnie thrust. The petrographic-microstructural analyses on these faults demonstrated that deformation is marked by folding, boudinage, intense cleavage, shear surfaces/veins and enrichment of phyllosilicates in the fault zone of both thrusts. Similar to the PPVT, pressure-solution and dissolution-recrystallization mechanisms are the main mechanisms that control deformation and enhanced the enrichment of the newly-formed phyllosilicates in the fault zones of both thrusts. Based on the Kübler index measurements, the deformation in the Lakora and Torla faults occurred at relatively lower temperature compared to the PPVT. The youngest total gas ages obtained by the 40 Ar/ 39 Ar technique are very old for the activity time of both thrusts as they are older than the depositional ages of the sediments in the fault zones. Further investigations are proposed at the end of this dissertation in order to better understand this anomaly in age and to successfully obtain the right age of the two thrusts activity.

LIST OF FIGURES

GENERAL INTRODUCTION

View of the Pyrenees from Torla city, Spain "' The aim of this introduction is to describe the general context of the thesis and define the relevant terms that are used within this dissertation. This is followed by a review of the origin of phyllosilicates in fault zones, their formation mechanisms, and their use as thermochronology tools. Finally, the objectives of the thesis and descriptions of the study sites are presented.'"

General context

Movements within the Earth and at its surface are accommodated in domains of localized displacement referred as faults [START_REF] Grim | Clay Mineralogy: The clay mineral composition of soils and clays is providing an understanding of their properties[END_REF] that may range in length from a few millimeters to thousands of kilometers. Dating faults activity and understanding their behavior, their mechanisms, and conditions of deformation are critically important in a variety of fields and applications. For example (1) In sedimentary basins, faults are one of the main structures responsible for partitioning sedimentary basins, thus studying them will help to decipher and re-construct the basin tectonic history [START_REF] Fisher | The permeability of faults within siliciclastic petroleum reservoirs of the North Sea and Norwegian Continental Shelf[END_REF]. ( 2) In hydrocarbon explorations, the fault zones can be of major economic interest because they can be trap-forming structures that accumulate oil in porous reservoirs (e.g. [START_REF] Haig | The Hutton Field, Blocks 211/28, 211/27[END_REF][START_REF] Wibberley | Recent advances in the understanding of fault zone internal structure: a review[END_REF]. (3) In seismic areas assessment, active faults are zones of enhanced seismicity that are commonly associated with surface rupture and ground shaking [START_REF] Scholz | The Mechanics of Earthquakes and Faulting[END_REF]. Therefore studying the different fault motions allows to reconstruct the interval of seismicity which may provide important information about the timing of the next big earthquake that might take place in the region [START_REF] Tagami | Thermochronological investigation of fault zones[END_REF]. ( 4) In mountain belts evolution, fault movements have a large influence in the timing and spatial evolution of mountains, hence studying them is essential to better understand the structural and tectonic history of mountains (e.g. [START_REF] Butler | Time and space variability of «thin-skinned» and «thick-skinned» thrust tectonics in the Apennines (Italy)[END_REF][START_REF] Butler | Late Proterozoic rift faults and basement-cover relationships within the Ben More thrust sheet, NW Scotland[END_REF][START_REF] Tozer | Comparing thin-and thick-skinned thrust tectonic models of the Central Apennines, Italy[END_REF][START_REF] Welbon | Structural styles in thrust belts developed through rift basins: a view from the western Alps[END_REF]. [START_REF] Wiewióra | Crystallochemical classifications of phyllosilicates based on the unified system of projection of chemical composition: II. The chlorite group[END_REF] In ore deposits investigations, faults zones are rich in valuable minerals and metals of economic importance because the fluid circulations and dissolution-precipitation reactions in the fault zone can lead to the concentration of such deposits (e.g. [START_REF] Muto | Fractal particle size distribution of pulverized fault rocks as a function of distance from the fault core[END_REF][START_REF] Nouri | Correlation between Cu mineralization and major faults using multifractal modelling in the Tarom area (NW Iran)[END_REF][START_REF] Yousefi | Data-driven logistic-based weighting of geochemical and geological evidence layers in mineral prospectivity mapping[END_REF]. ( 6) In applied geology, faults are considered zones of weakness which may have environmental consequences in civil engineering and nuclear waste storage projects, among others. Therefore, studying faults, understanding their behavior and deformations mechanisms are very important for several fields and applications.

In fault zones, fault rocks refer to the rocks that result from deformation and shearing processes attributed to the fault motion [START_REF] Sibson | Fault rocks and fault mechanisms[END_REF]. They provide key evidence of the deformation process, therefore characterizing them is very important for understanding fault activity [START_REF] Scholz | The Mechanics of Earthquakes and Faulting[END_REF]. There are several types of fault rocks in fault zones such as breccia, gouge, phyllonite, pseudotachylyte, cataclasite, etc. The classification of the various fault rocks has been done by [START_REF] Sibson | Fault rocks and fault mechanisms[END_REF]and [START_REF] Scholz | The Mechanics of Earthquakes and Faulting[END_REF] based on textural criteria (see below for additional details).

In the present study, phyllosilicates (clay minerals) in fault zones within sedimentary environments are the focus of our investigations as they are major components in these zones [START_REF] Blatt | Origin of sedimentary rocks[END_REF]. The physical-chemical properties and the unique crystal structures of phyllosilicates give them special properties that can affect the behavior and deformation mechanisms of faults. For instance, the amount, type, distribution pattern and morphology of phyllosilicates in a fault zone have significant effects on its frictional and hydraulic properties (e.g. [START_REF] Haines | Clay fabric intensity in natural and artificial fault gouges: Implications for brittle fault zone processes and sedimentary basin clay fabric evolution[END_REF][START_REF] Sibson | Fault rocks and fault mechanisms[END_REF], Vrolijk and van der Pluijm, 1999). Acoording to these authors, the preferred orientation of phyllosilicates in natural faults is one of the key-parameters that controls the fault frictional behavior (e.g. [START_REF] Rice | Chapter 20 Fault Stress States, Pore Pressure Distributions, and the Weakness of the San Andreas Fault[END_REF]. Their high cation exchange capacity and their large specific surface area allow them to adsorb water molecules that may decrease the strength of the fault and consequently their presence in the fault will have significant implication on fault stability (e.g. [START_REF] Bird | Fault friction, regional stress, and crust-mantle coupling in southern California from finite element models[END_REF][START_REF] Morrow | The effect of mineral bond strength and adsorbed water on fault gouge frictional strength[END_REF][START_REF] Numelin | Frictional properties of natural fault gouge from a lowangle normal fault, Panamint Valley, California[END_REF][START_REF] Saffer | Laboratory results indicating complex and potentially unstable frictional behavior of smectite clay[END_REF]. Furthermore, the preferred alignment of phyllosilicate particles can act as a preferential fluid pathway in fault zones (e.g. [START_REF] Cavailhes | Influence of fault rock foliation on fault zone permeability: The case of deeply buried arkosic sandstones (Grès d'Annot, southeastern France)[END_REF][START_REF] Leclère | Formation of phyllosilicates in a fault zone affecting deeply buried arkosic sandstones: their influence on petrophysic properties (Annot sandstones, French external Alps)[END_REF]. In addition, the enrichment of clay minerals in the fault core zone can modify the original porosity and permeability that will control the reservoir quality in the fault (e.g. Faulkner et al., 2010, Fisher and[START_REF] Fisher | The permeability of faults within siliciclastic petroleum reservoirs of the North Sea and Norwegian Continental Shelf[END_REF].

The authigenic phyllosilicates in fault zones can occur as pore-bridging minerals that reduce the pore space and block fluid movement by reducing the permeability. However, in some cases authigenic phyllosilicates may preserve the permeability e.g. coats of chlorite on sand grains will prevent quartz cementation and consequently retain the reservoir quality (e.g. [START_REF] Bloch | Anomalously high porosity and permeability in deeply buried sandstone reservoirs: Origin and predictability[END_REF][START_REF] Heald | Influence of coatings on quartz cementation[END_REF][START_REF] Taylor | High temperature quartz cementation and the timing of hydrocarbon accumulation in the Jurassic Norphlet sandstone, offshore Gulf of Mexico, USA[END_REF]. All of the above demonstrates the importance of phyllosilicates in fault zones and shows their crucial role in fault behavior and properties.

Phyllosilicate composition, structure and textural arrangement are very sensitive to burial diagenesis, tectonic activity, and interactions with fluids. Consequently phyllosilicates can be used to decipher the basin evolutionary history, deformation mechanisms and P-T conditions of various geologic events [START_REF] Jiang | Clay Minerals from the Perspective of Oil and Gas Exploration[END_REF]. When the occurrence and/or the crystallization/recrystallization of newly-formed phyllosilicates in fault zones are attributed to fault activity, these minerals can be used for the estimation of variable parameters related to deformation. For example, the crystallinity index of newly-formed muscovite/illite has been used to quantify diagenetic and low-grade metamorphic conditions (e.g. [START_REF] Frey | Very low-grade metamorphism of clastic sedimentary rocks[END_REF][START_REF] Kisch | On the calibration of the illite Kubler index (illite "crystallinity")[END_REF][START_REF] Kübler | Les argiles, indicateurs de métamorphisme[END_REF][START_REF] Kübler | La cristallinité de l'illite et les zones tout a fait superieures du métamorphisme. étages tectoniques[END_REF][START_REF] Kübler | Evaluation quantitative du métamorphisme par la cristallinité d l'illite[END_REF][START_REF] Kübler | Illite crystallinity[END_REF][START_REF] Warr | Recommendations for Kübler index standardization[END_REF], Warr and Cox, 2016, among others). Temperature estimation from chlorite chemical composition by a thermodynamic modelling approach is also a common method for low grade metamorphic and diagenetic rocks. This method has been recently developed by several authors (e.g. Bourdelle et al., 2013b[START_REF] Inoue | Application of Chemical Geothermometry to Low-Temperature Trioctahedral Chlorites[END_REF], Lanari et al., 2012[START_REF] Lanari | A thermodynamic model for di-trioctahedral chlorite from experimental and natural data in the system MgO-FeO-Al 2 o 3 -SiO 2 -H 2 o: applications to P-T sections and geothermometry[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], 2006, 2016, among others). Chemical compositions of phyllosilicates can also be use to characterize fluid-rock GENERAL INTRODUCTION interactions and the redox conditions involved during fault activity (e.g. [START_REF] Lacroix | Formation of chlorite during thrust fault reactivation. Record of fluid origin and P-T conditions in the Monte Perdido thrust fault (southern Pyrenees)[END_REF][START_REF] Trincal | Fluid-rock interactions related to metamorphic reducing fluid flow in meta-sediments: example of the Pic-de-Port-Vieux thrust (Pyrenees, Spain)[END_REF]. Moreover, K-bearing phyllosilicates (muscovite/illite) has been used in K-Ar and 40 Ar/ 39 Ar geochronology since the earliest stages of development of these methods for dating fault activity (e.g. [START_REF] Bense | Fault gouge analyses: K-Ar illite dating, clay mineralogy and tectonic significance-a study from the Sierras Pampeanas, Argentina[END_REF][START_REF] Bui | Episodes of brittle deformation within the Dien Bien Phu Fault zone, Vietnam: Evidence from K-Ar age dating of authigenic illite[END_REF][START_REF] Campani | Geochronological evidence for continuous exhumation through the ductile-brittle transition along a crustal-scale low-angle normal fault: Simplon Fault Zone, central Alps[END_REF][START_REF] Haines | Clay quantification and Ar-Ar dating of synthetic and natural gouge: Application to the Miocene Sierra Mazatán detachment fault, Sonora, Mexico[END_REF][START_REF] Kellett | Influence of deformation and fluids on Ar retention in white mica: Dating the Dover Fault, Newfoundland Appalachians[END_REF][START_REF] Kralik | Dating fault gouges[END_REF][START_REF] Lyons | Dating faults[END_REF][START_REF] Ring | Faultgouge dating in the Southern Alps, New Zealand[END_REF][START_REF] Tagami | Thermochronological investigation of fault zones[END_REF], van der Pluijm et al., 2006, among others). In addition to dating faults, phyllosilicates are also used to date deformations (e.g. [START_REF] Dallmeyer | 40 Ar/ 39 Ar polyorogenic mineral age record in the northern Mauritanide orogen, West Africa[END_REF][START_REF] Fitz-Díaz | Fold dating: A new Ar/Ar illite dating application to constrain the age of deformation in shallow crustal rocks[END_REF][START_REF] Fitz-Díaz | Progressive, episodic deformation in the Mexican Fold-Thrust Belt (central Mexico): evidence from isotopic dating of folds and faults[END_REF], 2016[START_REF] Wang | Direct dating of folding events by 40 Ar/ 39 Ar analysis of synkinematic muscovite from flexural-slip planes[END_REF], metamorphism (e.g. [START_REF] Dong | 40 Ar/ 39 Ar illite dating of Late Caledonian (Acadian) metamorphism and cooling of K-bentonites and slates from the Welsh Basin[END_REF][START_REF] Liu | Mid-Late Triassic metamorphic event for Changhai meta-sedimentary rocks from the SE Jiao-Liao-Ji Belt, North China Craton: Evidence from monazite U-Th-Pb and muscovite Ar-Ar dating[END_REF][START_REF] Reuter | 40 Ar/ 39 Ar dating of cleavage formation in tuffs during anchizonal metamorphism[END_REF][START_REF] Sanchez | Dating low-temperature deformation by 40 Ar/ 39 Ar on white mica, insights from the Argentera-Mercantour Massif (SW Alps)[END_REF][START_REF] Skipton | Deciphering the Paleoproterozoic cooling history of the northeastern Trans-Hudson Orogen, Baffin Island (Canada), using 40 Ar/ 39 Ar step-heating and UV laser thermochronology[END_REF][START_REF] Verdel | Variation of illite/muscovite 40 Ar/ 39 Ar age spectra during progressive low-grade metamorphism: an example from the US Cordillera[END_REF], and can also estimate the age of oil and gas migration (e.g. [START_REF] Aronson | K/Ar Dating of Illitic Clays in Jurassic Nugget Sandstone and Timing of Petroleum Migration in Wyoming Overthrust Belt: ABSTRACT[END_REF][START_REF] Feiyu | Timing of petroleum accumulation: Theory and new methods[END_REF][START_REF] Hamilton | K-Ar dating of illite in hydrocarbon reservoirs[END_REF][START_REF] Hesheng | Timing of hydrocarbon fluid emplacement in sandstone reservoirs in Neogene in Huizhou sag, Southern China Sea, by authigenic illite 40 Ar-39 Ar laser stepwise heating[END_REF][START_REF] Liu | 40 Ar/ 39 Ar geochronology constraints on hydrocarbon accumulation and destruction periods in the Bankeng paleo-reservoir in the southern margin of the middle Yangtze block[END_REF].

Clearly, phyllosilicates in fault zones provide very important information about the timing, conditions and mechanisms of fault activity. Therefore, the aim of the present thesis is to use synkinematic phyllosilicates from thrust faults in the Pyrenees orogen in order to establish the conditions, the mechanism of deformations, and the timing of thrusting. Before listing all of the objectives and the study areas (faults) of this work, a briefly summary of some terms and concepts that are used within this dissertation are presented. Then, this is followed by a review for the origin of phyllosilicates in fault zones, and the methodology of extracting information from their structure, texture,composition, and crystallinity in fault zones.

Terminology and definitions

Fault, fault zone and fault rocks

A fault can be defined as a volume of rock consisting of a central slip surface or a core, formed by intense shearing, and a surrounding volume of rock that has been affected by less intense deformation [START_REF] Fossen | Structural geology[END_REF]. Faults result from tectonic movements that may occur rapidly, in the form of an earthquake, or may occur slowly in the form of a creep. There are several types of faults, and their classification is based on the kind of movements which occur along them, such as normal faults, reverse faults, and strike-slip faults (Figure 0.1). In normal faults, the hanging wall (the body of a rock above the fault plane) is downthrown (vertically displaced) relative to the footwall (the body of a rock below the fault plane). When the hanging wall is upthrown relative to the footwall, the fault is a reverse fault. If the dip angle is less than 30 • , the fault is called a low-angle fault, and low-angle GENERAL INTRODUCTION 2. TERMINOLOGY AND DEFINITIONS reverse faults are called thrust faults. In the case of lateral movement in the horizontal plane, the fault is called strike-slip fault; it can be sinistral (left lateral) or dextral (right lateral). More information and description of faults, their tectonic and seismic settings, and their formation processes can be found in several textbooks (e.g. [START_REF] Fossen | Structural geology[END_REF][START_REF] Handy | Tectonic faults: agents of change on a dynamic Earth[END_REF][START_REF] Hobbs | An outline of structural geology[END_REF], Scholz, 2002, and references therein). The fault zone refers to a volume of rock that has been totally or partially deformed by the fault movement. The well-developed fault zones consist of three structural components: the core zone, the damage zone and the protolith as shown in Figure 0.2 (e.g. [START_REF] Chester | Implications for mechanical properties of brittle faults from observations of the Punchbowl fault zone, California[END_REF], Chester et al., GENERAL INTRODUCTION 1993[START_REF] Scholz | The permeability of faults. The Mechanical Involvement of Fluids in Faulting[END_REF]. The core zone is the central part of the fault where most or all of the original structures of the rock are obliterated [START_REF] Fossen | Structural geology[END_REF]. According to [START_REF] Caine | Fault zone architecture and permeability structure[END_REF], the core zone is defined as " a portion of the fault zone where the majority of slip is accommodated ". Whereas the damage zone is less-intense deformed zone that bounds the core zone, and is composed of a network of subsidiary structures. It consists of rock volumes affected by fault-related fracturing (e.g. [START_REF] Micarelli | Structural evolution and permeability of normal fault zones in highly porous carbonate rocks[END_REF] and it was interpreted as the remnants of failed or abandoned fault surfaces by [START_REF] Ben-Zion | Characterization of fault zones[END_REF]. The core and damage zones are surrounded by an undeformed host rock zone known as the protolith. The width of fault zones ranges from centimeters or meters to the order of a kilometer or more in large-scale faults (e.g. the San Andreas Fault). As previously mentioned, fault rocks refers to the rocks in the fault zone that formed as result of faulting; the first description of a fault rock related to faulting was reported by [START_REF] Lapworth | The Highland controversy in British geology: its causes, course and consequences[END_REF] who introduced the term mylonite to describe certain types of rocks associated with the Moine thrust of northwestern Scotland. The most influential classification for the various types of fault rocks is the one proposed by [START_REF] Sibson | Fault rocks and fault mechanisms[END_REF] that is based mainly on textural criteria. This classification has been revised by [START_REF] Scholz | The Mechanics of Earthquakes and Faulting[END_REF], as shown in Table 0.1. The main divisions of Sibson's classification are based mainly on cohesion (cohesive or incohesive) and fabric (random or foliated) of the rocks while the grain/clast size and the matrix percentage define the subdivisions of this classification. For example,

GENERAL INTRODUCTION

the incohesive rocks are classified based on grain size, from breccia to gouge. While the cohesive rocks are divided based on the tectonic reduction of grain size from that of the host rock and the fraction of fine-grained matrix relative to lithic fragments. In the mylonite series the large fragments are referred to as porphyroclasts, and as porphyroblasts in case of blastomylonites (rocks that have experienced growth during or after plastic deformation). The term phyllonite that appears within the mylonite series refers to cohesive foliated phyllosilicate-rich rocks and it is defined by [START_REF] Sibson | Fault rocks and fault mechanisms[END_REF] as a "mica-rich mylonite and/or ultramylonite rock that has the silky appearance of phyllites".

Note that foliated gouge has been added by [START_REF] Scholz | The Mechanics of Earthquakes and Faulting[END_REF] to the original classification of Sibson because it occurs in nature and can be produced in the laboratory. According to the Scholz classification, fault gouge is an incohesive rock, composed of < 30% of large clasts (> 2 mm in size) and may be non-foliated (random-fabric orientation) or foliated. Some recent modifications added more subdivisions to that classification and include more parameters such as the lithology and the metamorphic degree (e.g. [START_REF] Brodie | Structural terms including fault rock terms[END_REF][START_REF] Killick | Fault rock classification: an aid to structural interpretation in mine and exploration geology[END_REF], Passchier and Trouw, 2005, Snoke et al., 1998, among others). Recently [START_REF] Woodcock | Classification of fault breccias and related fault rocks[END_REF] suggested a revised classification of the original classification of [START_REF] Sibson | Fault rocks and fault mechanisms[END_REF]. The major difference in their revised classification concerns fault breccia; they proposed that fault breccia is better defined by its coarse grain size than by its lack of cohesion at the time of faulting.

The deformation mechanisms associated with these fault rocks have also been reported by [START_REF] Sibson | Fault rocks and fault mechanisms[END_REF] and are shown in Figure 0.3. The deformation in fault zones can be brittle deformation, which occurs at shallow depth and is generated by elastico-frictional mechanisms such as fracturing and frictional sliding. The fault rocks associated with these deformation conditions and mechanisms are gouges, breccias and pseudotachylytes. The second type of deformation that occurs at higher depth and higher metamorphic conditions compared to brittle deformation is known as ductile deformation. The pressure-solution, twinning, kinking, dislocation, diffusion creep and grain boundary sliding are the main quasi-plastic mechanisms characteristic of this type [START_REF] Sibson | Fault rocks and fault mechanisms[END_REF].

The phyllonite and mylonite series are the typical rocks characteristic for this type of deformation.

According to Sibson's model, phyllonite rocks started to be observed at ∼ 300 • C; however, it has been described in other studies at lower temperatures in fault zones (e.g. [START_REF] Abad | The structure and the phyllosilicates (chemistry, crystallinity and texture) of Talas Ala-Tau (Tien Shan, Kyrgyz Republic): comparison with more recent subduction complexes[END_REF][START_REF] Torgersen | Structural and temporal evolution of a reactivated brittle-ductile fault -Part II: Timing of fault initiation and reactivation by K-Ar dating of synkinematic illite/muscovite[END_REF]. Semi-brittle or brittle-ductile deformation can be observed at the frictional-plastic/viscous transition and involves a mixture of brittle and ductile features at the microscale [START_REF] Scholz | The Mechanics of Earthquakes and Faulting[END_REF].

Phyllosilicates and clay minerals

Phyllosilicates (from the Greek word "phyllon" meaning leaf) are among the most important stable minerals within the earth's crust. They are one of the silicate subclasses beside the tectosilicates, nesosilicates, sorosilicates, cyclosilicates and inosilicates. The differentiation between these silicates subclasses is based on the linking and internal arrangement of the SiO 4 -4 tetrahedra i.e., the basic structural unit of all the silicate minerals [START_REF] Mukherjee | The science of clays: applications in industry, engineering, and environment[END_REF]. In phyllosilicates, tetrahedrons are linked together to form a two-dimensional sheet-like arrangement, therefore they are called sheetsilicates. Clay minerals belong to the phyllosilicates group with mainly Si, Al, Mg, Fe, Na, K and Ca in GENERAL INTRODUCTION their chemical composition [START_REF] Deer | An introduction to the rock-forming minerals[END_REF]. According to the recent definition of both the AIPEA (Association Pour l'Etude des Argiles) and CMS (Clay Mineral Society) Nomenclature Committees (Guggenheim andMartin, 1995, Guggenheim et al., 2006), clay minerals are defined as " fine-grained hydrous phyllosilicate minerals of planar or non planar structures " while, the term clay is a " natural mixture that is composed largely of clay minerals and some other materials ".

Clay minerals are composed of tetrahedral and octahedral sheets that are stacked on top of each other in the c-axis direction and are linked to each other by sharing oxygen ions. One or more tetrahedral sheet plus an octahedral sheet define one 'layer' and the space between the different layers, known as 'interlayer' space, which is empty when the layers are electrostatically neutral. In instances of some substitutions within the tetrahedral and/or octahedral sheets, the layers will bear a charge and consequently interlayer material is required for charge balance [START_REF] Bailey | Report of the clay minerals society nomenclature committee for 1982 and 1983[END_REF]. The interlayer materials that neutralized this layer charge may consist of non-hydrated cations, hydrated cations, organic material, and/or hydroxide octahedral sheets [START_REF] Christidis | Industrial Minerals: Significance and Important Characteristics[END_REF].

Based Nomenclature Committee [START_REF] Guggenheim | Summary of recommendations of nomenclature committees relevant to clay mineralogy: report of the Association Internationale pour l'Etude des Argiles (AIPEA) Nomenclature Committee for 2006[END_REF], the 2:1 layer (plus a hydroxide sheet interlayer) should be used to describe the chlorite layer type instead of the 2:1:1 layer structure.

Clay minerals are also classified according to the type of cations present in the octahedral layer.

When cations are trivalent (e.g. Al 3+ ) they are called dioctahedral phyllosilicates (e.g. kaolinite, pyrophyllite, muscovite, etc.), and when cations are divalent (Mg 2+ or Fe 2+ ) they are called trioctahedral phyllosilicates (e.g. talc, biotite, Mg-chlorite, etc.). Sometimes two clay minerals are interstratified within the same structure; this clay structure is called mixed-layer clay minerals [START_REF] Srodo Ń | Nature of mixed-layer clays and mechanisms of their formation and alteration[END_REF]. Mixedlayer minerals contain mainly smectite as a swelling component in this structure, e.g. illite/smectite and chlorite/smectite mixed layers.

More details about the classification and structure of all clay minerals can be found in several textbooks (e.g. [START_REF] Bailey | Report of the clay minerals society nomenclature committee for 1982 and 1983[END_REF][START_REF] Bergaya | Handbook of clay science[END_REF][START_REF] Brigatti | Structure and Mineralogy of Clay Minerals[END_REF], Meunier, 2005[START_REF] Moore | X-ray Diffraction and the Identification and Analysis of Clay Minerals[END_REF], Velde, 2000, and references therein). A general overview of the clay minerals that are used in this manuscript is presented in the next section.

Mica group

The general structure of mica group minerals is shown in Figure 0.5. Micas are 2:1(TOT) layer structure clay; based on their layer charge (X) they are divided into true mica (X ∼ 1) and brittle mica (X ∼ 2).

The layer charge is balanced by univalent interlayer cations in the case of true micas and divalent cations in the case of brittle micas. The true and brittle micas are subdivided on the basis of whether the species are dioctahedral (muscovite type) or trioctahedral (biotite type) [START_REF] Weaver | The chemistry of clay minerals[END_REF].

According to [START_REF] Brigatti | Mica crystal chemistry and the influence of pressure, temperature, and solid solution on atomistic models[END_REF], who discussed the structural and chemical features of more than 200 micas, the mica structure has a general formula of : is the abundant cation in the tetrahedral sites (e.g. celadonite, polylithionite, tainiolite and norrishite), whereas in the most common mica species Al 3+ substitutes Si 4+ in a ratio close to 1:3 (e.g. muscovite and phlogopite) [START_REF] Brigatti | Structure and Mineralogy of Clay Minerals[END_REF]. In addition, substitution in the octahedral sheet can occur through the replacement of trivalent cations by divalent cations (in dioctahedral micas) and the replacement of divalent cations by trivalent cations (in trioctahedral micas)( (Meunier, 2005)). For a given layer of identical structure and composition, micas may stacked together in a variety of stacking sequences (polytypes) due to different pressure-temperature conditions during formation (Christidis, 2010, Weaver and[START_REF] Weaver | The chemistry of clay minerals[END_REF]. According to the AIPEA Nomenclature Committee, the term 'polytypism' is used to define the existence of an element or compound in two or more layer-like crystal structures that differ in layer-stacking sequences [START_REF] Brigatti | Structure and Mineralogy of Clay Minerals[END_REF]. The principles of polytypism are reviewed by several authors (e.g. [START_REF] Bailey | X-ray diffraction of the polytypes of mica, serpentine, and chlorite[END_REF][START_REF] Baronnet | Some aspects of polytypism in crystals[END_REF], Nespolo, 1997, Sato et al., The occurrence of these polytypes is a function of increasing grades of diagenesis-metamorphism [START_REF] Velde | Experimental determination of muscovite polymorph stabilities[END_REF]. With increasing temperature, micas show the following irreversible polytype transformation: 1M d →1M→2M 1 [START_REF] Hunziker | The evolution of illite to muscovite: mineralogical and isotopic data from the Glarus Alps, Switzerland[END_REF][START_REF] Lonker | Formation of coexisting 1M and 2M polytypes in illite from an active hydrothermal system[END_REF][START_REF] Weaver | muds, and shales[END_REF][START_REF] Zöller | 1M and 2M illites: different minerals and not polytypes[END_REF].The 1M d and 1M polytypes are commonly formed below 200 • C whereas 2M 1 polytype is considered to form above 280 • C and it is the most stable mica polytype (Srodo ń and Eberl, 1984[START_REF] Velde | Experimental determination of muscovite polymorph stabilities[END_REF]. Therefore, the determination of mica polytypism can be of a major importance for the investigation of thermal history during their formation. The distinction between these different polytypes is commonly made through X-ray powder patterns because each regular stacking produces a series of distinctive reflections [START_REF] Moore | X-ray Diffraction and the Identification and Analysis of Clay Minerals[END_REF].

Illite has a composition similar to muscovite, the term was first proposed by [START_REF] Grim | The mica in argillaceous sediments[END_REF], as a general term for the mica-like clay minerals and not as a specific mineral name. Several definitions for illite have been proposed by [START_REF] Bailey | Report of the clay minerals society nomenclature committee for 1982 and 1983[END_REF], [START_REF] Guggenheim | Summary of recommendations of nomenclature committees relevant to clay mineralogy: report of the Association Internationale pour l'Etude des Argiles (AIPEA) Nomenclature Committee for 2006[END_REF], [START_REF] Martin | Report of the clay minerals society nomenclature committee; revised classification of clay materials[END_REF], Meunier GENERAL INTRODUCTION and Velde (2004). According to these authors, illite is a low-potassium mica (with a K content per unit cell near 0.9) with a 10 Å basal spacing. It is also defined as a non-expandable dioctahedral clay mineral with ionic substitutions in both octahedral and tetrahedral sheets. It has the following structure formula:

[Si 4-x Al x ] O 10 (R 3+ 2-y R 2+ y ) (OH) 2 K x+y with 0.75 x + y 0.95
Where R 3+ and R 2+ refer to trivalent and divalent cations respectively. This structural formula of illite is different from muscovite that has the following structural formula:

[Si 3 Al] O 10 Al 2 (OH) 2 K with x =1
Both muscovite and illite have similar basal d-spacing, thus with X-ray diffraction it is not possible to distinguish between them. Therefore, the differentiation between muscovite and illite is based mainly on the chemical composition; illite has less K in the interlayer and less Al on the tetrahedral sites and some Mg and Fe in the octahedral layer compared to muscovite (Meunier, 2005, Meunier andVelde, 2004).

Chlorite

As mentioned before, the fundamental unit layer of chlorite consists of a regularly stacked, negatively charged 2:1 layers and a single positively charged interlayer octahedral sheet connected by H-bonds.

The basic unit layer-structure thickness is 14 Å as shown in Figure 0.7.

As chlorite has two octahedral sheets i.e. one octahedral sheet in the 2:1 layer and one in the interlayer sheet, it is classified into four sub-groups based on the types of these sheets (dioctahedral vs. trioctahedral): (1) Tri-tri-(e.g. clinochlore, chamosite), (2) Di-di-(e.g. donbassite), (3) Di-tri-(e.g. cookeite and sudoite), and (4) Tri-di structures (unknown) [START_REF] Bailey | Summary of recommendations of AIPEA nomenclature committee[END_REF]. The first group (trioctahedral chlorites) is the most common representative of chlroite [START_REF] Bailey | Soil components[END_REF], the second and third types are rarer and the trioctahedral-dioctahedral chlorites are unknown (Meunier, 2005). The tetrahedral sheet in chlorites hosts tri-or tetravalent cations (Si 4+ , Al 3+ ), while the octahedral sheet is composed of dior trivalent cations (usually Fe 2+ ,Mg 2+ ,Mn 2+ ,Al 3+ and Fe 3+ ). The following general structure formula of chlorite was proposed by [START_REF] Bailey | X-ray diffraction of the polytypes of mica, serpentine, and chlorite[END_REF], [START_REF] Wiewióra | Crystallochemical classifications of phyllosilicates based on the unified system of projection of chemical composition: II. The chlorite group[END_REF]:

[Si 4-x R 3+ x ] O 10 (R + 6-x-3y R 3+ x+2y y ) (OH) 8
( refers to octahedral vacancies)

This structural specificity of chlorites allows for a wide range of ionic substitutions (Meunier, 2005);

the main chemical substitutions occurring in chlorites are: (iii) Di-trioctahedral substitutions (DT) 2Al 3+

(i) Tschermak substitutions (TK) Si 4+ (I V ) + (Fe 2+ , Mg 2+ ) (V I ) = Al 3+ (I V ) +Al 3+ (V I ) (ii) Ferromagnesian substitutions (FM) Mg 2+ (I V ) = Fe 2+ (V I )
(V I ) + (I V ) = 3(Mg 2+ , Fe 2+ ) (V I )
These substitution variations in chlorite depend on several parameters: bulk-rock composition, and physicochemical conditions at the time of formation, such as temperature, pressure, pH, and the activities of various metal cations dissolved in fluid (e.g. [START_REF] Hillier | Octahedral Occupancy and the Chemical Composition of Diagenetic (Low-Temperature) Chlorites[END_REF][START_REF] Inoue | Application of Chemical Geothermometry to Low-Temperature Trioctahedral Chlorites[END_REF][START_REF] Lanari | A thermodynamic model for di-trioctahedral chlorite from experimental and natural data in the system MgO-FeO-Al 2 o 3 -SiO 2 -H 2 o: applications to P-T sections and geothermometry[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]. Because of the large variety of chemical substitutions many names have been given to end-members of the chlorite group (Walshe, 1986, Weaver and[START_REF] Weaver | The chemistry of clay minerals[END_REF].

The most common chlorite end-members are:

-Al-free chlorite Several studies have shown that the incorporation of ferric iron in chlorite can be significant in lowgrade conditions (see e.g. [START_REF] Inoue | Application of Chemical Geothermometry to Low-Temperature Trioctahedral Chlorites[END_REF]references therein Munoz et al., 2013). Therefore, [START_REF] Trincal | Al-free di-trioctahedral substitution in chlorite and a ferri-sudoite end-member[END_REF] suggested a new chlorite end-member: ferri-sudoite that has the following general structural formula:[Si 3 Al] O 10 ((Fe 2+ ,Mg) 2 Fe 3+ 2 Al) (OH) 8 with 2 atoms of Fe 3+ . They associate this ferri-sudoite end-member to a new substitution: di-trioctahedral substitution 3(Fe 2+ , Mg 2+ ) = 2Fe 3+ . However, they conclude that further studies are still required to confirm the existence of this substitution.

Origin of clay minerals in fault zones

Clay minerals formation occur at surface or subsurface in all types of sediments and in different geological environments (e.g. weathering, sedimentary, diagenetic-hydrothermal and low-grade metamorphism) [START_REF] Eberl | Clay mineral formation and transformation in rocks and soils[END_REF], Meunier, 2005). They can have three different origins in these geological systems [START_REF] Millot | Geology of clays: Weathering, sedimentation, geochemistry[END_REF]):

• Inheritance (or heritage): clay minerals can be transported by weathering agents and accumulate in a other place different from the initial parent rocks. The modifications are limited during this process, thus they are known as inherited/detrital clays.

• New formation: clay minerals can also form or precipitate directly from saturated solutions/fluids or through chemical reactions from amorphous materials.

• Transformation: the inherited or newly-formed clay minerals can be partially or completely changed by prograde or retrograde mineralogical reactions. This change can occurs through mineralogical transformation and dissolution-recrystallization processes.

Clay minerals are the most abundant minerals in sedimentary rocks, representing as much as 40% of the minerals in these rocks [START_REF] Weaver | The chemistry of clay minerals[END_REF], hence they are major constituents of faults affecting sedimentary rocks. The origin and formation mechanisms of phyllosilicate minerals in fault zones have been described in several studies (e.g. Buatier et al., 2012a[START_REF] Egholm | The mechanics of clay smearing along faults[END_REF][START_REF] Fisher | The permeability of faults within siliciclastic petroleum reservoirs of the North Sea and Norwegian Continental Shelf[END_REF][START_REF] Jefferies | Origin and mechanical significance of foliated cataclastic rocks in the cores of crustal-scale faults: Examples from the Median Tectonic Line, Japan: FOLIATED CATACLASITES IN FAULTS[END_REF], Kettermann et al., 2016[START_REF] Kuo | Temperature estimates of coseismic heating in clay-rich fault gouges, the Chelungpu fault zones, Taiwan[END_REF][START_REF] Lacroix | Microtectonic and geochemical characterization of thrusting in a foreland basin: Example of the South-Pyrenean orogenic wedge (Spain)[END_REF][START_REF] Laurich | Microstructures and deformation mechanisms in Opalinus Clay: insights from scaly clay from the Main Fault in the Mont Terri Rock Laboratory (CH)[END_REF][START_REF] Leclère | Formation of phyllosilicates in a fault zone affecting deeply buried arkosic sandstones: their influence on petrophysic properties (Annot sandstones, French external Alps)[END_REF][START_REF] Liao | Analysis of fault rock deformation and clay minerals from fault cores of Chelungpu fault zone[END_REF][START_REF] Mancktelow | Timing and conditions of brittle faulting on the Silltal-Brenner Fault Zone, Eastern Alps (Austria)[END_REF][START_REF] Solum | fabrics and age of clay minerals from an exposure of the Moab Fault, Utah[END_REF], 2010[START_REF] Warr | Clay mineral transformations and weakening mechanisms along the Alpine Fault, New Zealand[END_REF], Yuan et al., 2015, among others). According to these studies, phyllosilicates can GENERAL INTRODUCTION be incorporated in the fault zones as a result of various processes depending on the deformation mechanisms:

1. Mechanical incorporation of protolith rocks into a fault zone (such as clay smear, wall abrasion and clay gouge) (e.g. [START_REF] Egholm | The mechanics of clay smearing along faults[END_REF], Kettermann et al., 2016[START_REF] Van Der Zee | Processes of normal fault evolution in a siliciclastic sequence: a case study from Miri, Sarawak, Malaysia[END_REF].

According to [START_REF] Vrolijk | Clay smear: Review of mechanisms and applications[END_REF], the clay smear forms in normal faults that affects layered sedimentary sequences; it is composed of pelite sediments which have been incorporated to the fault zone during displacement. The same authors defined wall abrasion as "mechanical wearing, grinding, scraping, or rubbing away (or down) of rock surfaces by friction". While clay gouge is incohesive fine-grained fault rock that is composed mainly of clay minerals [START_REF] Sibson | Fault rocks and fault mechanisms[END_REF]. It has been described as a common product of near-surface faulting at low temperature conditions that is formed by brittle deformation processes (e.g. [START_REF] Buatier | Microtextural investigation (SEM and TEM study) of phyllosilicates in a major thrust fault zone (Monte Perdido, southern Pyrenees): impact on fault reactivation[END_REF][START_REF] Haines | Patterns of mineral transformations in clay gouge, with examples from low-angle normal fault rocks in the western USA[END_REF], Vrolijk and van der Pluijm, 1999). Comminution, fragmentation and mechanical abrasion of the fault host rocks are the main mechanisms responsible for the incorporation of clay gouge in fault zones (e.g. [START_REF] Buhay | ESR dating of fault gouge: The effect of grain size[END_REF][START_REF] Haines | Clay fabric intensity in natural and artificial fault gouges: Implications for brittle fault zone processes and sedimentary basin clay fabric evolution[END_REF][START_REF] Solum | Quantification of fabrics in clay gouge from the Carboneras fault, Spain and implications for fault behavior[END_REF].

2. Dissolution-recrystallization and pressure solution mechanisms that lead to passive concentration of phyllosilicates in fault core zone through the dissolution of soluble minerals and/or recrystallization of inherited/detrital clay minerals (e.g. Buatier et al., 2012a, 2015[START_REF] Lacroix | Microtectonic and geochemical characterization of thrusting in a foreland basin: Example of the South-Pyrenean orogenic wedge (Spain)[END_REF][START_REF] Leclère | Formation of phyllosilicates in a fault zone affecting deeply buried arkosic sandstones: their influence on petrophysic properties (Annot sandstones, French external Alps)[END_REF]. These mechanisms can occurred in presence of fluids that may lead to accelerating the pressure solution by developing diffusion shortcut (e.g. [START_REF] Gratier | Aseismic sliding of active faults by pressure solution creep: Evidence from the San Andreas Fault Observatory at Depth[END_REF][START_REF] Janssen | Microstructures and their implications for faulting processes -Insights from DGLab core samples from the Gulf of Corinth[END_REF][START_REF] Richard | Rock and mineral transformations in a fault zone leading to permanent creep: Interactions between brittle and viscous mechanisms in the San Andreas Fault: Fault rock changes leads to steady creep[END_REF].

3. Direct precipitation from fluids (within shear and extensional veins) and/or as a product of chemical reactions between fluids circulating in the fault zone and the host rocks (e.g. [START_REF] Haines | Clay quantification and Ar-Ar dating of synthetic and natural gouge: Application to the Miocene Sierra Mazatán detachment fault, Sonora, Mexico[END_REF][START_REF] Lacroix | Formation of chlorite during thrust fault reactivation. Record of fluid origin and P-T conditions in the Monte Perdido thrust fault (southern Pyrenees)[END_REF][START_REF] Trincal | Temperature micro-mapping in oscillatory-zoned chlorite: Application to study of a green-schist facies fault zone in the Pyrenean Axial Zone (Spain)[END_REF][START_REF] Wibberley | Recent advances in the understanding of fault zone internal structure: a review[END_REF].

Phyllosilicates in fault zones as source of information

As mentioned above, when phyllosilicate formation in the fault core zone is synkinematic to the fault, they can be an important a source of information about the fault activity conditions. Therefore, the focus of this section is to describe the methods/techniques that are based on newly-formed phyllosilicates in fault zones as source of information as they can be used as geothermometers (Kübler index of muscovite/illite and chlorite thermometry) and as geochronological tools ( 40 Ar/ 39 Ar dating of GENERAL INTRODUCTION muscovite/illite).

Kübler index of muscovite/illite

The Kübler index of muscovite/illite is a commonly used method for evaluating diagenetic and lowtemperature metamorphic history of the host-rocks (Abad, 2007, Meunier andVelde, 2004). The measurement of this crystallinity index is determined by X-ray diffraction (XRD). The regular change in the shape of the 001 basal reflection of illite/muscovite at 10 Å was first realized by [START_REF] Weaver | Possible uses of clay minerals in the search for oil[END_REF] who suggested that the shape of this reflection peak is a function of burial (increasing temperature and pressure). Then, [START_REF] Kübler | Les argiles, indicateurs de métamorphisme[END_REF][START_REF] Kübler | La cristallinité de l'illite et les zones tout a fait superieures du métamorphisme. étages tectoniques[END_REF][START_REF] Kübler | Evaluation quantitative du métamorphisme par la cristallinité d l'illite[END_REF]) proposed an illite 'crystallinity' index that is based on the full width at half maximum (FWHM) of the 001 peak reflection that is measured on the < 2 µm size-fraction of the oriented air dried samples using Cu-Kα radiation. This index is called the Kübler index (KI) and it is expressed as small changes in the Bragg angle, • 2θ. It was first introduced to identify the transition between the dry-gas zone and the zone of unproductive rocks (i.e. the transition from deep diagenesis to anchizone) for hydrocarbon exploration. The anchizone boundaries were first defined by [START_REF] Kübler | La cristallinité de l'illite et les zones tout a fait superieures du métamorphisme. étages tectoniques[END_REF] at 0.42 • 2θ to 0.25 • 2θ, corresponding to the disappearance of mixed layered illite-smectite and the appearance of chloritoid respectively [START_REF] Kübler | Sur le pouvoir réflecteur de la vitrinite dans quelques roches du Jura, de la Molasse et des Nappes préalpines[END_REF]. When the metamorphic conditions increase, muscovite/illite display well-defined crystallinity and the peak at 10 Å becomes narrower (lower KI values). The decreasing of KI values with increasing metamorphic conditions is a consequence of the increase in number of layers (i.e. thick particles that correspond to higher domains of coherence for X-ray diffraction) and the disappearance of expanding layers (e.g. [START_REF] Abad | Physical meaning and applications of the illite Kübler index: measuring reaction progress in low-grade metamorphism. Diagenesis and Low-Temperature Metamorphism[END_REF].

However, analytical variation between the different laboratories was a serious problem when calculating and comparing the Kübler index values [START_REF] Frey | Very low-grade metamorphism of clastic sedimentary rocks[END_REF]. These variations arise from sample preparation techniques, XRD instrumental settings and measurement methods [START_REF] Blenkinsop | Definition of low-grade metamorphic zones using illite crystallinity[END_REF][START_REF] Eberl | Beyond the Kübler index[END_REF][START_REF] Kisch | Calibration of the anchizone: a critical comparison of illite 'crystallinity'scales used for definition[END_REF][START_REF] Krumm | Sample preparation effects on illite crystallinity measurement: grain-size gradation and particle orientation[END_REF][START_REF] Robinson | The illite 'crystallinity'technique: a critical appraisal of its precision[END_REF]. Such differences can be reduced by following the recommendations of the IGCP 294 IC working group [START_REF] Kisch | Illite crystallinity: recommendations on sample preparation, X-ray diffraction settings, and interlaboratory samples[END_REF].

Furthermore, [START_REF] Warr | Interlaboratory standardization and calibration of day mineral crystallinity and crystallite size data[END_REF], proposed a calibration approach using four available international standards in the form of chips that must be prepared and measured by each laboratory in a routine way. The same authors proposed an international standardized scale to express KI, termed the "Crystallinity Index Standard" (CIS) that maintains the original boundaries proposed by Kübler.

The directly and quantitatively compared. In spite of the advantages of the CIS method, not all laboratories have followed this procedure due to uncertainty in the equivalent of the CIS scale with the original scale of Kübler (e.g. Ferreiro Mählmann and Frey, 2012, Ferreiro Mählmann et al., 2012[START_REF] Kisch | On the calibration of the illite Kubler index (illite "crystallinity")[END_REF]. For example, [START_REF] Kisch | On the calibration of the illite Kubler index (illite "crystallinity")[END_REF] considered the limits of the anchizone produced by the CIS scale of [START_REF] Warr | Interlaboratory standardization and calibration of day mineral crystallinity and crystallite size data[END_REF] to be higher than those obtained by other laboratories. Therefore, after a round-table discussion that took place at the Mid-European Clay Conference in Dresden, Germany, on 17 September 2014, agreement has now been reached on a reliable correlation between Kübler-Frey values and the CIS scale [START_REF] Warr | Recommendations for Kübler index standardization[END_REF]. Based on that, the upper and lower boundary limits of the CIS anchizone are now set at 0.32 • and 0.52 • 2θ, respectively. In order to be compatible with the original anchizone boundaries of [START_REF] Kübler | La cristallinité de l'illite et les zones tout a fait superieures du métamorphisme. étages tectoniques[END_REF], the CIS values can be calibrated to the traditional Kübler-Kisch scale by using the equation:

Kübler values (CIS) = 1.1523 * Kübler values (Basel laboratory) + 0.036 which is presented in the figure 1 of [START_REF] Warr | Recommendations for Kübler index standardization[END_REF].

Because of the simplicity and reproducibility of the KI method, and thanks to the development of computerized XRD treatments, the method became one of the most common tools to evaluate diagenesis and metamorphic grade conditions of clastic rocks in different geotectonic regimes (e.g. Bayan and GENERAL INTRODUCTION Hower, 2012[START_REF] Chen | Microstructure characteristics of illite from Chuanlingou Formation of Changcheng System in Jixian County, Tianjin City[END_REF][START_REF] Doublier | Very low-grade metamorphism of Rheno-Hercynian allochthons (Variscides, Germany): facts and tectonic consequences[END_REF], Guggenheim et al., 2002[START_REF] Gunal-Turkmenoglu | Clay mineralogy, chemistry, and diagenesis of Late Devonian K-bentonite occurrences in northwestern Turkey[END_REF][START_REF] Potel | Very low-grade metamorphism in the para-autochtonous sedimentary cover of the Pelvoux massif (Western Alps, France)[END_REF][START_REF] Warr | Correlating illite (Kübler) and chlorite (Árkai) "crystallinity" indices with metamorphic mineral zones of the South Island, New Zealand[END_REF]. In fault zones, several studies have demonstrated that the KI is a reliable method in estimating the deformation conditions of fault activity (e.g. [START_REF] Abad | The structure and the phyllosilicates (chemistry, crystallinity and texture) of Talas Ala-Tau (Tien Shan, Kyrgyz Republic): comparison with more recent subduction complexes[END_REF][START_REF] Bense | Fault gouge analyses: K-Ar illite dating, clay mineralogy and tectonic significance-a study from the Sierras Pampeanas, Argentina[END_REF], Buatier et al., 2015[START_REF] Dellisanti | The role of tectonic shear strain on the illitization mechanism of mixed-layers illite-smectite. A case study from a fault zone in the Northern Apennines, Italy[END_REF][START_REF] Girard | The Dutung-Thaktote extensional fault zone and nappe structures documented by illite crystallinity and clay-mineral paragenesis in the Tethys Himalaya between Spiti river and Tso Morari[END_REF], Tanaka et al., 1995, among others).

Chlorite thermometry

Chlorite is widely distributed in the earth's crust in a variety of geologic environments including diagenetic, low-to high-grade metamorphic, and hydrothermally altered rocks [START_REF] Laird | metamorphic petrology[END_REF]. The chemical composition of chlorite is sensitive to the formation conditions, i.e. pressure, temperature, the redox conditions, as well as to bulk-rock and fluid composition. Therefore, chlorite composition variation has attracted interest as a potential source of information on the physicochemical conditions of its formation [START_REF] Walshe | A six-component chlorite solid solution model and the conditions of chlorite formation in hydrothermal and geothermal systems[END_REF]. The use of chlorite composition in estimating the formation temperature is referred to as 'chemical chlorite geothermometry'. Three approaches have been proposed to the chemical chlorite geothermometry; (1) empirical calibrations, (2) thermodynamic modeling and (3)

semi-empirical calibrations. The first approach directly links the tetrahedral Al or vacancy content of chlorite with temperature (e.g. [START_REF] Cathelineau | Cation site occupancy in chlorites and illites as function of temperature[END_REF][START_REF] Cathelineau | A chlorite solid solution geothermometer the Los Azufres (Mexico) geothermal system[END_REF][START_REF] Hillier | Octahedral Occupancy and the Chemical Composition of Diagenetic (Low-Temperature) Chlorites[END_REF][START_REF] Jowett | Fitting iron and magnesium into the hydrothermal chlorite geothermometer[END_REF][START_REF] Kranidiotis | Systematics of chlorite alteration at the Phelps Dodge massive sulfide deposit, Matagami, Quebec[END_REF][START_REF] Zang | Chloritization of the hydrothermally altered bedrock at the Igarapé Bahia gold deposit, Carajás, Brazil[END_REF]. However, this empirical approach failed to obtain accurate estimates in several instances (see e.g. Bourdelle et al., 2013a[START_REF] De Caritat | Chlorite geothermometry: a review[END_REF][START_REF] Essene | Thermobarometry gone astray[END_REF][START_REF] Essene | Clay mineral thermometry-a critical perspective[END_REF]. These authors have demonstrated that the method is lacking theoretical backgrounds and it does not take into account the three main cationic substitutions occurring in chlorites (i.e. Ferromagnesian, Tschermak and di/trioctahedral substitutionss). Moreover, they argued that chlorite compositions are not only sensitive to conditions of metamorphism but also to bulk rock composition (e.g. [START_REF] Zane | New data on metamorphic chlorite as a petrogenetic indicator mineral, with special regard to greenschist-facies rocks[END_REF]. Consequently, this empirical approach can be only applied to a restricted range of chlorite composition and pressure at which they were calibrated [START_REF] Bourdelle | Low-temperature chlorite geothermometry: a graphical representation based on a T-R 2+ -Si diagram[END_REF]. The second approach is based on the thermodynamic calculation of equilibrium conditions for chlorites whose composition is expressed as a linear combination of a set of end-members of known thermodynamic properties [START_REF] Inoue | Application of Chemical Geothermometry to Low-Temperature Trioctahedral Chlorites[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], 2006, 2016). The thermodynamic approach offers an alternative to the empirical approach as it has many advantages: it takes into account the variations of the rock mineralogy (including elemental partitioning between coexisting minerals) and the influence of additional physicochemical parameters such as fluid composition and redox conditions. The third approach, which is known as semi-empirical, uses the relationship between temperature (1/T) and the equilibrium constant (K) of a reaction involving chlorite end-members and quartz + water (e.g. Bourdelle et al., 2013b[START_REF] Inoue | Application of Chemical Geothermometry to Low-Temperature Trioctahedral Chlorites[END_REF][START_REF] Lanari | A thermodynamic model for di-trioctahedral chlorite from experimental and natural data in the system MgO-FeO-Al 2 o 3 -SiO 2 -H 2 o: applications to P-T sections and geothermometry[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]. According to [START_REF] Bourdelle | Low-temperature chlorite geothermometry: a graphical representation based on a T-R 2+ -Si diagram[END_REF] these semi-empirical models have to be used with caution as they do not consider the contributions of non-ideality, P and water activity.

The thermodynamic models (second approach) appear to be applicable to chlorite that is formed under diagenetic and/or low-grade metamorphic conditions during thrust fault activity (e.g. [START_REF] Cantarero | Long-term fluid circulation in extensional faults in the central Catalan Coastal Ranges: P-T constraints from neoformed chlorite and K-white mica[END_REF][START_REF] Lacroix | Formation of chlorite during thrust fault reactivation. Record of fluid origin and P-T conditions in the Monte Perdido thrust fault (southern Pyrenees)[END_REF][START_REF] Leclère | Formation of phyllosilicates in a fault zone affecting deeply buried arkosic sandstones: their influence on petrophysic properties (Annot sandstones, French external Alps)[END_REF], Trincal et al., 2015, among others). Therefore, the thermodynamic model proposed by [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-T-deformation-Fe 3+ /Fe 2+ mapping at the thin section scale and comparison with XANES mapping: application to a garnetbearing metapelite from the Sambagawa metamorphic belt (Japan)[END_REF] has been used for the chlorite temperature estimations in the present study using the CHLMICAEQUI program [START_REF] Lanari | Micro-cartographie P-T-» dans les roches métamorphiques[END_REF], Lanari et al., 2012). In this model, chlorite compositions are modeled using the amesite, clinochlore, daphnite and sudoite end-members with an extension to Fe-amesite (fames) end-members. The choice of these end-members allows for a description of the Fe-Mg, Tschermak, and dioctahedral-trioctahedral substitutions that occur in trioctahedral chlorites. Moreover, the model takes into account the possibility of Fe 3+ substitutions that may modify the number of vacancies in the chlorite structure, and also the activity of the chlorite end-members.

40

Ar/ 39 Ar radiometric dating of muscovite/illite A radiometric age is the time since a mineral starts to accumulate/trap the daughter isotope which results from the natural decay of its parent isotope. There is a critical temperature below which accumulation of the daughter isotope occurs quantitatively in the dated rock or mineral and above which the daughter isotope begins to be lost by diffusion. This temperature is termed closure temperature (T c ) which is different for different decay schemes and different minerals [START_REF] Hamilton | A review of radiometric dating techniques for clay mineral cements in sandstones[END_REF][START_REF] Harrison | Diffusion of 40 Ar in muscovite[END_REF]. The T c is defined as the temperature at the time corresponding to the apparent age of a geochronological system [START_REF] Dodson | Closure temperature in cooling geochronological and petrological systems[END_REF]. According to the equation proposed by Dodson, closure temperature values change with different cooling rates and with the grain size of the targeted mineral. Smaller grains will yield lower closure temperatures compared to larger gains because they have smaller effective diffusional radii (see e.g. [START_REF] Duvall | Direct dating of Eocene reverse faulting in northeastern Tibet using Ar-dating of fault clays and low-temperature thermochronometry[END_REF][START_REF] Goodwin | Effects of progressive mylonitization on Ar retention in biotites from the Santa Rosa mylonite zone, California, and thermochronologic implications[END_REF][START_REF] Mulch | In-situ UV-laser 40 Ar/ 39 Ar geochronology of a micaceous mylonite : an example of defect-enhanced argon loss[END_REF][START_REF] Scharf | Grainsize effects on the closure temperature of white mica in a crustal-scale extensional shear zone -Implications of in-situ 40 Ar/ 39 Ar laser-ablation of white mica for dating shearing and cooling (Tauern Window, Eastern Alps)[END_REF][START_REF] Verdel | Variation of illite/muscovite 40 Ar/ 39 Ar age spectra during progressive low-grade metamorphism: an example from the US Cordillera[END_REF].

The 40 Ar/ 39 Ar radiometric technique is based on the conventional K-Ar method, the basics and advantages and limitations of both methods have been reviewed in several publications and text-books (see e.g. [START_REF] Clauer | The K-Ar and 40 Ar/ 39 Ar methods revisited for dating fine-grained K-bearing clay minerals[END_REF][START_REF] Hamilton | A review of radiometric dating techniques for clay mineral cements in sandstones[END_REF][START_REF] Harrison | Fundamentals of Noble Gas Thermochronometry[END_REF][START_REF] Harrison | Diffusion of 40 Ar in muscovite[END_REF][START_REF] Kelley | K-Ar and Ar-Ar Dating[END_REF], McDougall GENERAL INTRODUCTION and Harrison, 1999, among others)

t = 1 λ l n[1 + J ( 40 Ar * 39 Ar K )]
Where t is the time since closure, λ is the decay constant, J is a dimensionless parameter that is calculated using standard minerals (flux monitors) of know ages intermittent between samples of unknown age to deduce the neutron flux across its axis, 40 Ar* is the radiogenic argon that is formed by decay of the 40 K and 39 Ar k is the 39 Ar produced from 39 K during irradiation.

Following irradiation, the sample is either fused or incrementally heated under vacuum and the 40 Ar/ 39 Ar ratio is measured by mass spectrometry. The 40 Ar/ 39 Ar method has the potential to overcome some of the drawbacks and limitations of the K-Ar technique for dating fine-grain clay minerals, including the measurement of K and Ar on two different aliquots. Due to potential sample heterogeneity, the isotopic ratios are less precise and consequently less accurate age determinations are expected. I addition, duplicate analyses should be done to ensure the homogeneity of K and Ar distribution in the sample, requiring relatively large sample sizes. Conversely, in the 40 Ar/ 39 Ar method the measurements are made with a single isotopic analysis, thus reducing the effect of sample heterogeneity [START_REF] Dong | Mechanisms of argon retention in clays revealed by laser 40 Ar-39 Ar dating[END_REF]. Besides that, the 40 Ar/ 39 Ar method is able to achieve higher levels of internal precision than K-Ar dating since the isotopic ratios are measured more precisely compared to elemental abundances. In addition, it requires much smaller sample quantities (a few milligrams) compared to the K-Ar method.

Moreover, it offers the possibility of in situ dating (in thin-sections) using laser microprobe and ob-

GENERAL INTRODUCTION

taining ages for individual grains [START_REF] Onstott | Laser 40 Ar/ 39 Ar microprobe analyses of fine-grained illite[END_REF]. The K-Ar method only provides a total fusion age and does not give any information on the distribution of argon isotopes in the dated material. In the 40 Ar/ 39 Ar method, total fusion ages can be also measured by melting the sample after irradiation.

However, a major important advantage of the 40 Ar/ 39 Ar method is that after irradiation of the sample, argon can be progressively released by step-heating until fusion. That will give information about the argon isotope distribution in the dated sample and identify the different mica generations within the same sample.

The step-heating technique or incremental heating was first proposed by [START_REF] Merrihue | Potassium-Argon dating by activation with fast neutrons[END_REF] and it is described in more detail by [START_REF] Mcdougall | Geochronology and Thermochronology by the 40 Ar/ 39 Ar Method[END_REF]. The 40 Ar* and 39 Ar are likely to occur in the same sites with similar proportion inside the grains because both of them have been derived from potassium (if the system remained closed since initial crystallization of muscovite/illite).

During the incremental heating procedure, the two isotopes are released with the same proportion because they have similar transport behaviour [START_REF] Mcdougall | Geochronology and Thermochronology by the 40 Ar/ 39 Ar Method[END_REF]. Thus, they will yield a constant 40 Ar* and 39 Ar ratio in each gas fraction extracted and consequently similar apparent ages. A plotting of these apparent ages against the accumulative proportion of released 39 Ar should yields a flat pattern termed plateau and this plotting is known as an age spectrum. In such cases, the age is defined from the plateau [START_REF] Dalrymple | 40 Ar/ 39 Ar age spectra of some undisturbed terrestrial samples[END_REF] and this plateau indicates that the sample is thermally undisturbed since its initial closure for argon diffusion. A plateau age is calculated on at least three consecutive steps with ages that agree within 2 sigma error and that represent at least 50% of the total amount of 39 Ar (e.g. [START_REF] Clauer | Comparative 40 Ar/ 39 Ar and K-Ar dating of illite-type clay minerals: A tentative explanation for age identities and differences[END_REF][START_REF] Dallmeyer | 40 Ar/ 39 Ar polyorogenic mineral age record in the northern Mauritanide orogen, West Africa[END_REF][START_REF] Fleck | Interpretation of discordant 40 Ar/ 39 Ar age-spectra of mesozoic tholeiites from antarctica[END_REF]. In case of partial resetting due to a thermo-tectonic overprint (i.e. the sample was reheated or deformed after the initial crystallization), the proportions of K and Ar, no longer reflect the original distribution and no flat shape spectrum will be obtained. If significant accumulation of radiogenic argon has occurred since the reheating-event, the step-heating technique may offer the possibility for estimating the time of both the re-heating and the initial closure events. The apparent age of the first steps (at low experimental extraction temperature) in the age spectrum may represent the age of the late thermal event and the high temperature step ages will reflect the minimum age of the initial closure of a sample. These interpretations are well explained in the schematic diagram of (Harrison, 2005, McDougall and[START_REF] Mcdougall | Geochronology and Thermochronology by the 40 Ar/ 39 Ar Method[END_REF]) that shows different types of 40 Ar* and 39 Ar age spectra related to different thermal histories (Figure 0.9). On the other hand, the staircase-shape of an age spectrum has been interpreted either as a mineral mixing of different grain-sizes with different ages and Ar retentivity or inhomogeneous compositions within the individual grain (e.g. Dong et al., 2000, Forster and Lister, 2004, [START_REF] Kirschner | Staircase 40 Ar/ 39 Ar spectra of fine-grained white mica: Timing and duration of deformation and empirical constraints on argon diffusion[END_REF][START_REF] Verdel | Variations in the Illite to Muscovite Transition Related to Metamorphic Conditions and Detrital Muscovite Content: Insight from the Paleozoic Passive Margin of the Southwestern United States[END_REF], 2012). In this specific case, in situ laser probe dating has provided in recent years very useful information about the distribution of argon isotopes within and between the different grains that can grow during a long-lasting evolution (e.g. [START_REF] Agard | Exhumation of the Schistes Lustrés complex: in situ laser probe 40 Ar/ 39 Ar constraints and implications for the Western Alps[END_REF][START_REF] Augier | doming and slab retreat in the Betic Cordillera (SE Spain): in situ 40 Ar/ 39 Ar ages and P-T-d-t paths for the Nevado-Filabride complex[END_REF][START_REF] Berger | Microstructures, mineral chemistry and geochronology of white micas along a retrograde evolution: An example from the Aar massif (Central Alps, Switzerland)[END_REF][START_REF] Vincenzo | Evidence of a close link between petrology and isotope records: constraints from SEM, EMP, TEM and in situ 40 Ar-39 Ar laser analyses on multiple generations of white micas (Lanterman Range, Antarctica)[END_REF], 2016[START_REF] Mulch | In-situ UV-laser 40 Ar/ 39 Ar geochronology of a micaceous mylonite : an example of defect-enhanced argon loss[END_REF]. This give one more advantage to the 40 Ar/ 39 Ar step-heating technique i.e. extracting information from samples with more than one mica generations related to a complex thermal and geological history.

In spite of all these advantages, the 40 Ar/ 39 Ar method also has some inconveniences and the interpretation of age spectra is not straightforward, in particular when dating very fine mica grains in sedimentary environments [START_REF] Hamilton | A review of radiometric dating techniques for clay mineral cements in sandstones[END_REF]. In the following section, summary of the major problems arising when dating fine-grained clay minerals and how to partially treat them are presented.

Dating mixtures of micas with different origins/ages and compositions

To get a meaningful age of the fault activity, the synkinematic micas that formed during faulting should be dated separately from other mica phases/generations. Unfortunately, in a case of low grade metamorphism and diagenesis, the dated sample is commonly a mixture of detrital, diagenetic and authigenic phases with different ages [START_REF] Van Der Pluijm | Fault dating in the Canadian Rocky Mountains: Evidence for late Cretaceous and early Eocene orogenic pulses[END_REF]. Moreover, samples from faults which registered several stages of deformation and fluid circulation may record partial resetting of pre-existing micas and several growths of authigenic micas through Ostwald ripening and/or dissolution/precipitation processes (e.g. Eberl andSrodo ń, 1988, Jaboyedoff and[START_REF] Jaboyedoff | Dating incipient metamorphism using 40 Ar/ 39 Ar geochronology and XRD modeling: a case study from the Swiss Alps[END_REF]. As a consequence, the individual mica/illite grain can preserve more than one age resulting in a complex age spectrum whose interpretation represents a real challenge. Therefore, detailed characterization of the samples before dating is highly recommended to get information about the different mica generations, and homogeneity of the chemical compositions in the different grains or within the individual grain. For example, combining the 40 Ar/ 39 Ar technique with other techniques such as X-ray diffraction (XRD), optical microscopy and scanning electron microscopy (SEM-EDX) is highly recommended [START_REF] Clauer | The K-Ar and 40 Ar/ 39 Ar methods revisited for dating fine-grained K-bearing clay minerals[END_REF].

To overcome the difficulty arising from the presence of mica with multiple origins/ages in a lowgrade fault zone, many authors proposed the use of grain-size separation techniques combined with muscovite/illite polytypism characterization to calculate the age of fault activity (e.g. [START_REF] Duvall | Direct dating of Eocene reverse faulting in northeastern Tibet using Ar-dating of fault clays and low-temperature thermochronometry[END_REF][START_REF] Haines | Dating the detachment fault system of the Ruby Mountains, Nevada: Significance for the kinematics of low-angle normal faults: FAULT GOUGE AGES FOR RUBY MOUN-TAINS[END_REF][START_REF] Hnat | Fault gouge dating in the Southern Appalachians, USA[END_REF][START_REF] Rahl | Links between orogenic wedge deformation and erosional exhumation: Evidence from illite age analysis of fault rock and detrital thermochronology of syntectonic conglomerates in the Spanish Pyrenees[END_REF][START_REF] Ring | Faultgouge dating in the Southern Alps, New Zealand[END_REF][START_REF] Solum | Reconstructing the Snake River-Hoback River Canyon section of the Wyoming thrust belt through direct dating of clay-rich fault rocks. In Special Paper 433: Whence the Mountains? Inquiries into the Evolution of Orogenic Systems: A Volume in Honor of Raymond A. Price[END_REF][START_REF] Solum | fabrics and age of clay minerals from an exposure of the Moab Fault, Utah[END_REF][START_REF] Van Der Pluijm | The dating of shallow faults in the Earth's crust[END_REF], 2006). When textural and petrographic observations suggest a correlation between grain-size and different mica generations, size-fraction separation can be used to separate newly-formed micas from other generations. Then, different size-fractions of the same sample will be dated to estimate the ages of both detrital and newlyformed micas. When separating pure newly-formed mica is not possible, many authors have proposed the use of mica polytypism to interpret the calculated ages (e.g. [START_REF] Duvall | Direct dating of Eocene reverse faulting in northeastern Tibet using Ar-dating of fault clays and low-temperature thermochronometry[END_REF][START_REF] Hnat | Fault gouge dating in the Southern Appalachians, USA[END_REF][START_REF] Solum | Reconstructing the Snake River-Hoback River Canyon section of the Wyoming thrust belt through direct dating of clay-rich fault rocks. In Special Paper 433: Whence the Mountains? Inquiries into the Evolution of Orogenic Systems: A Volume in Honor of Raymond A. Price[END_REF]. In this approach, the percentages of the different mica polytypes are calculated through quantitative XRD analysis on different size-fractions and the percentages of detrital mica are plotted against the age of the individual size-fractions. These authors assumed that the 2M 1 polytype is the detrital component as it crystallizes under high temperature conditions ( > 280 • C, Srodo ń and Eberl, 1984), whereas, the 1M d /1M polytype is interpreted as the authigenic phase as it growths in the fault zone at low temperature conditions (< 200 • C, [START_REF] Velde | Experimental determination of muscovite polymorph stabilities[END_REF].

From the plotting of detrital phase (2M 1 ) % against the age, the intercept of the regression line at 0% of the detrital phase and 100% of the authigenic phase will give the age of the fault activity (e.g. [START_REF] Panȃ | Orogenic pulses in the Alberta Rocky Mountains: Radiometric dating of major faults and comparison with the regional tectono-stratigraphic record[END_REF][START_REF] Rahl | Links between orogenic wedge deformation and erosional exhumation: Evidence from illite age analysis of fault rock and detrital thermochronology of syntectonic conglomerates in the Spanish Pyrenees[END_REF][START_REF] Van Der Pluijm | The dating of shallow faults in the Earth's crust[END_REF]. This approach (see Figure 0.10) was successfully applied to clay-gouges that are formed at low temperature conditions (shallow crustal GENERAL INTRODUCTION depth faults) through brittle deformation mechanisms. However, the polytypism approach is not applicable to phyllonite fault rocks which formed at higher temperature because synkinematic micas can be of the 2M 1 polytype (e.g. [START_REF] Löbens | Exhumation and uplift of the Sierras Pampeanas: preliminary implications from K-Ar fault gouge dating and low-T thermochronology in the Sierra de Comechingones (Argentina)[END_REF][START_REF] Torgersen | Structural and temporal evolution of a reactivated brittle-ductile fault -Part II: Timing of fault initiation and reactivation by K-Ar dating of synkinematic illite/muscovite[END_REF][START_REF] Viola | K-Ar illite age constraints on the Proterozoic formation and reactivation history of a brittle fault in Fennoscandia[END_REF][START_REF] Zwingmann | Dating of shallow faults: New constraints from the AlpTransit tunnel site (Switzerland)[END_REF]. Moreover, in sedimentary rocks the detrital 2M 1 polytype populations within the same sample may have different origins/ages, thus in such cases, correlation between the age and the polytypes is meaningless.

Problems associated with irradiation when dating fine-grained micas

One of the potential problems of the 40 Ar/ 39 Ar geochronology when dating fine-grained micas is the ejection of 39 Ar from their structure during irradiation which is termed argon recoil. During the nuclear transformation of 39 K into 39 Ar, displacement of 39 Ar (around 0.1 µm) from the site of the original K atom may occur [START_REF] Mcdougall | Geochronology and Thermochronology by the 40 Ar/ 39 Ar Method[END_REF]. As this displacement distance can be equal to the average grain thickness of clay minerals, it will lead to a significant loss of 39 Ar that cannot be neglected (e.g. [START_REF] Duvall | Direct dating of Eocene reverse faulting in northeastern Tibet using Ar-dating of fault clays and low-temperature thermochronometry[END_REF][START_REF] Hall | Direct measurement of recoil effects on 40 Ar/ 39 Ar standards[END_REF][START_REF] Onstott | Recoil refinements: Implications for the 40 Ar/ 39 Ar dating technique[END_REF]. This recoiled argon can go outside the mineral lattice or be redistributed inside its lattice or it can be incorporated into the lattice of the surrounding grains (mica and/or other minerals) [START_REF] Dong | Mechanisms of argon retention in clays revealed by laser 40 Ar-39 Ar dating[END_REF]. Therefore, erroneously old ages could be expected in such samples and moreover, the age spectrum shape of these samples will no longer reflect the original distribution of Ar inside the grains. In addition, the markedly discordant pattern of age spectra should be expected as a result of the release of argon from adjacent minerals that can occur at different temperatures compared to argon from mica (e.g. [START_REF] Ghanem | Dating slate belts using 40 Ar/ 39 Ar geochronology and zircon ages from crosscutting plutons: A case study from east-central Maine, USA[END_REF][START_REF] Kunk | Contrasting tectonothermal domains and faulting in the Potomac terrane, Virginia-Maryland-discrimination by 40 Ar/ 39 Ar and fission-track thermochronology[END_REF]. One last problem during irradiation is the temperature increase in the reactor core and the high energy of incident neutrons which can led to lattice rearrangement, mineral decomposition and possibly polytypic transitions. For this reason the choice of the neutron flux value is very critical [START_REF] Mcdougall | Geochronology and Thermochronology by the 40 Ar/ 39 Ar Method[END_REF]. In order to overcome or limit these problems, the following steps and recommendations have been performed in the present work:

1. Sample preparation and size-fraction separation were performed without chemical treatments to avoid any impact on the structure of clay minerals and to inhibit any influence of the 40 Ar/ 39 Ar results.

2. Mechanical compaction of the samples to coarse aggregates was done in order to artificially increase the diffusional transport distance and minimize the potential for diffusive Ar loss during irradiation [START_REF] Hamilton | A review of radiometric dating techniques for clay mineral cements in sandstones[END_REF].

3. Encapsulation of the different fractions in evacuated quartz tubes prior to irradiation was performed; this allows the amount of recoiled 39 Ar to be measured after opening the quartz tube under vacuum. The encapsulation technique is described in more details in several publications (e.g. [START_REF] Dong | Mechanisms of argon retention in clays revealed by laser 40 Ar-39 Ar dating[END_REF][START_REF] Foland | 40 Ar/ 39 Ar dating of very fine-grained samples: An encapsulated-vial procedure to overcome the problem of 39 Ar recoil loss[END_REF][START_REF] Mcdougall | Geochronology and Thermochronology by the 40 Ar/ 39 Ar Method[END_REF][START_REF] Seidemann | An 40 Ar/ 39 Ar age spectrum for a cordierite-bearing rock: Isolating the effects of excess radiogenic 40 Ar[END_REF][START_REF] Smith | First successful 40 Ar-39 Ar dating of glauconies: Argon recoil in single grains of cryptocrystalline material[END_REF].

4. To get low energy of the fast neutrons during irradiation and to avoid damage on mineral lattice, a neutron flux of < 10 18 n cm -2 has been used at the Triga Mark II nuclear reactor of Pavia, Italy [START_REF] Mcdougall | Geochronology and Thermochronology by the 40 Ar/ 39 Ar Method[END_REF].

Re-integration of 39 Ar recoil

As mentioned above, in case of fine grained micas the amount of recoiled argon is relatively high and can't be neglected because the age deduced from the total amount of released argon will be GENERAL INTRODUCTION too old compared to the corresponding K-Ar age. Thanks to the vacuum encapsulation method, applied before irradiation, the recoiled argon can be evaluated, and reintegrated in the calculated ages.

When including the recoiled argon in the calculation, the calculated age is called the Total Gas Age (TGA) whereas, neglecting the recoiled fraction in the age calculation (i.e. taking into account only the 39 Ar that is retained in the crystal after irradiation) is called the Retention Age (RA) [START_REF] Dong | Mechanisms of argon retention in clays revealed by laser 40 Ar-39 Ar dating[END_REF]. Several studies showed that the age of large mica grains is measured by the RA while TGA fits stratigraphic constraints of geological processes in case of fine grained muscovite/illite (e.g. [START_REF] Dong | Mechanisms of argon retention in clays revealed by laser 40 Ar-39 Ar dating[END_REF], 1997, 2000, Hall et al., 1997, 2000[START_REF] Hnat | Fault gouge dating in the Southern Appalachians, USA[END_REF]. The addition of recoiled argon to the total gas released by step-heating is a simple task but re-integration of this recoiled Ar to the age spectrum is still not straightforward. In order to restore recoiled argon on the age spectrum, the behaviour and mechanisms underpinning this phenomenon should be well known. Some studies have used numerical models and experimental data to explain the possible mechanisms for this Ar recoil (e.g. [START_REF] Dong | Mechanisms of argon retention in clays revealed by laser 40 Ar-39 Ar dating[END_REF][START_REF] Lin | Backscattered 39 Ar loss in fine-grained minerals: Implications for 40 Ar/ 39 Ar geochronology of clay[END_REF][START_REF] Sletten | The Effect of the Instability of Muscovite During In Vacuo Heating on 40 Ar/ 39 Ar Step-Heating Spectra[END_REF], York et al., 1992) and they have been summarized by [START_REF] Clauer | Episodic and simultaneous illitization in oil-bearing Brent Group and Fulmar Formation sandstones from the northern and southern North Sea based on illite K-Ar dating[END_REF]. Negative correlations between the amount of the recoiled argon and either grain-size and/or the muscovite/illite crystallinity index have been reported in several studies (see e.g. [START_REF] Dong | Mechanisms of argon retention in clays revealed by laser 40 Ar-39 Ar dating[END_REF], 1997[START_REF] Markley | The relation between grain size and 40 Ar/ 39 Ar date for Alpine white mica from the Siviez-Mischabel Nappe, Switzerland[END_REF][START_REF] Reuter | 40 Ar/ 39 Ar dating of cleavage formation in tuffs during anchizonal metamorphism[END_REF]. For example, [START_REF] Dong | Mechanisms of argon retention in clays revealed by laser 40 Ar-39 Ar dating[END_REF] suggested that 39 Ar recoil is only relevant for low temperature heating-steps, and therefore it recoils from low-retentive sites of muscovite/illite particles such as surfaces or crystal defects. Others authors related the high fraction of recoil 39 Ar in the small size-fractions to the higher surface areas of the grains (e.g. Reuter andDallmeyer, 1987, van der Pluijm et al., 2001). On the other hand, [START_REF] Lin | Backscattered 39 Ar loss in fine-grained minerals: Implications for 40 Ar/ 39 Ar geochronology of clay[END_REF] suggested that the recoiled is linked to the 39 Ar backscattering. According to this model, the recoiling 39 Ar that has a low energy and a travel direction not perpendicular to a clay particle's layered structure will reflect (backscatter) from its original path upon encountering the particle surface. As the energy of the backscattered 39 Ar remains below that required for re-entering the clay particle,it will be lost from the structure. However, all these models depend on the crystallographic model chosen in each model [START_REF] Clauer | The K-Ar and 40 Ar/ 39 Ar methods revisited for dating fine-grained K-bearing clay minerals[END_REF]. Therefore, caution should be taken when using the age spectra in the case of fine grain micas, and the total gas age should be prioritized for interpretation.

Study areas and thesis objectives

The Pyrenees is a range of mountains in southwest Europe that forms a natural border between France and Spain. The Pyrenees range was formed by the convergence of the Iberian and European plates during the late Cretaceous-early Miocene periods [START_REF] Muñoz | Evolution of a continental collision belt: ECORS-Pyrenees crustal balanced cross-section[END_REF][START_REF] Roure | Ecors deep seismic data and balanced cross sections: Geometric constraints on the evolution of the Pyrenees[END_REF], Teixell et al., 2016).

GENERAL INTRODUCTION

The Pyrenees is divided into three main parts as shown in Figure 0.11: the North Pyrenean Zone, corresponds to a Mesozoic extensional basin system inverted and transported northward during the Pyrenean compression, the South Pyrenean Zone characterized by south-vergent folds and thrusts (e.g. [START_REF] Choukroune | Major Hercynian thrusts along the ECORS Pyrenees and Biscay lines[END_REF][START_REF] Teixell | The Ansó transect of the southern Pyrenees: basement and cover thrust geometries[END_REF], and the inner part of the Pyrenees (Axial Zone), which corresponds to an antiformal stack of south-vergent basement units that expose Paleozoic rocks deformed during the Hercynian [START_REF] Barnolas | Synthèse géologique et géophysique des Pyrénées: géophysique: cycle hercynien[END_REF].

The range is well suited to study the evolution of tectonic activity, deformation-sedimentation rela- tionships and metamorphism because it has well exposed deformation structures and exceptionally well preserved syntectonic sedimentary strata (e.g. [START_REF] Fernández | 3D structure and evolution of an oblique system of relaying folds: the Ainsa basin (Spanish Pyrenees)[END_REF], Labaume et al., 2016[START_REF] Teixell | The Ansó transect of the southern Pyrenees: basement and cover thrust geometries[END_REF]. However, studying faults activities, re-establishing their history and understanding their deformation conditions/mechanisms are a challenging subject. This difficulty arises from the superposition of multiple tectonic events by exhumation and uplifting processes which are characteristic features of the Pyrenees range. Moreover, in some locations within the Pyrenees belt, the biostratigraphic and paleomagnetic constraints or stratigraphic units which are used to determine the timing of fault motion are not always preserved and their ages are often poorly defined. In addition, fault activity may occur through several stages of deformation and fluid circulation that make understanding their behaviour and conditions a very complicated task. Consequently, following fault activities within the Pyrenees range and dating them are not straightforward.

However, as mentioned previously in the above sections, synkinematic phyllosilicates (clay minerals) in fault zones are important indicators of P-T-fluid conditions prevailing during fault activities and represent useful thermochronological tools to date fault activity. Therefore in the present thesis, phyllosilicates minerals from three selected thrusts faults in the Pyrenees were used to study fault activities.The three thrusts are related and/or affected by the Gavarnie thrust which is a major thrust in the Pyrenees belt. These three studied faults are:

(i) Pic de Port Vieux Thrust (PPVT)
The PPVT fault is located in the south-western part of the Pyrenean Axial Zone (Figure 0.11). The fault is a second-order thrust related to the the major Gavarnie thrust. The latter involves a minimum southward displacement of 11.5 km of Upper Paleozoic strata on Variscan to Lower Paleozoic basement covered with Permo-Triassic and Upper Cretaceous strata [START_REF] Grant | Deformation and fluid processes in thrust sheets from the central Pyrenees[END_REF]. The PPVT occurs in the footwall of the Gavarnie thrust, with a minimum southward displacement of 0.85 km [START_REF] Grant | Chemistry, source, and behavior of fluids involved in alpine thrusting of the Central Pyrenees[END_REF]. The PPVT footwall has a 10 m thick layer of Upper Cretaceous dolomitic limestones progressively transformed into mylonitic limestones near the fault contact. The hanging wall consists of lower Triassic red pelites and sandstones that transformed to intensely foliated green pelites closer to the fault contact.

(ii) Lakora thrust

The Lakora thrust is one of the major Pyrenean basement-involved faults located on the southern edge of the North Pyrenean Zone (Figure 0.11). The thrust is a result of an inversion of the North Pyrenean basin margin and is named after the classic locality at Pico Lakora (Lakhoura) [START_REF] Fournier | Études géologiques sur la partie occidentale de la chaîne des Pyrénées entre la vallée d'Aspe et celle de la Nive[END_REF]. The Gavarnie thrust and the associated Axial Zone antiform deformed the Lakora thrust suggesting that Gavarnie is younger. The hanging wall of the Lakora thrust is composed of Santonian-Albian breccias and conglomerates while the footwall is made of Campanian-Maastrichtian turbidites.

(iii) Torla (Monte Perdido thrust)

The Torla outcrop is related to the Monte Perdido thrust fault located on the western part of the South-Pyrenean Zone (northern part of the Jaca Basin) (Figure 0.11). The thrust is uplifted and folded by the hanging wall culmination of the Gavarnie basement thrust in the Jaca Basin, suggesting that it is older than the latter [START_REF] Séguret | Etude tectonique des nappes et séries décollées de la partie centrale du versant sud des Pyrénées: caractère synsédimentaire, rôle de la compression et de la gravité[END_REF]. According to [START_REF] Teixell | Alpine thrusts at the western termination of the Pyrenean axial zone[END_REF], the Monte Perdido thrust system is deeply rooted northward in the Lakora thrust, suggesting that the Lakora and the Monte Perdido thrusts have close ages. The footwall of the Torla comprises Hecho Group turbidites (alternating sandstone and pelite layers) of the Gavarnie thrust unit and the hanging wall is composed of Alveolina limestone. The

GENERAL INTRODUCTION

fault zone consists of intensely deformed clay-bearing rocks (∼ 6 m thick) bounded by major shear surfaces.

Aims of the thesis

The main objectives of this thesis are to use phyllosilicates minerals (muscovite/illite and chlorite) present in the three thrust fault zones to estimate their deformation conditions and to date the thrust activities. Specific objectives and problems that will be covered in the present thesis include:

1. Characterization of phyllosilicate minerals in the fault zone of each thrust and the identification of their different types/generations, mineralogy, texture, chemical composition, polytype and crystallinity.

2. Identification of the origin of the phyllosilicate minerals in fault zones, the mechanisms of their formation and the key parameters that control their texture and chemical changes.

3. Estimation of the deformation conditions of the three faults by using the crystallinity index, polytypes of newly-formed mica and chemical composition of synkinematic chlorite.

4. Differentiation and separation of newly-formed muscovite/illite from other mica phases/generations and the estimation of their ages and thrust timing using their isotopic compositions.

5. Discussion of the ages obtained from the present work with other available data from the same area, in order to evaluate the significance of 40 Ar/ 39 Ar step-heating ages.

According to these objectives, this dissertation is divided into four chapters:

Chapter Chapter (4) is a general discussion; it includes a discussion and comparison of the results for the three thrust faults and explains the similarities/differences. In addition, we evaluate some existing principles when applying the 40 Ar/ 39 Ar dating method and the validity and limitations of the method based on the thesis results. We finish with some suggestions for future research.

Introduction

Phyllosilicates are major constituents of fault zones in a broad range of geological contexts and particularly in sedimentary environments [START_REF] Blatt | Origin of sedimentary rocks[END_REF]. During the evolution of sedimentary basins, phyllosilicates record changes in their composition, crystal structure and texture in response to burial diagenesis, tectonic activity, and interactions with fluids. Consequently they are used to decipher the basin evolution history, deformation mechanisms, P-T conditions and the timing of various geologic events [START_REF] Jiang | Clay Minerals from the Perspective of Oil and Gas Exploration[END_REF]. For example, illite/ muscovite has been commonly used to quantify diagenetic and lowgrade metamorphic conditions [START_REF] Frey | Very low-grade metamorphism of clastic sedimentary rocks[END_REF][START_REF] Kisch | On the calibration of the illite Kubler index (illite "crystallinity")[END_REF][START_REF] Kübler | Les argiles, indicateurs de métamorphisme[END_REF][START_REF] Kübler | La cristallinité de l'illite et les zones tout a fait superieures du métamorphisme. étages tectoniques[END_REF][START_REF] Kübler | Evaluation quantitative du métamorphisme par la cristallinité d l'illite[END_REF][START_REF] Kübler | Illite crystallinity[END_REF][START_REF] Warr | Correlating illite (Kübler) and chlorite (Árkai) "crystallinity" indices with metamorphic mineral zones of the South Island, New Zealand[END_REF][START_REF] Warr | Recommendations for Kübler index standardization[END_REF]. Temperature estimation from chlorite composition as well is a very often used method; recently the thermodynamic modelling approach has been proposed and developed by Bourdelle et al. (2013), [START_REF] Inoue | Application of Chemical Geothermometry to Low-Temperature Trioctahedral Chlorites[END_REF], [START_REF] Lanari | Diachronous evolution of the alpine continental subduction wedge: Evidence from P-T estimates in the Briançonnais Zone houillère (France -Western Alps)[END_REF][START_REF] Lanari | A thermodynamic model for di-trioctahedral chlorite from experimental and natural data in the system MgO-FeO-Al 2 o 3 -SiO 2 -H 2 o: applications to P-T sections and geothermometry[END_REF] and [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-T-deformation-Fe 3+ /Fe 2+ mapping at the thin section scale and comparison with XANES mapping: application to a garnetbearing metapelite from the Sambagawa metamorphic belt (Japan)[END_REF][START_REF] Vidal | Deciphering temperature, pressure and oxygen-activity conditions of chlorite formation[END_REF] among others.

In fault zones, phyllosilicates may form contemporaneously with fault activity as deformation and fluid/rock interactions promote the

Introduction

Phyllosilicates are major constituents of fault zones in a broad range of geological contexts and particularly in sedimentary environments [START_REF] Blatt | Origin of sedimentary rocks[END_REF]. During the evolution of sedimentary basins, phyllosilicates record changes in their composition, crystal structure and texture in response to burial diagenesis, tectonic activity, and interactions with fluids. Consequently they are used to decipher the basin evolution history, deformation mechanisms, P-T conditions and the timing of various geologic events [START_REF] Jiang | Clay Minerals from the Perspective of Oil and Gas Exploration[END_REF]. For example, illite/muscovite has been commonly used to quantify diagenetic and low-grade metamorphic conditions [START_REF] Frey | Very low-grade metamorphism of clastic sedimentary rocks[END_REF][START_REF] Kisch | On the calibration of the illite Kubler index (illite "crystallinity")[END_REF][START_REF] Kübler | Les argiles, indicateurs de métamorphisme[END_REF][START_REF] Kübler | La cristallinité de l'illite et les zones tout a fait superieures du métamorphisme. étages tectoniques[END_REF][START_REF] Kübler | Evaluation quantitative du métamorphisme par la cristallinité d l'illite[END_REF][START_REF] Kübler | Illite crystallinity[END_REF][START_REF] Warr | Recommendations for Kübler index standardization[END_REF][START_REF] Warr | Correlating illite (Kübler) and chlorite (Árkai) "crystallinity" indices with metamorphic mineral zones of the South Island, New Zealand[END_REF]. Temperature estimation from chlorite composition as well is a very often used method; recently the thermodynamic modelling approach has been proposed and developed by Bourdelle et al. (2013a), [START_REF] Inoue | Application of Chemical Geothermometry to Low-Temperature Trioctahedral Chlorites[END_REF], [START_REF] Lanari | Diachronous evolution of the alpine continental subduction wedge: Evidence from P-T estimates in the Briançonnais Zone houillère (France -Western Alps)[END_REF][START_REF] Lanari | A thermodynamic model for di-trioctahedral chlorite from experimental and natural data in the system MgO-FeO-Al 2 o 3 -SiO 2 -H 2 o: applications to P-T sections and geothermometry[END_REF]and [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-T-deformation-Fe 3+ /Fe 2+ mapping at the thin section scale and comparison with XANES mapping: application to a garnetbearing metapelite from the Sambagawa metamorphic belt (Japan)[END_REF][START_REF] Vidal | Deciphering temperature, pressure and oxygen-activity conditions of chlorite formation[END_REF] among others.

In fault zones, phyllosilicates may form contemporaneously with fault activity as deformation and fluidrock interactions promote the growth of synkinematic phyllosilicates during faulting episodes [START_REF] Duvall | Direct dating of Eocene reverse faulting in northeastern Tibet using Ar-dating of fault clays and low-temperature thermochronometry[END_REF]. There are several formation mechanisms for those minerals in fault zones: (1) direct precipitation from fluids in veins or (2) alteration from less stable minerals or (3) recrystallization of detrital clay minerals as a result of shearing, comminution, pressure solutions and dissolution/recrystallization processes. Newly formed phyllosilicates in fault zone can be a good proxy for the estimation of variable parameters related to deformation. For example, they can provide the ages of different fault episodes based on their isotopic composition [START_REF] Bui | Episodes of brittle deformation within the Dien Bien Phu Fault zone, Vietnam: Evidence from K-Ar age dating of authigenic illite[END_REF][START_REF] Clauer | The K-Ar and 40 Ar/ 39 Ar methods revisited for dating fine-grained K-bearing clay minerals[END_REF], Lanari et al., 2014a[START_REF] Rolland | Constraining deformation stages in brittle-ductile shear zones from combined field mapping and 40 Ar/ 39 Ar dating: The structural evolution of the Grimsel Pass area (Aar Massif, Swiss Alps)[END_REF][START_REF] Sanchez | Dating low-temperature deformation by 40 Ar/ 39 Ar on white mica, insights from the Argentera-Mercantour Massif (SW Alps)[END_REF][START_REF] Torgersen | Structural and temporal evolution of a reactivated brittle-ductile fault -Part II: Timing of fault initiation and reactivation by K-Ar dating of synkinematic illite/muscovite[END_REF]. Moreover, they are a useful tool for characterizing fluid-rock interactions that occurred in the fault zone (e.g. [START_REF] Lacroix | Microtectonic and geochemical characterization of thrusting in a foreland basin: Example of the South-Pyrenean orogenic wedge (Spain)[END_REF]. All this information can 1.2. GEOLOGICAL SETTING AND SAMPLE LOCATIONS CHAPTER 1 assist in reconstruction of the basin history and improve understanding of the fault behavior (Buatier et al., 2012a[START_REF] Faulkner | A review of recent developments concerning the structure, mechanics and fluid flow properties of fault zones[END_REF][START_REF] Niwa | Kinematic analysis of sinistral cataclastic shear zones along the northern margin of the Mino Belt, central Japan[END_REF][START_REF] Pei | A review of fault sealing behaviour and its evaluation in siliciclastic rocks[END_REF].

Following the evolution of tectonic activities is one of the challenging topics in particular in sedimentary basins due to multiple exhumations, uplifting, multistage of activation, mixing sediments of different ages and variable fluid influxes of different origins. The Pyrenees orogen is one of the best areas to study thrust faults and deformation/sedimentation relationships because it has well exposed deformation structures and exceptionally well preserved syntectonic sedimentary rocks [START_REF] Teixell | The Ansó transect of the southern Pyrenees: basement and cover thrust geometries[END_REF].The focus of the present study is the Pic de Port Vieux thrust (PPVT) fault located in the southern central part of the Axial Zone of the Pyrenees. The fault is a suitable candidate for the present study as it is a complex thrust with multistage deformation and fluid circulations at low-grade metamorphic conditions [START_REF] Grant | Post-emplacement extension within a thrust sheet from the central Pyrenees[END_REF]. Six deformation stages have been identified by [START_REF] Banks | The chemistry of brines from an Alpine thrust system in the Central Pyrenees: An application of fluid inclusion analysis to the study of fluid behaviour in orogenesis[END_REF], [START_REF] Grant | Deformation and fluid processes in thrust sheets from the central Pyrenees[END_REF] and McCaig et al. (2000a). Previous studies on the PPVT focused mainly on synkinematic veins and suggested that deformation PT conditions are about 250-300°C and 1.5-2 kbar [START_REF] Grant | Post-emplacement extension within a thrust sheet from the central Pyrenees[END_REF]corresponding to a burial depth of 5-7.5 km. They demonstrated that fluids have been buffered by host rock composition and would originate from buried Triassic sediments (McCaig et al., 2000a). [START_REF] Trincal | Temperature micro-mapping in oscillatory-zoned chlorite: Application to study of a green-schist facies fault zone in the Pyrenean Axial Zone (Spain)[END_REF] thoroughly characterized oscillatory zoning chlorite from veins, but the behavior and the mechanisms of deformation of phyllosilicates in the PPVT core zone have never been studied. Therefore, we focus our present study on phyllosilicates from the fault zone to determine the deformation conditions and geochemical changes attributed to thrust activity. For that purpose a transect in the fault hanging wall was investigated to (1) characterize the phyllosilicates, comparing their mineralogy, texture and chemical composition as a function of distance from the fault contact;

(2) define their origin and mechanisms of formation in the fault zone; (3) estimate the deformation conditions from their crystallinity and chemical compositions; (4) understand the key parameters that control the mineralogical changes in the fault zone.

Geological setting and sample locations

The Pyrenees orogen is a doubly-vergent orogenic wedge formed by the convergence of the Iberian and European plates during the Late Cretaceous to early Miocene periods (Choukroune et al., 1990, Roest and[START_REF] Roest | Kinematics of the plate boundaries between Eurasia, Iberia, and Africa in the North Atlantic from the Late Cretaceous to the present[END_REF]. Three main structural zones constitute this orogeny (Figure 1.1 a). First, the North-Pyrenean zone corresponds to a Mesozoic extensional basin system inverted and transported northward by the Pyrenean compression. Secondly, the Axial Zone (the core zone of the range) corresponds to the inner part of the south-vergent thrust belt. It exposes the most deeply exhumed rocks, a series of pre-Cambrian through Carboniferous basement thrust sheets initially stacked during Variscan orogenesis [START_REF] Masini | The tectono-sedimentary evolution of a hyper-extended rift basin: the example of the Arzacq-Mauléon rift system (Western Pyrenees, SW France)[END_REF][START_REF] Muñoz | Evolution of a continental collision belt: ECORS-Pyrenees crustal balanced cross-section[END_REF][START_REF] Zwart | The variscan geology of the Pyrenees[END_REF]. Thirdly, the South Pyrenean fold and thrust belt comprises a deformed Mesozoic succession detached on Triassic evaporites and overlain by syn-deformational Tertiary sediments [START_REF] Metcalf | Thermochronology of a convergent orogen: Constraints on the timing of thrust faulting and subsequent exhumation of the Maladeta Pluton in the Central Pyrenean Axial Zone[END_REF], Teixell et al., 2016).

The PPVT fault is located in the south-western part of the Pyrenean Axial Zone. The fault is a second-order thrust related to the major thrust in the area, which is the Gavarnie thrust. The latter involves a minimum southward displacement of 11.5 km of Upper Paleozoic strata on Variscan to Lower Paleozoic basement covered with Permo-Triassic and Upper Cretaceous strata [START_REF] Grant | Deformation and fluid processes in thrust sheets from the central Pyrenees[END_REF]. Stratigraphic correlation suggests a Priabonian-Rupelian age for Gavarnie thrust activity [START_REF] Teixell | The Ansó transect of the southern Pyrenees: basement and cover thrust geometries[END_REF] and a Priabonian age (36.5 ± 1.4 Ma) based on 40 Ar/ 39 Ar radiometric dating [START_REF] Rahl | Links between orogenic wedge deformation and erosional exhumation: Evidence from illite age analysis of fault rock and detrital thermochronology of syntectonic conglomerates in the Spanish Pyrenees[END_REF]. The PPVT emplacement, which folded and deformed the overlying Gavarnie thrust, is thought to occur later (Figure 1.1 b, c and d). However, it is not excluded that both thrusts are related to the same global tectonic event and should have a similar age. The PPVT occurs in the footwall of the Gavarnie thrust, with a minimum southward displacement of 0.85 km [START_REF] Grant | Episodic discrete and distributed deformation: consequences and controls in a thrust culmination from the central Pyrenees[END_REF]. The PPVT footwall has a ten-meter thick layer of Upper Cretaceous dolomitic limestones progressively transformed into mylonitic limestones near the fault contact. The hanging wall consists of lower Triassic red pelites and sandstones that turned to be intensely foliated green pelites close to the fault contact. The hanging wall of PPVT is the focus of the present study as no phyllosilicate is present in the fault footwall. The damage zone of the hanging wall features numerous fractures affecting several meters thick of red pelites, whereas the core zone is composed of a 0.6 m-thick layer of intensely foliated green pelites.

Therefore, a vertical transect along the hanging wall was investigated to characterize the mineralogical and geochemical changes induced by deformation and fluids that are attributed to the fault activity.

The GPS coordinates for the transect location are 42 • 43'40.52" N and 0 • 9'44.67" E. Eight samples were collected along the transect in the Triassic pelites, covering the green core zone and the red damage zone (Figure 1.2 a and b).

Analytical methods

Bulk composition and phyllosilicates mineralogy

The samples were analyzed at the Université de Bourgogne Franche-Comté by using a Bruker D8 Advance diffractometer system, Cu-Kα radiation equipped with a fast LynxEye linear detector. Samples were hand ground to < 50 µm and the < 16 µm fraction obtained by sedimentation was submitted to ultra-centrifugation in order to extract the < 2 µm fractions. For the bulk powder samples, the X-ray diffractograms were acquired between 5 to 70 • 2θ at a step size of 0.02, a number of steps 3450, a time/step 1 s at 40 kV and 40 mA. While for the < 2 µm fractions, oriented specimens preparation were analyzed in air dried conditions between 5 to 30 • 2θ at a step size of 0.01, a number of steps 2228 and time/step 0.5 s. No expandable or interstratified minerals were found confirmed by ethylene-glycol saturation and after heating at 550 • C.

Petrographic and geochemical characterizations 1.3.2.1 Scanning Electron Microscope (SEM)

The analyses by SEM were performed at the FEMTO-ST Institute (Université de Bourgogne Franche-Comté). Microstructures and mineral assemblages were analyzed with a JEOL JSM 5600 (SEM) equipped with Secondary Electron (SEI), backscatter electron (BSE) and Energy Dispersive X-ray Spectroscopy (EDX) detectors.

Electron Probe Micro-Analyzer (EPMA)

Quantitative chemical analyses of chlorite and K-white mica were performed using an electron probe micro-analyzer (EPMA) JEOL 8200 at the Institute of Geological Sciences (University of Bern). Total number of 169 spot analyses for chlorite and 50 analyses for mica from both the damage and core fault zones were performed. The following natural and synthetic standards have been used: orthoclase

(SiO 2 , K 2 O), anorthite (Al 2 O 3 , CaO) albite (Na 2 O), almandine (FeO), forsterite (MgO), tephroite (MnO)
and ilmenite (TiO 2 ). The analyses were performed at 15 keV accelerating voltage, 10 nA specimen current and 40 s dwell time (including 2×10s of background measurement). Quantitative X-ray maps were carried out to check the variation of chemistry in each mineral phase and the relationships with the microstructures. The maps were acquired using the wavelength dispersive spectrometers (WDS) at 15 KeV accelerating voltage, 10 nA specimen current, dwell time of 200 ms and 1 µm spot size. The X-ray maps were classified and standardized into maps of oxide weight percentage concentrations using the program XMapTools 2.3.1 [START_REF] Lanari | XMapTools: A MATLAB©-based program for electron microprobe X-ray image processing and geothermobarometry[END_REF].

Deformations conditions 1.3.3.1 Kübler Index (KI)

The Kübler Index (KI) was measured on muscovite (001) at 10 Å for five samples in oriented preparations of the < 2 µm fraction to determine the metamorphic grade conditions. Interlaboratory variations have been reduced by following the recommendations of [START_REF] Kisch | Illite crystallinity: recommendations on sample preparation, X-ray diffraction settings, and interlaboratory samples[END_REF]and using the widely applied standardized Crystallinity Index Scale (CIS) procedure recommendations for measurements. The calibration of the crystallinity results to CIS scale was achieved by measuring the crystallinity of the four standards proposed by [START_REF] Warr | Interlaboratory standardization and calibration of day mineral crystallinity and crystallite size data[END_REF]. A regression analysis allows a correction to be made by using the equation: KI (CIS) = 1.52 * KI (my lab) -0.0121. The evaluation of metamorphic conditions boundaries was performed by using the boundaries of the anchizone originally defined by [START_REF] Kübler | La cristallinité de l'illite et les zones tout a fait superieures du métamorphisme. étages tectoniques[END_REF] at IC values of 0.25 • 2θ and 0.42 • 2θ. In order to be compatible with the original Anchizone boundaries of [START_REF] Kübler | La cristallinité de l'illite et les zones tout a fait superieures du métamorphisme. étages tectoniques[END_REF], the CIS values were calibrated to the traditional Kübler-Kisch scale by using the equation: Kübler Index (CIS) = 1.1523 * Kübler Index (Basel lab) + 0.036 which is presented in the figure 1 of [START_REF] Warr | Recommendations for Kübler index standardization[END_REF].

Chlorite thermometer

Temperatures of chlorite crystallization in the current study were estimated through multi-equilibrium thermodynamic calculations using the method and solid solution models of [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-T-deformation-Fe 3+ /Fe 2+ mapping at the thin section scale and comparison with XANES mapping: application to a garnetbearing metapelite from the Sambagawa metamorphic belt (Japan)[END_REF] by the program CHLMICAEQUI [START_REF] Lanari | Micro-cartographie P-T-» dans les roches métamorphiques[END_REF], Lanari et al., 2012). This method is based on thermodynamic calculations of equilibrium conditions for chlorite whose composition is expressed as the activities of end-member components of known thermodynamic properties [START_REF] Berman | Thermobarometry using multi-equilibrium calculations; a new technique, with petrological applications[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 to 600 C, 1 to 25 kb range[END_REF]. In addition, the calculation of XFe 3+ which is equal to (Fe 3+ /Σ Fe) chl was approximated by the numerical method of [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-T-deformation-Fe 3+ /Fe 2+ mapping at the thin section scale and comparison with XANES mapping: application to a garnetbearing metapelite from the Sambagawa metamorphic belt (Japan)[END_REF]. This method is based on the achievement of convergence of four reactions (chlorite + quartz and internal chlorite equilibria). 89 spot analyses of CHAPTER 1 1.4. RESULTS newly formed chlorite were performed on the damage zone and 80 spot analyses on the core zones and used for chlorite thermometry.

Fluid-rock interaction modelling

In order to understand the chemical reactions that occurred between fluids and rocks in the PPVT, modelling of fluid-rock interactions was performed. The version 2.15 of PhreeqC software [START_REF] Parkhurst | User's guide to PHREEQC -a computer program for speciation, reaction-path, advective-transport, and inverse geochemical calculations[END_REF][START_REF] Parkhurst | User's guide to PHREEQC (Version 2): A computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations[END_REF] was used for speciation of the solution and mineral saturation index calculations with respect to the solution. Mineral dissolution (under-saturation) is characterized by a negative saturation index and its precipitation (supersaturation) is characterized by a positive saturation index. Equilibrium batch reactions were performed to determine the stable rock composition at the chosen conditions and to compare it with the observed composition (EPMA analyses).

Results

The hanging wall is composed of Triassic pelites and sandstones at the outcrop scale and has been divided into two zones based on their lithology (Figure 1.2). The core fault zone is intensely foliated, contains numerous mineralized veins and is characterized by a green color observed up to one meter perpendicular to the main thrust. The second zone is the damage zone that is composed of several meters of red pelites. In addition, secondary normal faults are observed in this damage zone marked by green color (a few centimeters in width) inside the red pelites.

Mineralogy

XRD results of the bulk powder samples from the damage and core zones revealed similar mineralogical compositions with mainly K-white mica, quartz, chlorite, calcite, minor rutile and apatite (Figure 1.3).

The only difference is the absence of hematite in the core fault zone as indicated by the disappearance of hematite reflections peaks, the most intense peak for hematite (104) at 2.70 Å is highlighted in Figure 1.3. Reflections at 1.50 Å and 1.55 Å are correspond to phyllosilicates 060 reflections, they confirm the presence of di-octahedral phase (di-white mica) and tri-octahedral phase (chlorite) respectively. XRD patterns of < 2 µm for five representative samples along the pelitic transect are presented in Figure 1.4. The K-white mica is characterized by reflections at 10.02 Å, 5.00 Å and 3.33 Å corresponding to 001, 002, and 003 basal reflections respectively. Reflections at 14.16 Å, 7.08 Å, 4.73 Å and 3.54 Å are corresponding to 001, 002, 003 and 004 reflections of chlorite. The 002 and 004 reflections of chlorite are more intense compared to 001 and 003 reflections suggesting the presence of a Fe-rich chlorite [START_REF] Brown | Crystal structures of clay minerals and their X-ray identification[END_REF]Brindley, 1980, Moore and[START_REF] Moore | X-ray Diffraction and the Identification and Analysis of Clay Minerals[END_REF]. The intensity of K-white mica

Petrographic observations

In order to compare the textural and microstructural features of the core and damage zones, two representative samples (PPV12-05 from the core zone and PPV12-07 from the damage zone) were investigated in details. At the rock chip and thin section scales (Figure 1.5), there are several textural and mineralogical differences between these two samples:

• The change of pelite color from red to green toward the fault contact; SEM images, EDS analyses beside XRD results confirmed that the color change is related to hematite that is presents only in the damage zone.

• The presence of more mineralized veins and veinlets within the pelitic matrix of the core zone compared to the damage zone (Figure 1.5 a and b). Those veins are composed mainly of quartz + chlorite ± calcite, they are folded and crosscut each other suggesting several stages of deformation. Moreover there is a strong foliation and a well-defined cleavage marked by the • The matrix of the damage zone sample contains more quartz grains with random orientation and larger grain size (Figure 1.5 e). While in the matrix of the core zone sample, quartz grains become less abundant and display elongated shape and smaller grain size formed by pressure solution mechanisms. The decrease in quartz content in the fault core zone is balanced by K-white mica enrichment (Figure 1.5 f). SEM-BSE images with higher magnification for samples PPV12-07(damage zone) and PPV12-05 (core zone) are illustrated in Figure 1.6. In the damage zone, chlorite is mainly located in the matrix as elongated large grains (50 µm) suggesting a detrital origin (Figure 1.6 a) and also appears as stacks with mica (Figure 1.6 c). Moreover, chlorite also occurs locally inside rare veins (Figure 1.6 e). K-white mica is present in the matrix of the damage zone sample as large elongated grains (probably of detrital origin) (Figure 1.6 a) and as randomly-oriented coarse stacks with chlorite (diagenetic). Their grain size ranges from 30 to 80 µm and only few smaller grains can be observed in this matrix.

Conversely, in the core zone sample, newly formed chlorite is abundant and preferentially located in 1.4. RESULTS CHAPTER 1 veins (Figure 1.6 f) The chlorite/mica stacks are folded, kinked and display smaller grain size (Figure 1.6 d) compared to the large stacks in the damage zones (Figure 1.6 c). The well-defined cleavage in the core zone sample is underlined by preferentially oriented K-white mica with a smaller grain size (< 5 µm) compared to larger mica from the damage zone. Mica grains that have step like shaped boundaries with quartz grains in the core zone suggest that a significant recrystallization process occurred along this strongly deformed zone ( Figure 1.6 b).

Chemical composition variation of phyllosilicates 1.4.3.1 Chlorite

EPMA analyses were performed on newly formed chlorite from both the damage zone (sample PPV12-07) and the core zone (sample PPV12-05). Structural formulas were calculated on a 14 oxygen basis and some representative analyses are listed in Table 1 The only difference observed between chlorite from the damage and core zones is that, close to the fault contact ( the green pelite zone) newly formed chlorite has relatively more Fe (1.80 to 2.23 apfu) compared to newly formed chlorite from the damage zone which has an Fe content that varies from 1.59 to 1.85 apfu.

K-white mica

EPMA analyses were achieved on K-white micas from both the damage zone (sample PPV12-07) and the core zone (sample PPV12-05) and are presented in Table 1.2. In the damage zone, analyses for both large mica (10 analyses) and small mica (10 analyses) were performed. The structural formulas have been calculated on the basis of 11 oxygens. The results are then plotted in a M + -4Si -R 2+ ternary diagram [START_REF] Meunier | Solid solutions in I/S mixed-layer minerals and illite[END_REF] and in a Na/ (Na + K) vs. Si diagram (Figure 1.7 b). Mica compositions from both samples are located close to muscovite end member with a small trend toward celadonite. As Si content varies between 3.11 to 3.30 apfu, it suggests that muscovite is the dominant end member; so hereafter muscovite will be used to describe K-white mica within the present paper. [START_REF] Meunier | Solid solutions in I/S mixed-layer minerals and illite[END_REF] and Na/ (Na + K) vs. Fe plot for muscovite. M + = Na + + K + + 2Ca 2+ , 4Si = (Si/4) and R 2+ = (Mg + Fe + Mn) and Di-Tri is (dioctahedral-trioctahedral substitutions). Chlorite and muscovite initial and average compositions obtained by modelling at high reductive conditions are highlighted with the star icon.

Al total content varies between 2.50 to 2.72 apfu, K from 0.80 to 0.93 apfu and Na from 0.02 to 0.14 apfu. There is a small Tschermak substitution with Mg values between 0.10 and 0.20 apfu and Fe between 0.06 and 0.16 apfu. Muscovite from the core zone displays homogenous composition with an average structural formula of (Si 3.18 Al 0.82 ) O 10 (Al 1.79 Mg 0.12 Fe 0.13 Ti 0.01 ) (OH) 2 K 0.91 Na 0.03 . Conversely, muscovite from the damage zone displays higher dispersion in composition, due to Na-K substitution in interlayer space and also divalent cation substitutions in the octahedral sheet. The large and small muscovite grains in the damage zone have different composition; large grains have lower Si, Fe, Mg contents and a higher Na/(Na + K) ratio in the interlayer space, whereas small grains have higher Si, Fe, Mg contents and a lower Na/(Na + K) ratio in the interlayer space as illustrated in a Na /(Na + K) direction in the matrix. In addition, smaller grains of chlorite are located in the veins (Figure 1.8 b).

The most important compositional variation of muscovite is derived from the maps of Na 2 O (in wt%, see Figure 1.8 c and d). The maps show that larger grains have higher Na 2 O (1% to 2%) than the smaller grains (0.1% to 0.5%). In addition, Na is higher in muscovite from the damage zone compared to those from the core zone. Moreover, the compositional maps demonstrate that Na 2 O is higher in the core of the grains compared to the rims of the grains which suggests alteration from detrital mica/illite with paragonitic substitution into muscovite. Another possibility is alteration from detrital feldspar into muscovite during diagenesis and fault deformation.

Deformation conditions

The Kübler index was measured on five samples along the hanging wall transect. The KI values of muscovite (001) range from 0.20°2θ to 0.26°2θ (Kübler-Kisch scale) see Table 1.3. These values are corresponding to upper anchizone/epizone grade conditions.

The average temperature estimated by chlorite thermometry (through multi-equilibrium thermodynamic calculations) is presented in Table 1.4. The temperature in the damage zone ranges between 218°C to 317°C with an average value of 270°C ± 23°C. The core zone temperature is between 225°C and 359°C with an average value 285°C ± 28°C. The redox conditions can be evaluated by assessing the variation of XFe 3+ . In red pelites XFe 3+ values are between 11% and 44% with an average value of 25% and standard deviation of ± 7%. In green pelites the values are relatively lower, they range from 3 to 34% with an average value of 16% and standard deviation of ± 7%. This indicates less Fe 3+ is stored in chlorite of the green pelite. Such as variation can be linked to changes in P-T conditions or in the oxidation state [START_REF] Lanari | A thermodynamic model for di-trioctahedral chlorite from experimental and natural data in the system MgO-FeO-Al 2 o 3 -SiO 2 -H 2 o: applications to P-T sections and geothermometry[END_REF][START_REF] Trincal | Temperature micro-mapping in oscillatory-zoned chlorite: Application to study of a green-schist facies fault zone in the Pyrenean Axial Zone (Spain)[END_REF][START_REF] Vidal | P-T-deformation-Fe 3+ /Fe 2+ mapping at the thin section scale and comparison with XANES mapping: application to a garnetbearing metapelite from the Sambagawa metamorphic belt (Japan)[END_REF].

Table 1.3: The FWHM (raw data), the calibrated KI (CIS) , KI (Basel lab) values in °2 θ and the corresponding crystallinity zone of five samples along the transect in the hanging wall of the Pic de Port Vieux thrust fault.

Table 1.4: Illustrating number of analyses of chlorite that have been used in temperature estimation using chlorite thermometry, the average estimated temperature, XFe 3+ = (Fe 3+ / Σ Fe) chl and the standard deviation for both damage and core zone samples respectively.

Fluid-rock interactions modelling 1.4.5.1 Conditions

In the PPVT, the Triassic red pelites transformed into green pelites in the core fault zone due to dissolution of hematite in the core zone. In order to better understand their mineralogical changes, a simulation of the fluid-rock interactions was performed.

The Triassic red pelites compositions was used as an initial composition and the relative proportion of each mineral is presented in Table 1.5 (data are from [START_REF] Trincal | Interactions fluide-roche, conditions physico-chimiques et transferts de matiere dans des zones de failles en milieux sedimentaires -exemple de failles chevauchantes pyreneennes[END_REF]. The chemical compositions of detrital chlorite and muscovite from the red pelites matrix are based on the EPMA analyses of the present study. The newly formed chlorite that is present in a few veins in the red pelites is excluded during this simulation.

As it is not possible to analyze the pore fluids in the Triassic pelites, a first simulation was performed to simulate their composition. The initial pore fluid was assumed to be at equilibrium with the red Table 1.5: The initial red pelites composition (data are from Trincal ( 2014)) which was used as input data for the modelling. The quantity of each phase is presented as a number of moles.

Table 1.6: The composition of the pore fluids that result from equilibrium between low charge fluid and the red pelite mineralogy.

pelites minerals before thrusting at 270 • C (burial diagenetic conditions). The pore fluid composition (Table 1.6) was obtained by simulating interactions between the red pelites and low charge fluid (rain water data from [START_REF] Apello | Geochemistry, Groundwater and Pollution[END_REF]. The equilibrium was reached by dissolving very small quantities of the detrital minerals. Then the mineralogical changes were simulated by batch reactions between the pore fluids (previously calculated) and the initial red pelites composition at 285 • C (temperature which was estimated by chlorite thermometry in the green pelites). To test the impact of redox condition change, a series of calculations were performed at various redox conditions (from reduction potential (Eh) = 0.420V to Eh = -0.841V). The precipitation possibility was tested for iron oxi/hydroxides (hematite, goethite, and magnetite), iron sulfur and sulfates (pyrite, gypsum and anhydrite), phyllosilicates (muscovite, celadonite, illite, annite, paragonite, pyrophyllite and phlogopite), chlorite solid-solutions (amesite, chamosite, clinochlore and daphnite) and other initial minerals (such as, calcite and quartz).

Modelling results

The calculated composition of the resulting interstitial fluids in equilibrium with the red pelite mineralogy is given in Table 6. The mineralogical transformations of red pelite minerals at various redox conditions were calculated and illustrated in Figure 1.9 a. According to the model, the same calcite content is predicted when modifying the redox conditions. Furthermore, muscovite seems to be slightly under-saturated whatever the redox conditions. At oxidative to low reductive conditions quartz content increases compared to the initial pelite composition. However at moderate to high reducing conditions, quartz content does not change. The observed change during the simulation concerns iron bearing minerals as illustrated in Figure 1.9 b. The increase in the reducing conditions promotes an increase in hematite dissolution and this dissolution is complete at Eh < 0.410 V. Magnetite is the iron-rich mineral predicted for precipitation in the system when going to higher reducing conditions. However at Eh= -0.819 V magnetite is progressively replaced by chlorite which is the only iron bearing phase predicted to precipitate in extreme reducing conditions (Eh = -0.819 V).

The chlorite and muscovite compositions as a combination of different end members are displayed in Figure 1.10. During the simulation, the noticeable change is the variation in proportion of the different end members at high reducing conditions. In Figure 1.10 a, chamosite, daphnite, clinochlore and amesite correspond to the four end-members of chlorite that were used to calculate the composition of chlorite. When increasing the reducing conditions a decrease in the proportion of amesite (Mg-rich end member) and an increase in the proportion of daphnite and chamosite (Fe-rich end members) is observed. The composition of chlorite formed after total hematite dissolution (without magnetite) at Eh < -0.830 V, has the following structural formula (Si 2.85 Al 1.15 )O 10 (Al 1.14 Mg 2.41 Fe 2.44 )(OH) 8 .

Illite, celadonite, annite, paragonite and muscovite are the end members used for mica composition simulation. The average muscovite composition is slightly modified when increasing the reducing conditions with the presence of iron instead of magnesium (Figure 1.10 b), which is simulated by annite component precipitation. The muscovite average structural formula calculated from modelling results at Eh < -0.830 V is (Si 3.00 Al 1.00 ) O 10 (Al 1.81 Fe 0.28 ) (OH) 2 K 0.90 Na 0.10 .

Discussion

Mineralogical and textural changes attributed to fault activity

In the present study, the variations in texture, mineralogy and chemistry between the damage zone and core fault zone deepen our understanding of the impact of deformation and fluid circulation on phyllosilicates.

The core zone of the PPVT is clearly different from the damage zone; it is characterized by a change in pelite color from red to green toward the fault contact, attributed to the dissolution of hematite. The parameters and conditions of that process will be discussed in the following. The second remarkable difference is the presence of numerous veins and veinlets of quartz + chlorite ± calcite in the core fault zone which can be observed even at the chip rock scale. These veins are associated with the fractures and micro-fractures opening and attributed to fluid circulation coeval to the fault movement [START_REF] Grant | Episodic discrete and distributed deformation: consequences and controls in a thrust culmination from the central Pyrenees[END_REF]. Pelites from the core zone have been affected by several stages of deformation and fluid circulation as shown by the distribution of several vein generations that crosscut each other, as well their folded and deformed shape.

Quartz dissolution by pressure solution was observed in the matrix of the core zone and is characterized by smaller grain size and elongation of the grains compared to quartz present in the damage zone. Furthermore, the core zone shows a well-developed foliation, enrichment in phyllosilicates and a pervasive cleavage with preferential orientation of muscovite that facilitated the circulation of the fluids. The results of the present study indicate that deformation and fluid circulation in the fault zone are connected and are related to the same tectonic event. These observations suggest aseismic behavior of the PPVT fault with a pressure solution creep mechanism that involves coupling deformation and recrystallizations in the presence of fluids (e.g. [START_REF] Hadizadeh | A microstructural study of fault rocks from the SAFOD: Implications for the deformation mechanisms and strength of the creeping segment of the San Andreas Fault[END_REF][START_REF] Richard | Rock and mineral transformations in a fault zone leading to permanent creep: Interactions between brittle and viscous mechanisms in the San Andreas Fault: Fault rock changes leads to steady creep[END_REF]. Moreover, this deformation mechanism is consistent with the results from the footwall obtained by [START_REF] Trincal | Fluid-rock interactions related to metamorphic reducing fluid flow in meta-sediments: example of the Pic-de-Port-Vieux thrust (Pyrenees, Spain)[END_REF] who suggested that mylonitisation that occurred in the core zone of the footwall limestone is related to both mechanical grain size reduction processes and interaction with fluids.

Similarly, [START_REF] Gratier | Geological control of the partitioning between seismic and aseismic sliding behaviours in active faults: Evidence from the Western Alps, France[END_REF] and [START_REF] Janssen | Microstructures and their implications for faulting processes -Insights from DGLab core samples from the Gulf of Corinth[END_REF] demonstrated the same mechanism through the dissolution of soluble minerals (feldspars, quartz and calcite) and passive concentration of phyllosilicates in the presence of fluids in active faults from the Western Alps and the San Andreas. In addition, they suggested that fracturing can accelerate pressure solution by developing diffusion shortcut (e.g. [START_REF] Gratier | Aseismic sliding of active faults by pressure solution creep: Evidence from the San Andreas Fault Observatory at Depth[END_REF][START_REF] Lockner | Low strength of deep San Andreas fault gouge from SAFOD core[END_REF]. In the present study, the same diffusion process was observed and appears clearly in the fractures within the red pelites and is indicated by the development of green zones around the veins.

Origin and deformation conditions of phyllosilicates in the PPVT

Many recent studies have focused on phyllosilicates in fault zones (e.g. Alpine Fault, [START_REF] Warr | Clay mineral transformations and weakening mechanisms along the Alpine Fault, New Zealand[END_REF]Moab Fault, Solum et al., 2005;Carbonera Fault, Solum and van der Pluijm, 2009;San Andreas Fault, Wenk et al., 2010;Bogd fault, Buatier et al., 2012a;Chelungpu fault, Janssen et al., 2016;JFAST fault Kameda et al., 2015) to study their origin and the deformation conditions. They demonstrated that phyllosilicates in fault zone can be formed by various mechanisms; the passive concentration of clays by pressure solution and dissolution-recrystallization mechanisms (e.g. Buatier et al., 2012a[START_REF] Lacroix | Microtectonic and geochemical characterization of thrusting in a foreland basin: Example of the South-Pyrenean orogenic wedge (Spain)[END_REF], the precipitation of synkinematic clays as a result of fluid-rock interactions (e.g. [START_REF] Haines | Clay quantification and Ar-Ar dating of synthetic and natural gouge: Application to the Miocene Sierra Mazatán detachment fault, Sonora, Mexico[END_REF][START_REF] Wibberley | Quantifying orthoclase and albite muscovitisation sequences in fault zones[END_REF][START_REF] Wibberley | Recent advances in the understanding of fault zone internal structure: a review[END_REF]or mechanical incorporation (e.g. [START_REF] Egholm | The mechanics of clay smearing along faults[END_REF][START_REF] Fisher | The permeability of faults within siliciclastic petroleum reservoirs of the North Sea and Norwegian Continental Shelf[END_REF][START_REF] Loveless | Fault architecture and deformation processes within poorly lithified rift sediments, Central Greece[END_REF]. Phyllosilicate minerals that were observed in the PPVT are chlorite and muscovite. Based on their texture and their chemistry, we can discuss their origin in the fault zone.

Chlorite

In the damage zone, chlorite is observed mainly in the matrix and in a few veins, while in the core zone, chlorite is abundant in the numerous veins and veinlets. The presence of chlorite in veins suggests that it is mainly formed by direct precipitation from fluids, whereas the large chlorite grains located in the matrix are probably inherited and a result of diagenetic reactions. The chlorite/muscovite stacks that are present in the damage zone indicate that chlorite formed through mica-chloritization. Those stacks have been commonly described in sediments that have undergone diagenesis and low-grade metamorphism [START_REF] Jiang | Formation of corrensite, chlorite and chlorite-mica stacks by replacement of detrital biotite in low-grade pelitic rocks[END_REF][START_REF] Milodowski | The origin and sedimentary, diagenetic and metamorphic evolution of chlorite-mica stacks in Llandovery sediments of central Wales[END_REF][START_REF] Randive | Paragenesis of Cr-rich muscovite and chlorite in green-mica quartzites of Saigaon-Palasgaon area, Western Bastar Craton, India[END_REF].

They are formed by alteration of detrital biotite into chlorite through a layer-by-layer transformation and then muscovite progressively fills the chlorite cleavages [START_REF] Bartier | Lithological control on the occurrence of chlorite in the diagenetic Wealden complex of the Bilbao anticlinorium (Basco-Cantabrian Basin, Northern Spain)[END_REF][START_REF] Li | TEM and AEM constraints on the origin and significance of chlorite-mica stacks in slates: an example from Central Wales[END_REF]. The association of titanium oxide to chlorite in the fault zone matrix confirmed that the alteration of biotite might have occurred in the PPVT [START_REF] Eggleton | The alteration of granitic biotite to chlorite[END_REF][START_REF] Parry | Geochemistry of hydrothermal chlorite replacing igneous biotite[END_REF][START_REF] Ren | Distribution and Origin of Clay Minerals During Hydrothermal Alteration of Ore Deposits[END_REF][START_REF] Veblen | A TEM study of the biotite-chlorite reaction and comparison with petrologic observations[END_REF]). In the core fault zone those stacks have been subjected to size reduction and a folding, reflecting more impact by shearing mechanisms compared to the damage zone.

The proportion of inherited chlorite in the matrix decreases toward the fault contact and its grain size decreases, while newly formed chlorite is more abundant in the core zone compared to the damage zone. The only observed difference is that, in the core fault zone chlorite is more Fe-rich and has a homogenous composition compared to chlorite from the damage zone. All these features suggest that newly formed chlorite is synkinematic to the fault activity and probably precipitated from iron rich fluids in the core zone.

Muscovite

Muscovite is present in the matrix of both damage and core fault zones in three form: (1) randomly oriented coarse aggregates, (2) elongated large grains, and as (3) smaller grains with sharp grain boundaries. All of them have a composition close to muscovite end-member. The large grains of muscovite are mainly observed in the damage zone and probably have a detrital origin. (Na 2 O) content is higher in the core of those grains compared to the rims suggesting either transformation or alteration of detrital mica (with high paragonite content) or from detrital feldspars and the excess Na moved away with the fluids.

Muscovite that has a smaller grain size with well-defined grain boundaries displays homogenous composition and contains less Na in the interlayer space. Close to the fault contact this muscovite contains relatively more Fe and less Na compared to muscovite from the damage zone. The step like shape grain boundary of those grains with quartz indicates dissolution /recrystallization mechanism though the recrystallization/growth of muscovite and the dissolution of quartz.

Based on these results, the newly formed phyllosilicates in the fault core zone are considered as synkinematic and related to deformation processes /fluid circulations coeval with the activity of the PPVT. This is in agreement with previous studies of [START_REF] Cavailhes | Influence of fault rock foliation on fault zone permeability: The case of deeply buried arkosic sandstones (Grès d'Annot, southeastern France)[END_REF]and [START_REF] Leclère | Formation of phyllosilicates in a fault zone affecting deeply buried arkosic sandstones: their influence on petrophysic properties (Annot sandstones, French external Alps)[END_REF] among others who found a correlation between fluid-flow and abundance of newly formed phyllosilicates.

Deformation conditions of PPVT activity

As mentioned above, muscovite and chlorite are synkinematic to the fault activity, hence they are a good thermometer for obtaining the deformation conditions of the PPVT. According to (KI) values that range between 0.20 to 0.26 • 2θ, the PPVT has experienced deformation under upper-anchizone/epizone grade conditions (sub-greenschist to greenschist facies), where the anchizone grade boundaries are defined at 0.25 to 0.42 • 2θ [START_REF] Kübler | La cristallinité de l'illite et les zones tout a fait superieures du métamorphisme. étages tectoniques[END_REF].

Thermodynamic calculations from synkinematic chlorite chemistry suggest that fault deformation occurred under average temperatures of 270 • C in the damage zone and 285 • C in the fault core zone.

Those results are consistent with previous estimates deduced from fluid inclusions in quartz veins of the same outcrop that suggested a temperature range of 250 • C-300 • C [START_REF] Banks | The chemistry of brines from an Alpine thrust system in the Central Pyrenees: An application of fluid inclusion analysis to the study of fluid behaviour in orogenesis[END_REF][START_REF] Grant | Episodic discrete and distributed deformation: consequences and controls in a thrust culmination from the central Pyrenees[END_REF], McCaig et al., 2000a). This temperature is also in agreement with a stable isotope study on quartz and chlorite from the same geological area with a mean temperature value of 320 ± 30 • C (Lacroix and Vennemann, 2015).

Key parameters that control mineralogical changes in the fault zone

Based on the petrographic observation and geochemistry data, there are several parameters that appear to control the mineralogical changes in the PPVT fault zone. The pressure solution and recrystallization processes play a major role in deformation in the core zone. Moreover, the existence of numerous veins in the core zone corroborates the strong influence of fluid circulations.

However, the parameters that control the hematite dissolution/Fe-rich phyllosilicates formation and induce the color change in the core zone were not clearly identified. Increasing the temperature does not allow dissolution of hematite in the core zone and the chlorite formation temperatures from both the green pelites and red pelites are similar within analytical uncertainty. However, it well known that to mobilize Fe, interaction with reducing fluids is required [START_REF] Busigny | Tracing paleofluid circulations using iron isotopes: A study of hematite and goethite concretions from the Navajo Sandstone (Utah, USA)[END_REF]. In addition, the decrease of XFe 3+ in newly formed chlorite from the core zone (green pelites) of the PPVT shows a change in the oxidation state of Fe.

Based on the results of numerical modelling of the present study, the dissolution of hematite is due to interaction with reducing fluids. Hematite dissolution was described in the Entrada Sandstone (United States) and was explained by the interaction with reducing brine involving an iron reduction [START_REF] Wigley | Fluid-mineral reactions and trace metal mobilization in an exhumed natural CO2 reservoir, Green River, Utah[END_REF][START_REF] Wigley | Controls of sluggish, CO 2 -promoted, hematite and K-feldspar dissolution kinetics in sandstones[END_REF]. Furthermore, the modelling results indicate that hematite dissolution can be a source of iron for the newly formed phyllosilicates in the core zone. The chemical composition of chlorite and muscovite obtained by the modelling at high reductive conditions is in agreement with the composition calculated by EPMA analyses regarding iron content (Figure 1.7). However Na content in muscovite calculated by the model is a bit different; this can be explained by the modelling limitation due to lack of mica end members in the database or by the variation in the initial white mica composition in the red pelites which arises from their different detrital origin and subsequent diagenesis.

Conclusion

The characterization of phyllosilicates (chlorite and muscovite) in the PPVT fault helps to better understand their origin, deduce the deformation conditions and the chemical evolution during deformation in the fault zone. The majority of chlorite and muscovite grains are inherited and affected by burial diagenesis in the red pelite damage zone, while in the green pelite core zone, they are mainly newly formed and are synkinematic to the fault activity. Chlorite preferentially formed in veins through direct precipitation from fluids, while muscovite formed through recrystallization of inherited minerals.

Newly formed chlorite and muscovite in the green pelites have more Fe compare to those from the red pelites.

Based on the crystallinity and chemical composition of those synkinematic phyllosilicates, the deformation in the PPVT occurred under upper-anchizone/epizone conditions (sub-greenschist to greenschist facies) with an average temperature of 270 • C and 285 • C in the damage zone and core zone respectively. The strong foliation and enrichment of phyllosilicates in the core zone as well as the numerous generations of deformed veins reveal the strong impact of deformation and fluid circulation.

The change in the pelites color from red to green toward the fault contact is related to hematite dissolution and the enrichment of newly formed chlorite in the core zone. Modelling of fluid-sediment interactions shows that the redox condition is the main parameter that controls the chemical changes in the core fault zone. It suggests that highly reductive fluids may have dissolved hematite by bleaching the red pelites in the core fault zone and precipitated Fe-rich chlorite, thus inducing the green color in the core zone. Moreover, it demonstrates that those mineralogical changes in the core zone occurred at extreme reducing conditions. The results suggest that deformation and fluid circulation in the PPV thrust zone are connected processes and are related to different stages of fault activation. Diagnostic reflections for mica polytypes indicate that muscovite 2M 1 is the major polytype in all grainsize fractions with relatively small amount of 1M. Petrographic observations confirm the occurrence of higher deformation microtextures in the core zone compared to the damage zone. Pressure solution and recrystallization/dissolution processes in the presence of fluids are the main mechanisms that controlled the chemical/textural changes in the fault core zone. Three groups of muscovite are identified in the fault zone i.e. detrital, diagenetic and newly-formed muscovites. The detrital and diagenetic muscovites are mainly present in the damage zone and characterized by large grain-size and inhomogeneous compositions. Moreover, they contain some Na in their interlayer and less Fe in the octahedral layer compared to muscovite in the core zone. The newly-formed muscovite is abundant in the core zone and is synkinematic to the fault activity. They are characterized by smaller grain-size, homogenous composition with only K in their interlayer and more Fe compared to muscovite from the damage zone. Five grain-size fractions of two samples from the core and damage zones were dated using the 40 Ar/ 39 Ar step-heating method. All the size-fractions of the core zone sample have younger ages compared to ones from the damage zone and the ages decrease with grain-size reduction.

This indicates the strong effect of deformation in the core zone that enhanced the recrystallization of younger muscovite. All the coarse fractions from both samples produced staircase-shaped spectra typical of mixing of different muscovite generations. The spectra reach a maximum age of about c. 280.7 ± 0.8 Ma that corresponds to the minimum age of the detrital muscovite in the fault zone. The

Introduction

The Pyrenean orogen formed by the convergence of the Iberian and European plates during the Late Cretaceous to early Miocene periods [START_REF] Mouthereau | Placing limits to shortening evolution in the Pyrenees: Role of margin architecture and implications for the Iberia/Europe convergence[END_REF][START_REF] Muñoz | Evolution of a continental collision belt: ECORS-Pyrenees crustal balanced cross-section[END_REF][START_REF] Roure | Ecors deep seismic data and balanced cross sections: Geometric constraints on the evolution of the Pyrenees[END_REF], Teixell et al., 2016). The range is well suited to study the evolution of tectonic activity and metamorphism because it features well exposed deformation structures and exceptionally well preserved syntectonic sedimentary strata in the foreland basins (e.g. [START_REF] Fernández | 3D structure and evolution of an oblique system of relaying folds: the Ainsa basin (Spanish Pyrenees)[END_REF], Labaume et al., 2016[START_REF] Teixell | The Ansó transect of the southern Pyrenees: basement and cover thrust geometries[END_REF]. However, dating the tectonic activity in the Pyrenees is still a challenging subject due to the superposition of multiple tectonic events and related uplifting and exhumation processes. When biostratigraphic or paleomagnetic constraints from foreland basin strata are insufficient to precisely date fault activity" the radiometric dating of authigenic K-bearing minerals was found to be a reliable alternative to provide the timing of the tectonic events in the Pyrenees (e.g. [START_REF] Costa | Use of the 40 Ar-39 Ar stepwise heating method for dating mylonite zones: An example from the St. Barthe´le´my massif (Northern Pyrenees, France)[END_REF][START_REF] Metcalf | Thermochronology of a convergent orogen: Constraints on the timing of thrust faulting and subsequent exhumation of the Maladeta Pluton in the Central Pyrenean Axial Zone[END_REF][START_REF] Moniè | Les cisaillements mylonitiques du granite de Millas (Pyrenees, France); age Cretace 40 Ar/ 39 Ar et interpretation tectonique[END_REF][START_REF] Rahl | Links between orogenic wedge deformation and erosional exhumation: Evidence from illite age analysis of fault rock and detrital thermochronology of syntectonic conglomerates in the Spanish Pyrenees[END_REF]. As mica/illite are one of the major K-rich components in the sedimentary rocks, they have been used for the K-Ar and 40 Ar/ 39 Ar geochronology since the earliest stages of development of these methods, for dating metamorphism (e.g. [START_REF] Clauer | The K-Ar and 40 Ar/ 39 Ar methods revisited for dating fine-grained K-bearing clay minerals[END_REF], Dong et al., 1997[START_REF] Verdel | Variation of illite/muscovite 40 Ar/ 39 Ar age spectra during progressive low-grade metamorphism: an example from the US Cordillera[END_REF], deformation (e.g. [START_REF] Fitz-Díaz | Fold dating: A new Ar/Ar illite dating application to constrain the age of deformation in shallow crustal rocks[END_REF][START_REF] Skipton | Deciphering the Paleoproterozoic cooling history of the northeastern Trans-Hudson Orogen, Baffin Island (Canada), using 40 Ar/ 39 Ar step-heating and UV laser thermochronology[END_REF][START_REF] Wang | Direct dating of folding events by 40 Ar/ 39 Ar analysis of synkinematic muscovite from flexural-slip planes[END_REF] and fault activity (e.g. [START_REF] Campani | Geochronological evidence for continuous exhumation through the ductile-brittle transition along a crustal-scale low-angle normal fault: Simplon Fault Zone, central Alps[END_REF][START_REF] Haines | Clay quantification and Ar-Ar dating of synthetic and natural gouge: Application to the Miocene Sierra Mazatán detachment fault, Sonora, Mexico[END_REF][START_REF] Kellett | Influence of deformation and fluids on Ar retention in white mica: Dating the Dover Fault, Newfoundland Appalachians[END_REF][START_REF] Van Der Pluijm | Fault dating in the Canadian Rocky Mountains: Evidence for late Cretaceous and early Eocene orogenic pulses[END_REF].

In order to date fault activity by the 40 Ar/ 39 Ar step-heating method, it is essential to identify, characterize and separate synkinematic mica/illite (attributed to the fault activity) from other phases (e.g. [START_REF] Duvall | Direct dating of Eocene reverse faulting in northeastern Tibet using Ar-dating of fault clays and low-temperature thermochronometry[END_REF]. However, for low grade metamorphism and diagenetic sediments this approach is not straightforward for several reasons. Firstly, the sample aliquots that have to be dated usually contain a mixture of mica/illite with different origins, i.e. comprise a mixture of grains ages [START_REF] Van Der Pluijm | Fault dating in the Canadian Rocky Mountains: Evidence for late Cretaceous and early Eocene orogenic pulses[END_REF]. Moreover, the growth of authigenic minerals can occur at the expense of pre-existing grains through Ostwald ripening and/or dissolution/precipitation processes (Eberl andSrodo ń, 1988, Jaboyedoff and[START_REF] Jaboyedoff | Dating incipient metamorphism using 40 Ar/ 39 Ar geochronology and XRD modeling: a case study from the Swiss Alps[END_REF], which can lead to the trapping of inherited argon if the rock remains partially closed system. As a consequence, the individual mica/illite grain from the fault core zone can preserve more than one age resulting in a complex age spectrum, its interpretation represent a real 2.1. INTRODUCTION challenge. In such complex geological conditions, to get meaningful age information, the 40 Ar/ 39 Ar geochronology must be combined with detailed structural, textural and chemical observations. For example, combining the 40 Ar/ 39 Ar technique with X-ray diffraction, optical microscopy and scanning electron microscopy (SEM-EDX) is highly recommended [START_REF] Clauer | The K-Ar and 40 Ar/ 39 Ar methods revisited for dating fine-grained K-bearing clay minerals[END_REF]. This integrated approach provide useful information about the proportion of the different generations of mica/illite (newly-formed, diagenetic and detrital), the different polytypes, the grain-size, crystallinity and chemical composition facilitating the interpretation of the 40 Ar/ 39 Ar results.

To overcome the difficulty rising from the presence of mica with multiple origins/ages in a fault zone, many authors proposed to use separation techniques for these micas based on mica/illite granulometry and polytypism to constrain the age of fault activity (e.g. [START_REF] Duvall | Direct dating of Eocene reverse faulting in northeastern Tibet using Ar-dating of fault clays and low-temperature thermochronometry[END_REF][START_REF] Haines | Dating the detachment fault system of the Ruby Mountains, Nevada: Significance for the kinematics of low-angle normal faults: FAULT GOUGE AGES FOR RUBY MOUN-TAINS[END_REF][START_REF] Solum | fabrics and age of clay minerals from an exposure of the Moab Fault, Utah[END_REF][START_REF] Van Der Pluijm | The dating of shallow faults in the Earth's crust[END_REF]. This approach was applied to fault gouges where clay minerals formed as result of intense fracturing and comminution processes and sometimes retrograde hydration reactions. The 1M d /1M polytype is commonly interpreted as the authigenic phase as it growths in the fault zone at low temperature conditions (< 200 • C, [START_REF] Velde | Experimental determination of muscovite polymorph stabilities[END_REF]. The 2M 1 is thought to be the detrital component derived from the wall rock as it crystalizes under high temperature conditions (> 280 • C, Srodo ń and Eberl, 1984). While, in the phyllonites fault rocks that form at the frictional-viscous (or brittle-ductile) transition (at 8-15 km depths), synkinematic mica can be of 2M 1 polytype [START_REF] Scholz | The Mechanics of Earthquakes and Faulting[END_REF][START_REF] Sibson | Fault rocks and fault mechanisms[END_REF], precluding any correlation between the age and the polytypes as both the detrital and newly formed components are of 2M 1 type. Therefore, characterization of mica polytypes is necessary for such conditions before applying this approach.

In the present study white di-octahedral mica from phyllonitic fault rocks is the target mineral for dating by the 40 Ar/ 39 Ar step-heating method as it is the only K-bearing phase in the fault zone. The studied thrust fault is the Pic de Port Vieux Thrust (PPVT), located in the south-western part of the Pyrenean Axial Zone (Figure 2.1). The PPVT footwall is composed of Upper Cretaceous mylonitic limestones, while the hanging wall consists of Lower Triassic red pelites and sandstones that turn to intensely foliated green pelites close to the fault contact. The PPV thrust-sheet is a minor unit in the footwall of the major Gavarnie thrust (GT) [START_REF] Grant | Deformation and fluid processes in thrust sheets from the central Pyrenees[END_REF]. According to [START_REF] Grant | Post-emplacement extension within a thrust sheet from the central Pyrenees[END_REF], [START_REF] Grant | Chemistry, source, and behavior of fluids involved in alpine thrusting of the Central Pyrenees[END_REF], the PPVT post-dated and deformed the GT while branching onto the latter. Both thrusts have been affected by several stages of deformation/fluid circulations and their activation was probably related to the same major tectonic episode. Consequently the thrusting events in this area are difficult to be dated precisely [START_REF] Grant | Chemistry, source, and behavior of fluids involved in alpine thrusting of the Central Pyrenees[END_REF]. Moreover, there is still considerable disagreement in literature about the precise timing of the GT activity based on stratigraphic and sedimentation/structural relationship in [START_REF] Grant | Episodic discrete and distributed deformation: consequences and controls in a thrust culmination from the central Pyrenees[END_REF]. PPVT and GT refer to the Pic de Port Vieux thrust and the Gavarnie thrust respectively.

Geological setting and previous results

The Axial Zone of the Pyrenees corresponds to an antiformal stack of south-vergent basement units that expose Paleozoic rocks deformed during the Hercynian [START_REF] Barnolas | Synthèse géologique et géophysique des Pyrénées: géophysique: cycle hercynien[END_REF]. These rocks are intruded by late Hercynian granitoids and are overlined unconformably by Permian-Triassic continental red beds. In the study area, the post-Triassic succession begins with unconformable Cenomanian platform limestones which, on the southern edge of the Axial Zone, pass upward to the Upper Cretaceous to Oligocene succession of the south-Pyrenean Ainsa and Jaca basin [START_REF] Fernández | 3D structure and evolution of an oblique system of relaying folds: the Ainsa basin (Spanish Pyrenees)[END_REF], Labaume et al., 2016[START_REF] Muñoz | The Ainsa Fold and thrust oblique zone of the central Pyrenees: Kinematics of a curved contractional system from paleomagnetic and structural data[END_REF][START_REF] Teixell | The Ansó transect of the southern Pyrenees: basement and cover thrust geometries[END_REF]. The PPVT which is the focus of the present study has a minimum southward displacement of about 0.85 km [START_REF] Grant | Deformation and fluid processes in thrust sheets from the central Pyrenees[END_REF]) (Figure 2.1). It is located in the footwall of the GT which is one of the main southward-verging thrusts in the west-central Pyrenees (e.g. [START_REF] Labaume | Tectonothermal history of an exhumed thrust-sheet-top basin: An example from the south Pyrenean thrust belt: JACA THRUST-SHEET-TOP BASIN[END_REF][START_REF] Martinez-Peña | Cretaceous-tertiary tectonic inversion of the Cotiella Basin (southern Pyrenees, Spain)[END_REF][START_REF] Séguret | Etude tectonique des nappes et séries décollées de la partie centrale du versant sud des Pyrénées: caractère synsédimentaire, rôle de la compression et de la gravité[END_REF] with a minimum displacement of about 10 km as deduced from mapping constraints. The GT emplaces low grade Upper Paleozoic strata over Upper Cretaceous carbonates and Lower Triassic red pelites and sandstones which in turn lie unconformably on Hercynian high-grade migmatitic metasediments and granodiorite [START_REF] Grant | Chemistry, source, and behavior of fluids involved in alpine thrusting of the Central Pyrenees[END_REF]. The emplacement of the GT was followed in its footwall by that of the PPVT, duplicating the Triassic and Cretaceous strata and deforming the overlying GT. Deeper thrust movements then caused both regional and local folding of these earlier thrusts and formed the Pic de Port Vieux culmination [START_REF] Grant | Deformation and fluid processes in thrust sheets from the central Pyrenees[END_REF].

The PPVT and GT were the focus of several studies that investigated the structural pattern [START_REF] Grant | Deformation and fluid processes in thrust sheets from the central Pyrenees[END_REF], 1990, 1992, Grant et al., 1990[START_REF] Parish | A structural interpretation of a section of the Gavarnie nappe and its implications for Pyrenean geology[END_REF], fluid-rock interactions (McCaig et al., 2000a,b,c, 1995[START_REF] Trincal | Fluid-rock interactions related to metamorphic reducing fluid flow in meta-sediments: example of the Pic-de-Port-Vieux thrust (Pyrenees, Spain)[END_REF], phyllosilicate characterization and temperature estimation [START_REF] Abd Elmola | Textural-chemical changes and deformation conditions registered by phyllosilicates in a fault zone (Pic de Port Vieux thrust, Pyrenees)[END_REF].

The PPVT emplacement occurred in low-grade metamorphic conditions (green schist facies) with PT conditions of about 1.5-2 kbar and 250-300 • C respectively [START_REF] Grant | Post-emplacement extension within a thrust sheet from the central Pyrenees[END_REF]. The structural analysis reveals a complex history of cleavage formation and faulting with several stages of activation and fluid circulation registered in the hanging wall Triassic pelites by several generations of synkinematic extension and shear veins of quartz, chlorite and calcite [START_REF] Grant | Deformation and fluid processes in thrust sheets from the central Pyrenees[END_REF]. These veins are contemporaneous with the bleaching by highly reducing fluids with a probable evaporitic origin in the Triassic (McCaig et al., 2000a). In the PPVT, fluid-flow assisted the dolomite dissolution and calcite recrystallization in the mylonitic Cretaceous limestones of the footwall core zone [START_REF] Trincal | Fluid-rock interactions related to metamorphic reducing fluid flow in meta-sediments: example of the Pic-de-Port-Vieux thrust (Pyrenees, Spain)[END_REF]. In the hanging wall, the fluids turned the Triassic red pelites into green pelites close to the fault contact as a result of hematite dissolution and chlorite precipitation [START_REF] Abd Elmola | Textural-chemical changes and deformation conditions registered by phyllosilicates in a fault zone (Pic de Port Vieux thrust, Pyrenees)[END_REF].

CHAPTER 2

Based on our previous detailed study of the pelite samples from a vertical transect in the hanging wall fault zone of the PPVT [START_REF] Abd Elmola | Textural-chemical changes and deformation conditions registered by phyllosilicates in a fault zone (Pic de Port Vieux thrust, Pyrenees)[END_REF], three representative samples were selected for petrographic and chemical characterization in the present study (Figure 2.2a). Several grain-size fractions of two of these samples were then dated using the 40 Ar/ 39 Ar step-heating technique.

Analytical methods

Petrographic and textural observations

The samples were characterized first by optical microscopy at the UMR 6249 Chrono-environnement laboratory (Université de Bourgogne Franche-Comté). Then the analyses by Scanning Electron Microscopy (SEM) were performed at the FEMTO-ST Institute (Université de Bourgogne Franche-Comté).

Microstructures and mineral assemblages were analyzed with a JEOL JSM5600 (SEM) equipped with Secondary Electron (SEI), backscatter electron (BSE) and Energy Dispersive X-ray Spectroscopy (EDX) detectors.

Mineralogy and mica polytype characterization

The samples were analyzed at ITINAM laboratory (Université de Bourgogne Franche-Comté) by using a Bruker D8 Advance diffractometer system, Cu-Kα radiation equipped with a fast LynxEye linear detector. Samples were hand ground to < 50 µm and the < 16 µm fraction obtained by sedimentation was submitted to ultra-centrifugation in order to extract the < 2 and < 0.5 µm fractions. For the 16-2 µm, 2-0.5 and < 0.5 µm fractions, the oriented specimens were analyzed in air dried conditions between 5 and 30 • 2θ at a step size of 0.01, a number of steps 2228 and time/step 0.5 s. No expandable or interstratified minerals were found confirmed by ethylene-glycol saturation and after heating at 550 • C.

The Fityk software© v0.9.8 [START_REF] Wojdyr | Fityk: a general-purpose peak fitting program[END_REF] was used for the decomposition of overlapped peaks to better identify the different mica components. For mica polytypes determination, the X-ray diffractograms were acquired between 20 and 32 • 2θ at a step size of 0.02, a number of steps 3450, a time/step 1 s at 40 kV and 40 mA. Rietveld quantification for the polytypes were performed by using the Bruker-AXS's Topas software.

40 Ar/ 39 Ar step-heating

The samples preparation was performed without any chemical treatment to avoid any impact on the structure of the phyllosilicates. Calcite separation from the samples was made by hand picking based on their oxidized yellowish color. The fractions (50-16, 16-2, 2-0.5 , < 0.5 µm and the bulk) of the samples PPVT12-05 and PPVT12-07 have been compacted mechanically and about 1 to 2 mg of these fractions were encapsulated in quartz tubes at 10-8 bar. Thus, the recoil 39 Ar which is expelled from the crystal structure of the grains during irradiation is retained for the analysis [START_REF] Dong | Mechanisms of argon retention in clays revealed by laser 40 Ar-39 Ar dating[END_REF]. The samples were then irradiated for 40 hours in the core of the Triga Mark II nuclear reactor of Pavia (Italia) with several aliquots of the Taylor Creek sanidine standard (c. 28.34 ± 0.10 Ma) as flux monitor. Argon isotopic interferences on K and Ca were determined by irradiation of KF and CaF 2 pure salts from which the following correction factors were obtained: ( 40 Ar/ 39 Ar)K = 0.00969 ± 0.00038, ( 38 Ar/ 39 Ar)K = 0.01297 ± 0.00045, ( 39 Ar/ 37 Ar)Ca = 0.0007474 ± 0.000021 and ( 36 Ar/ 37 Ar)Ca = 0.000288 ± 0.000016.

Atmospheric 40 Ar was estimated using a value of the initial 40 Ar/ 36 Ar ration of 295.5. Argon analyses were performed at Géosciences Montpellier (France) with an analytical system that consists of: (a) a UV laser used to pierce the quartz tubes and an infra-red laser for the step-heating experiments, (b) a lenses system for UV beam focusing, (c) a steel sample chamber, maintained at 10-8 -10-9 bar, with a drilled copper plate and 5 tubes, (d) an inlet line for purification of gases including two Zr-Al getters, (e) a multi-collector mass spectrometer (Argus VI from Thermo-Fisher). A custom-made software was used to control the laser intensity, the timing of extraction/purification and the data acquisition. The ArArCalc software© v2.5.2 was used for data reduction and plotting.

Results

Macroscopic structure of the PPVT fault zone and sample location

On the studied transect, the thrust fault superposes a hanging wall of Lower Triassic pelites over a footwall of Upper Cretaceous carbonates (Figure 2.2). In the footwall, the fault zone comprises dolomitic limestone progressively transformed into mylonitic limestone near the fault contact. In the hanging wall fault zone, we define two members differentiated by the intensity and organization of deformation:

• In the lower part, the core zone is a 0.4 m thick shear zone featuring a typical top-to-the-south S-C fabric in intensely foliated green pelites.

• Above, the damage zone, several meters thick comprises pelites featuring a north-dipping, macroscopically penetrative cleavage. The pelites in the lowermost 25 cm have the same green color as the underlying core zone, and they turn to their regional red color above. The color change is transitional by rapid and does not correspond to a change of deformation intensity. Cleavage in This detailed characterization allows to decipher the several generations of mica targeted for the 40 Ar/ 39 Ar analyses. From here on, the term "muscovite" will be used instead of "mica" as it was used in our previous study [START_REF] Abd Elmola | Textural-chemical changes and deformation conditions registered by phyllosilicates in a fault zone (Pic de Port Vieux thrust, Pyrenees)[END_REF]. studies demonstrate that this color change is related to hematite dissolution and Fe-rich chlorite precipitation due to interaction with highly reductive fluids [START_REF] Abd Elmola | Textural-chemical changes and deformation conditions registered by phyllosilicates in a fault zone (Pic de Port Vieux thrust, Pyrenees)[END_REF][START_REF] Trincal | Fluid-rock interactions related to metamorphic reducing fluid flow in meta-sediments: example of the Pic-de-Port-Vieux thrust (Pyrenees, Spain)[END_REF]. The presence of fluids during deformation is attested by the abundance of the quartz-chlorite-CHAPTER 2 2.4. RESULTS calcite veins and veinlets increasing downward across the fault zone, consistent with several stages of deformation and fluid circulation in the PPVT [START_REF] Banks | The chemistry of brines from an Alpine thrust system in the Central Pyrenees: An application of fluid inclusion analysis to the study of fluid behaviour in orogenesis[END_REF][START_REF] Grant | Deformation and fluid processes in thrust sheets from the central Pyrenees[END_REF], McCaig et al., 2000a).

Petrological

Optical microscope and BSE images also show the gradual decrease in the proportion and grain-size of quartz grains toward the fault contact. Conversely, there is a gradual enrichment of muscovite and decreasing in grain-size when passing from the damage zone toward the core zone (Figure 2.

Changes in strain pattern

The macroscopic organization of the hanging wall fault zone traduces a bottomward strain gradient toward the fault contact as shown in Figure 2.2b. This strain gradient is also observed at the microscopic scale, where the cleavage is marked by the preferred orientation of phyllosilicates and elongated quartz grains (Figure 2.3).

In the damage zone, quartz + chlorite ± calcite veins and veinlets are parallel to the shear surfaces All this observations show that the increase of deformation intensity toward the fault contact was related to increased fluid-rock interactions.

Changes in muscovite textural and compositional features

From the outer damage zone toward the core zone, SEM-images reveal a gradual enrichment of muscovite and decrease in quartz and hematite content (Figure 2.4). Muscovite grains become smaller, folded and deformed close to the fault contact (Figure 2.4a-h). It is worth to note that the large rounded quartz grains in the outer damage zone became less, elongated and smaller when getting closer to the fault contact (Figure 2.4e-h). The BSE images show the oblique cleavage defined by the preferential orientation of muscovite which is observed throughout the studied vertical section, in agreement with the microstructural observations mentioned above.

Based on the grain-size, texture and chemical composition of muscovite, three groups were identified as shown in Figure 2.5. In the damage zone, muscovite displays a very large grain-size (> 50 µm) and is referred as "Mus (1)", with probably a detrital origin (Figure 2.5a). Furthermore, smaller muscovite (∼ 5 -15 µm) is also present in the damage zone and is called "Mus (2)". In the sample PPV12-02a

Characterization of muscovite crystallinity and polytypes

Based on the petrographic and textural observations, a correlation between the grain size and the chemical composition of muscovite toward the fault contact was observed. Therefore investigation by XRD was performed on the different size fractions of two samples from the damage and core zones to compare the crystallinity and polytypes of muscovite. XRD results of the oriented specimen CHAPTER 2 2.4. RESULTS preparations for the fractions 16-2 µm, 2-0.5 µm and < 0.5 µm in air dried conditions are presented in Figure 2.6 for the samples PPV12-07 (outer damage zone) and PPV12-05 (core zone).

The results show that muscovite is present in all fractions of the damage and core fault zones. The quantities of quartz and rutile decrease or almost disappear in the finer fractions while calcite is present only in the finest fraction < 0.5 µm. On both samples, the 001 reflection peak of muscovite shows asymmetrical peak shape with a small shoulder on the low angle side of the diffractograms. The decomposition of this reflection peak with the Fityk software© v0.9.8 confirms the presence of two muscovite components: well crystallized (WC) and poorly crystallized (PC) indicated by two Gaussian peaks (Figure 2.7). The WC phase has an intense reflection peak at 10.04 Å and 10.02 Å in the damage and the core zones respectively. The PC phase has a broad reflection peak at 10.12 Å in both the damage and core zones. The WC/PC peak intensity ratio is equal to 1.45 in the damage zone and 1.92 in the core zone of the < 0.5 µm fraction. These values suggest a higher proportion of the well crystalline muscovite in the core zone compared to the damage zone.

In order to characterize muscovite polytypes, randomly oriented specimens preparations for the fractions 16-2 µm, 2-0.5 µm and < 0.5 µm of both samples were investigated and are shown in Figure 2.8.

CHAPTER 2

The reflection peaks at 3.88 Å, 3.73 Å, 3.46 Å, 3.20 Å, 2.99 Å, 2.86 Å and 2.79 Å are corresponding to the 2M 1 muscovite polytype. The occurrence of 1M muscovite polytype was confirmed by the reflection peaks at 4.12 Å, 3.66 Å, 3.07 Å and 2.93 Å. The 1M d was not detected as no hump shape was found at the 003 muscovite reflection position. The proportion of 2M 1 and 1M polytypes were calculated by using Rietveld refinement method and is presented in Table 2.1. The results indicate that the 2M 1 is the dominant muscovite polytype in all the fractions in both the damage and core zones. In the damage zone, the 2M 1 /1M ratio slightly increases with decreasing grain-size from 5.3 to 6.9. While in the core zone the ratio increases from 4.8 (in the coarse fraction) to 13.7 (in the finest fraction) confirming that the < 0.5 µm fraction of the core zone has the highest content of 2M 1 muscovite polytype.

40 Ar/ 39 Ar step-heating geochronology

Based on the field and the petrographic observations, two representative samples, PPV12-07 (damage zone) and PPV12-05 (core zone) were selected for 40 Ar/ 39 Ar dating. Step-heating experiments were performed on the bulk and on the fractions 50-16 µm, 16-2 µm, 2-0.5 µm and < 0.5 µm of both samples. Summary of the calculated ages are presented in Table 2.1 and a complete isotopic data list is presented in Appendix A. The age spectra are shown in Figure 2.9 and are corrected from 39 Ar recoil CHAPTER 2 2.4. RESULTS effects corresponding to the first increment on the spectra with a zero age. In the present study, we determine the age of the various muscovite fractions by using the total gas age (including 39 Ar recoil ) rather than retention age (excluding 39 Ar recoil), due to the high amount of 39 Ar recoil that can reach ∼ 25% in the finer fractions (see e.g. [START_REF] Dong | Mechanisms of argon retention in clays revealed by laser 40 Ar-39 Ar dating[END_REF][START_REF] Solum | fabrics and age of clay minerals from an exposure of the Moab Fault, Utah[END_REF][START_REF] Van Der Pluijm | The dating of shallow faults in the Earth's crust[END_REF].

Sample PPV12-07 (damage zone)

In the PPV12-07 sample, all the grain-size fractions except the finest fraction < 0.5 µm, produced spectra with three distinct segments: a hump shaped profile for the low temperature steps followed by a staircase profile with steadily climbing apparent ages at intermediate temperatures and a peak-like at higher temperatures (Figure 2.9). This indicates a mixing of muscovite generations with different ages and different Ar retentivity, this was also reported by Fitz-Díaz and van der Pluijm (2013), [START_REF] Kirschner | Staircase 40 Ar/ 39 Ar spectra of fine-grained white mica: Timing and duration of deformation and empirical constraints on argon diffusion[END_REF], [START_REF] Verdel | Variation of illite/muscovite 40 Ar/ 39 Ar age spectra during progressive low-grade metamorphism: an example from the US Cordillera[END_REF]. By contrast the fraction < 0.5 µm has a relatively a flat spectrum for the intermediate part of the degassing experiment. The maximum age which is reached during the step-heating experiments decreases with decreasing the grain-size and ranges between c. 280.7 ± 0.8 Ma (bulk sample) to c. 78.1 ± 0.6 Ma (< 0.5 µm fraction). The total gas age is also directly proportional to the grain-size and decreases from c. 127.4 ± 0.9 Ma (50-16 µm) to c. 47.6 ± 0.6 Ma (< 0.5 µm fraction).

At the same time the fraction of 39 Ar recoil increases when decreasing the grain-size, the finest fraction (< 0.5 µm) having the highest value of 24.7% of the total 39 Ar (Table 2.1). For all these fractions, the 37 Ar/ 39 Ar (or Ca/K) ratios are low which indicate low calcium content (Appendix A), that reflect the successful removal of calcite by hand-picking. The fraction < 0.5 µm has slightly higher Ca/K ratio compared to the other fractions, consistent with the XRD results that detected calcite in this fraction.

In addition, the low-temperature heating-steps for all the five fractions show high 38 Ar/ 39 Ar (or Cl/K) 83 2.4. RESULTS CHAPTER 2 ratios compared to the remaining steps which suggests some interaction with Cl-rich fluids loosely bound to the mineral lattice.

Figure 2.9: 40 Ar/ 39 Ar step-heating results for the samples PPV12-07 (red color) and PPV12-05 (green color).The results show the age spectra for the bulk powder, 50-16 µm, 16-2 µm, 2-0.5 µm and < 0.5 µm fractions respectively. TGA refers to total gas age.

Sample PPV12-05 (core zone)

In a similar way to the damage zone, the bulk, 50-16 µm fraction, 16-2 µm fraction and the 2-0.5 µm fractions of the core zone sample produced staircase shaped spectra. The finer fraction < 0.5 µm displays a relatively flat spectrum of 48% of the 39 Ar released, that does not fulfill the required criteria of a plateau; three consecutive steps with ages that agree within 2 sigma error and that represent at least 50% of the total amount of 39 Ar (e.g. [START_REF] Clauer | Comparative 40 Ar/ 39 Ar and K-Ar dating of illite-type clay minerals: A tentative explanation for age identities and differences[END_REF][START_REF] Fleck | Interpretation of discordant 40 Ar/ 39 Ar age-spectra of mesozoic tholeiites from antarctica[END_REF]. The maximum age ranges between c. 237.9 ± 0.9 Ma (bulk sample) to c. 54.4 ± 0.4 Ma (< 0.5 µm fraction). The total gas age ranges between c. 88.5 ± 0.5 Ma (16-2 µm fraction) to c. 36.9 ± 0.2 Ma (< 0.5 µm fraction). The < 0.5 µm fraction experienced the highest amount of 39 Ar recoil compared to the coarser fractions with a value equal to 22.6%. In addition, the same fraction shows the highest proportion of 2M 1 muscovite polytype (Table 2.1). Similar to the damage zone, all the fractions have low calcite content (low Ca/K ratios) which slightly increase in the fraction < 0.5 µm (Appendix A). Again, the Cl/K ratios are relatively high for the low-temperature steps, especially for the first one used to evaluate recoil effects.

These results show that the finer fractions on both samples have younger total gas ages compared to the coarser fractions. Moreover, all the fractions from the core zone sample have a younger ages compared to the same fractions from the damage zone sample. Finally the finest fraction (< 0.5 µm) in the fault core zone has the youngest ages compared to all the fractions from both samples. These results are consistent with the observed inhomogeneous chemical and textural characteristics of the individual muscovite grains in both zones and point to the presence of more authigenic muscovite in the fault core zone confirming the petrographic observations (e.g. Markley et al., 2002, West and[START_REF] West | Dating mylonitic deformation by the 40 Ar-39 Ar method: An example from the Norumbega Fault Zone[END_REF]. For the two samples, no significant correlation can be observed between the total gas ages and the proportion of 2M 1 and 1M polytypes (Table 1).

Discussion

Summary and interpretation of the petrographic and chemical data

Several studies have been focused on the microstructure, origin and growth mechanisms of phyllosilicates in faults (e.g. Buatier et al., 2012a, 2015[START_REF] Solum | fabrics and age of clay minerals from an exposure of the Moab Fault, Utah[END_REF]. They demonstrated that phyllosilicates can be incorporated into the fault zones as a result of various processes depending on the deformation mechanisms: (1) Mechanical incorporation of protolith rocks into a fault zone (such as clay smear, wall abrasion) (e.g. Egholm et al., 2008, Fisher and[START_REF] Fisher | The permeability of faults within siliciclastic petroleum reservoirs of the North Sea and Norwegian Continental Shelf[END_REF], (2) Dissolution-recrystallization and pressure solution mechanisms that lead to passive concentration of phyllosilicates through the dissolution of soluble minerals and/or recrystallization of detrital clay minerals (e.g. [START_REF] Buatier | Microtextural investigation (SEM and TEM study) of phyllosilicates in a major thrust fault zone (Monte Perdido, southern Pyrenees): impact on fault reactivation[END_REF][START_REF] Lacroix | Microtectonic and geochemical characterization of thrusting in a foreland basin: Example of the South-Pyrenean orogenic wedge (Spain)[END_REF], (3) As a product of chemical reactions between fluids circulating in the fault zone and the host rocks and/or by direct precipitation from fluids (e.g. Haines andvan der Pluijm, 2008, Wibberley et al., 2008).

The results of the present study demonstrate the differences in microstructures and chemical composition between the damage and core zones in the pelites of the PPVT hanging wall. The change in the Triassic pelites color from red to green, the strong deformation with S-C structure, the grainsize reduction and the enrichment in phyllosilicates in the fault core zone are the main observed differences. These changes are related to the increase of deformation by pressure-solution processes and are also due to the interaction with highly reducing fluids circulating along the fault contact on the Triassic pelites as demonstrated by Abd Elmola et al. ( 2017). In the PPVT footwall limestones, a mylonitization process is observed close to the fault contact (e.g. [START_REF] Grant | Chemistry, source, and behavior of fluids involved in alpine thrusting of the Central Pyrenees[END_REF], McCaig et al., 2000a). [START_REF] Trincal | Fluid-rock interactions related to metamorphic reducing fluid flow in meta-sediments: example of the Pic-de-Port-Vieux thrust (Pyrenees, Spain)[END_REF] suggested that in the footwall, thrusting is associated to dolomite dissolution and dynamic calcite recrystallization of carbonates with the assistance of fluid flow. Furthermore, they demonstrated that fluid flow is 4 orders of magnitude higher parallel to the fault than perpendicularly in the calcareous footwall. In the hanging wall, fluid circulation affect 0.65 meter of the Triassic pelite thickness confirming that fluid-rock interaction and fluid flow are concentrated along the major thrust interface.

In the present study we focused on the microtextures and chemistry of muscovite from the damage and core zones of the hanging wall of the PPVT fault zone. Major mineralogical changes related to deformation and fluid-rock interaction have been observed and three types of muscovite have been distinguished, i.e. detrital, diagenetic, and newly formed muscovites corresponding to Mus (1), Mus

(2) and Mus (3) respectively (Figure 2.5):

• The detrital muscovite (Mus ( 1)) is characterized by large grain size, inhomogeneous composition and it is more abundant in the damage zone. The grains are generally preferentially oriented along the cleavage. This detrital muscovite is probably derived from the metamorphic or granitic basement rocks where 40 Ar/ 39 Ar variscan ages are still locally preserved [START_REF] Maurel | The Meso-Cenozoic thermotectonic evolution of the Eastern Pyrenees: an 40 Ar/ 39 Ar fission track and (U-Th)/He thermochronological study of the Canigou and Mont-Louis massifs[END_REF][START_REF] Metcalf | Thermochronology of a convergent orogen: Constraints on the timing of thrust faulting and subsequent exhumation of the Maladeta Pluton in the Central Pyrenean Axial Zone[END_REF].

• Newly-formed muscovite of diagenetic origin (Mus (2)) is found in both the damage and core zones. It is characterized by smaller grain-size compared to the detrital one and is randomly oriented. Its chemical composition changes from the grain core to the rim are evidenced by the electronic contrast variation of the BSE images and confirmed by the EDX spot analyses (Figure 2.5c). The rims contain only K in the interlayer, while the cores contain Na + K, indicating an origin by alteration of detrital feldspars or K-bearing clay minerals. This chemical change is the result of recrystallization processes which occurred in the Triassic pelites probably during diagenesis and/or fault activity.

• In the core zone, another type of newly-formed muscovite is present (Mus (3)), characterized by a small grain-size, homogenous composition (K and Fe-rich compared to the diagenetic muscovite) and preferential orientation along the cleavage. The source of this Fe is the hematite dissolved in the green pelites [START_REF] Abd Elmola | Textural-chemical changes and deformation conditions registered by phyllosilicates in a fault zone (Pic de Port Vieux thrust, Pyrenees)[END_REF].

The folded and deformed muscovite grains aligned along the oblique cleavage coherent with the top-to-the-south shearing in the red pelites show that deformation affected the red pelites and not only the core zone (green phyllonites). It demonstrates as well that the color change boundary represents only the upper limit of fluid circulation impact on hematite, while the deformation continued to affect the red pelites above. The petrographic results suggest that the dissolution by pressure solution mechanism and the recrystallization that was enhanced by fluids are the main mechanisms control the growth of muscovite in the PPVT.

To conclude, the detrital and diagenetic muscovite are distinguished from their large grain-size, their inhomogeneous compositions (with some Na in the interlayer) and their random grains orientation.

On the other hand, the smaller grain-size, the homogenous composition (with only K in the interlayer) and the preferential orientation are the main characteristics of the newly-formed muscovite in the fault core zone. Consequently this confirms that the Mus (3) in the core zone is synkinematic to the PPVT activity and then can be used to date the thrusting.

Muscovite 40

Ar/ 39 Ar dating: general observations 40 Ar/ 39 Ar dating of illite/ muscovite has been commonly used to date fault activity (e.g. [START_REF] Duvall | Direct dating of Eocene reverse faulting in northeastern Tibet using Ar-dating of fault clays and low-temperature thermochronometry[END_REF][START_REF] Mcwilliams | Determining ages of multiple muscovitebearing foliations in phyllonites using the 40 Ar/ 39 Ar step heating method: Applications to the Alleghanian orogeny in central New England[END_REF][START_REF] Verdel | Variation of illite/muscovite 40 Ar/ 39 Ar age spectra during progressive low-grade metamorphism: an example from the US Cordillera[END_REF], Vrolijk and van der Pluijm, 1999). Because of the common coexistence of two or more generations of illite/mica in fault rocks, correlation of the total gas ages calculated by the 40 Ar/ 39 Ar method with the proportion of 1M d and 2M 1 mica polytypes has been proposed (e.g. [START_REF] Van Der Pluijm | The dating of shallow faults in the Earth's crust[END_REF]. In order to obtain the age of the two components, 1M d and/or 1M was assumed to be the authigenic component and 2M 1 is the detrital component. This method has been successfully used for dating clay gouges (e.g. [START_REF] Haines | Clay quantification and Ar-Ar dating of synthetic and natural gouge: Application to the Miocene Sierra Mazatán detachment fault, Sonora, Mexico[END_REF][START_REF] Hnat | Fault gouge dating in the Southern Appalachians, USA[END_REF][START_REF] Kellett | Influence of deformation and fluids on Ar retention in white mica: Dating the Dover Fault, Newfoundland Appalachians[END_REF][START_REF] Van Der Pluijm | Fault dating in the Canadian Rocky Mountains: Evidence for late Cretaceous and early Eocene orogenic pulses[END_REF] but it is not applicable for cohesive foliated phyllosilicate-fault rocks which formed at high temperature ( > 280 • C) where the authigenic muscovite can be of 2M 1 and not only 1M or 1M d polytypes (e.g. [START_REF] Fitz-Díaz | XRD-based 40 Ar/ 39 Ar age correction for fine-grained illite, with application to folded carbonates in the Monterrey Salient (northern Mexico)[END_REF].

In the present study, XRD confirmed the abundance of 2M 1 polytypes with a small amount of 1M in all size fractions from the damage and core zones of the PPVT. Furthermore, an increase of 2M 1 polytype with decreasing grain-size is observed in the fault core zone. As newly-formed muscovite is the major phase in the finest fraction (< 0.5 µm) as discussed above, the majority of the newly-formed muscovite is 2M 1 . The decomposition of the XRD peaks is a commonly used when overlapping between two components reflection occurs (e.g. [START_REF] Lanson | Characterization of the end of smectite-to-illite transformation: Decomposition of X-ray patterns[END_REF]. The decomposition of the 001 reflection peak of muscovite (< 0.5 µm fraction) suggests the presence of both well-and poorly-crystallized muscovite that could correspond to the 2M 1 and 1M polytypes respectively. The occurrence of the newly-formed muscovite (2M 1 ) is consistent with the deformation conditions of the PPVT with a temperature of more than 250 • C, i.e. under upper-anchizone to epizone conditions (e.g. Abd [START_REF] Abd Elmola | Textural-chemical changes and deformation conditions registered by phyllosilicates in a fault zone (Pic de Port Vieux thrust, Pyrenees)[END_REF][START_REF] Banks | The chemistry of brines from an Alpine thrust system in the Central Pyrenees: An application of fluid inclusion analysis to the study of fluid behaviour in orogenesis[END_REF], Grant et al., 1990, McCaig et al., 2000a[START_REF] Trincal | Fluid-rock interactions related to metamorphic reducing fluid flow in meta-sediments: example of the Pic-de-Port-Vieux thrust (Pyrenees, Spain)[END_REF]. However, this temperature is very high and less favorable to the growth of 1M polytype (Srodo ń and Eberl, 1984), which suggests that the formation of 1M in the core zone is probably related to a lower-temperature tectonic event during the activity of the PPVT. This assumption is in agreement with the history of the PPVT activity that experienced several stages of deformation and fluid circulations (e.g. [START_REF] Banks | The chemistry of brines from an Alpine thrust system in the Central Pyrenees: An application of fluid inclusion analysis to the study of fluid behaviour in orogenesis[END_REF][START_REF] Grant | Deformation and fluid processes in thrust sheets from the central Pyrenees[END_REF], 1992, Grant et al., 1990). In the Mexican Fold-Thrust Belt (northeastern Mexico), [START_REF] Fitz-Díaz | XRD-based 40 Ar/ 39 Ar age correction for fine-grained illite, with application to folded carbonates in the Monterrey Salient (northern Mexico)[END_REF], also suggested that both 2M 1 and 1M d polytypes are authigenic, since their ages are younger than the deposition age.

In the present study, the newly-formed and detrital muscovites are of the 2M 1 polytype consequently, the polytype approach to separate the different age components cannot be used here. However the petrographic and texture observations suggest that a discrimination between the different muscovite generations is possible through their grain-size (van der [START_REF] Van Der Pluijm | The dating of shallow faults in the Earth's crust[END_REF][START_REF] Van Der Pluijm | Fault dating in the Canadian Rocky Mountains: Evidence for late Cretaceous and early Eocene orogenic pulses[END_REF]. The coarse fractions are enriched in detrital muscovite and accordingly, they should have older ages. The diagenetic muscovite is concentrated in the intermediate-size fractions and is probably formed through alteration of K-feldspars and/or detrital clay minerals. Because of the inhomogeneous composition within the individual grain of this diagenetic muscovite, a precise estimations for whose ages will be difficult.

Moreover, partial reset of their ages by the fault activity is not excluded as both the core and damage zones display microstructure attributed to the fault deformation as discussed above. Conversely, the finer fraction might be younger as it is composed mainly of synkinematic authigenic muscovite and consequently its age should represents the age of fault activity.

Significance of the 40 Ar/ 39 Ar step-heating data

In the present study, with the exception of the finest fraction (< 0.5 µm), all spectra have a staircase shaped profile due to mixing of grains with various ages, grain-size, chemistry and crystal lattice properties (e.g. [START_REF] Dong | Thermal 40 Ar/ 39 Ar separation of diagenetic from detrital illitic clays in Gulf Coast shales[END_REF][START_REF] Verdel | Variations in the Illite to Muscovite Transition Related to Metamorphic Conditions and Detrital Muscovite Content: Insight from the Paleozoic Passive Margin of the Southwestern United States[END_REF]. According to [START_REF] Verdel | Variation of illite/muscovite 40 Ar/ 39 Ar age spectra during progressive low-grade metamorphism: an example from the US Cordillera[END_REF], at low grade metamorphism the staircase shape is not only related to the difference in crystallization age but also due to differences in Ar retentivity between thick muscovite packets (high retentivity) and thin packets (low retentivity).

For the sample PPV12-07 (in the damage zone), the coarse fraction (50-16 µm) contains predominantly detrital and diagenetic muscovites that contribute variably to the shape of the age spectrum. By contrast, the finest fraction (< 0.5 µm) has the largest proportion of diagenetic illite/muscovite. This difference is supported by the total gas ages of these two fractions, respectively of c. 127.4 ± 0.6 Ma and c. 47.6 ± 0.6 Ma. Considering the fact that the well-crystallized, thick packets of detrital muscovite have high Ar retentivity compared to diagenetic one, the final part of the degassing with ages up to c. 280.7 ± 0.8 Ma (Permian) is thought to give a minimum age for the detrital component (Mus ( 1)). This age probably corresponds to the exhumation of the Hercynian rocks during the Permian, subsequently reworked in the Triassic sedimentation. On the other hand, the thinner muscovite (diagenetic) packets have lower retentivity and therefore release Ar at much lower temperatures (e.g. [START_REF] Dong | Thermal 40 Ar/ 39 Ar separation of diagenetic from detrital illitic clays in Gulf Coast shales[END_REF][START_REF] Hunziker | The evolution of illite to muscovite: mineralogical and isotopic data from the Glarus Alps, Switzerland[END_REF][START_REF] Reuter | 40 Ar/ 39 Ar dating of cleavage formation in tuffs during anchizonal metamorphism[END_REF]. In the damage zone sample, the total gas age (c. 47.6 ± 0.6 Ma) of the finest fraction (< 0.5 µm) is younger compared to the other coarser fractions ages. This decrease in age is probably a combined result of:

(1) Diagenesis processes as the Lower Triassic sediments have experienced the following diagenetic history:

-First diagenesis during the Jurassic-Early Cretaceous burial, probably not exceeding 2-3 km, followed by exhumation by erosion during the end of Early Cretaceous (Aptian-Albian).

-A new burial below the Upper Cretaceous -Early Tertiary of the northern Jaca basin, which may have reached 5-6 km in the PPVT area [START_REF] Labaume | Tectonothermal history of an exhumed thrust-sheet-top basin: An example from the south Pyrenean thrust belt: JACA THRUST-SHEET-TOP BASIN[END_REF].

-Then burial below the Gavarnie nappe up to 7-8 km occurred at the middle-late Eocene [START_REF] Labaume | Tectonothermal history of an exhumed thrust-sheet-top basin: An example from the south Pyrenean thrust belt: JACA THRUST-SHEET-TOP BASIN[END_REF].

(2) Deformation, as the structural and petrographic results show that the red pelites are affected by shearing related to the PPVT activity. However, it is not excluded that the Gavarnie thrust had also an impact on the red pelites as the latter are located only a few tens of meters below the Gavarnie thrust (see Figure 4.5 from [START_REF] Grant | Deformation and fluid processes in thrust sheets from the central Pyrenees[END_REF]. Based on this observation it is possible that the formation of cleavage in the Triassic pelites begun as a footwall deformation of the Gavarnie thrust, subsequently enhanced as a hanging wall deformation of the PPVT.

Therefore, the age (c. 47.6 ± 0.6 Ma) of the fraction < 0.5 µm (damage zone) is a result of a partial resetting during diagenesis and deformation of the PPVT ± the Gavarnie thrust.

For the sample PPV12-05 (in the core zone), the same fraction < 0.5 µm produced a plateau-like segment that cannot be considered as a true plateau according to the age plateau definition (see above). The absence of true plateau can be related to 39 Ar recoil effects which artificially modify the original distribution of 39 Ar/ 40 Ar ratio in the grains (e.g. [START_REF] Dong | Mechanisms of argon retention in clays revealed by laser 40 Ar-39 Ar dating[END_REF]. Moreover, the presence of chlorite in all the studied fractions, as shown by XRD results, could be another reason for the discordant pattern of the age spectra. [START_REF] Ghanem | Dating slate belts using 40 Ar/ 39 Ar geochronology and zircon ages from crosscutting plutons: A case study from east-central Maine, USA[END_REF] and [START_REF] Kunk | Contrasting tectonothermal domains and faulting in the Potomac terrane, Virginia-Maryland-discrimination by 40 Ar/ 39 Ar and fission-track thermochronology[END_REF] interpreted the hump-shaped profile recorded by the first heating increments as a result of 39 Ar recoil from the rim of muscovite into adjacent chlorite grains during irradiation. Hence, they suggested that the very young ages observed at the first heating steps corresponding to 39 Ar incorporated into chlorite as the degassing temperature of chlorite is lower compared to that of muscovite (Ching-Hua and Onstott, 1989, Sletten and[START_REF] Sletten | The Effect of the Instability of Muscovite During In Vacuo Heating on 40 Ar/ 39 Ar Step-Heating Spectra[END_REF]. Given these considerations, the total gas age of c. 36.9 ± 0.2 Ma given by the fraction < 0.5 µm from the core zone sample is the best estimate of the age of synkinematic Mus (3) which is the dominant component in this fraction.

The other coarser fractions of the sample PPV12-05 show decreasing of the maximum age with the decrease of grain-size and a systematic age difference with the sample PPV12-07 for the same fractions. This results support our interpretation for the partial recrystallization of detrital muscovite (Mus ( 1)) during late diagenesis and subsequent shearing [START_REF] Kirschner | Staircase 40 Ar/ 39 Ar spectra of fine-grained white mica: Timing and duration of deformation and empirical constraints on argon diffusion[END_REF], resulting in the presence of two additional generations of muscovite, Mus (2) and Mus (3). As a consequence, the behavior of argon isotopes in these coarser fractions is far from being simple since it is likely that detrital Mus (1) experienced two episodes of recrystallization and argon loss by volume diffusion while diagenetic Mus (2) suffered only one during the crystallization of synkinematic Mus (3). The proportion of these three generations of muscovite and the amount of argon lost by Mus (1) and Mus (2) remain unknown parameters that could help for interpreting their age spectra. For these fractions, none of the individual apparent ages can receive unambiguous interpretation concerning the age of detrital, diagenetic or authigenic muscovite components.

In the core-zone sample, the complete resetting of the finest fraction (< 0.5 µm) of muscovite vs. the partial resetting of the other size fractions suggests that temperature during shearing was above the closure temperature of the dated fine grained phyllosilicates. According to [START_REF] Dodson | Closure temperature in cooling geochronological and petrological systems[END_REF], the small grains must have a lower closure temperature compared to the larger grains. We calculated this closure temperature using muscovite diffusion parameters from [START_REF] Harrison | Diffusion of 40 Ar in muscovite[END_REF] and assuming that the cooling rate of the PPVT ranged within 5 to 50 • C/My. According to these calculations, muscovite with grain-size of 0.5 µm has a closure temperature that ranges from 278 • C to 300 • C for a cooling rate of 5 to 50 • C/My respectively. While muscovite with a grain-size of 2 µm has closure temperature of 304 • C to 328 • C for cooling rate of 5 to 50 • C/My. As the core zone of the PPVT recorded peak temperature during shearing of 285 • C ± 28 • C, it is very likely that only muscovite with grain-size equal or smaller than 0.5 µm experienced complete resetting during thrusting while micas with larger grain size will preserve some inherited argon. This correlation between closure temperature and grain-size in fault zones was also reported by other studies (see e.g. [START_REF] Duvall | Direct dating of Eocene reverse faulting in northeastern Tibet using Ar-dating of fault clays and low-temperature thermochronometry[END_REF][START_REF] Rahl | Links between orogenic wedge deformation and erosional exhumation: Evidence from illite age analysis of fault rock and detrital thermochronology of syntectonic conglomerates in the Spanish Pyrenees[END_REF][START_REF] Scharf | Grainsize effects on the closure temperature of white mica in a crustal-scale extensional shear zone -Implications of in-situ 40 Ar/ 39 Ar laser-ablation of white mica for dating shearing and cooling (Tauern Window, Eastern Alps)[END_REF][START_REF] Verdel | Variation of illite/muscovite 40 Ar/ 39 Ar age spectra during progressive low-grade metamorphism: an example from the US Cordillera[END_REF].

To summarize this part, these geochronological data indicate that only the < 0.5 µm fraction of the sample PPV12-05 (the core zone) yields a meaningful constraint on the age of the PPVT activity. Among all the dated grain-size fractions, it has the youngest total gas age of c. 36.9 ± 0.2 Ma, corresponding to the Late Eocene (Priabonian age). As the results of the present study demonstrate that this fraction is mainly composed of newly-formed muscovite with homogenous chemical composition and is completely reset during the PPVT activity. It follows that the age of this fraction can be interpreted in first approximation as the age of activity of the PPVT fault. However, it must be considered as a maximum i.e. the oldest possible age for the last activity of the PPVT as the < 0.5 µm fraction consists of 2M 1 and 1M polytypes corresponding probably to two periods of thrust activity as discussed before.

The delay between the crystallization of the two muscovite polytypes is difficult to evaluate but the limited (<1 km) displacement on the PPVT [START_REF] Grant | Deformation and fluid processes in thrust sheets from the central Pyrenees[END_REF] suggests that duration of its activity was short, probably not exceeding 1 million year. Consequently the age of c. 36.9 Ma remains our best estimate of the PPV thrusting.

Implication of the PPVT activity age in the basin tectonic history

In the present study, we provide the first geochronological 40 Ar/ 39 Ar age for the PPVT that is considered as a secondary branch of the major Gavarnie thrust (GT) system. This age can be used to assess the GT age as there is no agreement in the literature for its activation age. According to [START_REF] Grant | Post-emplacement extension within a thrust sheet from the central Pyrenees[END_REF], [START_REF] Grant | Chemistry, source, and behavior of fluids involved in alpine thrusting of the Central Pyrenees[END_REF] who thoroughly studied the structural sequence at Pic de Port Vieux, the GT has moved first as the PPVT is branched on, and deformed the GT. Figure 2.10 shows a partial restoration of the thrust system where we interpret the PPVT as a late minor branch in the footwall of the GT.

The GT has a complex history (e.g. McCaig et al., 2000a,b) and different scenarios for the timing of its activity were proposed based on structural observations, tectonic-sedimentary relationships and thermochronological data in the South-Pyrenean basin: a mid-to late Eocene age was proposed by some authors from studies in the central Pyrenees and the Ainsa basin [START_REF] Fernández | 3D structure and evolution of an oblique system of relaying folds: the Ainsa basin (Spanish Pyrenees)[END_REF][START_REF] Muñoz | The Ainsa Fold and thrust oblique zone of the central Pyrenees: Kinematics of a curved contractional system from paleomagnetic and structural data[END_REF][START_REF] Muñoz | Evolution of a continental collision belt: ECORS-Pyrenees crustal balanced cross-section[END_REF] while others argued for a late Eocene to early Oligocene age from studies in the Jaca basin and western Axial Zone [START_REF] Bosch | Timing of Eocene-Miocene thrust activity in the Western Axial Zone and Chaînons Béarnais (westcentral Pyrenees) revealed by multi-method thermochronology[END_REF][START_REF] Jolivet | Thermochronology constraints for the propagation sequence of the south Pyrenean basement thrust system (France-Spain)[END_REF], Labaume et al., 2016[START_REF] Teixell | The Ansó transect of the southern Pyrenees: basement and cover thrust geometries[END_REF]. Absolute dating by 40 Ar/ 39 Ar geochronology was performed by [START_REF] Rahl | Links between orogenic wedge deformation and erosional exhumation: Evidence from illite age analysis of fault rock and detrital thermochronology of syntectonic conglomerates in the Spanish Pyrenees[END_REF] on mixed detrital and authigenic illite in the GT fault zone at Plan de Larri (Figure 2.10). They suggest that the GT activity started in the late Cretaceous (c. 69.3 ± 0.7 Ma) however, they have mentioned four different ages (c. 36.5,35,32 and 31.6 Ma) within the same article for end of the GT activity. Thus, the true age they found in their study is still unknown. We note that the c. 69.3 Ma age has no clear geological meaning as geological evidence shows that thrust deformation was active more to the north at that time, while the domain corresponding to the present GT hanging wall was subsiding in the northern part of the Jaca basin (e.g. [START_REF] Teixell | The crustal evolution of the west-central Pyrenees revisited: Inferences from a new kinematic scenario[END_REF].

The 40 Ar/ 39 Ar dating results of the present study suggest a late Eocene age (c. 36.9 ± 0.2 Ma) for the PPVT activity. Based on the PPVT-GT structural relationships shown in Figure 2.10, this age suggests that the GT was active before c. 37 Ma and the PPVT moved around c. 37 Ma with its 0.8 km displacement transmitted to GT to the south. Finally, the culmination of the Pic de Port Vieux was accommodated by later thrusts beneath the PPVT (Phase 3 in Figure 2.10).

This result is compatible with the previous mid-to late Eocene age interpretation for the GT based on structural and tectonic-sedimentary interpretations [START_REF] Fernández | 3D structure and evolution of an oblique system of relaying folds: the Ainsa basin (Spanish Pyrenees)[END_REF], Muñoz et al., 2013, Figure 2.10: Structural sketch showing the structural relationships between the Pic de Port Vieux and Gavarnie thrusts at Pic de Port Vieux and Plan de Larri. The sketch shows the thrust system restored after the emplacement of the Gavarnie and Pic de Port Vieux thrusts and before the activation of the deeper younger thrusts that generated the present-day culmination (cf. Fig. 2).The Pic de Port Vieux thrust is here interpreted as a minor footwall branch of the major Gavarnie thrust. [START_REF] Muñoz | Evolution of a continental collision belt: ECORS-Pyrenees crustal balanced cross-section[END_REF]. For being compatible with the late Eocene to Early Oligocene age interpretation for the GT [START_REF] Bosch | Timing of Eocene-Miocene thrust activity in the Western Axial Zone and Chaînons Béarnais (westcentral Pyrenees) revealed by multi-method thermochronology[END_REF][START_REF] Jolivet | Thermochronology constraints for the propagation sequence of the south Pyrenean basement thrust system (France-Spain)[END_REF], Labaume et al., 2016[START_REF] Teixell | The Ansó transect of the southern Pyrenees: basement and cover thrust geometries[END_REF], two possibilities may be envisaged: (i) the GT stopped moving around 37 Ma on the PPV -Ainsa transect, but remained active later more to the west (Jaca basin), or (ii) the GT continued to move after 37 Ma also on the PPV-Ainsa transect. The basal thrust of the Gavarnie nappe being deformed/locked above the PPV thrust sheet, this hypothesis implies that the Gavarnie nappe had to move on a surface located higher than the basal thrust in order to "jump" the PPV thrust sheet. If we take into account (i) that the PPVT sheet is very thin (a few tens of meters) and (ii) the lower part of the Gavarnie nappe comprises a thick horizon of Silurian shales, we can speculate that the nappe may have continued to move on a surface located inside the Silurian.

Conclusion

The results of the present study along the PPVT demonstrate that coupling the 40 Ar/ 39 Ar step-heating method with a detailed structural analyses and precise textural observation facilitates the interpretation of the calculated ages.

Based on the petrographic, textural and chemical characteristics, three muscovite generations were identified in the PPVT fault zone: detrital, diagenetic and newly-formed muscovites. The newly-formed muscovite in the core zone is synkinematic to the fault activity and formed through pressure solution and recrystallization processes in the presence of fluids. They display smaller grain-size, homogenous composition and they mark a well-defined cleavage by their preferential orientation. X-ray diffraction suggests the dominance of the 2M 1 muscovite in all the size-fractions, in agreements with deformation conditions of the PPVT (∼ 300 • C). The small proportion of 1M polytype detected by XRD is probably related to a lower temperature event during the activity of the PPVT. 40 Ar/ 39 Ar step-heating results suggest a Permian age (c. 281 Ma) as a minimum age for the detrital muscovite, probably corresponds to the exhumation of the Hercynian rocks during the Permian. The age of the diagenetic muscovite was difficult to be estimated due to the difficulty of separating the effects of classical (i.e. burial-related) diagenesis and deformation. The newly-formed muscovite in the core zone has late Eocene age (c. 37 Ma) corresponding to the last activity of the PPVT. This results suggest that the GT which is the major thrust in the studied area started before c. 37 Ma and the PPVT moved around c. 37 Ma with its 0.8 km displacement transmitted to the GT to the south. This is consistent with previous dating results on the GT, with the possibility that it remained active later more to the west (Jaca basin).

Furthermore, the results of the present study demonstrate the validity of the muscovite 40 Ar/ 39 Ar CHAPTER 2 step-heating technique for dating thrust activity even in a complex tectonic geological conditions and with a limited number of samples. Hecho Group turbidites. The thermal conditions during shearing of these two thrusts are slightly lower compared to the PPVT, and moreover they are deformed by the major Gavarnie thrust. Thus, making them good candidates to test the validity of the 40 Ar/ 39 Ar step-heating method at lower temperature conditions compared to the PPVT. Furthermore, estimating the activity age of both Lakora and Monte Perdido thrusts may indirectly assists in the interpretation of the Gavarnie thrust activity age. Therefore, in the present study direct 40 Ar/ 39 Ar step-heating dating on synkinematic muscovite/illite was performed on different size fractions of samples from the Lakora and the Monte Perdido thrusts. Characterization of the mineralogy, texture, crystallinity and polytypes of phyllosilicates were performed by using XRD, optical microscope and SEM-EDX. In addition, determination of the deformation conditions of thrusting was achieved using the Kübler index method on synkinematic newly-formed muscovite/illite.

The petrographic results demonstrated that deformation is mainly marked by folding, boudinage, crenulation cleavages in the Lakora thrust and combination of intense cleavage, shear surfaces/veins in Torla. In both thrusts, pressure-solution and dissolution-recrystallization in presence of fluids are the main mechanisms that control the deformation and enhanced the enrichment of the newly-formed phyllosilicates in the fault zone. The XRD show that Fe-rich chlorite and abundant 2M 1 muscovite/illite with small amount of 1M polytype are the phyllosilicates minerals present in the two studied thrusts.

The newly-formed phyllosilicates are synkinematic to the fault activity and formed under diageneticanchizone conditions in Lakora, and upper-anchizone conditions in Torla based on the Kübler index values. These results demonstrate that the deformation gradient is slightly higher in Torla compared to the Lakora thrust. This indicates as well slightly lower deformation gradient in both thrust compared to the PPVT (upper anchizone-epizone).

For both thrusts, the 40 Ar/ 39 Ar step-heating results suggest that newly-formed muscovite is more abundant in the finer fractions as the total gas ages are inversely proportional to the grain-size. The 3.1. INTRODUCTION detrital muscovite/illite grains have a minimum age of c. 300.4 ± 1.5 Ma in the Lakora thrust, which probably derived from the low-grade metamorphic basement rocks (Hercynian basement). The finest fraction (< 0.5 µm) from the highly-deformed sample from the two thrust has the youngest total gas age of 73.5 ± 0.5 Ma (Lakora) and 75.8 ± 0.5 Ma (Monte Perdido). Comparison of these ages with previous geochronological studies from the same area suggests that these ages are very old for the activity of the Lakora and Monte Perdido thrusts. The stair-case shape spectra of the finest fractions indicates presence of more than one muscovite/illite generation and/or inhomogeneous chemical composition within the individual muscovite/illite grains. Moreover, the recorded peak temperature during shearing in the two thrusts is lower than the closure temperature of muscovite/illite in the dated size-fractions which indicate probably incomplete resetting during thrusting. Thus, those ages are mixed ages and don't represent the activity time of the two thrusts.

Introduction

As mentioned previously, dating the tectonic evolution and understanding the kinematic relationships in the Pyrenes orogen are not always straightforward and have been the subject of diverse interpretations (e.g. [START_REF] Fernández | 3D structure and evolution of an oblique system of relaying folds: the Ainsa basin (Spanish Pyrenees)[END_REF], Labaume et al., 2016[START_REF] Muñoz | Evolution of a continental collision belt: ECORS-Pyrenees crustal balanced cross-section[END_REF][START_REF] Teixell | The Ansó transect of the southern Pyrenees: basement and cover thrust geometries[END_REF]. Therefore, two thrust faults from the Pyrenees belt are the focus of this chapter in order to date their activity and to estimate their deformation mechanisms/conditions that are recorded by synkinematic phyllosilicate minerals in the two fault zones.

The two faults studied in this chapter are the Lakora thrust located on the southern edge of the North Pyrenean zone and the Monte Perdido thrust (at Torla location) in the NE of the South-Pyrenean Jaca Basin (Figure 3.1). These two thrust faults have been selected for the present study because (1) their thermal conditions during shearing are slightly lower compared to the PPVT activity [START_REF] Buatier | Microtextural investigation (SEM and TEM study) of phyllosilicates in a major thrust fault zone (Monte Perdido, southern Pyrenees): impact on fault reactivation[END_REF][START_REF] Grant | Post-emplacement extension within a thrust sheet from the central Pyrenees[END_REF], Grant et al., 1990[START_REF] Lacroix | Microtectonic and geochemical characterization of thrusting in a foreland basin: Example of the South-Pyrenean orogenic wedge (Spain)[END_REF], 2012, McCaig et al., 2000a), making them good candidates to test the validity of the 40 Ar/ 39 Ar step-heating method at lower temperature conditions, and (2) Estimating the activity age of both Lakora and Monte Perdido thrusts will improve the knowledge of the Pyrenean thrust sequence timing, including indirect assistance in the interpretation of the Gavarnie thrust activity age as the latter deformed the two thrusts (e.g. [START_REF] Bosch | Timing of Eocene-Miocene thrust activity in the Western Axial Zone and Chaînons Béarnais (westcentral Pyrenees) revealed by multi-method thermochronology[END_REF][START_REF] Fernández | 3D structure and evolution of an oblique system of relaying folds: the Ainsa basin (Spanish Pyrenees)[END_REF], Labaume et al., 2016[START_REF] Muñoz | Evolution of a continental collision belt: ECORS-Pyrenees crustal balanced cross-section[END_REF][START_REF] Teixell | Estructura alpina en la transversal de la termina-cion occidental de la Zona Axial pirenaica[END_REF][START_REF] Teixell | The Ansó transect of the southern Pyrenees: basement and cover thrust geometries[END_REF], Teixell et al., 2016). More details are given in the next section about the structural relationship between the Gavarnie thrust and the Lakora and Monte Perdido thrusts.

The phyllosilicates present in the fault zones of the two thrusts were investigated by XRD, optical microscopy, SEM in order to determine their mineralogy, texture, crystallinity, polytypes and their deformation conditions. Then, the 40 Ar/ 39 Ar step-heating on muscovite/illite was applied to different size-fractions of representative samples from the two thrust. Finally, the ages obtained in the present study are discussed with available data from the same areas to evaluate and understand their geological significance.

Geological setting

The location of the Lakora and Monte Perdido thrusts is shown in Figure 3.1. The Lakora thrust is located on the southern edge of the North Pyrenean Zone. The thrust is a result from inversion of the North Pyrenean extensional basin margin and is named after the classic locality at Pico Lakora (Lakhoura), where an isolated klippe of the thrust sheet was firstly recognized by [START_REF] Fournier | Études géologiques sur la partie occidentale de la chaîne des Pyrénées entre la vallée d'Aspe et celle de la Nive[END_REF].

This klippe contains a thin piece of Paleozoic basement (Iguntze massif) and overlying Cretaceous conglomerates. The North-Pyrenean detachment begun to propagate into its foreland as the Lakora thrust across Upper Cretaceous-Eocene rocks of the Axial Zone cover and northern part of the Jaca basin which form the thrust footwall, as shown in Figure 3.2a [START_REF] Teixell | Stress and fluid control on décollement within competent limestone[END_REF]. Then, the Larra thrust formed as a footwall splay of the Lakora thrust during the Middle Eocene [START_REF] Teixell | Estructura alpina en la transversal de la termina-cion occidental de la Zona Axial pirenaica[END_REF]. According to Teixell (1996) the Lakora thrust was probably initiated in the Early Eocene, as indicated by flexure in its footwall sediments, and its main activity continued until the middle Eocene (Bartonian). The major Gavarnie thrust and the associated Axial Zone antiform deformed both the Lakora and Larra thrusts suggesting that the Gavarnie thrust is younger in age.

The second fault studied is the Monte Perdido thrust fault on the Torla outcrop (Figure 3.1), located in the north-eastern part of the Jaca Basin. Above the Triassic decollement level, the stratigraphy of the Jaca basin comprises Cenomanian to Santonian limestones followed by the Cretaceous-Paleogene synorogenic succession that includes: Campanian to earliest Eocene platform carbonates, the Ypresian-Lutetian siliciclastic turbidites of the Hecho Group, Bartonian to Lower Oligocene coastal, and continental deposits (Figure 3.2b). At the northern edge of the Jaca basin, the Triassic evaporites are absent and the Cretaceous limestones rest directly on the Paleozoic basement of the Axial Zone. The Monte Perdido thrust is uplifted and folded by the hanging wall culmination of the Gavarnie basement thrust in the Jaca Basin suggesting as well that Gavarnie is younger [START_REF] Séguret | Etude tectonique des nappes et séries décollées de la partie centrale du versant sud des Pyrénées: caractère synsédimentaire, rôle de la compression et de la gravité[END_REF]. According to [START_REF] Teixell | The Ansó transect of the southern Pyrenees: basement and cover thrust geometries[END_REF], the Monte Perdido thrust system is analogous to the Larra thrust that is deep rooted northward in the Lakora thrust. As the Lakora thrust branches laterally eastward with the Eaux Chaudes basement thrust, 101 3.3. OUTCROPS DESCRIPTION AND SAMPLING CHAPTER 3 [START_REF] Jolivet | Thermochronology constraints for the propagation sequence of the south Pyrenean basement thrust system (France-Spain)[END_REF] suggested that the Monte Perdido thrust roots within the Lakora-Eaux Chaudes thrust system. The Monte Perdido thrust activity is dated from the latest Lutetian to earliest Priabonian (about c. 47-37 Ma) by the syntectonic deposition of the latest Hecho Group turbidites [START_REF] Teixell | The Ansó transect of the southern Pyrenees: basement and cover thrust geometries[END_REF]. This indicates close ages for both the Lakora and the Monte Perdido thrusting.

Outcrops description and sampling

Lakora outcrop

The hanging wall of the Lakora thrust is composed of Albian to Santonian (110-84 Ma) breccias and conglomerates resting of Paleozoic metasediments, while the footwall is made of Campanian-Maastrichtian (84-66 Ma) turbidites (Figure 3.3a and b). The latter display evidences of deformation marked by cleavage, folding, boudinage structures and shear zones. However the contact between the hanging wall breccias and footwall turbidites is not well exposed at the outcrop. Several samples have been collected from the footwall turbidites, a few meters below the main contact and were investigated by XRD, optical microscopy and SEM-EDX. Two representative samples have been selected for the 40 Ar/ 39 Ar step-heating dating: sample 15 LAK 3 from a highly-deformed shear zone and sample 15 LAK 1 collected from a less-deformed area.

Torla outcrop

The Torla outcrop is located at the north-eastern edge of the Jaca thrust sheet-top basin and exposes the sole thrust of the Monte Perdido thrust system. In the studied outcrop (Figure 3.4a and b), the footwall comprises Ypresian (56-49 Ma) Hecho Group turbidites (alternating sandstone and pelite layers) of the Gavarnie thrust unit. Whereas, the hanging wall is composed of Paleocene (65-56 Ma) Alveolina limestone (Torla 1 outcrop) and the lower Ypresian Millaris marls ∼ 70 m more to the south (Torla 2 outcrop). In the present study we focus on the Torla 1 outcrop where the fault core zone ∼ 6 m thick, consists of intensely deformed clay-bearing rocks bounded by major shear surfaces [START_REF] Buatier | Microtextural investigation (SEM and TEM study) of phyllosilicates in a major thrust fault zone (Monte Perdido, southern Pyrenees): impact on fault reactivation[END_REF], Lacroix et al., 2011) (Figure 3.4b). The presence of sandstone lenses allows the identification of the footwall turbidites as the protolith of the fault rock. The fault zone rocks is characterized by a darker color compared to the protolith and displays an intense cleavage and abundant calcite-quartz shear veins. In the hanging wall, the deformation in the limestone is marked by stylolites and calcite veins while in the footwall, the turbidites are deformed by cm to m-scale south-vergent folds associated with local shear surfaces and north-dipping axial plane cleavage [START_REF] Lacroix | Microtectonic and geochemical characterization of thrusting in a foreland basin: Example of the South-Pyrenean orogenic wedge (Spain)[END_REF]. Based on previous microstructural investigations on the same outcrop [START_REF] Buatier | Microtextural investigation (SEM and TEM study) of phyllosilicates in a major thrust fault zone (Monte Perdido, southern Pyrenees): impact on fault reactivation[END_REF][START_REF] Lacroix | Microtectonic and geochemical characterization of thrusting in a foreland basin: Example of the South-Pyrenean orogenic wedge (Spain)[END_REF], 2013), one representative sample from the core fault zone and one from the footwall turbidites have been

Methodolgy

Petrographic and textural observations

The samples (polished thin-sections) were characterized first by optical microscopy at the UMR 6249 Chrono-environnement laboratory (Université de Bourgogne Franche-Comté). Then the analyses by Scanning Electron Microscopy (SEM) were performed at the FEMTO-ST Institute (Université de Bourgogne Franche-Comté). Microstructures and mineral assemblages were analyzed with a JEOL JSM5600 (SEM) equipped with Secondary Electron (SEI), backscatter electron (BSE) and Energy Dispersive X-ray Spectroscopy (EDX) detectors.

Bulk composition, phyllosilicates mineralogy and polytype characterization

The samples were analyzed at ITINAM laboratory (Université de Bourgogne Franche-Comté) by using a Bruker D8 Advance diffractometer system, Cu-Kα radiation equipped with a fast LynxEye linear detector. Samples were hand ground to < 50 µm and the < 16 µm fraction obtained by sedimentation was submitted to ultra-centrifugation in order to extract the < 2 and < 0.5 µm fractions. For the bulk compositions characterizations, the X-ray diffractograms of the random powder mounts, were acquired between 5 and 70 • 2θ at a step size of 0.02, a number of steps 3450, a time/step 1 s at 40 kV and 40 mA. For the 16-2 µm, 2-0.5 and < 0.5 µm fractions, the oriented specimens on a glass slides were analyzed in air dried conditions between 5 and 30 • 2θ at a step size of 0.01, a number of steps 2228 and time/step 0.5 s. No expandable or interstratified minerals were found confirmed by ethylene-glycol saturation and after heating at 550 • C. The Fityk software© v0.9.8 [START_REF] Wojdyr | Fityk: a general-purpose peak fitting program[END_REF] was used for the decomposition of overlapped peaks to get better identification of the different components. For mica polytypes determination, the X-ray diffractograms of random powder mounts were acquired between 20 and 32 • 2θ at a step size of 0.02, a number of steps 3450, a time/step 1 s at 40 kV and 40 mA.

Kübler index (KI) calculation

The Kübler Index (KI) was measured on muscovite 001 reflection at around 10 Å in oriented preparations (< 2 µm) fractions to determine the metamorphic grade conditions. Interlaboratory variations have been reduced by following the recommendations of [START_REF] Kisch | Illite crystallinity: recommendations on sample preparation, X-ray diffraction settings, and interlaboratory samples[END_REF] and using the widely applied standardized Crystallinity Index Scale (CIS) procedure recommendations for measurements. The calibration of the crystallinity results to CIS scale was achieved by measuring the crystallinity of the 104 CHAPTER 3 3.5. RESULTS four standards proposed by [START_REF] Warr | Interlaboratory standardization and calibration of day mineral crystallinity and crystallite size data[END_REF]. Our measurements (y) were transformed into CIS values (x) according to the equation: y = 0.6574 x + 0.0082, (R² = 0.9993). The evaluation of metamorphic conditions boundaries was performed by using the boundaries of the anchizone originally defined by [START_REF] Kübler | La cristallinité de l'illite et les zones tout a fait superieures du métamorphisme. étages tectoniques[END_REF] at 0.25 • 2θ and 0.42 • 2θ. In order to be compatible with the original anchizone boundaries of [START_REF] Kübler | La cristallinité de l'illite et les zones tout a fait superieures du métamorphisme. étages tectoniques[END_REF], the CIS values were calibrated to the traditional Kübler-Kisch scale by using the equation: Kübler Index(CIS) = 1.1523 * Kübler Index (Basel lab) + 0.036 which is presented in the Figure 1 of [START_REF] Warr | Recommendations for Kübler index standardization[END_REF].

40 Ar/ 39 Ar step-heating

Samples preparation for the 40 Ar/ 39 Ar step-heating method was performed without any chemical treatment to avoid any impact on the structure of the phyllosilicates. The bulk , 50-16 µm, 16-2 µm, 2-0.5 and < 0.5 fractions of two samples from the Lakora and Torla outcrops (15 LAK 1, 15 LAK 3, 15 TO 1 and 15 TO 4) have been compacted mechanically and about 1 to 2 mg of these fractions were encapsulated in quartz tubes at 10-8 bar. Thus, the recoil 39 Ar which is expelled from the crystal structure of the grains during irradiation is retained for the analysis [START_REF] Dong | Mechanisms of argon retention in clays revealed by laser 40 Ar-39 Ar dating[END_REF]. The samples were then irradiated for 40 hours in the core of the Triga Mark II nuclear reactor of Pavia (Italy) with several aliquots of the Taylor Creek sanidine standard (c. 28.34 ± 0.10 Ma) as flux monitor.

Argon isotopic interferences on K and Ca were determined by irradiation of KF and CaF 2 pure salts.

Atmospheric 40 Ar was estimated using a value of the initial 40 Ar/ 39 Ar ration of 295.5. Argon analyses were performed at Géosciences Montpellier (France) with an analytical system that consists of: (a) a UV laser used to pierce the quartz tubes and an infra-red laser for the step-heating experiments, (b) a lenses system for UV beam focusing, (c) a steel sample chamber, maintained at 10-8 -10-9 bar, with a drilled copper plate and 5 tubes, (d) an inlet line for purification of gases including two Zr-Al getters, (e) a multi-collector mass spectrometer (Argus VI from Thermo-Fisher). A custom-made software was used to control the laser intensity, the timing of extraction/purification and the data acquisition. The ArArCalc software© v2.5.2 was used for data reduction and plotting.

Results

The petrographic observations, phyllosilicates textural/composition characterizations were investigated by Rafia Nazir during an associated master project. Several samples along the footwall turbidities of the Lakora thrust have been studied and the results of some representative samples are presented below. Based on these results, two representative samples (15 LAK 1 and 15 LAK 3) have been dated by 3.5. RESULTS CHAPTER 3 the 40 Ar/ 39 Ar step-heating technique and the result are presented below.

In case of the Torla outcrop, summary of the petrographic-microstructures results and the phyllosilicates characterizations that have been previously done by [START_REF] Buatier | Microtextural investigation (SEM and TEM study) of phyllosilicates in a major thrust fault zone (Monte Perdido, southern Pyrenees): impact on fault reactivation[END_REF], [START_REF] Lacroix | Microtectonic and geochemical characterization of thrusting in a foreland basin: Example of the South-Pyrenean orogenic wedge (Spain)[END_REF][START_REF] Lacroix | Formation of chlorite during thrust fault reactivation. Record of fluid origin and P-T conditions in the Monte Perdido thrust fault (southern Pyrenees)[END_REF][START_REF] Lacroix | Weakening processes in thrust faults: insights from the Monte Perdido thrust fault (southern Pyrenees, Spain)[END_REF] are presented in the following section. Based on these results, two samples (15 TO 1 and 15 TO 4) were selected and have been characterized by XRD and then Kübler index calculations have been performed to estimate the deformation conditions. As the 40 Ar/ 39 Ar step-heating experiments for these two samples are still in progress, the age spectra of only the three finest fractions of the sample 15 TO 1(from the fault core zone) are presented in the results part. While the results of the rest of the fractions of this sample + the fractions of other sample will be latterly added.

Lakora thrust

Bulk composition and phyllosilicates mineralogy

The XRD results of the bulk powder of five representative samples (15 LAK 1,3,4,6,and 9) are presented in Figure 3.5. The results show that all the samples from the footwall turbidites have similar mineralogical assemblages composed of quartz, K-white mica, chlorite, albite and rutile. Calcite is present only the samples 15 LAK 4, 6, and 9. The 060 reflections at 1.50 Å and 1.55 Å correspond to di-octahedral phyllosilicate phase (muscovite/illite) and tri-octahedral phase (chlorite) respectively. The oriented preparations of the fractions 16-2 µm, 2-0.5 µm and < 0.5 µm of the samples 15 LAK 1 and 15 LAK 3 confirmed that muscovite/illite and chlorite are present in all the fractions (Figure 3.6).

The muscovite/illite is characterized by reflections at 10.02 Å, 5.00 Å and 3.33 Å corresponding to 001, 002, and 003 basal reflections respectively. Reflections at 14.16 Å, 7.08 Å, 4.73 Å and 3.54 Å are corresponding to 001, 002, 003 and 004 reflections of chlorite. The 002 and 004 reflections of chlorite are more intense compared to 001 and 003 reflections suggesting that it is Fe-rich chlorite (Brown 107 3.5. RESULTS CHAPTER 3 andBrindley, 1980, Moore and[START_REF] Moore | X-ray Diffraction and the Identification and Analysis of Clay Minerals[END_REF]. There is enrichment in muscovite/illite in the finest fraction (< 0.5 µm) which is marked by increment in its reflections peaks intensity. On both 15 LAK 1 and 15 LAK 3 samples, the 001 reflection peak of muscovite shows asymmetrical peak shape with a small shoulder on the low angle side of the diffractograms that suggests a peak overlapping between more than one mica component. This shoulder is broader in case of the sample 15 LAK 1 reflecting probably the presence of more mica phases compared to the other sample. Moreover, beside chlorite and muscovite/illite, the XRD patterns show the presence of quartz and a small amount of rutile and albite in the16-2 µm, 2-0.5 µm and < 0.5 µm fractions.

Microstructures and petrography

The results of two representative samples (15 LAK 1 and 15 LAK 3) from the footwall turbidites of the Lakora thrust are presented in this part. The microstructural and textural differences observed between these two samples are shown in Figure 3. The BSE images for the 15 LAK 1(less-deformed sample) and 15 LAK (highly-deformed sample) are presented in Figure 3.8. In the less-deformed sample, quartz, chlorite and muscovite/illite are elongated and have preferential orientation parallel to S 0 /S 1 direction (Figure 3.8a). Moreover, two generations of chlorite and muscovite/illite are identified in this sample: a detrital one with large grain-size (∼ 50 µm) that is parallel to S 0 /S 1 and a newly-formed one characterized by smaller grain-size (< 5 µm) (Figure 3.8c and e). The newly-formed phyllosilicates probably result from dissolution-alteration of old detrital feldspars and/or micas. The preferential orientation and the sigmoidal shape of the large chlorite grains (Figure 3.8c) suggest a pressure solution mechanism affecting these turbidites.

Chlorite/mica stacks that are observed in the matrix of this sample are typical of diagenetic origin (e.g. 108 CHAPTER 3 3.5. RESULTS [START_REF] Jiang | Formation of corrensite, chlorite and chlorite-mica stacks by replacement of detrital biotite in low-grade pelitic rocks[END_REF][START_REF] Milodowski | The origin and sedimentary, diagenetic and metamorphic evolution of chlorite-mica stacks in Llandovery sediments of central Wales[END_REF][START_REF] Randive | Paragenesis of Cr-rich muscovite and chlorite in green-mica quartzites of Saigaon-Palasgaon area, Western Bastar Craton, India[END_REF].

In the highly-deformed sample, the two cleavage plans can be clearly observed in its matrix (Figure 3.8b). The detrital chlorite grains are strongly deformed and folded compared to chlorite present in the less-deformed sample (Figure 3.8d). In addition, deformation is coeval with enrichment in newly

Characterization of muscovite crystallinity and polytypes

As mentioned above, the muscovite/illite 001 reflection has asymmetrical peak shape with a small shoulder on the low angle side of the diffractograms, therefore decomposition for this peak was done CHAPTER 3 3.5. RESULTS These two components correspond to two mica phases. Moreover, the WC phase has more intense peak compared to the less-deformed sample which suggests the presence of higher proportion of well-crystallized mica in the highly-deformed sample. The XRD diffractograms (20-32 • 2θ) of the randomly oriented preparations of bulk powder and < 2 µm fraction of the two samples are shown in Figure 3.11. On both samples, the results indicate that the 2M 1 muscovite/illite is the abundant polytype with relatively small amount of 1M confirmed from their peaks intensity ratio. The 1M d polytype is not present in the samples as no hump shape was observed at the 003 muscovite reflection position which is a characteristic of 1M d mica polytype.

In the < 2 µm fraction, the 2M 1 reflections are more intense compared to the 1M suggesting that the newly formed muscovite can be of the 2M 1 and not only 1M.

The Kübler index (KI) calculations of the 001 muscovite reflection for five representative samples are presented in Table 3.1. The samples have a Kübler index values range from 0.31 • 2θ to 0.49 • 2θ (Kübler-Kisch scale) correspond to diagenetic to anchizone grade conditions. The less-deformed sample (15 LAK 1) has the highest KI value of 0.49 • 2θ (Kübler-Kisch scale) corresponds to diagenetic conditions while the highly-deformed sample (15 LAK 3) has the lowest value of 0.31 • 2θ that indicates upperanchizone conditions. This based on the anchizone boundaries of 0.25 • 2θ to 0.42 • 2θ and 0.335 • 2θ as a limit between upper and lower anchizone on the KF scale (Kübler, 1967, Warr andFerreiro Mählmann, 113 3.5. RESULTS CHAPTER 3 2015). These results are consistent with the petrographic observations that suggest high deformation gradient for the 15 LAK 3 sample.

Table 3.1: The FWHM (raw data), the calibrated KI (CIS), KI (Basel lab) values in • 2θ and the corresponding crystallinity zones of the Lakora and Torla samples.

40 Ar/ 39 Ar step-heating data

Step-heating experiments were performed on the bulk and on the fractions 50-16 µm, 16-2 µm, 2-0.5 µm and < 0.5 µm of both 15 LAK 1 and 15 LAK 3 samples. Summary of the calculated ages are presented in Table 3.2 and a complete isotopic data is presented in Appendix B. The age spectra are shown in Figure 3.12 and they are corrected from 39 Ar recoil effects through adding the recoil fractions at the first step on the spectra with a zero age. We determine the age of the various muscovite/illite fractions by using the total gas age (including 39 Ar recoil) rather than retention age (excluding 39 Ar recoil), due to the high amount of 39 Ar recoil that can reach ∼ 23% in the finer fractions of the samples.

(i) Sample 15 LAK 1 (less deformed)

The bulk, 50-16 µm fraction and the 16-2 µm fractions of this sample produced spectra with three distinct segments: a hump shaped profile for the low temperature steps followed by a staircase profile with steadily climbing apparent ages at intermediate temperatures and a peak-like at higher temperatures (Figure 3.12). This indicates a mixing of muscovite/illite generations with different ages and different Ar retentivity. By contrast the spectra of the fine fractions (2-0.5 and < 0.5 µm) have a relatively a flat shape for the last part of the degassing experiment. The maximum age which is reached during the step-heating experiments decreases with decreasing the grain-size and ranges between c. 300.4 ± 1.5 Ma (50-16 µm) to c. 124.6 ± 2.2 Ma (< 0.5 µm fraction). The total gas age is also directly proportional to the grain-size and decreases from c. 136.1 ± 0.8 Ma (50-16 µm) to c. 82.0 ± 0.5 114 CHAPTER 3 3.5. RESULTS Ma (< 0.5 µm fraction). In addition, the amount of 39 Ar recoil increases as well when decreasing the grain-size, the finest fraction (< 0.5 µm) has the highest value of 19.9% of the total 39 Ar (Table 3.2).

Figure 3.12: 40 Ar/ 39 Ar step-heating results of Lakora samples, 15 LAK 1(in blue color) and 15 LAK 3 (in brown color).The results show the age spectra for the bulk powder, 50-16 µm, 16-2 µm, 2-0.5 µm and < 0.5 µm fractions respectively. TGA refers to total gas age.

RESULTS

CHAPTER 3 (ii) Sample 15 LAK 3 (highly deformed)

In a similar way to the less-deformed sample, the bulk and the coarse fractions of the highly-deformed sample produced staircase shaped spectra (Figure 3.10). The fine fractions 2-0.5 µm and < 0.5 µm also display relatively flat spectra for the high temperature steps. The maximum age ranges between c. 272.3 ± 1.6 Ma (16-2 µm fraction) to c. 114.6 ± 1.3 Ma (< 0.5 µm fraction). The total gas age range between c. 126.7 ± 1.1 Ma (16-2 µm fraction) to c. 73.5 ± 0.5 Ma (< 0.5 µm fraction). The < 0.5 µm fraction experienced the highest amount of 39 Ar recoil compared to the coarser fractions with a value of 23.3% (Table 3.2).

Table 3.2 Summary of the 40 Ar/ 39 Ar step-heating data of the Lakora and Torla samples.

These results show that the finer fractions for both samples have younger total gas ages compared to the coarser fractions. Moreover, all the fractions from the highly-deformed sample (15 LAK 3) have younger ages compared to the same fractions from the less-deformed sample (15 LAK 1). Finally the finest fraction (< 0.5 µm) in the highly-deformed sample has the youngest ages compared to all the fractions from both samples. These results are consistent with the petrographic observations that suggest higher deformation and presence of more authigenic muscovite/illite in the highly-deformed sample and are consistent with the general observation that deformation plays a major role on the resetting of K-Ar chronometers.

Torla outcrop

Summary of previous results

Several studies have been focused on the Monte Perdido thrust fault (Torla outcrop). The macro and microstructures related to the fault activity were described in details by [START_REF] Lacroix | Microtectonic and geochemical characterization of thrusting in a foreland basin: Example of the South-Pyrenean orogenic wedge (Spain)[END_REF], deformation mechanisms in the thrust presented by [START_REF] Lacroix | Weakening processes in thrust faults: insights from the Monte Perdido thrust fault (southern Pyrenees, Spain)[END_REF], temperature and burial conditions were evaluated by [START_REF] Lacroix | Formation of chlorite during thrust fault reactivation. Record of fluid origin and P-T conditions in the Monte Perdido thrust fault (southern Pyrenees)[END_REF], while origin and behavior of phyllosilicates in fault zones were studied by [START_REF] Buatier | Microtextural investigation (SEM and TEM study) of phyllosilicates in a major thrust fault zone (Monte Perdido, southern Pyrenees): impact on fault reactivation[END_REF]. At the macroscopic scale, the deformation of the phyllosilicate-rich sediments in the fault core zone (∼ 6 m thick) is marked by the combination of intense cleavage and shear surfaces forming Shear-Cleavage (S-C) networks [START_REF] Lacroix | Microtectonic and geochemical characterization of thrusting in a foreland basin: Example of the South-Pyrenean orogenic wedge (Spain)[END_REF].

Calcite-quartz-chlorite shear veins along the shear planes are abundant. The cleavage orientation, the asymmetry of S-C structures and steps along shear vein striations all indicate a top to the S-SW displacement. Moreover, in the hanging wall Alveolina limestones, the deformation is marked by stylolites and calcite extension veins. The footwall turbidites are deformed as well by cm-to m-scale asymmetric, south-vergent folds with north-dipping axial plane cleavage. Calcite extension veins are also present and crosscut the cleavage. In the fault core zone, the pervasive pressure solution cleavage associated with shear and extension calcite-quartz veins are the main characteristics for the deformation [START_REF] Lacroix | Weakening processes in thrust faults: insights from the Monte Perdido thrust fault (southern Pyrenees, Spain)[END_REF]. These deformation characteristics together with the crack-seal mechanism of the veins opening and the mechanical reorientation of the grains indicate a slow and aseismic deformation mechanism for thrusting with several stages of deformation. [START_REF] Lacroix | Microtectonic and geochemical characterization of thrusting in a foreland basin: Example of the South-Pyrenean orogenic wedge (Spain)[END_REF][START_REF] Lacroix | Formation of chlorite during thrust fault reactivation. Record of fluid origin and P-T conditions in the Monte Perdido thrust fault (southern Pyrenees)[END_REF] suggested two stages of deformation; a first stage related to the Monte Perdido unit emplacement associated to the formation of SV1 calcite-quartz-chlorite shear veins at a temperature of about 210 • C (chlorite thermometry). While a second deformation episode corresponds to a fault reactivation associated to the development of the chlorite shear veins in highly foliated phyllosilicates-rich core zone at about 240 • C (chlorite thermometry). Moreover, they suggested temperature conditions of 234 • C to 265 • C based on stable isotope thermometry with a burial depth of 6.5 km.

According to the study of [START_REF] Buatier | Microtextural investigation (SEM and TEM study) of phyllosilicates in a major thrust fault zone (Monte Perdido, southern Pyrenees): impact on fault reactivation[END_REF] that is based on detailed SEM and TEM observations on highly-deformed samples from the fault zone, the phyllosilicate enrichment in the core zone of the fault is not only related to passive increase by pressure-solution mechanism but also to dissolution-117 3.5. RESULTS CHAPTER 3 recrystallization during deformation. In addition, the newly formed muscovite/illite in the matrix and chlorite crystals that fill shear veins suggest a syntectonic growth of phyllosilicates in the presence of fluids. These authors show that most of muscovite/illite particles are preferentially oriented along the cleavage and locally in quartz pressure shadows and some grains with a different orientation are also present. The muscovite/illite grains are not deformed by the quartz grains and they display well defined grain boundaries. Consequently, they concluded that muscovite/illite are authigenic and precipitated in the open spaces created by the increase of normal stress at the quartz mica interface during burial. Furthermore, they demonstrated that muscovite /illite 2M 1 polytype is the dominant mica phase but a small proportion of 1M polytype is also present in all the samples based on Rietveld quantification performed on the < 2 µm fraction (random-oriented powders). Detrital chlorite-muscovite aggregates of various size, sometimes accumulated along pressure-solution surfaces as an insoluble residue were also found in these samples.

X-ray diffraction

In the present study, oriented preparations for the fractions 16-2 µm, 2-0.5 µm and < 0.5 µm of the samples 15 TO 1 (core zone) and 15 TO 4 (10 m away from fault contact) were performed and are presented in Figure 3.13. The results show the presence of muscovite/illite and chlorite in all the fractions of both samples. Quartz, calcite, rutile and albite are also associated with the phyllosilicates in these fractions and their quantities decrease with decreasing the grain-size. On contrary, there is enrichment of chlorite and muscovite in the fine fractions (< 0.5 µm) as indicated by the increment of their peak intensity. The 002 and 004 reflections of chlorite are more intense compared to 001 and 003 reflections suggesting the occurrence of Fe-rich chlorite [START_REF] Brown | Crystal structures of clay minerals and their X-ray identification[END_REF]Brindley, 1980, Moore and[START_REF] Moore | X-ray Diffraction and the Identification and Analysis of Clay Minerals[END_REF].

The decomposition of 001 muscovite/illite peak (< 0.5 µm fraction) of both samples are shown in Figure 3.14, the results suggest the presence of two muscovite/illite components. The two Gaussian peaks at 10.03 Å correspond to a well-crystallized (WC) muscovite/illite in both samples, while the

CHAPTER 3

Gaussian peaks at 10.16 Å and 10.19 Å correspond to a poorly-crystallized (PC) muscovite/illite in the 15 TO 1 and 15 TO 4 samples respectively. The peaks intensity ratio of WC/PC is higher in the core zone sample (15 TO 1) indicating a higher proportion of WC muscovite/illite compared to the other sample.

40 Ar/ 39 Ar step-heating data

Step-heating experiments were performed on the 6-2 µm, 2-0.5 µm and < 0.5 µm fractions of the sample 15 TO 1 (core zone; 10 cm from the limestone contact). Summary of the calculated ages are presented in Table 3.2, a complete isotopic data is presented in Appendix B and the age spectra are shown in Figure 3.15.

All the three fractions produced spectra with staircase shaped that reflect the degassing of different argon reservoirs with different ages with a major contribution of muscovite/illite to the argon budget as indicated by the X-ray data. The maximum age ranges between c.230.9± 0.9 Ma (16-2 µm fraction) to c. 120.1 ± 0.7 Ma (< 0.5 µm fraction). The total gas age decrease with grain-size and it ranges between c.116.3 ± 0.9 Ma (16-2 µm fraction) to c. 75.8 ± 0.5 Ma (< 0.5 µm fraction). The < 0.5 µm fraction experienced the highest amount of 39 Ar recoil with a value of 11% (Table 3.2).

Discussion

Mineralogy, petrography and texture interpretations

In both Lakora and Torla samples, the XRD results suggest similar bulk mineralogy composed of quartz, muscovite/illite, Fe-rich chlorite, rutile, albite, and ± calcite. As the 002 and 004 chlorite reflections are more intense in case of the Torla samples compared to the Lakora ones, this suggests that chlorite is more Fe-rich in the former thrust [START_REF] Brown | Crystal structures of clay minerals and their X-ray identification[END_REF]Brindley, 1980, Moore and[START_REF] Moore | X-ray Diffraction and the Identification and Analysis of Clay Minerals[END_REF]. The data indicate also that muscovite/illite is typically of 2M 1 polytype with a small amount of 1M polytype confirmed from their reflections peak intensity.

The structural and microstructural observations show that deformation is marked by folding, boudinage, combination of intense cleavage, shear surfaces and enrichment of phyllosilicates in the core zone of both thrusts. The pressure-solution and dissolution-recrystallization in the presence of fluids are the main mechanisms that control the deformation and enhanced the enrichment of the newlyformed phyllosilicates in both fault zone. These mechanisms are marked by the elongation of the grains, dissolution of quartz and detrital feldspars/micas and formation of newly formed phyllosilicates in pressure shadow areas. The same mechanisms were described in our previous study of the Pic de Port Vieux [START_REF] Abd Elmola | Textural-chemical changes and deformation conditions registered by phyllosilicates in a fault zone (Pic de Port Vieux thrust, Pyrenees)[END_REF]. Similarly, in active faults of the Western Alps and San Andreas, [START_REF] Gratier | Geological control of the partitioning between seismic and aseismic sliding behaviours in active faults: Evidence from the Western Alps, France[END_REF] and [START_REF] Janssen | Microstructures and their implications for faulting processes -Insights from DGLab core samples from the Gulf of Corinth[END_REF] suggested the same mechanisms through dissolution of soluble minerals (feldspars, quartz and calcite) and passive concentration of phyllosilicates in the presence of fluids.

In both Lakora and Torla samples, detrital muscovite/illite and chlorite aggregates are present, similar aggregates were described by [START_REF] Bauluz | Evolución Diagenética de las Turbiditas del Grupo Hecho (Eoceno) en la Cuenca de Jaca (España)[END_REF] in the Hecho Group turbidites further south in the Jaca basin. The newly-formed muscovite/illite and chlorite are located along cleavage in the matrix of the Lakora samples. Likewise, in the Torla samples, muscovite/illite is present in the matrix, while chlorite is mainly located in shear veins [START_REF] Buatier | Microtextural investigation (SEM and TEM study) of phyllosilicates in a major thrust fault zone (Monte Perdido, southern Pyrenees): impact on fault reactivation[END_REF][START_REF] Lacroix | Formation of chlorite during thrust fault reactivation. Record of fluid origin and P-T conditions in the Monte Perdido thrust fault (southern Pyrenees)[END_REF]. These results indicate that the formation of newly-formed phyllosilicates in both thrusts are synkinematic to the fault activity and are attributed to deformation and fluid circulation. Thus, their crystallinity, chemical and isotopic compositions can be used to estimate the deformation conditions and tentatively date the fault activity in both thrusts.

Deformation conditions of thrusting

The pressure solution mechanism, folding, elongation of the grains and crack-seal mechanism of shear vein formation suggest ductile, aseismic and slow rate deformations mechanisms in the Lakora and Torla thrusts (e.g. [START_REF] Gratier | Transition between seismic and aseismic deformation in the upper crust[END_REF][START_REF] Gratier | Aseismic sliding of active faults by pressure solution creep: Evidence from the San Andreas Fault Observatory at Depth[END_REF][START_REF] Lacroix | Microtectonic and geochemical characterization of thrusting in a foreland basin: Example of the South-Pyrenean orogenic wedge (Spain)[END_REF][START_REF] Renard | Kinetics of crack-sealing, intergranular pressure solution, and compaction around active faults[END_REF]. The Kübler index values of muscovite/illite suggest upper-anchizone conditions for the fault activity in both thrusts. This is based on the KI values of the highly-deformed samples from each thrust which is slightly higher in Torla, that reflect relatively higher deformation grade for the Monte Perdido thrust compared to the Lakora thrust. Moreover, the KI values of the less-deformed samples are higher in Torla (upper-anchizone conditions) compared to diagenetic conditions of the Lakora samples. In agreement with these conditions, chlorite/mica stacks that are typical of diagenesis were observed in the Lakora thrust host rocks. These stacks have been commonly described in sediments that have undergone diagenesis and low-grade metamorphism (e.g. [START_REF] Bartier | Lithological control on the occurrence of chlorite in the diagenetic Wealden complex of the Bilbao anticlinorium (Basco-Cantabrian Basin, Northern Spain)[END_REF][START_REF] Jiang | Formation of corrensite, chlorite and chlorite-mica stacks by replacement of detrital biotite in low-grade pelitic rocks[END_REF][START_REF] Li | TEM and AEM constraints on the origin and significance of chlorite-mica stacks in slates: an example from Central Wales[END_REF][START_REF] Milodowski | The origin and sedimentary, diagenetic and metamorphic evolution of chlorite-mica stacks in Llandovery sediments of central Wales[END_REF][START_REF] Randive | Paragenesis of Cr-rich muscovite and chlorite in green-mica quartzites of Saigaon-Palasgaon area, Western Bastar Craton, India[END_REF].According to these authors, the stacks are formed by alteration of detrital biotite into chlorite through a layer-by-layer transformation and then muscovite progressively fills the chlorite cleavages. Furthermore, the presence of newlyformed 2M 1 and 1M muscovite/illite in both thrusts suggests that their formation in the fault zones are related to two different stages of fault activities. This is because the two polytype have different growth temperature [START_REF] Srodo Ń | Nature of mixed-layer clays and mechanisms of their formation and alteration[END_REF]Eberl, 1984, Velde, 1965), therefore the 1M polytype is probably related to a low-temperature event before or during the fault activity. This is consistent with the interpretations of [START_REF] Lacroix | Microtectonic and geochemical characterization of thrusting in a foreland basin: Example of the South-Pyrenean orogenic wedge (Spain)[END_REF][START_REF] Lacroix | Formation of chlorite during thrust fault reactivation. Record of fluid origin and P-T conditions in the Monte Perdido thrust fault (southern Pyrenees)[END_REF][START_REF] Lacroix | Weakening processes in thrust faults: insights from the Monte Perdido thrust fault (southern Pyrenees, Spain)[END_REF] on Torla outcrop, where they proposed two stages of deformations during the activity of Monte Perdido thrust.

40 Ar/ 39 Ar step-heating data

As mentioned above, the majority of the newly-formed muscovite/illite in the two studied thrusts are 2M 1 polytype (confirmed by XRD and TEM results). Moreover, the decomposition of the XRD peak for the 001 muscovite reflection (in the finest fraction) indicates the coexistence of well-crystallized (WC) muscovite/illite with a poorly-crystallized muscovite (PC) in both thrusts. The WC and PC phases are probably corresponding to the newly-formed 2M 1 and 1M muscovite/illite respectively. This preclude the use of the polytype-age correlation method in the present study (e.g. [START_REF] Van Der Pluijm | The dating of shallow faults in the Earth's crust[END_REF] since in this method the 2M 1 is assumed to be a detrital in origin. However the petrographic and textural observations suggest that a discrimination between the different muscovite/illite generations is possible through their grain-size (e.g. [START_REF] Van Der Pluijm | The dating of shallow faults in the Earth's crust[END_REF][START_REF] Van Der Pluijm | Fault dating in the Canadian Rocky Mountains: Evidence for late Cretaceous and early Eocene orogenic pulses[END_REF]. As the detrital muscovite/illite grains have a larger grain-size than the newly-formed ones, hence the coarse fractions should have older ages compared to the fine fractions. Therefore our strategy was to compare the behavior of argon in different granulometric fractions and to discuss the results with respect to deformation intensityconditions, thermal conditions of mineral crystallization and the closure temperature of the different grains.

Significance of the 40 Ar/ 39 Ar step-heating data

For Lakora samples, the spectra of the bulk and the coarse fractions have a staircase shaped profile, while the two fine fractions (2-0.5 µm and < 0.5 µm) have a flat-like profile on the right side of their age spectra (high-temperature degassing steps). On the other hand, the three dated fractions of Torla core-zone sample (16-2 µm, 2-0.5 µm and < 0.5 µm) have a stair-case shaped profile. The staircase shaped spectra and the absence of a plateau or plateau-like segment (in the three fractions of Torla and in the coarse fractions of Lakora) may result from several factors: mixing of several micas generations, partial argon resetting, chemical zoning, variability of closure temperature partly dependent on grain size, grain comminution, density of lattice defects and argon recoil [START_REF] Dong | Thermal 40 Ar/ 39 Ar separation of diagenetic from detrital illitic clays in Gulf Coast shales[END_REF][START_REF] Verdel | Variations in the Illite to Muscovite Transition Related to Metamorphic Conditions and Detrital Muscovite Content: Insight from the Paleozoic Passive Margin of the Southwestern United States[END_REF]. The discordant age profile recorded by the first heating increments in all fractions from all thrusts samples is a result of 39 Ar recoil during irradiation which artificially modifies the original distribution of 40 Ar/ 39 Ar ratio in the muscovite/illite grains (e.g. [START_REF] Dong | Mechanisms of argon retention in clays revealed by laser 40 Ar-39 Ar dating[END_REF]. The occurrence of chlorite in all these fractions could be a second reason for the young ages at the low temperature steps. Abd Elmola et al. (submitted), [START_REF] Ghanem | Dating slate belts using 40 Ar/ 39 Ar geochronology and zircon ages from crosscutting plutons: A case study from east-central Maine, USA[END_REF]and [START_REF] Kunk | Contrasting tectonothermal domains and faulting in the Potomac terrane, Virginia-Maryland-discrimination by 40 Ar/ 39 Ar and fission-track thermochronology[END_REF] suggested that part of recoiled 39 Ar from the rim of muscovite could be trapped by adjacent chlorite grains during irradiation (this is explained in more details in section 2.5.3 of chapter 2).

The maximum age that is reached during step-heating experiments in the less-deformed sample of Lakora thrust is c. 300.4 ± 1.5 Ma. As in the case of Pic de Port Vieux, this age is interpreted to the contribution of detrital micas from the host rocks. This detrital grains are probably derived from the 123 3.6. DISCUSSION CHAPTER 3 low-grade metamorphic basement rocks (Hercynian basement) outcropping in the foreland margin during the Hecho group sedimentation [START_REF] Bauluz | Evolución Diagenética de las Turbiditas del Grupo Hecho (Eoceno) en la Cuenca de Jaca (España)[END_REF]. Whatever the dated grain-size fraction of Lakora samples, the maximum ages and total gas ages of the highly-deformed sample (15 LAK 3) is younger than the less-deformed sample (Table 3.2) indicating a more pronounced recrystallization of detrital muscovite during late diagenesis and subsequent shearing in the core zone (e.g. [START_REF] Kirschner | Staircase 40 Ar/ 39 Ar spectra of fine-grained white mica: Timing and duration of deformation and empirical constraints on argon diffusion[END_REF]. This is consistent with the petrographic-structural observations and KI results that suggest higher deformation conditions in the 15 LAK 3 sample.

In the two highly-deformed samples (15 LAK 3 and 15 TO 1) of Lakora and Torla, the total gas ages are inversely proportional to the grain-size suggesting the preferential abundance of newly-formed muscovite in the finer fractions. The finest fraction (< 0.5 µm) of the highly-deformed samples in Lakora and Torla display the youngest total gas ages of c. 73.5 ± 0.5 Ma and c. 75.8 ± 0.5 Ma respectively. By contrast with our previous study in Pic de Port Vieux (Abd Elmola et al., submitted), these ages cannot be related to the age of deformation, as according to the stratigraphic constraints on both thrusts, these ages are older than the depositional ages of the host sediments (66 Ma in Lakora and 49 Ma in Torla, see sections 3.3. 1 and 3.3.1). This indicates that the finest size-fraction in both faults comprises mainly two K-bearing components: newly-formed muscovite/illite and detrital muscovite/illite that have not been totally reset by shearing during fault activity.

The partial resetting of muscovite grains can be related to the closure temperature of grains that have different grain-size. Based on the chlorite thermometry and stable isotope investigations, [START_REF] Lacroix | Formation of chlorite during thrust fault reactivation. Record of fluid origin and P-T conditions in the Monte Perdido thrust fault (southern Pyrenees)[END_REF] suggested temperature conditions with a mean value of 240 • C for the last activity of the Monte Perdido thrust (Torla outcrop). As the Kübler index measurements (obtained in the present thesis) suggest that deformation conditions are relatively close in the Lakora and Monte Perdido thrusts, thus we can assume that 240 • C prevailed during the activity of both the Lakora and Torla thrusts. These temperature conditions (240 • C) are not high enough to induce a complete resetting of muscovite/illite with a grain-size of 0.5 µm in both thrust fault zones. This is based on closure temperature calculations [START_REF] Dodson | Closure temperature in cooling geochronological and petrological systems[END_REF] that show that muscovite with grain-size of 0.5 µm has a closure temperature of 278 • C to 300 • C for a cooling rate of 5 to 50 • C/My respectively. Hence, the finest fraction < 0.5 µm probably contains mica grains that have experienced only partial resetting and consequently will result in older total gas ages for this fraction. This interpretation suggests that it would be useful to perform additional dating on smaller granulometric fractions in these samples in order to reach conditions where the closure temperature and that of shearing are in the same range.

Comparison of the 40 Ar/ 39 Ar ages with other previous studies

According to [START_REF] Teixell | Estructura alpina en la transversal de la termina-cion occidental de la Zona Axial pirenaica[END_REF][START_REF] Teixell | The Ansó transect of the southern Pyrenees: basement and cover thrust geometries[END_REF], [START_REF] Teixell | Stress and fluid control on décollement within competent limestone[END_REF][START_REF] Teixell | The crustal evolution of the west-central Pyrenees revisited: Inferences from a new kinematic scenario[END_REF], the Lakora thrust activity started in Early Eocene times (∼ 50 Ma) until the Mid-Late Eocene (∼ 45-33 Ma) based on tectonic-sedimentation and thermochronological constraints. Moreover, ZHe analyses on Zircon grains from the Lakora thrust hanging wall indicate Early-Eocene age for the activity of the Lakora thrust itself and a Late-Eocene to Oligocene age to the reactivation by the Gavarnie thrust [START_REF] Bosch | Timing of Eocene-Miocene thrust activity in the Western Axial Zone and Chaînons Béarnais (westcentral Pyrenees) revealed by multi-method thermochronology[END_REF]. These results suggest that the c. 73.5 ± 0.5 Ma age obtained in the present study (< 0.5 µm fraction) is very old for the activity of the Lakora thrust. This supports our interpretation of the coexistence of partially reset detrital mica and newly-formed synkinematic illite/muscovite in the < 0.5 µm fraction.

As mentioned above, the Lakora and Monte Perdido thrusts are related to each other as [START_REF] Teixell | Alpine thrusts at the western termination of the Pyrenean axial zone[END_REF][START_REF] Teixell | The Ansó transect of the southern Pyrenees: basement and cover thrust geometries[END_REF] showed that the Monte Perdido thrust system is analogous to the Larra thrust, and it deeps rooted northward in the Lakora thrust. The same author suggested that the Monte Perdido thrust activity started at the latest Lutetian to earliest Priabonian (47-37 Ma) (Early-middle Eocene). Therefore, the c. 75.8 ± 0.5 Ma, i.e. the youngest age of the Torla highly-deformed sample (15 TO 1), is also a mixed age due to contamination by partially reset detrital mica.

Conclusion

The results of the present study in the Lakora and the Monte Perdido thrusts (Torla outcrop) demonstrated the following:

• The pressure-solution and dissolution-recrystallization mechanisms in presence of fluids are the main mechanisms that control the deformation in both thrusts, and responsible for the enrichment of newly-formed phyllosilicates in the fault core zone.

• The petrographic and microstructures observations suggest aseismic and ductile deformation with several stages of deformations and fluid circulations in the two studied thrusts. This was confirmed by the folding, sigmoidal-elongation shape of the grains, development of more than one cleavage, cross-cut relationship, and crack-seal mechanism for the veins formations.

• The newly-formed phyllosilicates in the fault zone are Fe-rich chlorite, muscovite/illite (abundant 2M 1 and small amount of 1M). They are synkinematic to the fault activity, their chemical composition, polytypes and crystallinity suggest upper-anchizone conditions (∼ 240 • C) that is slightly lower in the Lakora thrust compared to the Monte Perdido thrust.

• The 40 Ar/ 39 Ar step-heating performed on muscovite/illite demonstrated that the finest grain-125 3.7. CONCLUSION CHAPTER 3 size fractions of the highly-deformed samples from both thrusts have the youngest total gas age of about c. 73.5 ± 0.5 Ma and c. 75.8 ± 0.5 Ma in the Lakora and Torla respectively.

• Comparison of these ages with previous geochronology results that based on tectonics-sedimentation relationships and thermochronological constraints also suggest that they are very old ages and do not represent the age of thrusting.

• The calculated closure temperature for all the dated grain-size fractions are high compared to the thermal conditions during shearing, suggesting a partial reset for mica grains and this is the main reason for these old ages.

Origin and formation mechanisms of phyllosilicates in fault zones

Phyllosilicates minerals have three main origin in all the geological environments; they can be inherited, newly-formed, and/or transformed-altered minerals [START_REF] Eberl | Clay mineral formation and transformation in rocks and soils[END_REF], Meunier, 2005[START_REF] Millot | Geology of clays: Weathering, sedimentation, geochemistry[END_REF][START_REF] Weaver | The chemistry of clay minerals[END_REF]. In fault zones, phyllosilicates can be incorporated by various processes such as mechanical mechanisms (i.e. comminution, fragmentation, mechanical abrasion of fault host rocks), dissolution-recrystallization, pressure solution mechanisms, and through direct precipitation from fluids (e.g. Buatier et al., 2012a[START_REF] Egholm | The mechanics of clay smearing along faults[END_REF][START_REF] Gratier | Aseismic sliding of active faults by pressure solution creep: Evidence from the San Andreas Fault Observatory at Depth[END_REF][START_REF] Wibberley | Recent advances in the understanding of fault zone internal structure: a review[END_REF] see section 3 of the general introduction for more details and references). In the present thesis, the origin and formation mechanisms of phyllosilicate minerals have been investigated in three thrust faults (PPVT, Lakora and Monte Perdido) from the Pyrenees orogen. The results demonstrated that chlorite and muscovite/illite are the phyllosilicate minerals present in the studied fault zones. These minerals have mainly three origins in the studied fault zones; detrital, diagenetic and newlyformed. The newly-formed chlorite and muscovite/illite are synkinematic to the fault activity and their formations are attributed to dissolution-recrystallization, pressure solution and fluid-rock interactions mechanisms. The same formation mechanisms have been reported in other studies in different fault zones (e.g. [START_REF] Gratier | Aseismic sliding of active faults by pressure solution creep: Evidence from the San Andreas Fault Observatory at Depth[END_REF][START_REF] Haines | Clay quantification and Ar-Ar dating of synthetic and natural gouge: Application to the Miocene Sierra Mazatán detachment fault, Sonora, Mexico[END_REF][START_REF] Janssen | Microstructures and their implications for faulting processes -Insights from DGLab core samples from the Gulf of Corinth[END_REF][START_REF] Lacroix | Formation of chlorite during thrust fault reactivation. Record of fluid origin and P-T conditions in the Monte Perdido thrust fault (southern Pyrenees)[END_REF], Richard et al., 2014, among others). Moreover, the microstructure, texture and grain-shape of these phyllosilicate suggest that the activity of the three faults occurred by a seismic and ductile deformation mechanisms.

Phyllosilicates as a proxy for deformation conditions in fault zones

Phyllosilicates minerals have been widely used to determine the deformation conditions of fault activity and fluid-rock interactions (see e.g. [START_REF] Abad | The structure and the phyllosilicates (chemistry, crystallinity and texture) of Talas Ala-Tau (Tien Shan, Kyrgyz Republic): comparison with more recent subduction complexes[END_REF], Buatier et al., 2015[START_REF] Girard | The Dutung-Thaktote extensional fault zone and nappe structures documented by illite crystallinity and clay-mineral paragenesis in the Tethys Himalaya between Spiti river and Tso Morari[END_REF][START_REF] Trincal | Temperature micro-mapping in oscillatory-zoned chlorite: Application to study of a green-schist facies fault zone in the Pyrenean Axial Zone (Spain)[END_REF], Warr and Cox, 2016, among others) as mentioned in details in section 4 of the general introduction. However, before using these phyllosilicate minerals to extract information about the fault activity conditions, their formation must be synkinematic to the fault activity. Therefore, detailed characterization for their texture and chemistry, origin and formation mechanisms are highly recommended before applying/using them in fault zones to extract information about fault activity conditions.

In the present thesis, the Kübler index of synkinematic muscovite/illite and thermodynamic modelling of chlorite were used to evaluate the diagenesis-metamorphic conditions and to estimate the tempera- In addition, characterization of the chemical composition of phyllosilicates allows also to better understand the fluid/rock interaction that are related to fault activity. This is because the chemical composition of newly-formed phyllosilicate can record the composition of fluids circulating in the fault zones (e.g. [START_REF] Lacroix | Formation of chlorite during thrust fault reactivation. Record of fluid origin and P-T conditions in the Monte Perdido thrust fault (southern Pyrenees)[END_REF][START_REF] Trincal | Temperature micro-mapping in oscillatory-zoned chlorite: Application to study of a green-schist facies fault zone in the Pyrenean Axial Zone (Spain)[END_REF], 2017). In the present thesis, the characterization of chlorite and muscovite chemical compositions in the PPVT helped to better understand the mineralogical changes in the fault zone that are attributed to fluid circulations [START_REF] Abd Elmola | Textural-chemical changes and deformation conditions registered by phyllosilicates in a fault zone (Pic de Port Vieux thrust, Pyrenees)[END_REF]. At the outcrop scale of the PPVT, the red Triassic pelites of the hanging wall is transformed to a green foliated layer in the core zone. Therefore, we have coupled experimental date (electron microprobe analyses) with fluid-rock interactions modelling to determine the favorable conditions for this transformations in the PPV fault zone. Based on these results, the main critical parameter favoring the mineralogical changes in the core zone, was the change in redox conditions. The formation of Fe-rich phyllosilicates in the core fault zone were attributed to the highly reductive Fe-rich fluid that bleached the fault zone.

Moreover, the results suggests that the change in color is related to the dissolution of hematite and the precipitation of Fe-rich chlorite in the fault core zone.

Clearly, all that confirm the validity of muscovite/illite and chlorite as reliable proxies for the estimation of deformation and fluid/rock interaction conditions of fault activity. There are as well, numerous studies that have successfully estimated the deformation conditions based on crystallinity and chemical compositions of phyllosilicate in several faults from different localities (e.g. Beichuan fault, China, [START_REF] Airaghi | Total exhumation across the Beichuan fault in the Longmen Shan (eastern Tibetan plateau, China): Constraints from petrology and thermobarometry[END_REF]Sierras Pampeanas, Argentina, Bense et al., 2014;Point Vert fault, Alps, France, Buatier et al., 2015[START_REF] Leclère | Formation of phyllosilicates in a fault zone affecting deeply buried arkosic sandstones: their influence on petrophysic properties (Annot sandstones, French external Alps)[END_REF]Catalan coastal ranges, Spain, Cantarero et al., 2014;Livorno-Sillaro Line, Italy, Dellisanti et al., 2008;Akaishi Tectonic Line, Japan, Tanaka et al., 1995;Bogd fault, Mongolia, Buatier et al., 2012a;the Talas Ala Tau, Kyrgyz Republic, Abad et al., 2003, among others).

Phyllosilicates as geochronology tool for dating fault activity

One of the most interesting use of phyllosilicates (muscovite/illite) in fault zones is the estimation of fault activity age based on their isotopic composition. As previously mentioned, to use muscovite and illite for radiometric dating of faults, they have to be synchronous to the fault activity and have to be separated from other mica generations that formed before this activity (i.e. detrital and diagenetic micas) [START_REF] Mcdougall | Geochronology and Thermochronology by the 40 Ar/ 39 Ar Method[END_REF]. In the present work, the studied thrusts (PPV, Torla and Lakora) have been dated by the 40 Ar/ 39 Ar step-heating technique. Two representative samples of each thrust have been selected; one sample from the core zone (or highly-deformed zone) and the other sample from the damage zone (or less-deformed zone). Samples from the core zone were assumed to give the thrusting age as they contain mainly synkematic newly-formed mica, while those from the damage zone should give mixed ages due to the abundant of detrital, and diagenetic micas.

Polytypism approach vs. grain-size separation method

The petrographic, texture observation, X-ray diffraction and chemical analysis of the studied samples suggest the following:

-The newly-formed muscovite/illite has smaller grain-size and hence is concentrated in the fine fractions of the highly-deformed sample.

-The newly-formed muscovite/illite in the finest fraction (< 0.5 µm) is typically of 2M 1 polytype with a small proportion of 1M polytype in the studied samples. Therefore, the polytypism approach which is commonly used to separate the different age components assuming that 2M 1 polytype has a detrital origin and 1M/1M d is newly-formed (e.g. Duvall et al., 2011, Hnat andvan der Pluijm, 2014) is not applicable in the studied thrusts. Indeed this polytypism approach is suitable for dating fault gouge where newly-formed micas are related to low temperature hydration reactions associated to brittle faulting (e.g. Haines andvan der Pluijm, 2008, van der Pluijm et al., 2001, see section 4.3.1 of the general introduction for more detail and references). In the studied faults, the core zone is composed of a phyllonite fault rock which has been deformed by ductile mechanism at higher temperature (∼ 250 • C). These thrusting conditions are close to the formation temperature of the 2M 1 polytype and consequently detrital and newly-formed muscovite/illite cannot be distinguished based on polytypes determination. Newly-formed 2M 1 muscovite/illite has been described by other authors (e.g. [START_REF] Löbens | Exhumation and uplift of the Sierras Pampeanas: preliminary implications from K-Ar fault gouge dating and low-T thermochronology in the Sierra de Comechingones (Argentina)[END_REF][START_REF] Torgersen | Structural and temporal evolution of a reactivated brittle-ductile fault -Part II: Timing of fault initiation and reactivation by K-Ar dating of synkinematic illite/muscovite[END_REF][START_REF] Viola | K-Ar illite age constraints on the Proterozoic formation and reactivation history of a brittle fault in Fennoscandia[END_REF][START_REF] Zwingmann | Dating of shallow faults: New constraints from the AlpTransit tunnel site (Switzerland)[END_REF]. Moreover, [START_REF] Fitz-Díaz | XRD-based 40 Ar/ 39 Ar age correction for fine-grained illite, with application to folded carbonates in the Monterrey Salient (northern Mexico)[END_REF] showed that 2M 1 and 1M d mica polytypes have authigenic origin as their ages are younger than the deposition age in the Mexican Fold-Thrust Belt. Furthermore, in oil-bearing reservoirs from the northern and southern North Sea, [START_REF] Clauer | Episodic and simultaneous illitization in oil-bearing Brent Group and Fulmar Formation sandstones from the northern and southern North Sea based on illite K-Ar dating[END_REF] showed also that newly-formed 2M 1 illite can crystallize at temperatures slightly above 125 • C. They argued this low-temperature crystallization of 2M 1 polytype by its synthesis at room temperature, together with 1M illite based on the study of [START_REF] Flehmig | The synthesis of 2M 1 -illitic micas at 20°C[END_REF]. Therefore, the polytypism approach should not be automatically used in fault zones to differentiate the detrital and authigenic origin of mica since the 2M 1 polytype is not only detrital origin but could be authigenic [START_REF] Clauer | The K-Ar and 40 Ar/ 39 Ar methods revisited for dating fine-grained K-bearing clay minerals[END_REF].

In our study, the texture observations and chemical compositions suggested that a discrimination between the different muscovite/illite phases is possible through their grain-size. Therefore, a grainsize fraction separation by sedimentation and centrifugation techniques was performed in order to separate newly-formed muscovite/illite from other micas. The 40 Ar/ 39 Ar results showed a decrease in the total gas age with decreasing the grain-size, confirming that the newly-formed muscovite is concentrated in the fine fractions. Furthermore, the finest fraction (< 0.5 µm) from the highlydeformed sample of the three thrusts has the youngest total gas age of 36.9 ± 0.2 Ma (PPVT), 73.5 ± 0.5 Ma (Lakora), and 75.8 ± 0.5 Ma (Torla). All the ages are older in the less-deformed samples compared to the highly-deformed samples, demonstrating the validity of our choice of the samples that is based on petrographic and textural observations. By considering the 40 Ar/ 39 Ar step-heating results of this study and the relationships between grain-size and age, the size-fraction separation is proved to be a reliable alternative to separate the newly-formed muscovite/illite from other mica phases (see e.g. [START_REF] Van Der Pluijm | The dating of shallow faults in the Earth's crust[END_REF][START_REF] Van Der Pluijm | Fault dating in the Canadian Rocky Mountains: Evidence for late Cretaceous and early Eocene orogenic pulses[END_REF].

Difficulties in interpreting 40

Ar/ 39 Ar data One of the major problems of the 40 Ar/ 39 Ar step-heating technique when dating fine-grain minerals is the recoil argon that is released from minerals during irradiation [START_REF] Mcdougall | Geochronology and Thermochronology by the 40 Ar/ 39 Ar Method[END_REF][START_REF] Onstott | Recoil refinements: Implications for the 40 Ar/ 39 Ar dating technique[END_REF], York et al., 1992). Since the amount of recoiled argon can be significant in case of fine-grain clay minerals, the calculated age could be erroneously old if this recoiled argon is not taken into account (e.g. [START_REF] Dong | Mechanisms of argon retention in clays revealed by laser 40 Ar-39 Ar dating[END_REF][START_REF] Duvall | Direct dating of Eocene reverse faulting in northeastern Tibet using Ar-dating of fault clays and low-temperature thermochronometry[END_REF][START_REF] Hall | Direct measurement of recoil effects on 40 Ar/ 39 Ar standards[END_REF]. Therefore, in the present work, the samples have been encapsulated in evacuated quartz tubes prior to irradiation and then the tubes have been opened with a UV laser under vacuum before starting step-heating experiments. Thanks to this encapsulation technique, the recoiled 39 Ar has been preserved in the tube, measured by mass spectrometry and re-integrated to calculate the total gas age (e.g. [START_REF] Foland | 40 Ar/ 39 Ar incremental heating plateaus for biotites with excess argon[END_REF][START_REF] Foland | 40 Ar/ 39 Ar dating of very fine-grained samples: An encapsulated-vial procedure to overcome the problem of 39 Ar recoil loss[END_REF][START_REF] Onstott | Laser 40 Ar/ 39 Ar microprobe analyses of fine-grained illite[END_REF][START_REF] Smith | First successful 40 Ar-39 Ar dating of glauconies: Argon recoil in single grains of cryptocrystalline material[END_REF].

In the studied samples, the quantity of recoiled argon is inversely proportional to grain-size and the highest value of recoil was found in the finest grain-size fraction (< 0.5 µm); 25%, 23% and 11% for the PPVT, Lakora and Torla respectively. Moreover, the decomposition of muscovite/illite 001 peak reflection in the < 0.5 µm fraction suggests the occurrence of some poorly-crystalized mica.

Consequently, this probably indicates that the poor crystallinity and the presence of crystallographic defects in muscovite/illite could be also a second reason for the recoiled argon. This interpretation is consistent with other studies (e.g. [START_REF] Clauer | The K-Ar and 40 Ar/ 39 Ar methods revisited for dating fine-grained K-bearing clay minerals[END_REF][START_REF] Dong | Mechanisms of argon retention in clays revealed by laser 40 Ar-39 Ar dating[END_REF], 1997[START_REF] Fitz-Díaz | XRD-based 40 Ar/ 39 Ar age correction for fine-grained illite, with application to folded carbonates in the Monterrey Salient (northern Mexico)[END_REF][START_REF] Foland | 40 Ar/ 39 Ar dating of very fine-grained samples: An encapsulated-vial procedure to overcome the problem of 39 Ar recoil loss[END_REF][START_REF] Hall | Direct measurement of recoil effects on 40 Ar/ 39 Ar standards[END_REF][START_REF] Hnat | Fault gouge dating in the Southern Appalachians, USA[END_REF][START_REF] Hunziker | The evolution of illite to muscovite: mineralogical and isotopic data from the Glarus Alps, Switzerland[END_REF][START_REF] Lin | Backscattered 39 Ar loss in fine-grained minerals: Implications for 40 Ar/ 39 Ar geochronology of clay[END_REF][START_REF] Markley | The relation between grain size and 40 Ar/ 39 Ar date for Alpine white mica from the Siviez-Mischabel Nappe, Switzerland[END_REF][START_REF] Reuter | 40 Ar/ 39 Ar dating of cleavage formation in tuffs during anchizonal metamorphism[END_REF][START_REF] Sletten | The Effect of the Instability of Muscovite During In Vacuo Heating on 40 Ar/ 39 Ar Step-Heating Spectra[END_REF][START_REF] Van Der Pluijm | The dating of shallow faults in the Earth's crust[END_REF], York et al., 1992) that all reported a negative correlation between amount of recoiled 39 Ar and either grain size or muscovite/illite crystallinity index.

As mentioned above, the recoiled argon value can be re-integrated in order to calculate the total gas age and geological meaningful ages can be obtained [START_REF] Mcdougall | Geochronology and Thermochronology by the 40 Ar/ 39 Ar Method[END_REF]. However, integration of the recoiled Ar over all the heating-steps of the age spectrum is not straightforward. This is because the behavior of the fine-grain clay minerals during irradiation and releasing mechanism of Ar recoil are not clearly understood. Several models have been proposed to explain these mechanisms and the possible reasons for this Ar recoil phenomena (see section 4.3.3 of the general introduction references and more details). Some models for the integration of the recoiled 39 Ar have been suggested on the basis of various assumptions (e.g. [START_REF] Dong | Mechanisms of argon retention in clays revealed by laser 40 Ar-39 Ar dating[END_REF][START_REF] Lin | Backscattered 39 Ar loss in fine-grained minerals: Implications for 40 Ar/ 39 Ar geochronology of clay[END_REF][START_REF] Sletten | The Effect of the Instability of Muscovite During In Vacuo Heating on 40 Ar/ 39 Ar Step-Heating Spectra[END_REF], York et al., 1992). However, there is no agreement about the best crystallographic model that explain the recoil behavior and the best way of restoring it to the heating-steps of the age spectrum (e.g. [START_REF] Clauer | The K-Ar and 40 Ar/ 39 Ar methods revisited for dating fine-grained K-bearing clay minerals[END_REF]. For example, [START_REF] Dong | Mechanisms of argon retention in clays revealed by laser 40 Ar-39 Ar dating[END_REF] suggested that 39 Ar recoils only from low-retentive sites of muscovite/illite particles that is relevant for low temperature heating-steps and consequently it should be added to the first low temperature heating-steps in the age spectrum. Conversely, [START_REF] Clauer | Comparative 40 Ar/ 39 Ar and K-Ar dating of illite-type clay minerals: A tentative explanation for age identities and differences[END_REF], integrated the recoiled argon on the entire age spectrum only on the basis of the representative amount of each step in the total-gas age. In other words, they restored the recoiled argon on each step proportionally to the amount of 39 Ar released relatively to the total 39 Ar.

The present study results demonstrated that this redistribution of recoiled Ar and interpretation of the age spectrum of fine-grain muscovite/illite in low grade metamorphism are challenging subjects due to the following reasons:

1. Due to the high value of recoiled Ar that escaped from the grains structure and concentrated within the quartz tube during irradiation, the shape of the age spectrum is no longer reflecting the original distribution of 39 Ar/ 40 Ar ratio in the grain [START_REF] Dong | Mechanisms of argon retention in clays revealed by laser 40 Ar-39 Ar dating[END_REF][START_REF] Dong | 40 Ar/ 39 Ar illite dating of Late Caledonian (Acadian) metamorphism and cooling of K-bentonites and slates from the Welsh Basin[END_REF]. Hence, the attempt to re-integrate the recoiled argon to specific heating steps is complicated task.

2. Part of the recoiled 39 Ar can be incorporated into adjacent minerals during irradiation (e.g. [START_REF] Reuter | K-Ar and 40 Ar/ 39 Ar dating of cleavage formed during very low-grade metamorphism: a review[END_REF]. In our study, the presence of chlorite in all the dated fractions may also affect the shape of the age spectrum as 39 Ar can recoil from the rim of muscovite/illite into adjacent chlorite grains. Consequently, some young ages may be expected at the first heating steps because the degassing temperature of chlorite is lower compared to that of muscovite (see e.g. [START_REF] Ching-Hua | 39 Ar recoil artifacts in chloritized biotite[END_REF][START_REF] Ghanem | Dating slate belts using 40 Ar/ 39 Ar geochronology and zircon ages from crosscutting plutons: A case study from east-central Maine, USA[END_REF][START_REF] Kunk | Contrasting tectonothermal domains and faulting in the Potomac terrane, Virginia-Maryland-discrimination by 40 Ar/ 39 Ar and fission-track thermochronology[END_REF][START_REF] Sletten | The Effect of the Instability of Muscovite During In Vacuo Heating on 40 Ar/ 39 Ar Step-Heating Spectra[END_REF] .

3. In addition, the recoil of argon toward the internal structure of muscovite grains cannot be excluded. As a result 39 Ar will be redistributed inside the mineral structure, causing some discordant apparent ages in the age spectrum during step-heating [START_REF] Mcdougall | Geochronology and Thermochronology by the 40 Ar/ 39 Ar Method[END_REF].

4. The coexistence of inherited, diagenetic and newly-formed mica in the coarse factions and different polytypes of muscovite/illite (2M 1 , 1M) in the fine fractions, can be a reasons for the absence of plateau. This is because they have different crystallinity and crystallographic orders/defects and consequently difference in their Ar retentivity i.e. the degassing of Ar during step-heating will occur through different manners for the different polytypes (e.g. [START_REF] Clauer | The K-Ar and 40 Ar/ 39 Ar methods revisited for dating fine-grained K-bearing clay minerals[END_REF][START_REF] Fitz-Díaz | XRD-based 40 Ar/ 39 Ar age correction for fine-grained illite, with application to folded carbonates in the Monterrey Salient (northern Mexico)[END_REF].

Due to all these reasons, all the fractions of the studied samples didn't display a true plateau according to all the existing plateau definitions (e.g. [START_REF] Clauer | Comparative 40 Ar/ 39 Ar and K-Ar dating of illite-type clay minerals: A tentative explanation for age identities and differences[END_REF][START_REF] Dallmeyer | 40 Ar/ 39 Ar polyorogenic mineral age record in the northern Mauritanide orogen, West Africa[END_REF][START_REF] Fleck | Interpretation of discordant 40 Ar/ 39 Ar age-spectra of mesozoic tholeiites from antarctica[END_REF]. Thus, obviously the re-integration of the recoil argon to specific heating steps is far from being possible with the influences of all this parameters in the age spectrum shape. Therefore, the recoiled 39 Ar have been added at the beginning of the age spectra at zero age before the first heating-step.

Because of the plateau absence and the high fractions of the recoiled 39 Ar, the total gas age was used in the studied samples to represents the age of each fraction rather than plateau or retention ages.

Validity and limitations of the 40 Ar/ 39 Ar step-heating method

As mentioned previously, only the finest fractions of the highly-deformed samples from the three studied thrusts is assumed to give the time of thrusting since they concentrate the large amount of newly-formed muscovite/illite.In case of the PPVT, the total gas age is consistent with the tectonic history of thrusting proposed by other studies (e.g. [START_REF] Grant | Deformation and fluid processes in thrust sheets from the central Pyrenees[END_REF], 1992, Grant et al., 1990, Labaume et al., 2016[START_REF] Muñoz | The Ainsa Fold and thrust oblique zone of the central Pyrenees: Kinematics of a curved contractional system from paleomagnetic and structural data[END_REF][START_REF] Teixell | The Ansó transect of the southern Pyrenees: basement and cover thrust geometries[END_REF]. However, in case of the two other thrusts (Lakora and Torla), the total gas ages (74 Ma for Lakora and 76 Ma for Torla) don't represent the thrusting activity age since these ages are older than the depositional age of the host sediments (66 Ma in Lakora and 49 Ma in Torla). Moreover, this is not in agreement with the Mid-Late Eocene and Early-Mid Eocene ages that were proposed for Lakora and Monte Perdido thrust activity by [START_REF] Bosch | Timing of Eocene-Miocene thrust activity in the Western Axial Zone and Chaînons Béarnais (westcentral Pyrenees) revealed by multi-method thermochronology[END_REF], [START_REF] Teixell | Estructura alpina en la transversal de la termina-cion occidental de la Zona Axial pirenaica[END_REF][START_REF] Teixell | The Ansó transect of the southern Pyrenees: basement and cover thrust geometries[END_REF].

These results provided important information about the validity and limitations of the 40 Ar/ 39 Ar stepheating technique for dating faults in sedimentary environments at low grade metamorphism.

(i) The PPVT:

The decrease of total gas ages with grain-size in the sample PPV12-05 (core-zone) suggests that the large to medium muscovite/illite grains of detrital and diagenetic origin have experienced only partial Ar resetting in the core zone. By contrary, the fine-grains have been totally reset as the total gas age of the muscovite/illite present in the finest fractions (< 0.5 µm) gives the age of the PPVT activity.

Moreover, the X-ray maps of muscovite chemical composition demonstrated that the large grains have inhomogeneous compositions marked by a zoning from the rim to the core. While the individual fine-grains display homogenous chemical compositions. This clearly indicates a relationship between the evolution of chemical composition of phyllosilicates and the age record. Since the partial age resetting of the large mica grains is coeval with the preservation of chemical heterogeneity. This partial resetting suggests that temperature during shearing was not sufficient to induce a complete rest of the argon clock for the large grains. Therefore the behavior of these micas has been tentatively explained considering their closure temperature and experimental data on argon diffusion in muscovite. According to [START_REF] Dodson | Closure temperature in cooling geochronological and petrological systems[END_REF], [START_REF] Harrison | Fundamentals of Noble Gas Thermochronometry[END_REF], [START_REF] Harrison | Diffusion of 40 Ar in muscovite[END_REF], the large grains have higher closure temperature compared to the smaller grains and consequently they need higher temperatures to be totally reset. Based on the closure temperature calculations (see section 2.5.3), only muscovite with a grain-size smaller than 0.5 µm, experienced complete resetting during thrusting in the PPV while micas with larger grain-size preserved some inherited argon. This is because the recorded peak-temperature during shearing in the PPVT (∼ 285 • C) is in the same range of the temperature required to completely reset muscovite grains smaller than 0.5 µm (278 • C to 300 • C). This correlation between closure temperature and grain-size in fault zones was also reported by other studies in order to interpret the calculated 40 Ar/ 39 Ar ages with the thermal history during shearing (see e.g. [START_REF] Duvall | Direct dating of Eocene reverse faulting in northeastern Tibet using Ar-dating of fault clays and low-temperature thermochronometry[END_REF][START_REF] Rahl | Links between orogenic wedge deformation and erosional exhumation: Evidence from illite age analysis of fault rock and detrital thermochronology of syntectonic conglomerates in the Spanish Pyrenees[END_REF][START_REF] Scharf | Grainsize effects on the closure temperature of white mica in a crustal-scale extensional shear zone -Implications of in-situ 40 Ar/ 39 Ar laser-ablation of white mica for dating shearing and cooling (Tauern Window, Eastern Alps)[END_REF][START_REF] Verdel | Variation of illite/muscovite 40 Ar/ 39 Ar age spectra during progressive low-grade metamorphism: an example from the US Cordillera[END_REF].

(ii) The Lakora and Torla thrusts:

In the Lakora and Torla outcrops, the total gas ages of all the dated fractions are older than or close to the depositional age of the host sediments. The finest fraction (< 0.5 µm) of the highly-deformed samples has a total gas age of 73.5 ± 0.5 Ma in Lakora and 75.8 ± 0.5 Ma in Torla corresponding to Late Cretaceous (Campanian) age. However, these ages are not consistent with the Late Eocene age proposed by for thrusting along these faults [START_REF] Bosch | Timing of Eocene-Miocene thrust activity in the Western Axial Zone and Chaînons Béarnais (westcentral Pyrenees) revealed by multi-method thermochronology[END_REF][START_REF] Jolivet | Thermochronology constraints for the propagation sequence of the south Pyrenean basement thrust system (France-Spain)[END_REF][START_REF] Mutti | Sedimentation and deformation in the Tertiary Sequences of the Southern Pyrenees: Field trip 7[END_REF][START_REF] Séguret | Etude tectonique des nappes et séries décollées de la partie centrale du versant sud des Pyrénées: caractère synsédimentaire, rôle de la compression et de la gravité[END_REF][START_REF] Teixell | The Ansó transect of the southern Pyrenees: basement and cover thrust geometries[END_REF], Teixell et al., 2016). This incompatibility in age between those studies and our results can be also explained in term of closure temperature. By contrary to the PPVT, the recorded peak-temperatures during shearing in the Monte Perdido (∼ 240 • C) and in Lakora (< 240 • C) thrusts are relatively low to induce complete reset for all the dated grain-size fractions (see section 3.6.3.1). Thus, the calculated total gas ages of all the dated fractions in both Lakora and Torla samples will be a mixed ages. This interpretation suggests that the fraction < 0.5 µm has to be subdivided into finer fractions in case of the Lakora Torla samples, in order to concentrate the very fine-grains that could have experienced complete resetting during shearing. According to the CLOSURE program [START_REF] Ehlers | Computational tools for low-temperature thermochronometer interpretation[END_REF] and by using muscovite diffusion data of [START_REF] Harrison | Diffusion of 40 Ar in muscovite[END_REF], only grain-size fractions < 0.03 µm could have the chance to record the thrusting age in Torla and Lakora. That is if we assume a cooling rate of 50 • C/m.y while for a lower cooling rate of 10 • C/m.y., grain size of 0.07 µm should have a complete Ar reset and hence giving the age of thrusting.

Based on all what have been mentioned above, the temperature of fault activity can be an obstacle for applying the 40 Ar/ 39 Ar method on faults at low grade metamorphism. That means, if temperature that have been achieved during thrusting is less than closure temperature of muscovite, then the calculated ages will have no geological meaning. Moreover, the results show that deformation mechanisms of thrusting can modify the closure temperature of mica grains and consequently the 40 Ar/ 39 Ar results.

For example, deformation in fault zone can mechanically reduce mica grain-size/diffusion radii, consequently this will lower their Ar closure temperature (e.g. [START_REF] Harrison | Diffusion of 40 Ar in muscovite[END_REF][START_REF] Mulch | In-situ UV-laser 40 Ar/ 39 Ar geochronology of a micaceous mylonite : an example of defect-enhanced argon loss[END_REF].

Newly-formed Muscovite/illite that formed through alteration of pre-existing micas may partially preserve the isotopic signature of detrital micas that result in meaningless ages. While, newly-formed muscovite/illite that is formed by direct precipitation from fluids during fault activity will probably be less affected by such problems. Therefore, characterization of closure temperature, chemical composition, texture, grain-size and formation mechanisms of the targeted mineral in fault zone are very critical to understand and interpret the calculated ages by the 40 Ar/ 39 Ar method.

Combining the 40 Ar/ 39 Ar method with other techniques

In almost all the published studies that have used the 40Ar/39Ar method for dating faults and low grade metamorphism, they coupled the method with other techniques to facilities the interpretation of the calculated ages. These techniques include: X-ray diffraction, optical microscope, scanning electron microscope, electron microprobe, transmission electron microscope and structural analysis.

They techniques have assisted to successfully interpret the 40Ar/39Ar results in many several (e.g. [START_REF] Clauer | The K-Ar and 40 Ar/ 39 Ar methods revisited for dating fine-grained K-bearing clay minerals[END_REF][START_REF] Duvall | Direct dating of Eocene reverse faulting in northeastern Tibet using Ar-dating of fault clays and low-temperature thermochronometry[END_REF][START_REF] Fitz-Díaz | XRD-based 40 Ar/ 39 Ar age correction for fine-grained illite, with application to folded carbonates in the Monterrey Salient (northern Mexico)[END_REF][START_REF] Haines | Clay quantification and Ar-Ar dating of synthetic and natural gouge: Application to the Miocene Sierra Mazatán detachment fault, Sonora, Mexico[END_REF], Lanari et al., 2014a[START_REF] Mcwilliams | Determining ages of multiple muscovitebearing foliations in phyllonites using the 40 Ar/ 39 Ar step heating method: Applications to the Alleghanian orogeny in central New England[END_REF][START_REF] Rahl | Links between orogenic wedge deformation and erosional exhumation: Evidence from illite age analysis of fault rock and detrital thermochronology of syntectonic conglomerates in the Spanish Pyrenees[END_REF][START_REF] Van Der Pluijm | The dating of shallow faults in the Earth's crust[END_REF][START_REF] Verdel | Variation of illite/muscovite 40 Ar/ 39 Ar age spectra during progressive low-grade metamorphism: an example from the US Cordillera[END_REF].

The results of the present study also confirm that coupling the 40 Ar/ 39 Ar step-heating method with a detailed structural analysis, precise textural observations and chemical analyses provide first-order data for the interpretation of the calculated ages. For instance, for the Lakora and Torla thrusts, the incomplete characterization of the samples (due to time limitation) made interpretation of the 40 Ar/ 39 Ar results more difficult. In contrary, the detailed characterization of phyllosilicates in case of the PPVT helped to go further and deeply in the interpretation of the results.

According to our results, the X-ray diffraction technique proved to be one essential technique that must be used when applying the 40 Ar/ 39 Ar method. Since it gives information about the different mica types/generations, their polytypes, their crystallinity and deformation conditions of fault activity. Furthermore, the petrographic observation by optical microscope and SEM provided information about the different generations of clay minerals, their origin and their formation mechanisms. In addition, EDX and electron microprobe analyses demonstrated the difference of chemical compositions between different mica generations and homogeneity/heterogeneity within the individual grains. Moreover, the temperature estimation by chlorite thermometry and Kübler index aided to correlate the ages with the thermal history of the fault activity. Finally, the structural data of the studied areas helped to evaluate the obtained ages and to figure out if they are consistent or not with structural history of the area. Therefore, obviously coupling those techniques with the radiometric dating method is the key-parameter to better understand and interpret the 40 Ar/ 39 Ar results.

GENERAL CONCLUSIONS AND PERSPECTIVES

T he results of the present thesis demonstrate the reliability of using chlorite and muscovite/illite as a thermochronological tool to constrain the fault activity in sedimentary environment even in very complex geological/tectonic history. Moreover, the characterization of these phyllosilicates in fault zones enables the attendant deformation mechanisms to be identified and assessed to infer the fluid/rock interaction involved during thrusting activity. The main conclusions of the present thesis that are based on the results of the studied thrusts are outlined below.

• In order to successfully use phyllosilicate minerals to extract information about conditions/mechanisms of fault activity, their formation must be synkinematic to the fault activity.

Therefore, their origin and formation mechanisms should be studied precisely to get correct information about fault activity.

• In the three studied thrusts, textural and micro-structural investigations confirm that newlyformed phyllosilicates minerals are synkinematic to deformation and fluid circulations that are associated to these faults activities. Moreover, dissolution-recrystallization by pressure solution and precipitation from fluids appear to be the main mechanisms for phyllosilicate formation in the studied fault zones.

• The results confirm as well that the Kübler index of muscovite/illite and chlorite thermometry are reliable tools to evaluate diagenesis-low grade metamorphism conditions and to estimate the fault activity temperature. The results suggest high-anchizone to epizone grade conditions and a temperature of about 285 • C ± 28 • C for the activity of the PPVT. While in Lakora and Torla, the Kübler index values suggest high-anchizone conditions that are slightly lower the PPVT deformation conditions.

• Characterizing phyllosilicates in both the core and the damage zones of the fault, and comparing their chemical compositions helped to better understand the fluid/rock interaction. For instance, in the PPVT, the numerical modeling for the chemical compositions of the hanging wall pelites allowed to determine the favorable conditions for the mineralogical changes in the fault zone.

The results suggest that the color change between the core and the damage zone is related to high reducing fluid that bleached the Triassic pelites during thrusting.

• The results also show that dating muscovite/illite by the 40 Ar/ 39 step-heating technique is a reliable alternative to date fault activity when biostratigraphic or paleomagnetic constraints are insufficient to precisely date them. However, to successfully interpret the 40 Ar/ 39 step-heating results, combining the technique with other analytical methods such as XRD, optical microscope SEM-EDX, electron microprobe and structural data is highly recommended. In addition, careful sample disintegration, accurate grain-size separation and detailed mineral characterization of the synkinematic phyllosilicates greatly improve the understanding of the 40 Ar/ 39 results.

• The thermal history and deformation mechanisms of fault activity should be also well determined as they can restrict the type of formed mica polytypes and they may control the degree of the resetting of mica grains i.e. partial or complete reset of the grains. Thus, having information about these parameters greatly improve our understanding of the 40 Ar/ 39 Ar results.

The age obtained in the present work for the PPVT activity (37 Ma) is consistent with the other available date from the same area. While the ages of 73 Ma and 75 Ma ages for the Lakora and Torla activity respectively, are not in agreement with the age proposed by other studies for their last activity (Late Eocene). This difference of isotopic behavior is mainly related to higher thermal conditions during thrusting at PPV as suggested by the determination of closure temperature for argon in the fine-grained micas. Based on that, some directions of further research are proposed to figure out this inconsistency in ages. These future works may include:

1. Characterization for the chemical composition of muscovite/illite in both the Lakora and Torla samples by electron microprobe spot-analyses and by X-ray maps to investigate the homogeneity/heterogeneity within the individual mica grains 2. In addition, performing chemical spot-analyses for chlorite and use it for temperature estimation through thermodynamic modeling. This should be performed for the Lakora samples as chlorite thermometry has already been applied on Torla samples in previous studies.

3. Size-fraction separations for finer size fractions (0.05-0.01 µm and < 0.01 µm) should be performed to reach conditions where the closure temperature and that of shearing are in the same range and then analyzing these fractions by the 40 Ar/ 39 Ar step-heating method to unravel the age of both faults activity. Université Bourgogne Franche-Comté 32, avenue de l'Observatoire 25000 Besançon

Conditions de déformation et datation 40 Ar/ 39 Ar de l'activité de failles enregistrées par les phyllosilicates (minéraux argileux) en environnement sédimentaire : exemples de failles chevauchantes du versant-sud Pyrénéen. Résume: La chaîne pyrénéenne présente des structures de déformation bien exposées et des roches sédimentaires syntectoniques bien conservées qui en font un objet idéal pour étudier les failles. En effet, les textures, structures, compositions chimiques et isotopiques enregistrées par le coeur de la faille chevauchante peuvent renseigner sur les conditions et mécanismes de la déformation et aussi contraindre dans le temps l'activité de la faille étudiée. Dans la présente thèse, trois chevauchements du versant sud Pyrénéen ont été étudiés pour mieux appréhender le comportement mécanique, chimique et isotopique des phyllosilicates dans des roches sédimentaires déformées. Ces roches sont d'âge éocène à triasique et sont impliquées dans de grand chevauchements (zone cisaillantes) à vergence sud. Ce travail combine observation pétrographique, analyse chimique, modélisation thermodynamique et technique de datation radiométrique 40 Ar/ 39 Ar sur des minéraux de moscovite/illite et de chlorite. La première faille étudiée est le chevauchement du Pic de Port Vieux (PPV), chevauchement de second ordre lié au chevauchement majeur de Gavarnie dans le sud-ouest de la Zone Axiale Pyrénéenne. Des mécanismes de pression-dissolution et recristallisation, accompagnés d'interactions avec un fluide très réducteur sont les principaux paramètres responsables des changements minéralogiques/chimiques observés dans la zone centrale de la faille. L'indice Kübler de la moscovite et les données thermométrique sur chlorite suggèrent des températures de 285°C ± 28°C pour l'activité de PPV. De plus, la datation 40 Ar/ 39 Ar de la moscovite syn-cinématique indique que la faille a fonctionné il y a 36.9 ± 0.2 Ma, ce qui coïncide avec l'âge de l'activité du chevauchement de Gavarnie. Les deux autres failles étudiées sont le chevauchement de Lakora qui est situé sur le bord sud de la zone Nord Pyrénéenne et celui de Monte Perdido (au niveau de Torla) situé dans la partie ouest de la zone Sud-Pyrénéenne. Ces deux chevauchements ont été affectés (déformés) par la mise en place de chevauchement de Gavarnie. Les observations pétrographiques et les analyses microstructurales ont démontré que la déformation est marquée par du plissement, du boudinage, par le développement d'une schistosité intense, de surfaces de cisaillement, de veines et par un enrichissement en phyllosilicates au coeur de la zone de faille des deux chevauchements. De manière similaire au chevauchement du Pic de PPV, les mécanismes de pression-dissolution et recristallisation sont les principaux mécanismes qui contrôlent la déformation et ils sont à l'origine de l'enrichissement en phyllosilicates néoformés dans les zones de failles des deux chevauchements. En se basant sur les mesures de l'indice de Kübler, il apparait que la déformation de Lakora et Torla s'est produite dans des conditions de température plus basse que celles enregistrées pour le chevauchement du PPV. Par ailleurs, es âges les plus jeunes obtenus par la technique 40 Ar/ 39 Ar ne peuvent être rattachés à l'âge de la déformation car ils sont plus vieux que les âges des sédiments impliqués dans les zones de faille. D'autres hypothèses sont proposées à la fin de cette thèse afin de comprendre les raisons de cette incohérence dans les âges et afin de dater la déformation de Lakora et Torla. Ainsi l'ensemble des résultats de cette thèse montrent que les minéraux phyllosilicatés peuvent être des outils thermochronologiques fiables permettant de dater avec précision l'activité des failles lorsqu'ils ont été combinés avec des préparations d'échantillons précises et caractérisation détaillée des échantillons. The Pyrenees belt features well-exposed deformation structures and well preserved syntectonic sedimentary rocks that make it ideally suited to study thrust faults. The texture, structure and chemical-isotopic compositions of synkinematic phyllosilicates are widely used to estimate the deformation conditions-mechanisms and timing of fault activities. Therefore, in the present thesis, three thrusts from the Pyrenean orogen have been studied to better understand the mechanical, chemical and isotopic behavior of phyllosilicates from deformed sediments of Eocene-Triassic age that have been involved in large southverging shear zones. This work combined petrographic observation, chemical analyses, and thermodynamic modeling with 40 Ar/ 39 Ar geochronology on muscovite/illite and chlorite. The first studied fault is the Pic de Port Vieux thrust (PPVT), a secondorder thrust related to the major Gavarnie thrust (GT) in the south-western part of the Pyrenees Axial Zone. The dissolutionrecrystallization, pressure solution mechanisms, and interaction with highly reductive fluids are the main parameters responsible for the mineralogical and chemical changes in the fault core zone. The Kübler index and chlorite thermometry suggest upperanchizone to epizone conditions with a temperature of 285°C ± 28°C for the PPVT activity. Moreover, the 40 Ar/ 39 Ar step-heating dating of synkinematic muscovite indicates that the fault activity occurred at 36.9 ± 0.2 Ma which coincides with the activity of the GT. The two other faults are: Lakora thrust that is located on the southern edge of the North Pyrenean Zone, and the Monte Perdido thrust (Torla location) situated on the western part of the South Pyrenean Zone. The two thrust are affected (deformed) by the emplacement of the Gavarnie thrust. The petrographic-microstructural analyses on these faults demonstrated that deformation is marked by folding, boudinage, intense cleavage, shear surfaces/veins and enrichment of phyllosilicates in the fault zone of both thrusts. Similar to the PPVT, pressure-solution and dissolution-recrystallization mechanisms are the main mechanisms that control deformation and enhanced the enrichment of the newly-formed phyllosilicates in the fault zones of both thrusts. Based on the Kübler index measurements, the deformation in the Lakora and Torla faults occurred at relatively lower temperature compared to the PPVT. The youngest total gas ages obtained by the 40 Ar/ 39 Ar technique are very old for the activity time of both thrusts as they are older than the depositional ages of the sediments in the fault zones. Further investigations are proposed at the end of this dissertation in order to better understand this anomaly in age and to successfully obtain the right age of the two thrusts activity. Based on the results of this thesis, phyllosilicate minerals proved to be reliable thermochronological tools for fault activity at low-grade metamorphism, when such tools are combined with careful sample preparations and detailed sample characterization. Keywords: Muscovite/illite; Chlorite; Thrust faults; Pyrenees; 40 Ar/ 39 Ar dating.

Figure 0 . 1

 01 Figure 0.1 The different types of faults. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 0 . 2

 02 Figure 0.2 Schematic model showing the fault zone structure. . . . . . . . . . . . . . . . . . . .

Figure 0 . 3

 03 Figure 0.3 Schematic model of fault rocks distribution with the fault regimes and mechanisms.

Figure 0 . 4

 04 Figure 0.4 The layer structure of clay minerals. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 0 . 5

 05 Figure 0.5 The layer structure of mica. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 0 . 6

 06 Figure 0.6 The polytypes of mica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 0 . 7

 07 Figure 0.7 Schematic for the layer structure of chlorite . . . . . . . . . . . . . . . . . . . . . . .

Figure 0 . 8

 08 Figure 0.8 Plotting illustrates the interlaboratory standardization method . . . . . . . . . . . .

Figure 0 . 9

 09 Figure 0.9 Schematic diagram showing a different 40 Ar/ 39 Ar age spectra . . . . . . . . . . . . .

Figure 0 .

 0 Figure 0.10 Plot showing the correlation between the percentage of detrital illlite (2M 1 ) and age Figure 0.11 Structural map of the Pyrenees with the locations of the three study areas . . . . . .

Figure 1 . 1

 11 Figure 1.1 Structural map of the Pyrenees and photographs of the Pic de Port Vieux outcrop .

Figure 1 . 2

 12 Figure 1.2 Pic de Port Vieux outcrop and sample locations . . . . . . . . . . . . . . . . . . . . .

Figure 1 .

 1 Figure 1.3 XRD patterns of randomly oriented preparations for bulk powder samples . . . . .

Figure 1 .

 1 Figure 1.4 XRD patterns of oriented preparations for < 2 µm fractions . . . . . . . . . . . . . . .

Figure 1 . 5

 15 Figure 1.5 The differences in textural and microstructural features between samples PPV12-07 and PPV12-05 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 1 .

 1 Figure 1.6 BSE images of samples PPV12-07(damage zone) and PPV12-05 (core zone) . . . . .

Figure 1 . 7

 17 Figure 1.7 Ternary and di-diagrams of chlorite and mica chemical composition . . . . . . . . .

Figure 1 .

 1 Figure 1.8 BSE images and Na 2 O map for samples PPV12-07 and PPV12-05 . . . . . . . . . . .

Figure 1 . 9

 19 Figure 1.9 The simulation results at different redox conditions. . . . . . . . . . . . . . . . . . . .

Figure 1 .

 1 Figure 1.10 The quantities of the different end members expected by modelling for chlorite and mica. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 2 . 1

 21 Figure 2.1 Structural map of the Pyrenees with the location of the study area. . . . . . . . . . .

Figure 2 . 2

 22 Figure 2.2 The sample locations and the structural organization of the studied fault zone. . . .

Figure 2 . 3

 23 Figure 2.3 Optical microscope images illustrating the differences in textural and microstructural features in fault zone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 2

 2 Figure 2.4 BSE images of the samples PPV12-07, PPV12-02a and PPV12-05. . . . . . . . . . . .

Figure 2

 2 Figure 2.6 X-ray diffraction patterns of oriented preparations samples . . . . . . . . . . . . . .

Figure 2 . 7

 27 Figure 2.7 Muscovite 001 peak decomposition of the samples PPV12-07 and PPV12-05 . . . .

Figure 2

 2 Figure 2.8 X-ray diffraction patterns of randomly oriented preparations samples . . . . . . . .

Figure 2 .

 2 Figure 2.9 40 Ar/ 39 Ar step-heating results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 2 .

 2 Figure 2.10 Structural sketch showing the structural relationships between the Pic de Port Vieux and Gavarnie thrusts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 3 . 1

 31 Figure 3.1 Structural map of the Pyrenees with the location of the study areas . . . . . . . . . .

Figure 3 . 2

 32 Figure 3.2 Two cross sections showing the structural setting of Lakora and Torla . . . . . . . .

Figure 3 . 3

 33 Figure 3.3 Photograph and stratigraphic column of the Lakora thrust . . . . . . . . . . . . . . .

Figure 3 . 4

 34 Figure 3.4 Photograph and stratigraphic column of the Torla thrust . . . . . . . . . . . . . . . .

Figure 3 . 5

 35 Figure 3.5 XRD patterns of randomly oriented preparations for Lakora samples . . . . . . . . .

Figure 3

 3 Figure 3.6 XRD patterns of oriented preparations for Lakora samples . . . . . . . . . . . . . . .

Figure 3 .

 3 Figure 3.7 Photographs, thin sections scans and optical microscope images of samples 15 LAK 1 and 15 LAK 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 3

 3 Figure 3.8 BSE images of the samples 15 LAK 1(less deformed) and 15 LAK 3 (highly deformed) Figure 3.9 BSE images and EDX-analyses of the sample 15 LAK 3 (highly deformed) . . . . . .

Figure 3 .

 3 Figure 3.10 Muscovite 001 peak decomposition of the samples 15 LAK 1 and 15 LAK 3 (fraction < 0.5 µm) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 3 .

 3 Figure 3.11 XRD patterns of randomly oriented preparations for the bulk and < 2 µm fraction of the samples 15 LAK 1 and 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 3 .

 3 Figure 3.12 40 Ar/ 39 Ar step-heating results of Lakora samples, 15 LAK 1 and 15 LAK 3 . . . . . . .

Figure 3 .

 3 Figure 3.13 XRD patterns of oriented preparations for Torla samples;15 TO 1 and 15 TO 4 . . . .

Figure 3 .

 3 Figure 3.14 Muscovite 001 peak decomposition of Torla samples; 15 TO 1 and 15 TO 4 (fraction < 0.5 µm) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 3 .

 3 Figure 3.15 40 Ar/ 39 Ar step-heating results of Torla sample; 15 TO 1 . . . . . . . . . . . . . . . . .

Figure 4 . 1

 41 Figure 4.1 Kübler index values of representative samples from the PPVT, Lakora and Monte Perdido thrusts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure 0 . 1 :

 01 Figure 0.1: The different types of faults, normal fault (a), strike-slip fault (sinistral) (b) and reverse fault (c) (from Fossen, 2010).

Figure 0 . 2 :

 02 Figure 0.2: Schematic model showing the fault core zone, damage zone and protolith within a strike-slip fault zone ( from Lin and Yamashita, 2013).

Fault

  rocks formed by this deformation mechanism can display fractures/veins that are formed by brittle mechanisms beside enrichment of phyllosilicates by pressure-solution and recrystallization GENERAL INTRODUCTION 2. TERMINOLOGY AND DEFINITIONS mechanisms. The depth of the transition from ductile to brittle (frictional-viscous) deformation depends on several parameters such as the lithology and geothermal gradient, fluid pressure, grain-size and the stress field orientation, etc.

Figure 0 . 3 :

 03 Figure 0.3: Schematic model of fault rocks distribution in a normal fault with fault regimes, mechanisms and the corresponding metamorphic environments/facies (from Cantarero, 2013,originally synthesized from Sibson, 1977).

  on the layer structure, clay minerals are classified into 1:1 (T-O) layer structure and 2:1 (T-O-T) layer structure as shown in Figure 0.4. In the 1:1 layer structure, one tetrahedral sheet (T) is linked with one octahedral sheet (O) by O-H-O bonds with no interlayer cations (e.g. kaolinite and serpentine).The 2:1 layer structure has one octahedral sheet sandwiched between two tetrahedral sheets and the interlayer materials link the different layers together (e.g. smectite, illite, talc, etc.). In smectite, the interlayer cations have weak-bonds and are variably hydrated resulting in swelling characteristic of smectitic clay minerals. In some clay minerals such as chlorites, a hydroxyl octahedral sheet is present in the interlayer space instead of cations and it links with the 2:1 (T-O-T) layer structure yielding a 2:1:1 (T-O-T-O) layer structure. However, taking into account the recent recommendations of the AIPEA

Figure 0 . 4 :

 04 Figure 0.4: Schematic for tetrahedral and octahedral sheets and the 1:1 layer and the 2:1 layer structure. Large white circles are oxygens, large grey circles are hydroxyls, small white circles are octahedral ions and small black circles are tetrahedral ions (from Christidis, 2010).

Figure 0 . 5 :

 05 Figure 0.5: Schematic for the layer structure of micas, in this example K is the interlayer cation. The 10 Å refers to the d-spacing which include TOT + interlayer cation (modified from, Grim, 1962).

Figure 0 . 6 :

 06 Figure 0.6: Mica polytypes, (a) 1M polytype, (b) 2M 1 polytype and (c) 3T polytype. (modified from Moore and Reynolds, 1997).

Figure 0 . 7 :

 07 Figure 0.7: Schematic for the layer structure of chlorite. The 14 Å refers to the d-spacing which include TOT + octahedral interlayer (brucite-like sheet) (modified from, Grim, 1962).

  values measured at each laboratory should be plotted against the CIS values and then corrected with the equation: KI (CIS) = a * KI (my lab) + b as shown in Figure 0.8. This calibration method is called interlaboratory standardization and allows data sets produced by different research groups to be

Figure 0 . 8 :

 08 Figure 0.8: Plotting illustrates the interlaboratory standardization method. Experimental FWHM in the x axis represents full width at half maximum values of samples and the standards calculated at each laboratory. While in the y axis represents the crystallinity index standard (CIS) calibrated values. The equation of the regression curve is used to convert the experimental values into calibrated values.

Figure 0 . 9 :

 09 Figure 0.9: Schematic diagram showing a different 40 Ar/ 39 Ar age spectra.The top diagram shows the concentration of 40 Ar and 39 Ar across three crystals and the bottom diagram illustrates the associated 40 Ar/ 39 Ar age spectrum for each case. (a) Undisturbed subsequent to initial crystallization and rapid cooling yields a flat age spectrum. (b) The case of partial loss of radiogenic Ar in recent geological times. (c) Similar case to (b), except that significant accumulation of radiogenic Ar has occurred since the reheating event owing to the passage of time (from Harrison, 2005 and originally presented by McDougall and Harrison, 1999).

Figure 0 . 10 :

 010 Figure 0.10: Plotting correlates the percentage of detrital illlite (2M 1 polytype) and age in different size fractions (from van der Pluijm et al., 2001 ). The percentage of detrital illite (2M 1 ) is based on X-ray analyses quantification. The lower intercept at 0% detrital illite represents the age of faulting (∼ 52 Ma ago), whereas the upper intercept at 100% detrital illite represents the metamorphic/cooling age of micas in the exhumed source region (∼ 172 Ma ago).

Figure 0 . 11 :

 011 Figure 0.11: Structural map of the Pyrenees with the location of the three study areas (modified from Teixell, 2000).

1 )

 1 is focused on the Pic de Port Vieux Thrust (PPVT) and is written in the form of a scientific paper which has been published in the Applied Clay Science Journal. In this chapter[START_REF] Abd Elmola | Textural-chemical changes and deformation conditions registered by phyllosilicates in a fault zone (Pic de Port Vieux thrust, Pyrenees)[END_REF], phyllosilicate minerals (muscovite and chlorite) were used to study the textural-chemical changes attributed to the fault activity and fluid circulation. Moreover, the crystallinity and chemical composition of muscovite and chlorite respectively were used to estimate the deformation conditions of the PPVT activity. The analytical methods of this work include: X-ray diffractions (XRD), Scanning Electron Microscopy (SEM), Electron Probe Micro-Analyzer (EPMA), Thermodynamic modelling (with the CHLMICAEQUI program) and fluid-rock interaction modelling (with the PhreeqC program).Chapter (2) is also focused on the PPVT and is written in the form of a scientific paper which is submitted to the Journal of Metamorphic Geology. The main objective of this paper(Abd Elmola et al., submitted) is to date the PPVT activity using synkinematic muscovite. Characterization for the different types/generations of muscovite was performed and then different-sized fractions of two GENERAL INTRODUCTION samples from the fault zone have been dated by the 40 Ar/ 39 Ar step-heating method. In addition other techniques have been used to facilitate the interpretation of the 40 Ar/ 39 Ar results, including optical microscopy, XRD, SEM, XRD-peaks decomposition with the Fityk software, and Rietveld quantification of mica polytypes with the Topas software.Chapter (3) is focused on the Lakora and Torla outcrops. The aims of this chapter are to investigate the phyllosilicate minerals in both thrusts, define their origins and texture and estimate their deformation conditions. In addition, to date the different generations of micas and to estimate the timing of the two thrusts activities. The samples from each thrust have been characterized by optical microscopy, XRD, SEM, XRD-peak decomposition with the Fityk software and then two samples from each fault were dated by the 40 Ar/ 39 Ar step-heating method. In case of the Lakora fault, the choice of two representative samples for dating is based on the results of an associated project done by Rafia Nazir during her masters internship. In the case of Torla outcrop, the selection of samples is based on previous published works on the same outcrop.

Figure 1 . 1 :

 11 Figure 1.1: (a) Structural map of the Pyrenees with the location of the study area (modified from Teixell et al. (2000). (b), (c) Photograph and sketch respectively showing the Pic de Port Vieux culmination, modified from Grant (1989). (d) Stratigraphic log for the Pic de Port Vieux outcrop, modified from[START_REF] Grant | Episodic discrete and distributed deformation: consequences and controls in a thrust culmination from the central Pyrenees[END_REF] and[START_REF] Trincal | Temperature micro-mapping in oscillatory-zoned chlorite: Application to study of a green-schist facies fault zone in the Pyrenean Axial Zone (Spain)[END_REF].

Figure 1 . 2 :

 12 Figure 1.2: The Pic de Port Vieux outcrop, (a) Photograph showing the hanging wall and footwall of Pic de Port Vieux thrust. (b) Transect along the hanging wall with the sample locations.

  increases gradually toward the fault contact (Figure1.4) indicating a phyllosilicate enrichment toward the core fault zone.

Figure 1 .

 1 Figure 1.3: X-ray diffraction patterns of randomly oriented preparations for bulk powder of five representative samples along the transect in the hanging wall of the Pic de Port Vieux. Chl = chlorite, Mus = muscovite, Hm = hematite and Qz = Quartz. The 104 reflection of hematite and the 060 reflections of phyllosilicates are highlighted by a dashed rectangle in the figure.

Figure 1 .

 1 Figure 1.4: X-ray diffraction patterns for oriented preparations < 2 µm fractions (untreated, air dried conditions), for five representative samples along transect in the hanging wall of the Pic de Port Vieux. Chl = chlorite, Mus = muscovite, Qz = Quartz and Rt = rutile.

Figure 1 . 5 :

 15 Figure 1.5: Photographs illustrating the differences in textural and microstructural features between samples PPV12-07 and PPV12-05. (a), (b) Rock chip scans showing the difference in color and the presence of more veins in the PPV12-05 sample. (c), (d) Optical microscope pictures in cross-polarized light. The quartz grains in the matrix of sample PPV12-07 have a random orientation and large grain size. Toward the fault contact those grains became smaller and more elongate following the shearing direction indicated by dashed lines in the picture (d). There is enrichment in muscovite (characterized by bright 2nd order colors) in the matrix of the PPV12-05 sample. The change in the quantity and grain size of quartz are shown in SEM-BSE images in (e) and (f) images.

Figure 1 . 6 :

 16 Figure 1.6: Backscattered electron images (BSE) of samples PPV12-07(damage zone) and PPV12-05 (core zone). Qz refer to quartz, Chl = chlorite, Mus = muscovite, Hm = hematite, Ca = calcite and Rt = rutile. (a) and (b) images of the matrix of the damage zone and the core zone. Recrystallized muscovite in the matrix of the core zone presented in image (b) characterized by the step like shaped on the boundary with quartz grains. The chlorite-muscovite stacks are presented in images (c) and (d), in the core zone, these stacks are folded, broken and have smaller grain size (highlighted by black dashed lines in the image (d)). (e) and (f) images showing part of vein with newly formed chlorite.

Table 1 . 1 :

 11 Calculated chlorite structural formula of some representative analyses from the damage and core zones of the Pic de Port Vieux. Calculated temperatures using chlorite thermometry of each analysis are presented.

Figure 1 . 7 :

 17 Figure 1.7: Ternary and di-diagrams of chemical analyses for chlorite and micas from the core zone (sample PPV12-05) and the damage zone (sample PPV12-07). (a) Fe + Mg -Si-Al (t ot al ) ternary diagrams and Fe/(Fe + Mg) vs. Si plot for chlorite . (b) M + -4Si-R 2+ ternary diagrams[START_REF] Meunier | Solid solutions in I/S mixed-layer minerals and illite[END_REF] and Na/ (Na + K) vs. Fe plot for muscovite. M + = Na + + K + + 2Ca 2+ , 4Si = (Si/4) and R 2+ = (Mg + Fe + Mn) and Di-Tri is (dioctahedral-trioctahedral substitutions). Chlorite and muscovite initial and average compositions obtained by modelling at high reductive conditions are highlighted with the star icon.

  vs. Fe plot (Figure 1.7 b). Large muscovite grains have the following average structural formula, (Si 3.14 Al 0.86 ) O 10 (Al 1.86 Mg 0.08 Fe 0.07 Ti 0.01 ) (OH) 2 K 0.84 Na 0.10 . The small muscovite grains structural formula is (Si 3.26 Al 0.74 ) O 10 (Al 1.74 Mg 0.16 Fe 0.13 ) (OH) 2 K 0.91 Na 0.03 similar to the average composition of mica CHAPTER 1 1.4. RESULTS from the core zone. SEM-BSE images and compositional maps of muscovite Na 2 O wt% are presented in Figure 1.8 for samples PPV12-07(damage zone) and PPV2-05(core zone) respectively. The random coarse muscovite aggregates are shown in SEM-BSE image beside the large chlorite in the matrix of the damage zone (Figure 1.8 a); in the core zone muscovite grains are smaller and follow the foliation

Table 1 . 2 :

 12 Calculated muscovite structural formula from the damage and core zones of the Pic de Port Vieux thrust.

Figure 1 .

 1 Figure 1.8: (a) and (b) SEM-BSE images for the damage zone sample PPV12-07 and the core zone sample PPV12-05 respectively. (c) and (d) quantitative maps showing Na 2 O wt% in muscovite for the samples PPV12-07 and PPV12-05 respectively.

Figure 1 . 9 :

 19 Figure 1.9: The simulation results at different redox condition. The first column in the left represents the input data and the others column are corresponding to the minerals quantities obtained by the model at different reducing conditions. (a) Showing the simulation for all the minerals and (b) is zooming for iron rich minerals.

Figure 1 .

 1 Figure 1.10: The quantities of the different end members expected by modelling for chlorite and mica are shown in (a) and (c) respectively. The first column in the left is corresponding to the input composition. (b) and (d) are presenting the cation contents in chlorite and mica at Eh=-0.830:-0.841 respectively.

C

  Panorama from the summit of the Pic de Port Vieux "' In this chapter, the aim is to use the isotopic composition of synkinematic muscovite in order to date the Pic de Port Vieux thrust activity. The calculated age by the 40 Ar/ 39 Ar step-heating method is discussed with respect to available geochronological data on the same studied area. This chapter is presented in the form of a scientific article which was submitted to the JOURNAL OF METAMORPHIC GEOLOGY. '" features well-exposed deformation structures and exceptionally well preserved syntectonic sedimentary rocks in foreland basins that make it ideally suited to study thrust faults.In this paper, we present the first 40 Ar/ 39 Ar age of the Pic de Port Vieux thrust (PPVT) located in the south-western part of the Pyrenean Axial Zone. The PPVT is a second-order thrust related to the major Gavarnie thrust. The PPVT footwall comprises Upper Cretaceous dolomitic limestone, while the hanging wall consists of Lower Triassic pelites and sandstones. The core zone in the fault hanging wall is composed of intensely foliated green pelites. Whereas the damage zone comprises green (lower part) to red (upper part) pelites featuring macroscopic penetrative cleavage and numerous fractures and quartz-chlorite-calcite veins. Thrusting occurred under anchizone/epizone metamorphic conditions, i.e. temperature of about 250-300 • C. A vertical transect in the fault hanging wall was investigated in detail to characterize the different generations/types of muscovite and to date the thrust activity by using different grain-size fractions of muscovite from the core and damage zones.

  foreland basin. Thus, the aims of the present study are(1) to characterize micas in the hanging wall pelites, determine their origin, and their formation mechanisms. (2) To date the different generations of micas, determine the timing of the PPVT activity and discuss this age with respect to available data on the GT, which will help to reappraise part of the thrust tectonic history in the Axial Zone of the Pyrenees.

Figure 2 . 1 :

 21 Figure 2.1: Structural map of the Pyrenees with the location of the study area (modified from Teixell, 2000). (b), (c) Photograph and sketch, respectively, showing the Pic de Port Vieux thrust (modified from Grant, 1989). (d) Stratigraphic log for the Pic de Port Vieux outcrop (modified from[START_REF] Grant | Episodic discrete and distributed deformation: consequences and controls in a thrust culmination from the central Pyrenees[END_REF]. PPVT and GT refer to the Pic de Port Vieux thrust and the Gavarnie thrust respectively.

  is cut by numerous secondary faults, most of them being extensional faults with low-angle southward dips or high-angle northward dips. Quartz-chlorite-calcite veins are abundant in the damage zone, the largest being up to several cm thick and several meters long.They feature different generations and different kinematics (extensional and shear veins), with folded pre-cleavage (S) veins, S-parallel veins (syn-to post-S), veins along shear surfaces (also syn-to post S) and oblique late veins. The abundance of these veins/veinlets decreases when moving away from the fault contact as shown in Figure 2.2 (only the visible veins/veinlets at the scale of Figure 2.2a are presented in the schematic diagram of Figure 2.2b, while the smaller veins are shown in the thin sections of Figure 2.2c-e). Note that veins are also present in the core zone, but with geometries and kinematics difficult to analyze at the macroscopic scale.Three representative samples from a transect in the hanging wall pelites of the fault zone(Figure 2.2a) were investigated in details to characterize the changes in mineralogical assemblage, strain pattern and muscovite textural/compositional features. The three samples are, from top to bottom:-PPV12-07 from the red pelites zone of the damage zone (∼ 1.3 m from the fault contact), -PPV12-02a from the boundary between the red and green pelites in the lower part of the damage zone (∼ 0.65 m from the fault contact), -PPV12-05 from the intensely foliated green pelites of the core zone (a few cm from the fault contact).

1

 1 Changes in the bulk mineralogical assemblage The structural and mineralogical changes observed in the pelites across the hanging wall fault zone are shown in Figure 2.2, Figure 2.3 and Figure 2.4. At the outcrop scale, the main observed change is the color change of the Triassic pelites from red to green when getting closer to the fault contact. Previous

  Figure 2.4).

Figure 2 . 2 :

 22 Figure 2.2: The Pic de Port Vieux thrust outcrop, (a) Photograph showing the Pic de Port Vieux thrust fault zone with the sample locations. (b) Schematic diagram of the structural organization corresponding to the photograph in (a).The sketch shows the north-dipping cleavage (in blue), shear surface (in black) and veins (in green), labeled S, C and V respectively. In the footwall, the label F refers to the foliation in the mylonite. Only major veins visible at this scale of observation are shown on the sketch (with undifferentiated kinematics and generation), but there are also shear veins along the C surfaces and smaller veins are numerous throughout the outcrop (cf. thin sections). (c to e) Thin section scans for the three samples PPV12-07 (outer damage zone), PPV12-02a (damage zone at the red-green zone boundary) and PPV12-05 (core zone), respectively. The GPS coordinates of the sampled outcrop are 42 • 43'40.52" N and 0 • 9'44.67" E.

  cleavage or cut the latter at high-angle(Figure 2.2b, 2c and Figure 2.3a). The µm to mmscale veinlets that are S-parallel may correspond to en-echelon tension gashes recording back-shear thrusting as suggested by[START_REF] Grant | Chemistry, source, and behavior of fluids involved in alpine thrusting of the Central Pyrenees[END_REF]. The high-angle veinlets are commonly folded by cleavage and cut by the S-parallel veinlets. Moreover, the cleavage is sometimes deformed by mm-scale shear bands with a main top-the-south normal kinematic(Figure 2.3b). When getting closer to the fault, i.e. along the red /green pelites boundary, the veinlets parallel to the cleavage become more abundant (Figure 2.3c). Localized mm-scale high-strain zones show a well-foliated muscovite-rich matrix with elongated quartz grains (Figure 2.3d). Some S-parallel veins display boudinage while the high-angle veins are folded and rotated (Figure 2.3e) with cleavage as axial plane of folds. Increase of strain is also attested by strain concentration around the rigid quartz-calcite veins folded during cleavage-normal shortening of the soft mica-rich matrix, i.e. cleavage and folds are cogenetic and attest shortening normal to cleavage during shearing (Figure 2.3e). Closer to the fault contact, the cleavage intensity increases downwards, where it interferes with low-dip shear surfaces, defining the top-to-the-south S-C shear zone corresponding to the core zone. Veins and veinlets are more abundant compared to the damage zone, and they are intensely sheared, folded and boudinaged (Figure 2.2e, Figure 2.3f and Figure 2.3g). Moreover, the cleavage becomes more penetrative together with the decreasing of quartz quantity and enrichment of newly formed muscovite.

Figure 2 . 3 :

 23 Figure 2.3: Optical microscope images illustrating the differences in textural and microstructural features of the three samples PPV12-07 (a, b; outer damage zone), PPV12-02a (c, d, e; lower damage zone at the red-green zone boundary) and PPV12-05 (f, g; core zone), respectively (cf. location of samples on Figure 2.2). (a) Veinlets parallel to or at high angle of and deformed by cleavage (S). (b) Cleavage deformed by mm-scale shear bands with a top-the-south normal kinematic. (c) S-parallel veinlets. (d) Localized S-parallel mm-scale high-strain zone. (e) Folded quartz-calcite veins with axial plane cleavage in the matrix; Dark seams attest of strain concentration (pressure solution) around the rigid vein fragments, related to cleavage-normal shortening. (f) Sigmoidal cleavage in the S-C shear zone, indicating top-to-the left shearing. (g) Folded vein fragment showing top to the left shearing with axial plane cleavage in the matrix. Chl = chlorite; Qz = quartz; S: cleavage.

Figure 2 . 4 :

 24 Figure 2.4: Backscattered electron (BSE) images of the samples PPV12-07 (outer damage), PPV12-02a (damage zone at the red-green zone boundary) and PPV12-05 (core zone), respectively. (a) Showing quartz, muscovite, hematite and chlorite minerals in the damage zone with a left-dipping cleavage. (b), (c) Illustrating the presence of hematite only in the red part of the sample PPV12-02a and the decrease in the abundance and grain-size of quartz grains. (d) Showing the enrichment of muscovite in the matrix of the core zone and less abundant quartz compared to the damage zone. Large muscovite grains in the damage zone matrix are presented in image (e), they begin to be folded close to the green zone as shown in image (f). (g), (h) Showing the elongated shape of quartz grains and the brighter contrast of muscovite grains in the green zone compared to the red zone (cf. Figure 2.5). Chl = chlorite; Hm = hematite; Mus = muscovite; Qz = quartz; Rt = rutile.

Figure 2 . 5 :

 25 Figure 2.5: BSE images (a, b, c, e) and EDX analyses (d, f) illustrating the texture and chemistry of muscovite in the three samples PPV12-07 (outer damage zone), PPV12-02a (damage zone at the red-green zone boundary) and PPV12-05(core zone) respectively. (a), (b) Showing two groups of muscovite present in the damage zone matrix, muscovite 1 and 2 respectively. (c), (f) Images showing the third muscovite group termed muscovite 3 which is abundant in the core zone and characterized by smaller grain-size and brighter contrast. (d), (f) Showing the difference in the chemical composition between muscovite 2 and muscovite 3. Chl = chlorite; Hm = hematite; Mus = muscovite; Qz = quartz; Rt = rutile.

Figure 2 .

 2 Figure 2.6: X-ray diffraction patterns of oriented preparations (untreated, air dried conditions) for the fractions 16-2 µm, 2-0.5 µm and < 0.5 µm. The fractions are from the samples, PPV12-07 (outer damage zone) and PPV12-05(core zone). Chl = chlorite, Mus = muscovite, Qz = quartz, Ca= calcite and Rt = rutile.

Figure 2 . 7 :

 27 Figure2.7: Muscovite 001 peak decomposition using the Fityk 0.9.8 software[START_REF] Wojdyr | Fityk: a general-purpose peak fitting program[END_REF] of the fraction < 0.5 µm for the samples PPV12-07 (damage zone) and PPV12-05 (core zone). WC = well crystallized and PC= poorly crystallized.

Figure 2 .

 2 Figure 2.8: X-ray diffraction patterns of randomly oriented preparations for the fractions 16-2 µm, 2-0.5 µm and < 0.5 µm with highlighting muscovite polytypes. The fractions are from the samples, PPV12-07 (outer damage zone) and PPV12-05(core zone).

C

  40 AR/ 39 AR DATING OF THRUST-ING RECORDED BY PHYLLOSILICATES IN FAULT ZONES: EXAMPLES FROM LAKORA AND MONTE PERDIDO THRUSTS (PYRENEES). Panorama from Lakora outcrop "' In this chapter, the aim is to estimate the mechanisms, deformation mechanisms and the thrusting time of the Lakora and the Monte Perdido faults using synkinematic phyllosilicate minerals. The results of the present chapter are discussed with other available data from the same study areas. '" focus on two faults (the Lakora and the Monte Perdido thrusts) from the Pyrenees orogen. The two thrusts are located on the southern edge of the North Pyrenean Zone (Lakora thrust) and on the western part of the South-Pyrenean Zone (Monte Perdido thrust at Torla outcrop) of the central Pyrenees. The Lakora thrust exposes Albian-Santonian breccias and conglomerates in the hanging wall above Campanian-Maastrichtian turbidites in the footwall. While at Torla outcrop, the hanging wall is composed of Paleocene limestone and the footwall comprises Ypresian

Figure 3 . 1 :

 31 Figure 3.1: Structural map of the Pyrenees with the location of the study areas (from Teixell, 2000). The two studied outcrops (Lakora and Torla) are marked by star-shape in the map. The two green lines indicate cross-sections in Figure 3.2

Figure 3 . 2 :

 32 Figure 3.2: Two cross sections (locations in Figure 3.1) showing the structural setting of the two studied areas. (a) Regional cross-section of the west-central Pyrenees illustrating Lakora thrust structural setting (from Teixell, 2000). (b) Structural cross section of the Axial Zone and Jaca basin showing Monte Perdido thrust (from Jolivet et al., 2007).

Figure 3 . 3 :

 33 Figure 3.3: The Lakora thrust outcrop, (a) Photograph showing the hanging wall and footwall of the thrust fault zone. (b) Simplified stratigraphic column showing the position of the Lakora and Larra thrusts with the sample locations (simplified after[START_REF] Teixell | Geotectónica de los Pirineos[END_REF]. The sample are labelled as 15LAK 1,3,4,6 and 9.

  selected for the 40 Ar/ 39 Ar step-heating dating: sample 15 TO 1 from the core fault zone ∼ 10 cm from the limestone contact, and sample 15 TO 4 from the footwall ∼ 10 m away from the limestone contact (Figure 3.4b).

Figure 3 . 4 :

 34 Figure 3.4: The Torla outcrop, (a) Photograph showing the hanging wall, fault zone and upper part of the footwall of the Monte Perdido thrust. (b) Schematic diagram showing the structural organization in the studied fault zone with the sample locations (modified from Lacroix et al., 2011. The samples are labelled as 15 TO 1 and 15 TO 4.

Figure 3 . 5 :

 35 Figure 3.5: X-ray diffraction patterns of randomly oriented preparations for the bulk powder of Lakora samples (15 LAK 1,3,4,6 and 9). Chl = chlorite, Mus = muscovite, Qz = quartz, Rt = rutile, Alb = albite and Ca= calcite.

Figure 3

 3 Figure 3.6: X-ray diffraction patterns of oriented preparations (untreated, air dried conditions) for the fractions 16-2 µm, 2-0.5 µm and < 0.5 µm. The fractions are from the samples, 15 LAK 1 and 15 LAK 3. Chl = chlorite, Mus = muscovite, Qz = quartz, Rt = rutile and Alb = albite.

  7 and Figure 3.8. At the outcrop scale, the deformation gradient between the two samples can be clearly observed. Sample 15 LAK 3 shows more evidences of deformation structures compared to sample 15 LAK 1, such as folds and crenulation cleavage as shown in Figure 3.7a and b. At the thin-section scale, sample 15 LAK 1 has a horizontal cleavage parallel to the bedding plane with some cleavage-parallel quartz veins (Figure 3.7c). Moreover, the optical microscope image (Figure 3.7e) shows the abundance of quartz and muscovite/illite in the matrix. In the sample 15 LAK 3, quartz veins are deformed and folded reflecting higher deformation impact in this sample. Furthermore, there is development of a new cleavage S 2 oriented top to left (sub-vertical) along the fold axial plane that cuts the primary cleavage S 0 /S 1 (sub-horizontal) as shown in Figure 3.7d. The quartz and muscovite/illite grains follow the two cleavage directions as shown by the optical microscope image (Figure 3.7d).

Figure 3

 3 Figure 3.7: (a, b) Photographs showing the locations where the two samples 15 LAK 1 and 15 LAK 3 have been collected. (c, d) Scan for the thin sections of the two samples showing the quartz veins and cleavage. (e, f) Optical microscope images for the matrix of the two samples.

Figure 3 . 8 :

 38 Figure 3.8: Backscattered electron (BSE) images of the two samples 15 LAK 1(less deformed) and 15 LAK 3 (highly deformed). (a) Large quartz, muscovite and chlorite grains are parallel to the horizontal cleavage while in (b) the grains follow the oblique S 2 cleavage. (c) High magnification BSE image shows the large elongated grains and the chlorite/mica stacks in the matrix of the less deformed sample. In the highly-deformed sample, the chlorite and muscovite/illite are folded and located along the two cleavage S 0 /S 1 and S 2 as shown in (d).In (e, f) the newly formed chlorite and muscovite/illite in both samples display smaller grain-size. Chl = chlorite, Mus = muscovite, Qz = quartz, Rt = rutile, Pyr (pyrite) and Alb = albite.

Figure 3 . 9 :

 39 Figure 3.9: (a) Backscattered electron (BSE) image with high magnification of the sample 15 LAK 3 (highly deformed). (b, c and d ) EDX-spectra analyses for the muscovite, chlorite and albite respectively. Chl = chlorite, Mus = muscovite, Qz = quartz, Rt = rutile, Pyr (pyrite) and Alb = albite.

Figure 3 .

 3 Figure 3.11: X-ray diffraction patterns of randomly oriented preparations for the bulk and the < 2 µm fraction of the samples 15 LAK 1(less deformed) and 15 LAK 3 (highly deformed) with highlighting muscovite polytypes (2M 1 and 1M).

Figure 3 .

 3 Figure 3.13: X-ray diffraction patterns for oriented preparations (untreated, air dried conditions) for the fractions 16-2 µm, 2-0.5 µm and < 0.5 µm. The fractions are from Torla samples; 15 TO 1(fault core zone) and 15 TO 4 (footwall turbidites). Chl = chlorite, Mus = muscovite, Qz = quartz, Ca= calcite, Rt = rutile and Alb = albite.

Figure 3 . 14 :

 314 Figure 3.14: Muscovite 001 peak decomposition using the of the fraction < 0.5 µm for Torla samples; 15 TO 4 (footwall turbidites) and 15 TO 1 (fault core zone). WC = well crystallized and PC= poorly crystallized.

  Furthermore, calculation of the Kübler index was performed on the 001 muscovite reflection for the 15 TO 1 and 15 TO 4 samples and the results are shown in Table 3.1. The KI values range from 0.27 to 0.29 • 2θ (Kübler-Kisch scale) in the 15 TO 4 sample and 15 TO 1 respectively suggesting upperanchizone conditions.

Figure 3 .

 3 Figure 3.15: 40 Ar/ 39 Ar step-heating results for the Torla sample; 15 TO 1 (core zone).The results show the age spectra of the 16-2 µm, 2-0.5 µm and < 0.5 µm fractions. TGA refers to total gas age.

  ture conditions of fault activity. The results suggested the following deformation conditions for the activities of the three studied thrust faults: -In the Pic de Port Vieux thrust (PPVT) (southern central part of the Pyrenees Axial Zone), the deformation occurred under upper-anchizone to epizone grade conditions and a temperature of about 285 • C ± 28 • C based on Kübler index and chlorite thermometry results respectively (Abd Elmola et al., 2017). -In the Monte Perdido thrust (Torla outcrop) (western part of the South Pyrenean Zone), the thrusting occurred at upper-anchizone conditions based one Kübler index values. -In the Lakora thrust (southern edge of the North Pyrenean Zone), Kübler index results suggest diagenetic to anchizone conditions for thrusting activity. These KI results suggest relatively higher metamorphic grade conditions for the PPVT activity compared to the Monte Perdido and Lakora thrust activities as shown in Figure 4.1. These data are consistent with temperature estimations of other previous studies in the same areas. For example, for the PPVT Banks et al. (1991), Grant (1989), Grant et al. (1990), McCaig et al. (2000a) suggested a temperature

Figure 4 . 1 :

 41 Figure 4.1: Kübler index values of representative samples from the PPVT, Lakora and Monte Perdido thrusts. Only the two samples that have been selected for 40 Ar/ 39 Ar dating from each thrust are shown in this diagram.

  Mots clés: Moscovite/illite; Chlorite; Failles chevauchement; Pyrénées; Datation 40 Ar/ 39 Ar. Deformation conditions and 40 Ar/ 39 Ar dating of fault activity registered by phyllosilicates (clay minerals) in a sedimentary environment: examples of the south-verging thrust faults in the Pyrenees. Abstract:

Table 0 .

 0 1 Fault rocks classification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Table 1 .

 1 1 Calculated chlorite structural formula of Pic de Port Vieux samples. . . . . . . . . . .

Table 1 .

 1 2 Calculated muscovite structural formula of Pic de Port Vieux samples. . . . . . . . .

Table 1 .

 1 3 Kübler index data of five representative samples from the PPVT. . . . . . . . . . . . .

Table 1 .

 1 4 Temperature estimation using chlorite thermometry. . . . . . . . . . . . . . . . . . . .

Table 1 .

 1 5 The initial red pelites composition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Table 1 .

 1 6 The composition of the pore fluids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Table 2 .

 2 1 Summary of the 40 Ar/ 39 Ar data and polytype of muscovite . . . . . . . . . . . . . . .

Table 3 .

 3 1 Kubler index values of some representative samples from Lakora and Torla faults. . . Table3.2 Summary of the 40 Ar/ 39 Ar step-heating data of Lakora and Torla samples. . . . . . .

	xvii

  . In this section, basics of the two methods, principles, advantages and associated problems of the 40 Ar/ 39 Ar step-heating method are presented. The conventional K-Ar geochronology is based on the natural decay of the 40 K isotope into radiogenic 40 Ar (designated as

	40 Ar*). The ratio of 40 K to that of 40 Ar* in a sample is directly related to the time elapsed since the
	beginning of trapping of 40 Ar* in the mineral lattice. The amounts of 40 K and 40 Ar are measured by
	different techniques and thus, from separate aliquots of the sample. The potassium is quantified by
	flame photometry or atomic absorption spectroscopy, whereas 40 Ar is measured by mass spectrometry
	from the gases released after sample melting under vacuum.
	The 40 Ar/ 39 Ar geochronology has its foundations in the K-Ar isotopic dating technique. In this variant
	of the K-Ar technique, a sample is irradiated with fast neutrons to convert 39 K to 39 Ar (n,p) reaction
	in a nuclear reactor. The 39 Ar is proportional to the initial 40 K and as the 40 K/ 39 K ratio is essentially
	constant in nature, the 40 Ar/ 39 Ar ratio is proportional to the age. The 40 Ar/ 39 Ar age is calculated from
	the following equation:

  .1, then plotted in (Fe + Mg) -Si -Al (total) ternary diagram and in Fe/(Fe + Mg) vs. Si diagram (Figure 1.7 a). Newly formed chlorite from both the damage and the core zone is situated between clinochlore-daphnite, sudoite and amesite end-members. Si values vary from 2.68 to 2.87 apfu, Al total from 2.61 to 2.87 apfu, Fe from 1.59 to 2.23 apfu and Mg from 2.08 to 2.80 apfu. (Si 2.78 Al 1.22 )O 10 (Al 1.52 Mg 2.57 Fe 1.73 )(OH) 8 is an average structural formula for newly formed chlorite from the damage zone (based on 89 analyses) while the average structural formula for chlorite from the core zone is (Si 2.77 Al 1.23 )O 10 (Al 1.53 Mg 2.33 Fe 1.97 )(OH) 8 (based on 80 analyses).

Table 2 . 1 :

 21 Summary of the 40 Ar/ 39 Ar data and proportions of muscovite polytype for the samples PPV12-07 and PPV12-05.

Age (Ma) Error (Ma) Steps 40 Ar/ 39 Ar 38 Ar/ 39 Ar 37 Ar/ 39 Ar 36 Ar/ 39 Ar 40 Ar * / 39 Ar (k) 39 Ar (k) (%) 40 Ar * (%) Age (Ma) Error (Ma) Steps 40 Ar/ 39 Ar 38 Ar/ 39 Ar 37 Ar/ 39 Ar 36 Ar/ 39 Ar 40 Ar * / 39 Ar (k) 39 Ar (k) (%) Age (Ma) Error (Ma) Steps 40 Ar/ 39 Ar 38 Ar/ 39 Ar 37 Ar/ 39 Ar 36 Ar/ 39 Ar 40 Ar * / 39 Ar (k) 39 Ar (k) (%) 40 Ar * (%)

		18.937	0.013	0.000	0.002	18.387	97.1	4.8	111.2	0.4
		19.475	0.014	0.009	0.002	18.891	97.0	5.6	114.1	0.4
	20.168 Sample: PPV12-07 (Bulk) ; J = 0.00339410 ± 0.00001018 , Total gas age = 102.0 ± 0.6 Ma, 39 Ar recoil = 5.0 (%) 0.014 0.008 0.002 19.713 97.7 4.7 26.018 0.039 0.022 0.088 0.076 0.3 5.0 20.327 0.013 0.010 0.002 19.853 97.7 5.1 18.268 0.022 0.020 0.028 9.843 53.9 0.5 21.537 0.013 0.017 0.002 20.971 97.4 6.5 14.716 0.015 0.011 0.014 10.513 71.4 1.5 22.664 0.013 0.011 0.001 22.259 98.2 5.0 13.504 0.015 0.013 0.008 11.171 82.7 2.4 23.574 0.013 0.019 0.001 23.144 98.2 4.8 12.706 0.015 0.017 0.005 11.267 88.7 4.0 25.346 0.013 0.029 0.002 24.881 98.2 4.9 12.623 0.014 0.017 0.003 11.679 92.5 6.0 27.020 0.014 0.030 0.002 26.511 98.1 5.1 13.185 0.014 0.013 0.002 12.564 95.3 10.0 31.699 0.014 0.063 0.002 31.155 98.3 4.8 13.894 0.013 0.009 0.002 13.425 96.6 13.3 36.462 0.015 0.091 0.002 35.815 98.2 3.3 15.041 0.013 0.009 0.001 14.632 97.3 15.1 40.832 0.019 0.343 0.003 40.029 98.0 1.4	118.9 0.5 119.8 59.4 126.3 63.4 133.8 67.3 138.9 67.9 148.9 70.3 158.2 75.5 184.6 80.6 210.6 87.6 233.9	0.4 0.4 2.0 0.4 3.7 0.4 1.4 0.5 0.9 0.5 0.6 0.5 0.4 0.6 0.3 0.8 0.3 0.3 1.3
	10	16.975	0.013	0.008	0.001	16.581	97.7	13.9	99.0	0.4
	19.848 26.319 Sample: PPV12-07 (2-0.5 μm) ; J = 0.00328640 ± 0.00000986, Total gas age = 68.3 ± 0.4 Ma, 39 Ar recoil = 8.8 (%) 0.014 0.008 0.001 19.444 98.0 10.4 115.6 11 12 0.014 0.014 0.001 25.951 98.6 8.2 152.6	0.5 0.4
	13 1	32.828 35.485	0.015 0.039	0.021 0.016	0.001 0.120	32.416 0.000	98.7 0.0	3.9 8.8	188.8 0.0	0.6 0.0
	14 2	40.690 8.635	0.015 0.030	0.050 0.001	0.002 0.024	40.224 1.393	98.9 16.1	2.6 0.1	231.4 8.3	0.7 6.9
	15 3	45.355 12.071	0.017 0.021	0.108 0.018	0.002 0.031	44.785 2.868	98.7 23.8	2.2 0.8	255.9 17.0	0.7 0.9
	16 4	50.339 14.983	0.019 0.021	0.185 0.014	0.003 0.036	49.475 4.321	98.3 28.8	0.9 0.9	280.7 25.5	1.4 1.0
	5	16.882	0.021	0.014	0.033	7.170	42.5	1.4	42.1	0.9
	6	17.826	0.020	0.008	0.028	9.481	53.2	1.5	55.5	0.8
	7 Sample: PPV12-07 (50-16 μm) ; J = 0.00339410 ± 0.00001018, Total gas age = 127.4 ± 0.9 Ma, 39 Ar recoil = 5.0 (%) 17.627 0.019 0.014 0.023 10.745 61.0 1.8 62.8 113.007 0.097 0.041 0.385 0.000 0.0 5.0 0.0 8 17.194 0.017 0.012 0.019 11.572 67.3 1.9 67.5 17.783 0.025 0.018 0.041 5.794 32.6 2.4 35.2 9 16.161 0.017 0.012 0.014 11.916 73.7 2.4 69.5 20.304 0.020 0.018 0.031 11.162 55.0 2.1 67.2 15.356 0.016 0.012 0.011 12.138 79.0 3.2 70.7 18.471 0.020 0.011 0.020 12.417 67.2 1.9 74.6 14.941 0.015 0.010 0.008 12.480 83.5 3.7 72.7 16.526 0.015 0.008 0.011 13.247 80.2 2.9 79.5 14.645 0.014 0.011 0.005 13.029 89.0 6.2 75.8 16.303 0.015 0.013 0.007 14.306 87.7 4.2 85.7 14.645 0.014 0.009 0.005 12.543 90.6 6.6 73.0 16.967 0.014 0.012 0.005 15.573 91.8 8.6 93.1 14.690 0.014 0.011 0.004 12.701 91.4 6.7 73.9 18.726 0.013 0.015 0.002 18.009 96.2 4.8 107.3 14.744 0.014 0.011 0.004 12.860 92.2 6.1 74.9 19.713 0.013 0.010 0.002 19.126 97.0 6.3 113.7 14.824 0.014 0.010 0.003 13.046 93.1 7.2 75.9 10 20.658 0.013 0.006 0.002 20.142 97.5 6.4 119.6 14.922 0.014 0.010 0.003 13.207 93.6 6.6 76.8 11 21.527 0.013 0.010 0.002 21.045 97.8 7.2 124.8 14.985 0.013 0.010 0.003 13.341 94.2 6.6 77.6 12 22.585 0.013 0.013 0.001 22.142 98.0 6.7 131.0 15.036 0.013 0.009 0.003 13.492 94.9 5.7 78.5 13 23.602 0.013 0.013 0.001 23.182 98.2 6.7 137.0 15.148 0.013 0.010 0.002 13.637 95.2 5.9 79.3 14 25.176 0.013 0.012 0.001 24.756 98.3 7.3 145.9 15.262 0.013 0.010 0.002 13.770 95.4 5.4 80.0 15 26.677 0.014 0.014 0.001 26.251 98.4 6.4 154.3 15.532 0.014 0.011 0.002 14.062 95.8 4.6 81.7 16 29.055 0.013 0.018 0.001 28.634 98.5 6.2 167.7 16.519 0.014 0.014 0.002 14.964 95.8 3.7 86.8 17 32.063 0.014 0.028 0.002 31.609 98.6 5.3 184.3 18.950 0.015 0.027 0.003 17.067 95.2 2.1 98.7	0.6 0.6 0.0 0.5 1.0 0.4 0.8 0.4 0.7 0.3 0.4 0.6 0.3 0.6 0.3 0.6 0.3 0.6 0.3 0.6 0.4 0.6 0.4 0.6 0.4 0.6 0.4 0.6 0.4 0.6 0.4 0.7 0.5 0.6 0.8
	18	36.644	0.015	0.045	0.002	36.140	98.6	4.6	209.2	0.6
	19 20 Sample: PPV12-07 (< 0.5 μm) ; J = 0.00328640 ± 0.00000986, Total gas age = 47.6 ± 0.6 Ma, 39 Ar recoil = 24.7 (%) 40.564 0.016 0.077 0.002 40.003 98.6 3.2 230.2 43.842 0.016 0.152 0.002 43.164 98.4 2.0 247.2	0.7 0.7
	1	23.905	0.073	0.068	0.081	0.000	0.0	24.7	0.0	0.0
	2	9.300	0.040	0.057	0.025	1.934	20.8	0.9	11.5	1.2
	3 Sample: PPV12-07 (16-2 μm) ; J = 0.00344890 ± 0.00000414, Total gas age = 113.9 ± 0.6 Ma, 39 Ar recoil = 4.7 (%) 12.269 0.034 0.081 0.033 2.657 21.7 1.5 15.7 4 13.320 0.032 0.069 0.031 4.062 30.5 2.0 24.0	1.0 0.9
	5	125.647 13.792	0.103 0.031	0.102 0.066	0.424 0.023	0.418 6.902	0.3 50.0	4.7 2.6	2.6 40.6	10.8 0.7
	6	6.817 14.484	0.032 0.028	0.177 0.066	0.017 0.018	1.743 9.225	25.6 63.7	0.3 2.9	10.8 54.0	1.3 0.6
	7	12.768 13.811	0.024 0.027	0.183 0.066	0.033 0.015	2.945 9.369	23.1 67.8	0.6 3.4	18.3 54.8	1.5 0.5
	8	14.960 13.789	0.025 0.023	0.018 0.068	0.034 0.013	4.892 10.069	32.7 73.0	0.9 4.3	30.3 58.9	1.0 0.4
	9	16.712 14.207	0.020 0.019	0.072 0.061	0.030 0.010	7.898 11.115	47.3 78.2	0.9 4.2	48.6 64.9	0.9 0.4
		16.660 14.056	0.019 0.018	0.059 0.070	0.024 0.009	9.641 11.275	57.9 80.2	1.2 9.4	59.1 65.8	0.7 0.4
		16.420 14.159	0.020 0.016	0.104 0.093	0.020 0.007	10.637 11.995	64.8 84.7	1.2 9.2	65.2 69.9	0.6 0.3
		15.633 13.833	0.017 0.015	0.074 0.112	0.013 0.006	11.679 11.914	74.7 86.1	1.6 8.8	71.4 69.5	0.5 0.3
		14.730 13.500	0.017 0.014	0.077 0.115	0.010 0.006	11.826 11.815	80.3 87.5	1.5 6.6	72.3 68.9	0.4 0.3
	10	14.498 13.409	0.015 0.015	0.072 0.125	0.007 0.006	12.430 11.765	85.7 87.7	2.4 6.8	75.9 68.6	0.3 0.3
	11	14.788 13.183	0.015 0.015	0.026 0.128	0.005 0.006	13.325 11.489	90.1 87.1	3.2 7.5	81.3 67.0	0.4 0.3
	12	15.074 14.216	0.016 0.016	0.007 0.085	0.004 0.006	13.868 12.339	92.0 86.8	2.3 3.2	84.5 71.9	0.4 0.4
	13	15.823 15.550	0.014 0.015	0.026 0.102	0.003 0.007	14.876 13.424	94.0 86.3	5.2 2.1	90.5 78.1	0.3 0.6
	14 15 Steps	16.497 16.968 40 Ar/	0.013 0.013	0.025 0.009	0.003 0.002	15.693 16.290	95.1 96.0	5.9 3.8	95.3 98.8	0.3 0.4
	16 17 Sample: PPV12-05 (Bulk) ; J = 0.00339410 ± 0.00000849, Total gas age = 69.8 ± 0.4 Ma, 39 Ar recoil = 3.8 (%) 17.419 0.014 0.012 0.002 16.745 96.1 3.4 18.292 0.014 0.011 0.002 17.729 96.9 4.6 1 58.310 0.065 0.092 0.195 0.739 1.3 3.8	101.5 107.3 4.5	0.4 0.4 4.5

39 Ar 38 Ar/ 39 Ar 37 Ar/ 39 Ar 36 Ar/ 39 Ar 40 Ar * / 39 Ar (k) 39 Ar (k) (%) Age (Ma) Error (Ma) 40 Ar * (%) Steps 40 Ar/ 39 Ar 38 Ar/ 39 Ar 37 Ar/ 39 Ar 36 Ar/ 39 Ar 40 Ar * / 39 Ar (k) 39 Ar (k) (%) Age (Ma) Error (Ma) 40 Ar * (%)

	2	11.522	0.019	0.065	0.013	7.547	65.5	2.6	45.7	0.3
	3	10.605	0.015	0.086	0.009	7.941	74.9	2.0	48.1	0.3
	4	9.829	0.016	0.087	0.005	8.385	85.3	3.8	50.7	0.2
	5	9.111	0.015	0.101	0.003	8.192	89.9	4.4	49.6	0.2
	6	9.232	0.014	0.109	0.002	8.610	93.3	5.7	52.1	0.2
	7	9.404	0.013	0.102	0.002	8.947	95.1	5.5	54.1	0.2
	8	9.474	0.013	0.093	0.001	9.134	96.4	8.2	55.2	0.2
	9	9.671	0.013	0.077	0.001	9.388	97.1	9.8	56.7	0.2
		10.013	0.013	0.073	0.001	9.758	97.4	10.2	58.9	0.2
		10.549	0.013	0.049	0.001	10.311	97.7	9.8	62.2	0.2
		11.360	0.013	0.009	0.001	11.128	98.0	10.4	67.0	0.2
		13.244	0.013	0.011	0.001	12.994	98.1	12.3	78.0	0.2
	Steps	40 Ar/ 19.680 39 Ar 25.710	38 Ar/ 39 Ar 0.013 0.013	37 Ar/ 39 Ar 0.015 0.030	36 Ar/ 0.001 39 Ar 0.001	40 Ar 19.374 * / 39 Ar (k) 25.303	40 Ar 98.4 * (%) 98.4	39 Ar (k) (%) Age (Ma) Error (Ma) 3.8 115.2 0.4 3.6 149.0 0.5
		32.034	0.013	0.045	0.002	31.542	98.5	1.5	183.9	0.7
		37.162	0.015	0.081	0.002	36.581	98.4	1.2	211.6	0.8
		42.446	0.016	0.165	0.003	41.431	97.6	1.3	237.9	0.8
	Sample: PPV12-05 (50-16 μm) ; J = 0.00339410 ± 0.00000849, Total gas age = 74.2 ± 0.4 Ma, 39 Ar recoil = 2.9 (%)
	1	84.876	0.091	0.064	0.285	0.736	0.9	2.9	4.5	6.5
	2	5.441	0.022	0.025	0.010	2.404	44.2	0.8	14.7	1.8
	3	7.712	0.020	0.017	0.010	4.896	63.5	1.1	29.8	1.3
	4	8.800	0.019	0.020	0.006	7.020	79.8	1.4	42.6	1.0
	5	8.661	0.016	0.022	0.004	7.505	86.7	1.5	45.5	0.9
	6	8.677	0.017	0.040	0.003	7.856	90.5	1.6	47.6	0.9
	7	8.647	0.017	0.043	0.002	8.035	92.9	2.2	48.7	0.7
	8	8.853	0.014	0.051	0.001	8.428	95.2	3.2	51.0	0.5
	9	9.140	0.014	0.047	0.001	8.798	96.3	4.5	53.2	0.3
		9.488	0.014	0.043	0.001	9.183	96.8	6.0	55.5	0.3
		9.869	0.013	0.036	0.001	9.596	97.2	8.3	58.0	0.2
		10.294	0.013	0.026	0.001	10.042	97.6	7.8	60.6	0.2
		10.650	0.014	0.020	0.001	10.405	97.7	8.3	62.8	0.2
		11.235	0.014	0.009	0.001	11.025	98.1	6.8	66.4	0.3
		11.658	0.014	0.013	0.001	11.442	98.1	5.9	68.9	0.3
		12.115	0.013	0.010	0.001	11.947	98.6	5.3	71.9	0.3
		13.118	0.013	0.010	0.001	12.923	98.5	4.2	77.6	0.4
		13.772	0.014	0.012	0.001	13.572	98.5	3.5	81.4	0.5
		15.201	0.014	0.016	0.001	14.991	98.6	5.0	89.7	0.4
		15.681	0.013	0.014	0.001	15.470	98.7	3.0	92.5	0.6
		16.464	0.012	0.010	0.001	16.228	98.6	2.4	97.0	0.7
		17.734	0.013	0.006	0.001	17.490	98.6	2.2	104.3	0.7
		18.953	0.011	0.014	0.001	18.729	98.8	1.8	111.4	0.9
		20.343	0.014	0.016	0.001	20.086	98.7	1.6	119.3	1.0
		21.520	0.015	0.017	0.001	21.245	98.7	1.3	125.9	1.2
		23.598	0.015	0.028	0.001	23.268	98.6	1.4	137.5	1.2
		26.883	0.014	0.042	0.001	26.583	98.9	2.1	156.2	0.9
		29.286	0.015	0.063	0.001	28.967	98.9	1.5	169.6	1.2
		31.224	0.014	0.074	0.001	30.807	98.7	1.3	179.8	1.7
		34.154	0.017	0.109	0.002	33.578	98.3	0.9	195.2	2.1
	Steps	40 Ar/	39 Ar	38 Ar/ 39 Ar	37 Ar/ 39 Ar	36 Ar/	39 Ar	40 Ar	* / 39 Ar (k)	40 Ar	39 Ar (k) (%) Age (Ma) Error (Ma)
	Sample: PPV12-05 (16-2 μm) ; J = 0.00339410 ± 0.00000849, Total gas age = 88.5 ± 0.5 Ma, 39 Ar recoil = 3.3 (%)
	1	65.860	0.065	0.040	0.221	0.516	0.8	3.3	3.2	5.0
	2	5.856	0.023	0.073	0.013	2.029	34.6	0.4	12.4	2.2
	3	10.700	0.020	0.034	0.026	2.966	27.7	0.4	18.1	2.0
	4	12.936	0.019	0.030	0.027	4.860	37.6	0.6	29.6	1.5
	5	13.884	0.018	0.020	0.023	6.994	50.4	0.6	42.4	1.4
	6	13.744	0.016	0.022	0.019	8.140	59.2	0.9	49.3	1.1
	7	13.202	0.013	0.037	0.016	8.372	63.4	0.3	50.7	2.9
	8	12.529	0.016	0.032	0.012	8.930	71.3	1.3	54.0	0.7
	9	11.876	0.016	0.027	0.009	9.343	78.7	1.3	56.5	0.7
		11.613	0.013	0.028	0.006	9.780	84.2	1.5	59.1	0.6

* (

%) Steps 40 Ar/ 39 Ar 38 Ar/ 39 Ar 37 Ar/ 39 Ar 36 Ar/ 39 Ar 40 Ar

		11.538	0.014	0.024	0.005	10.136	87.8	2.1	61.2	0.4
		11.605	0.015	0.021	0.004	10.455	90.1	2.7	63.1	0.3
		11.811	0.014	0.021	0.003	10.917	92.4	3.3	65.8	0.3
		12.031	0.014	0.020	0.002	11.389	94.7	2.4	68.6	0.4
		12.263	0.013	0.018	0.002	11.594	94.5	4.0	69.8	0.3
		12.553	0.014	0.017	0.002	11.944	95.1	4.6	71.9	0.3
		12.809	0.014	0.016	0.002	12.295	96.0	4.3	73.9	0.3
		13.161	0.013	0.015	0.002	12.653	96.1	5.1	76.0	0.3
		13.639	0.014	0.016	0.002	13.161	96.5	5.8	79.0	0.3
		13.974	0.013	0.015	0.001	13.562	97.1	6.0	81.4	0.3
		14.523	0.013	0.016	0.001	14.093	97.0	6.4	84.5	0.3
		15.162	0.013	0.017	0.001	14.742	97.2	6.3	88.3	0.3
		15.855	0.013	0.017	0.001	15.509	97.8	6.5	92.8	0.3
		16.459	0.014	0.018	0.001	16.095	97.8	4.8	96.2	0.3
		17.643	0.013	0.022	0.001	17.209	97.5	5.6	102.7	0.3
		19.958	0.014	0.028	0.002	19.405	97.2	6.4	115.3	0.3
		22.400	0.014	0.041	0.001	22.015	98.3	5.7	130.3	0.4
		26.627 34.359	0.014 0.017	0.072 0.174	0.001 0.002	/ 39 Ar (k) 26.313 33.708	98.8 40 Ar * (%) 98.1	39 Ar (k) (%) Age (Ma) Error (Ma) 4.3 154.7 0.4 3.3 195.9 0.6
	Sample: PPV12-05 (2-0.5 μm) ; J = 0.00339410 ± 0.00000849, Total gas age = 50.6 ± 0.4 Ma, 39 Ar recoil = 6.9 (%)
	1	58.053	0.056	0.022	0.196	0.069	0.1	6.9	0.4	4.5
	2	6.125	0.016	0.002	0.017	1.194	19.5	0.4	7.3	3.2
	3	9.995	0.018	0.011	0.027	1.929	19.3	0.5	11.8	2.9
	4	12.554	0.020	0.017	0.034	2.523	20.1	0.8	15.4	1.9
	5	12.190	0.013	0.000	0.015	7.722	63.3	0.5	46.8	2.9
	6	11.656	0.013	0.009	0.013	7.893	67.7	0.7	47.8	1.8
	7	10.789	0.016	0.015	0.008	8.274	76.7	1.6	50.1	0.8
	8	10.355	0.014	0.013	0.007	8.402	81.1	2.5	50.8	0.6
	9	10.084	0.015	0.014	0.005	8.506	84.4	3.5	51.5	0.4
		9.816	0.014	0.010	0.004	8.510	86.7	4.5	51.5	0.3
		9.682	0.013	0.013	0.004	8.584	88.7	3.6	51.9	0.4
		9.647	0.014	0.013	0.003	8.653	89.7	7.2	52.3	0.2
		9.671	0.014	0.011	0.003	8.765	90.6	7.8	53.0	0.2
		9.654	0.013	0.010	0.003	8.875	91.9	7.6	53.7	0.2
		9.663	0.013	0.010	0.002	8.930	92.4	8.7	54.0	0.2
		9.698	0.013	0.009	0.002	9.024	93.1	8.2	54.6	0.2
		9.727	0.013	0.010	0.002	9.098	93.5	8.0	55.0	0.2
		9.719	0.013	0.010	0.002	9.201	94.7	6.9	55.6	0.2
		9.831	0.013	0.009	0.002	9.307	94.7	6.1	56.2	0.3
		10.054	0.013	0.011	0.002	9.525	94.7	5.0	57.5	0.3
		10.787	0.013	0.013	0.002	10.196	94.5	5.3	61.5	0.3
		12.494	0.013	0.018	0.002	11.857	94.9	3.8	71.3	0.4
	Sample: PPV12-05 (< 0.5 μm) ; J = 0.00339410 ± 0.00000849, Total gas age = 36.9 ± 0.2 Ma, 39 Ar recoil = 22.6 (%)
	1	7.428	0.098	0.073	0.025	0.080	1.1	22.6	0.5	0.6
	2	5.289	0.055	0.082	0.015	0.853	16.1	1.8	5.2	1.0
	3	11.622	0.045	0.073	0.033	1.945	16.7	2.4	11.9	1.1
	4	13.726	0.043	0.071	0.030	4.730	34.5	3.2	28.8	0.9
	5	13.428	0.036	0.077	0.022	7.066	52.6	4.4	42.9	0.6
	6	12.126	0.028	0.075	0.015	7.563	62.4	5.5	45.8	0.5
	7	11.513	0.021	0.077	0.011	8.195	71.2	6.8	49.6	0.4
	8	11.228	0.018	0.120	0.009	8.538	76.0	8.3	51.7	0.3
	9	10.709	0.016	0.143	0.007	8.586	80.2	10.6	51.9	0.3
		10.467	0.015	0.170	0.006	8.566	81.8	11.3	51.8	0.2
		10.229	0.015	0.198	0.006	8.470	82.8	11.2	51.3	0.2
		10.101	0.015	0.197	0.006	8.470	83.8	7.6	51.3	0.3
		10.746	0.014	0.200	0.006	9.000	83.7	4.3	54.4	0.4

*

Steps 40 Ar/ 39 Ar 38 Ar/ 39 Ar 37 Ar/ 39 Ar 36 Ar/ 39 Ar 40 Ar * / 39 Ar (k) 39 Ar (k) (%) Age (Ma) Error (Ma) 40 Ar * (%) Steps 40 Ar/ 39 Ar 38 Ar/ 39 Ar 37 Ar/ 39 Ar 36 Ar/ 39 Ar 40 Ar * / 39 Ar (k) 39 Ar (k) (%) Age (Ma) Error (Ma) 40 Ar * (%) Lakora samples: 15

  LAK1 (Bulk) ; J = 0.00310750 ± 0.00000684 , Total gas age = 126.6 ± 0.8 Ma, Lakora samples: 15 LAK1 (50-16 μm) ; J = 0.00310750 ± 0.00000684, Total gas age = 136.1 ± 0.8 Ma,39 Ar recoil = 15.3 (%) Lakora samples: 15 LAK1 (2-0.5 μm) ; J = 0.00310750 ± 0.00000684, Total gas age = 88.3 ± 0.9 Ma,

							39 Ar recoil = 16.4 (%)
	1	43.715	0.045	0.007	0.145	0.866	2.0	16.4	4.9	3.5
	2	7.852	0.027	0.004	0.020	1.859	23.7	1.8	10.4	1.9
	3	10.430	0.018	0.036	0.010	7.427	71.2	2.5	41.3	1.3
	4	17.950	0.017	0.009	0.005	16.541	92.1	2.7	90.6	1.3
	5	19.616	0.015	0.020	0.004	18.440	94.0	3.4	100.8	1.0
	6	20.184	0.013	0.007	0.003	19.261	95.4	4.8	105.1	0.8
	7	21.336	0.016	0.010	0.004	20.294	95.1	5.4	110.6	0.8
	8	22.900	0.017	0.010	0.003	21.990	96.0	6.8	119.5	0.7
	9	24.696	0.015	0.016	0.002	24.015	97.2	6.9	130.2	0.7
	10	26.580	0.014	0.014	0.002	25.909	97.5	8.3	140.0	0.7
	11	28.394	0.015	0.010	0.002	27.720	97.6	8.2	149.4	0.7
	12	30.462	0.012	0.009	0.001	30.091	98.8	7.2	161.6	0.5
	13	32.429	0.013	0.002	0.001	31.998	98.7	6.5	171.4	0.6
	14	35.148	0.013	0.001	0.001	34.698	98.7	6.1	185.2	0.6
	15	38.898	0.015	0.000	0.002	38.442	98.8	5.6	204.1	0.6
	16	48.055	0.013	0.006	0.002	47.339	98.5	4.6	248.2	0.8
	17	58.423	0.014	0.001	0.004	57.186	97.9	2.8	295.8	1.4
	1	43.667	0.046	0.010	0.145	0.834	1.9	15.3	4.7	3.5
	2	8.733	0.018	0.018	0.015	4.375	50.1	3.1	24.4	0.9
	3	15.978	0.014	0.012	0.007	13.975	87.5	2.2	76.9	1.3
	4	20.837	0.014	0.007	0.004	19.548	93.8	4.0	106.6	0.8
	5	20.887	0.014	0.021	0.004	19.686	94.2	3.0	107.4	1.0
	6	20.563	0.014	0.015	0.003	19.602	95.3	4.3	106.9	0.8
	7	22.235	0.014	0.012	0.003	21.287	95.7	5.0	115.8	0.7
	8	23.970	0.016	0.018	0.003	23.027	96.1	7.8	125.0	0.5
	9	25.945	0.015	0.013	0.003	25.157	97.0	9.1	136.1	0.5
	10	28.332	0.013	0.004	0.001	27.884	98.4	8.2	150.3	0.6
	11	30.697	0.014	0.009	0.002	30.205	98.4	8.8	162.2	0.6
	12	33.846	0.015	0.008	0.002	33.310	98.4	8.2	178.1	0.7
	13	37.473	0.016	0.004	0.002	36.946	98.6	6.5	196.5	0.8
	14	42.106	0.015	0.009	0.001	41.713	99.1	6.0	220.4	0.9
	15	52.367	0.013	0.004	0.002	51.912	99.1	4.5	270.4	1.3
	16	59.637	0.016	0.003	0.005	58.151	97.5	4.0	300.4	1.5
	Lakora samples: 15 LAK1 (16-2 μm) ; J = 0.00310750 ± 0.00000684, Total gas age = 135.5 ± 0.7 Ma,	39 Ar recoil = 15.5 (%)
	1	29.246	0.036	0.010	0.099	0.015	0.1	15.5	0.1	2.3
	2	7.420	0.020	0.036	0.018	2.137	28.8	1.4	12.0	0.7
	3	11.138	0.015	0.024	0.011	7.944	71.3	1.9	44.1	0.5
	4	17.811	0.015	0.014	0.005	16.200	91.0	2.2	88.8	0.6
	5	20.390	0.014	0.013	0.004	19.289	94.6	3.0	105.3	0.5
	6	20.782	0.013	0.010	0.003	19.895	95.7	5.2	108.5	0.4
	7	22.553	0.014	0.010	0.002	21.876	97.0	9.2	118.9	0.5
	8	25.020	0.013	0.009	0.002	24.364	97.4	7.7	132.0	0.5
	9	26.770	0.013	0.007	0.002	26.171	97.8	7.3	141.4	0.6
	10	28.592	0.013	0.006	0.002	28.103	98.3	7.3	151.4	0.6
	11	30.565	0.013	0.008	0.002	30.072	98.4	6.8	161.6	0.6
	12	32.241	0.014	0.004	0.002	31.770	98.5	5.7	170.3	0.7
	13	34.036	0.013	0.007	0.001	33.630	98.8	5.1	179.7	0.7
	14	36.448	0.014	0.006	0.002	35.994	98.8	5.8	191.7	0.7
	15	40.228	0.014	0.008	0.002	39.756	98.8	4.9	210.6	0.8
	16	45.255	0.014	0.011	0.002	44.680	98.7	4.5	235.1	0.9
	17	52.811	0.016	0.013	0.003	51.911	98.3	3.8	270.4	1.2
	18	54.293	0.015	0.023	0.005	52.847	97.3	2.7	275.0	1.1
								39 Ar recoil = 19.4 (%)
	1	53.158	0.055	0.012	0.177	0.959	1.8	19.4	5.4	4.1
	2	10.152	0.016	0.014	0.009	7.566	74.5	6.2	42.0	0.3

36 Ar/

39 Ar 40 Ar * / 39 Ar (k) 39 Ar (k) (%) 40 Ar * (%) 40 Ar * (%) Steps 40 Ar/ 39 Ar 38 Ar/ 39 Ar 37 Ar/ 39 Ar 36 Ar/ 39 Ar 40 Ar * / 39 Ar (k) 39 Ar (k) (%) Age (Ma) Error (Ma) Steps 40 Ar/ 39 Ar 38 Ar/ 39 Ar 37 Ar/ 39 Ar 36 Ar/ 39 Ar 40 Ar * / 39 Ar (k) 39 Ar (k) (%) 40 Ar * (%) 40 Ar * (%) Steps 40 Ar/ 39 Ar 38 Ar/ 39 Ar 37 Ar/ 39 Ar 36 Ar/ 39 Ar 40 Ar * / 39 Ar (k) 39 Ar (k) (%) Age (Ma) Error (Ma) Steps 40 Ar/ 39 Ar 38 Ar/ 39 Ar 37 Ar/ 39 Ar Age (Ma) Error (Ma) Age (Ma) Error (Ma) Appendix B: Lakora and Torla samples

		17.359	0.014	0.000	0.004	16.257	93.7	5.6	89.1	0.4
		16.940	0.014	0.011	0.003	16.129	95.2	7.1	88.4	0.4
		18.684	0.013	0.008	0.002	18.031	96.5	7.6	98.6	0.4
		20.446	0.013	0.007	0.002	19.888	97.3	10.3	108.4	0.4
		21.931	0.014	0.003	0.002	21.434	97.7	9.9	116.6	0.5
		23.153	0.013	0.001	0.001	22.715	98.1	10.3	123.3	0.5
		23.719	0.013	0.007	0.001	23.319	98.3	8.2	126.5	0.5
	10	23.518	0.013	0.007	0.001	23.083	98.2	7.4	125.3	0.5
	11	23.339	0.014	0.012	0.001	22.957	98.4	5.6	124.6	0.5
	12	25.800	0.016	0.004	0.004	24.748	95.9	2.6	134.0	0.7
	Lakora samples: 15 LAK3 (50-16 μm) ; J = 0.00310750 ± 0.00000684, Total gas age = 118.1 ± 1.0 Ma, 39 Ar recoil = 10.9 (%)
		117.100	0.099	0.027	0.395	0.331	0.3	10.9	1.9	8.7
		7.107	0.021	0.023	0.016	2.423	34.1	1.8	13.6	1.1
		13.304	0.017	0.018	0.007	11.267	84.7	3.9	62.2	0.6
		15.801	0.016	0.008	0.003	14.847	94.0	4.9	81.6	0.5
		17.347	0.013	0.010	0.002	16.779	96.7	7.3	91.9	0.4
		19.641	0.014	0.013	0.002	19.171	97.6	11.4	104.6	0.4
		21.832	0.013	0.010	0.001	21.432	98.2	12.6	116.6	0.4
		24.017	0.013	0.010	0.001	23.703	98.7	11.0	128.5	0.5
		26.460	0.013	0.010	0.001	26.133	98.8	10.5	141.2	0.5
	10	29.150	0.014	0.012	0.001	28.826	98.9	8.8	155.1	0.6
	11	32.904	0.014	0.016	0.001	32.592	99.1	7.1	174.5	0.7
	12	38.846	0.013	0.021	0.002	38.328	98.7	4.6	203.5	1.1
	13	45.192	0.016	0.032	0.004	43.977	97.3	3.2	231.6	1.4

Steps 40 Ar/ 39 Ar 38 Ar/ 39 Ar 37 Ar/ 39 Ar 36 Ar/ 39 Ar 40 Ar * / 39 Ar (k) 39 Ar (k) (%) Age (Ma) Error (Ma) 40 Ar * (%) Steps 40 Ar/ 39 Ar 38 Ar/ 39 Ar 37 Ar/ 39 Ar 36 Ar/ 39 Ar 40 Ar * / 39 Ar (k) 39 Ar (k) (%) Age (Ma) Error (Ma) 40 Ar * (%) Steps 40 Ar/ 39 Ar 38 Ar/ 39 Ar 37 Ar/ 39 Ar 36 Ar/ 39 Ar 40 Ar * / 39 Ar (k) 39 Ar (k) (%) Age (Ma) Error (Ma) 40 Ar * (%)

  Lakora samples: 15 LAK3 (16-2 μm) ; J = 0.00310750 ± 0.00000684, Total gas age = 126.7 ± 1.1 Ma,39 Ar recoil = 11.2 (%)Lakora samples: 15 LAK3 (2-0.5 μm) ; J = 0.00310750 ± 0.00000684, Total gas age = 84.9 ± 0.4 Ma, 39 Ar recoil = 19.7 (%)

	14	54.718	0.025	0.113	0.018	49.477	90.4		2.0	258.6	2.2
	1	116.880	0.140	0.029	0.393	0.667	0.6		11.2	3.7	9.2
	2	7.305	0.030	0.016	0.019	1.644	22.5		1.6	9.2	0.8
	3	10.224	0.029	0.004	0.014	6.107	59.7		1.4	34.0	0.8
	4	15.014	0.016	0.033	0.005	13.398	89.2		3.2	73.8	0.4
	5	16.534	0.015	0.028	0.004	15.403	93.2		3.8	84.5	0.4
	6	17.737	0.015	0.024	0.003	16.876	95.1		4.3	92.4	0.4
	7	19.478	0.013	0.008	0.002	18.906	97.1		6.0	103.2	0.4
	8	21.194	0.013	0.009	0.002	20.706	97.7		7.2	112.8	0.5
	9	22.848	0.012	0.010	0.002	22.390	98.0		8.9	121.6	0.5
	10	24.743	0.013	0.007	0.001	24.419	98.7		8.8	132.3	0.5
	11	26.541	0.013	0.010	0.001	26.162	98.6		9.6	141.3	0.5
	12	28.467	0.013	0.009	0.001	28.133	98.8		8.7	151.6	0.6
	13	31.582	0.013	0.011	0.001	31.318	99.2		8.2	167.9	0.5
	14	34.707	0.013	0.016	0.001	34.426	99.2		6.3	183.8	0.6
	15	40.890	0.013	0.014	0.001	40.555	99.2		4.6	214.6	0.8
	16	47.709	0.013	0.008	0.001	47.274	99.1		2.8	247.9	1.1
	17	52.446	0.017	0.013	0.003	51.476	98.1		1.8	268.3	1.5
	18	55.134	0.016	0.055	0.010	52.299	94.9		1.5	272.3	1.6
	1	39.466	0.058	0.018	0.130	1.005	2.5		19.7	5.6	1.7
	2	4.813	0.038	0.022	0.011	1.630	33.9		1.7	9.1	0.7
	3	7.794	0.035	0.063	0.015	3.286	42.2		1.9	18.4	0.7
	4	12.295	0.021	0.019	0.010	9.319	75.8		2.1	51.6	0.6
	5	15.652	0.019	0.019	0.007	13.613	87.0		2.8	74.9	0.5
	6	15.701	0.015	0.013	0.006	14.017	89.3		3.1	77.1	0.4
	7	16.046	0.016	0.016	0.004	14.869	92.7		4.4	81.7	0.3
	8	17.220	0.015	0.020	0.004	16.177	93.9		4.9	88.7	0.3
	9	19.023	0.014	0.015	0.003	18.106	95.2		6.9	99.0	0.3
	10	20.418	0.014	0.013	0.003	19.644	96.2		6.9	107.1	0.3
	11	21.539	0.014	0.017	0.003	20.764	96.4		8.2	113.1	0.3
	12	22.243	0.014	0.015	0.002	21.614	97.2		7.5	117.6	0.3
	13	22.749	0.013	0.014	0.002	22.210	97.6		7.7	120.7	0.3
	14	23.260	0.013	0.015	0.002	22.709	97.6		5.8	123.3	0.3
	15	23.406	0.014	0.004	0.002	22.805	97.4		6.7	123.8	0.3
	16	23.580	0.014	0.007	0.002	23.090	97.9		5.4	125.3	0.3
	17	23.864	0.013	0.012	0.002	23.288	97.6		4.1	126.3	0.4
	Lakora samples: 15 LAK3 (< 0.5 μm) ; J = 0.00310750 ± 0.00000684, Total gas age = 73.5 ± 0.5 Ma,	39 Ar recoil = 23.3 (%)
	1	15.435	0.033	0.104	0.052	0.007	0.0		23.3	0.0	1.1
	2	6.945	0.026	0.125	0.016	2.186	31.5		2.2	12.2	1.9
	3	10.993	0.018	0.089	0.010	7.969	72.5		2.4	44.2	2.3
	4	14.125	0.015	0.081	0.007	11.972	84.8		3.3	66.1	1.7
	5	14.554	0.017	0.089	0.006	12.750	87.6		3.5	70.3	1.6
	6	14.744	0.016	0.083	0.005	13.233	89.7		4.5	72.9	1.3
	7	15.742	0.015	0.081	0.004	14.526	92.3		4.8	79.8	1.2
	8	17.694	0.014	0.076	0.004	16.617	93.9		7.2	91.0	0.8
	9	18.842	0.014	0.072	0.003	17.838	94.7		5.1	97.6	1.1
	10	19.904	0.012	0.066	0.003	19.136	96.1		5.9	104.5	1.0
	11	20.569	0.014	0.068	0.003	19.813	96.3		7.2	108.0	0.8
	12	20.941	0.013	0.067	0.002	20.237	96.6		6.8	110.3	0.9
	13	21.191	0.012	0.066	0.002	20.619	97.3		6.7	112.3	0.9
	14	21.468	0.013	0.065	0.002	20.868	97.2		5.9	113.6	1.0
	15	21.631	0.013	0.072	0.002	21.062	97.4		4.6	114.6	1.3
	16	21.337	0.013	0.074	0.002	20.847	97.7		3.4	113.5	1.7
	17	20.965	0.015	0.092	0.002	20.307	96.9		3.1	110.7	1.9
	Torla samples: 15 TO1 (16-2 μm) ; J = 0.00310750 ± 0.00000684, Total gas age = 116.2 ± 0.9 Ma,	39 Ar recoil = 7.2 (%)
	1	157.720	0.127	0.644	0.520	4.237	2.7		7.2	23.7	11.3
					183

Steps 40 Ar/ 39 Ar 38 Ar/ 39 Ar 37 Ar/ 39 Ar 36 Ar/ 39 Ar 40 Ar * / 39 Ar (k) 40 Ar

* (%) 39 Ar (k) (%) Age (Ma) Error (

Ma) Steps 40 Ar/ 39 Ar 38 Ar/ 39 Ar 37 Ar/ 39 Ar 36 Ar/ 39 Ar 40 Ar * / 39 Ar (k) 39 Ar (k) (%) Age (Ma) Error (Ma) 40 Ar * (%) Steps 40 Ar/ 39 Ar 38 Ar/ 39 Ar 37 Ar/ 39 Ar 36 Ar/ 39 Ar 40 Ar * / 39 Ar (k) 39 Ar (k) (%) Age (Ma) Error (Ma) 40 Ar * (%) Steps 40 Ar/ 39 Ar 38 Ar/ 39 Ar 37 Ar/ 39 Ar 36 Ar/ 39 Ar 40 Ar * / 39 Ar (k) 39 Ar (k) (%) Age (Ma) Error (Ma) 40 Ar * (%)

  Torla samples: 15 TO1 (2-0.5 μm) ; J = 0.00310750 ± 0.00000684, Total gas age = 113.5 ± 0.5 Ma, 39 Ar recoil = 6.4 (%)

	2	8.175	0.022	0.884	0.008	5.979	73.1	2.2	33.3	0.6
	3	11.687	0.016	0.884	0.004	10.434	89.2	3.1	57.7	0.5
	4	11.348	0.017	0.880	0.004	10.375	91.4	2.7	57.4	0.7
	5	12.211	0.016	1.037	0.003	11.366	93.0	3.1	62.8	0.6
	6	12.856	0.016	1.219	0.003	12.065	93.8	3.8	66.6	0.5
	7	14.049	0.015	1.327	0.003	13.268	94.4	4.6	73.1	0.5
	8	15.892	0.015	1.457	0.003	15.029	94.5	5.3	82.5	0.4
	9	17.431	0.015	1.507	0.004	16.472	94.4	5.9	90.3	0.4
		19.377	0.016	1.568	0.004	18.316	94.4	6.4	100.1	0.4
		21.073	0.015	1.573	0.004	19.987	94.7	6.7	109.0	0.5
		23.278	0.015	1.614	0.005	22.052	94.6	7.9	119.9	0.5
		25.436	0.016	1.637	0.005	24.098	94.6	7.3	130.6	0.5
		27.555	0.015	1.810	0.006	26.079	94.5	6.3	140.9	0.6
		29.906	0.016	1.923	0.006	28.277	94.4	5.7	152.3	0.6
		32.223	0.017	2.316	0.007	30.345	94.0	4.4	163.0	0.8
		34.512	0.016	2.452	0.008	32.533	94.1	5.7	174.2	0.8
		37.672	0.017	2.136	0.007	35.762	94.8	5.5	190.6	0.8
		44.812	0.015	0.897	0.004	43.844	97.8	6.2	231.0	0.9
										Error (Ma)
	1	55.984	0.062	0.075	0.190	0.000	0.0	6.4	0.0	0.0
	2	5.424	0.019	0.073	0.011	2.072	38.2	1.1	11.6	1.0
	3	9.126	0.019	0.065	0.007	7.154	78.4	1.8	39.8	0.6
	4	11.026	0.018	0.071	0.006	9.212	83.5	2.5	51.0	0.5
	5	11.652	0.016	0.086	0.005	10.226	87.8	3.2	56.6	0.4
	6	12.744	0.015	0.088	0.004	11.518	90.4	3.9	63.6	0.3
	7	14.626	0.015	0.086	0.004	13.518	92.4	4.6	74.4	0.3
	8	16.329	0.014	0.083	0.004	15.291	93.6	5.8	83.9	0.3
	9	18.090	0.015	0.074	0.003	17.161	94.9	5.4	94.0	0.3
		19.987	0.014	0.074	0.003	19.019	95.2	6.8	103.8	0.3
		21.110	0.014	0.076	0.003	20.221	95.8	6.4	110.2	0.4
		22.185	0.014	0.071	0.003	21.323	96.1	5.3	116.0	0.4
		24.488	0.013	0.069	0.003	23.603	96.4	11.6	128.0	0.4
		26.601	0.013	0.071	0.003	25.733	96.7	10.8	139.1	0.4
		29.486	0.014	0.057	0.003	28.638	97.1	8.0	154.2	0.5
		32.436	0.013	0.048	0.003	31.578	97.4	6.4	169.3	0.6
		35.727	0.014	0.055	0.003	34.768	97.3	5.6	185.5	0.6
		42.238	0.014	0.086	0.004	41.062	97.2	4.2	217.2	0.8
	Torla samples: 15 TO1 (< 0.5 μm) ; J = 0.00310750 ± 0.00000684, Total gas age = 75.8 ± 0.5 Ma, 39 Ar recoil = 11.0 (%)
	1	48.272	0.055	0.065	0.161	0.792	1.6	11.0	4.4	3.6
	2	4.762	0.019	0.051	0.007	2.730	57.3	2.6	15.3	0.8
	3	9.560	0.019	0.063	0.007	7.540	78.9	3.0	41.9	0.8
	4	10.959	0.020	0.067	0.007	8.882	81.0	2.9	49.2	0.8
	5	11.449	0.019	0.069	0.006	9.553	83.4	3.7	52.9	0.7
	6	12.329	0.017	0.067	0.005	10.713	86.9	3.9	59.2	0.6
	7	13.416	0.016	0.071	0.005	11.923	88.9	5.1	65.8	0.5
	8	14.231	0.015	0.072	0.004	12.934	90.9	6.4	71.3	0.4
	9	15.533	0.015	0.067	0.004	14.424	92.9	7.2	79.3	0.4
		16.133	0.015	0.059	0.004	15.073	93.4	7.3	82.8	0.4
		17.351	0.014	0.062	0.003	16.358	94.3	6.8	89.7	0.5
		17.795	0.014	0.056	0.003	16.890	94.9	9.8	92.5	0.4
		19.037	0.013	0.053	0.003	18.127	95.2	9.5	99.1	0.4
		20.416	0.014	0.055	0.003	19.528	95.6	8.8	106.5	0.4
		21.575	0.014	0.054	0.003	20.633	95.6	7.0	112.4	0.5
		23.200	0.014	0.053	0.004	22.096	95.2	5.2	120.1	0.7

Steps 40 Ar/ 39 Ar 38 Ar/ 39 Ar 37 Ar/ 39 Ar 36 Ar/ 39 Ar 40 Ar * / 39 Ar (k) 40 Ar * (%) 39 Ar (k) (%) Age (Ma) Error (Ma) Steps 40 Ar/ 39 Ar 38 Ar/ 39 Ar 37 Ar/ 39 Ar 36 Ar/ 39 Ar 40 Ar * / 39 Ar (k) 40 Ar * (%) 39 Ar (k) (%) Age (Ma)

Table 0.1: Fault rocks classification proposed by[START_REF] Sibson | Fault rocks and fault mechanisms[END_REF] and completed by[START_REF] Scholz | The Mechanics of Earthquakes and Faulting[END_REF].

TO 4 (footwall turbidites). Chl = chlorite, Mus = muscovite, Qz = quartz, Ca= calcite, Rt = rutile and Alb = albite.

Ar * (%)Appendix A: PPVT samples

Acknowledgements

This work was supported by the INSU program (Tellus-syster). Access to SEM facilities of the MIMENTO center was made through the cooperative projects in the French Renatech network. The author would like to sincerely thank Vincent Trincal for collecting the samples, Didier Convert-Gaubier for the preparation of the thin sections, Nicolas Carry for organizing the illustrations and Virginie Moutarlier for her help during XRD analysis. Finally, many thanks for the reviewers (Fernando Nieto García and Sébastien Potel); your valuable comments and suggestions have led to a significant improvement on the quality of this paper.

Acknowledgements

The author would like to sincerely thank Charline Lanvin for her help during dating the samples at the laboratory of Géosciences Montpellier, Virginie Moutarlier for her help during XRD analysis and Rietveld quantifications for polytypes. This work was supported by the INSU program (Tellus-syster).

Access to SEM facilities of the MIMENTO center was made through the cooperative projects in the French Renatech network.

CHAPTER 3 by the Fityk software© v0.9.8 and the results are shown in Figure 3.10.

Figure 3.10: Muscovite 001 peak decomposition using the Fityk 0.9.8 software [START_REF] Wojdyr | Fityk: a general-purpose peak fitting program[END_REF] of the fraction < 0.5 µm for the samples 15 LAK 1(less deformed) and 15 LAK 3 (highly deformed). WC = well crystallized and PC= poorly crystallized.

The decomposition for this reflection on the < 0.5 um fraction suggests the presence of three components in the less deformed sample. The three phases have Gaussian peaks at the following d-spacing positions:

-10.03 Å: with relatively sharp peak shape corresponds to a well crystallized phase (WC).

-10.05 Å: with broad peak shape corresponds to a poorly crystallized phase (PC 1).

-10.76 Å: with very broad peak-shape corresponds to another poorly crystalline phase (PC 2).

Based on the d-spacing values, the WC and PC 1 phases correspond to two mica components while the PC 2 phase probably corresponds to an illite/smectite mixed layer with a very small proportion of smectite as the latter was not detected by XRD after ethylene glycol saturation. In the highly-deformed sample, only two Gaussian peaks were observed at the following d-spacing positions:

-10.02 Å: with relatively sharp peak shape corresponds to a well crystallized phase (WC).

-10.04 Å: with broad peak shape corresponds to a poorly crystallized phase (PC 1).

GENERAL DISCUSSION

View of the Pyrenees from the valley of Ordesa, Spain