Dominique Chardon
email: dominique.chardon@ird.fr

Markus Aretz

Damien Roques

Reappraisal of Variscan tectonics in the southern French Massif Central

Keywords: Nappe tectonics, Sheath fold, Transpression, Wildflysch, Montagne Noire, Cévennes fault, Iberian-Armorican syntax

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Lateral movements in collisional orogens are assisted by continental-scale transcurrent fault systems and accompanied by extension of the hot thickened crust. These displacements respond to continental indentation, the formation of syntaxes (i.e., bends in orogens) and/or the creation of a favorable boundary condition for escape. Such processes have significantly distorted the collisional structural pattern of the Variscides [START_REF] Burg | Syn-to post-thickening extension in the Variscan belt of Western Europe: Modes and structural consequences[END_REF][START_REF] Martínez-Catalán | Are the oroclines of the Variscan belt related to late Variscan strike-slip tectonics?[END_REF], as exemplified around the Iberian-Armorican syntax (Fig. 1a). Despite that distortion, the geotraverse of the Southern Variscides through the Eastern French Massif Central (Fig. 1a) has long been interpreted in terms of southward growth of the collisional prism at the expense of the foreland basin (e.g., [START_REF] Matte | Variscan thrust nappes, detachments, and strike-slip faults in the French Massif Central: Interpretation of the lineations[END_REF]. At the southern end of that geotraverse, the Montagne Noire (Fig. 1) is a type locality at the hinterland-foreland transition where outward orogen-normal thrusting during flysch sedimentation is classically postulated [START_REF] Matte | Two geotraverses across the Ibero-Armorican Variscan arc of Western Europe[END_REF][START_REF] Matte | Variscan thrust nappes, detachments, and strike-slip faults in the French Massif Central: Interpretation of the lineations[END_REF][START_REF] Franke | Synorogenic sedimentation in the Variscan belt of Europe[END_REF][START_REF] Soula | Thrustrelated, diapiric, and extensional doming in a frontal orogenic wedge: example of the Montagne Noire, Southern French Hercynian Belt[END_REF][START_REF] Malavieille | Impact of erosion, sedimentation, and structural heritage on the structure and kinematics of orogenic wedges: analog models and case studies[END_REF].

The Montagne Noire exposes a gneiss dome (or "Axial Zone") mantled by Paleozoic series folded together with the Visean -Serpukovian Kulm flysch sediments of the foreland basin [START_REF] Engel | Migration of folding and flysch sedimentation on the southern flank of the Variscan belt (Montagne Noire, Mouthoumet massif, Pyrenees)[END_REF]Fig. 1). In the southern flank of the dome, [START_REF] Bergeron | Sur les nappes de recouvrement du versant méridional de la Montagne Noire[END_REF] first suggested the occurrence of thrust nappes, for which Von Gaertner (1937aGaertner ( , 1937b) ) introduced the analogy with the Helvetic nappes of Switzerland (e.g., [START_REF] Ramsay | Role of shear in development of the Helvetic foldthrust belt of Switzerland[END_REF] i.e., the nappes originated in the northern flank of the dome and were extruded southward. The impressive work of [START_REF] Gèze | Étude géologique de la Montagne Noire et des Cévennes méridionales[END_REF] established the recumbent fold structure of the nappes, which he interpreted to result from north-vergent thrusting against the dome. In an exemplary fair play controversy published in a common paper with Gèze [START_REF] Gèze | Sur le sens de déversement des nappes de la Montagne Noire[END_REF], de Sitter and Trümpy relaunched the Helvetic analogy through a clever model of southward nappe emplacement. The 60' saw the advent of kinematic analysis of bedding / cleavage / fold asymmetry relationships in the Montagne Noire [START_REF] Rodgers | L'emploi pratique de la schistosité dans la tectonique locale[END_REF][START_REF] Mattauer | Sur le déversement vers le Sud et le style tectonique en têtes plongeantes des structures hercyniennes du versant sud de la Montagne Noire[END_REF]. That approach led to a model of south-verging fold nappes [START_REF] Arthaud | La structure et la microtectonique des nappes hercyniennes de la Montagne Noire, Étages tectoniques[END_REF][START_REF] Arthaud | Étude tectonique et microtectonique comparée de deux domaines hercyniens : les nappes de la Montagne Noire (France) et l'anticlinorium de l'Iglesiente (Sardaigne)[END_REF], which was later coupled to a tectonosedimentary model linking wildflysch sedimentation to southward nappe propagation [START_REF] Engel | Synorogenic gravitational transport in the Carboniferous of the Montagne Noire (S-France)[END_REF].

Several attempts were made at deciphering deformation of the Axial Zone, where predoming fabrics are inferred to have formed during thrust nappe tectonics (e.g., [START_REF] Ellenberger | Replis de micaschistes et tectonique d'infrastructure au sein du massif gneissique du Caroux (zone axiale de la Montagne Noire)[END_REF][START_REF] Van Den Driessche | Tectonic evolution of the Montagne Noire (French Massif Central) -A model of extensional gneiss dome[END_REF][START_REF] Demange | Contribution au problème de la formation des dômes de la Zone axiale de la Montagne Noire : Analyse géométrique des plissements superposés dans les séries métasédimentaires de l'enveloppe. Implications pour tout modèle géodynamique[END_REF][START_REF] Soula | Thrustrelated, diapiric, and extensional doming in a frontal orogenic wedge: example of the Montagne Noire, Southern French Hercynian Belt[END_REF][START_REF] Charles | The Montagne Noire migmatitic dome emplacement (French Massif Central): new insights from petrofabric and AMS studies[END_REF]. But the Axial zone and its southern envelop lack N-S shearing features. They are affected by pervasive ENE stretching and strike-slip deformation [START_REF] Nicolas | Geological aspects of deformation in continental shear zones[END_REF][START_REF] Beaud | Étude structurale de la Zone Axiale orientale de la Montagne Noire (Sud du Massif Central français)[END_REF][START_REF] Faure | Données cinématiques sur la mise en place du dôme migmatitique carbonifère moyen de la zone axiale de la Montagne Noire (Massif Central, France)[END_REF][START_REF] Echtler | Extensional tectonics, basement uplift and Stéphano-Permian collapse basin in a late Variscan metamorphic core complex (Montagne Noire, Southern Massif Central)[END_REF][START_REF] Aerden | Tectonic evolution of the Montagne Noire and a possible orogenic model for syncollisional exhumation of deep rocks, Variscan belt, France[END_REF][START_REF] Matte | La zone axiale hercynienne de la Montagne Noire n'est pas un "metamorphic core complex" extensif mais un anticlinal post-nappe à coeur anatectique[END_REF][START_REF] Schranzhofer | La zone de cisaillement polyphasée du versant Sud de la Montagne Noire (Massif Central, France) : Un "vecteur" pour l'exhumation des dômes migmatitiques[END_REF][START_REF] Franke | Hot metamorphic core complex in a cold foreland[END_REF][START_REF] Rabin | Strain partitioning along the anatectic front in the Variscan Montagne Noire massif (southern French Massif Central)[END_REF]. This, together with perceptive criticisms of the nappe kinematic model [START_REF] Collomb | Age relatif et signification de la linéation régionale dans la Montagne Noire (Massif du Caroux et ses enveloppes, Hérault)[END_REF][START_REF] Ellenberger | Le Paléozoïque au Sud du Massif Central : Montagne Noire et Massif de Mouthoumet[END_REF][START_REF] Lee | Mise en évidence d'un cisaillement ductile d'ouest en est dans les nappes du versant sud de la Montagne Noire (Sud du Massif Central)[END_REF] did not however lead to question the southward nappe emplacement paradigm.

In the present paper, we provide a critical review pointing to the disputable kinematics of the southward nappe emplacement model and recalling its paleogeographic inconsistencies. We then present the first comprehensive structural and kinematic analysis of the nappes in the southeastern Montagne Noire integrating deformation of the wildflysch. We show that the nappes were thrust northeastwardly during wildflysch sedimentation in a sinistral transpressional context. This result calls for a revision of the convergent deformation scheme of the southern Variscan foreland, with a preponderant role of orogen-scale transcurrent faulting before and during amplification of the Iberian-Armorican syntax.

Geological outline

The study area comprises the easternmost part of the Pardailhan unit and the underlying terrains located to the East (i.e., the Mont Peyroux, Faugères and Cabrières nappes of [START_REF] Arthaud | Étude tectonique et microtectonique comparée de deux domaines hercyniens : les nappes de la Montagne Noire (France) et l'anticlinorium de l'Iglesiente (Sardaigne)[END_REF] Figs. 1b and2). The nappes are supported by the schistose envelope of the Axial zone (the socalled Schistes X of Ediacarian to Early Cambrian age), which constitutes a mid-crustal décollement. The stratigraphic succession consists of Schistes X, Ordovician pelitic schists, Devonian-Tournaisian carbonate and chert series, and the Mississippian Kulm flysch grading upward into a wildflysch [START_REF] Engel | Synorogenic gravitational transport in the Carboniferous of the Montagne Noire (S-France)[END_REF][START_REF] Aretz | The Kulm Facies of the Montagne Noire (Mississippian, southern France)[END_REF]Fig. 2). The so-called Écailles de Cabrières are mostly slabs or slivers (écailles in French) of Ordovician to lower Carboniferous series transported upon the wildflysch [START_REF] Gèze | Étude géologique de la Montagne Noire et des Cévennes méridionales[END_REF]). The regional structure is marked by mapscale folds trending ENE in the western part of the map area (Figs. 2,3a and 3b). These folds (referred to as F2 in the present work) are inclined to slightly overturned northward and have been documented at various scales throughout the study area (e.g., [START_REF] Lee | Analyse structurale du versant sud de la Montagne Noire (Hérault -France). Aspects cinématiques de la mise en place des nappes[END_REF] and considered as post-nappe. The Pardailhan unit essentially consists in the lower limb of a ENE-trending and slightly S-dipping, faulted and refolded recumbent anticline cored by massive Cambrian sedimentary series [START_REF] Gèze | Étude géologique de la Montagne Noire et des Cévennes méridionales[END_REF][START_REF] Echtler | Geometry and kinematics of recumbent folding and low-angle detachment in the Pardailhan nappe (Montagne Noire, Southern French Massif Central)[END_REF].

Origin and kinematics of the nappes: old pending issues

Bedding / cleavage / fold asymmetry relationships that would be indicative of southward recumbent folding are actually restricted to portions of the Pardailhan nappe [START_REF] Arthaud | Étude tectonique et microtectonique comparée de deux domaines hercyniens : les nappes de la Montagne Noire (France) et l'anticlinorium de l'Iglesiente (Sardaigne)[END_REF].

But even in this unit, the north-facing folds affecting the inverted series have been shown to be F2 folds documented in both normal and overturned limbs of the nappes [START_REF] Lee | Analyse structurale du versant sud de la Montagne Noire (Hérault -France). Aspects cinématiques de la mise en place des nappes[END_REF]; see also [START_REF] Cassard | Variscan crustal thickening, extension and late overstacking during the Namurian-Westphalian in the Western Montagne Noire[END_REF] instead of second-order folds that would typify the overturned limb of a south-verging fold nappe (see [START_REF] Rodgers | L'emploi pratique de la schistosité dans la tectonique locale[END_REF]. The pervasive ENE-trending stretching lineation affecting the nappes was originally interpreted as B-type i.e., parallel to the axes of the southverging recumbent folds [START_REF] Arthaud | Un exemple de relations entre l'étirement dans B, la dispersion des linéations et la courbure des axes de plis : la virgation des plis couchés hercyniens du versant sud de la Montagne Noire[END_REF]. This lineation is however pervasive in the dome too and parallel to the F2 folds, which led [START_REF] Collomb | Age relatif et signification de la linéation régionale dans la Montagne Noire (Massif du Caroux et ses enveloppes, Hérault)[END_REF] to challenge N-S nappe emplacement kinematics deduced from the schistosity bearing that lineation. Besides, the development of overturned fold limbs several kilometers wide was not readily reconciled with stretching parallel to the recumbent fold axes and normal to a N-S nappe displacement direction (discussions in [START_REF] Burg | A cross section through the French Massif Central and the scope of its Variscan evolution[END_REF][START_REF] Harris | Strain distribution within the Pardailhan nappe (Montagne Noire, France) and structure of its basal thrust zone. Implications for events associated with nappe emplacement[END_REF][START_REF] Matte | Two geotraverses across the Ibero-Armorican Variscan arc of Western Europe[END_REF][START_REF] Echtler | Geometry and kinematics of recumbent folding and low-angle detachment in the Pardailhan nappe (Montagne Noire, Southern French Massif Central)[END_REF]. ENE stretching in the Mont Peyroux nappe and Western Faugères nappe (Figs 1b and2) was later to be shown to record eastward shearing [START_REF] Lee | Analyse structurale du versant sud de la Montagne Noire (Hérault -France). Aspects cinématiques de la mise en place des nappes[END_REF][START_REF] Lee | Mise en évidence d'un cisaillement ductile d'ouest en est dans les nappes du versant sud de la Montagne Noire (Sud du Massif Central)[END_REF]. These authors also first documented top-to the-S shear criteria in the upper (southern) part of the Pardailhan unit that they interpreted as due to gravitational gliding. [START_REF] Echtler | Geometry and kinematics of recumbent folding and low-angle detachment in the Pardailhan nappe (Montagne Noire, Southern French Massif Central)[END_REF] related these shears to postrecumbent folding, late orogenic extensional detachment faults coeval with dome emplacement.

To reconcile southward gliding and ENE stretching, [START_REF] Aerden | Origin of a large-scale fold nappe in the Montagne Noire, Variscan belt, France[END_REF] conceived a model combining coeval, syn-convergence southward collapse of the orogenic front -forming the recumbent folds -and N-S shortening producing the ENE F2 folds and stretching. But these authors seem to have overlooked eastward shearing, as did [START_REF] Mattauer | Plissement hercynien synschisteux post-nappe et étirement subhorizontal dans le versant sud de la Montagne Noire (Sud du Massif Central, France)[END_REF], who pleaded for post-nappe ENE coaxial stretching. More recently, [START_REF] Wiederer | Low-grade metamorphism in the Montagne Noire (S-France): Conodont Alteration Index (CAI) in Paleozoic carbonates and implications for the exhumation of a hot metamorphic core complex[END_REF] and [START_REF] Franke | Hot metamorphic core complex in a cold foreland[END_REF] interpreted top-to-the ENE shearing at the contact between the Mont Peyroux and Faugères nappes (Fig. 2) as indicative of an extensional detachment folded by the regional F2 folds. Their model takes up that of [START_REF] Echtler | Extensional tectonics, basement uplift and Stéphano-Permian collapse basin in a late Variscan metamorphic core complex (Montagne Noire, Southern Massif Central)[END_REF], in which the dome emplaced in a dextral transtensional releasing bend ("pull apart") of the Cévennes fault (Fig. 1b) but with superimposed N-S shortening to account for ENE F2 folding. However, top-to the ENE shearing and N-S shortening are not compatible with dextral slip along the dome's flank; it would instead require sinistral shearing. Furthermore, the subtractive break expected across such an extensional detachment at the Mont Peyroux -Faugères contact is not documented in the regional pattern of very low-grade metamorphism [START_REF] Franke | Hot metamorphic core complex in a cold foreland[END_REF][START_REF] Doublier | The tectono-metamorphic evolution of the very low-grade hangingwall constrains two-stage gneiss dome formation in the Montagne Noire (Southern France)[END_REF]. By emphasizing postnappe deformation in the Mont Peyroux and Faugères units, [START_REF] Franke | Hot metamorphic core complex in a cold foreland[END_REF] came to argue that no markers of original southward nappe emplacement remained but the overturned series. This would again not be reconcilable with the strain expected to account for the amplitude of the overturned fold limbs. Finally, it is noteworthy that the Montagne Noire south-vergent fold-andthrust model as extended by [START_REF] Arthaud | L'évolution structurale hercynienne du massif de Mouthoumet (Sud de la France)[END_REF] up to the Mouthoumet massif (Fig. 1b) shows no thrust emerging with a northern dip. All the thrusts would indeed be S-dipping and mostly cushioned in the flysch, casting further doubt on the south-verging thrusting model.

From paleogeographic and stratigraphic viewpoints, no evidence supports a northern origin for the nappes either [START_REF] Ellenberger | Le Paléozoïque au Sud du Massif Central : Montagne Noire et Massif de Mouthoumet[END_REF]. Even promoters of the southward nappe emplacement model acknowledged that paleogeography does not provide a decisive test of a northern or a southern origin for the nappes (see [START_REF] Gèze | Sur le sens de déversement des nappes de la Montagne Noire[END_REF][START_REF] Arthaud | Étude tectonique et microtectonique comparée de deux domaines hercyniens : les nappes de la Montagne Noire (France) et l'anticlinorium de l'Iglesiente (Sardaigne)[END_REF]. Besides, Devonian series and the Carboniferous flysch are not present in the northern thrust belt, but only in the southern flank of the Montagne Noire, in the Mouthoumet Massif and in the Pyrenees (Fig. 1b). Moreover, the Lower Paleozoic of the Écailles de Cabrières has long been known to have clear affinities with that of the Mouthoumet massif and the Pyrenees and not with the rest of the Montagne Noire or the Massif Central [START_REF] Engel | Synorogenic gravitational transport in the Carboniferous of the Montagne Noire (S-France)[END_REF]Fig. 1b). The interpretation of the Écailles de Cabrières as miniature nappes derived from southward propagating fold nappes in the Montagne Noire (De Sitter and Trümpy in [START_REF] Gèze | Sur le sens de déversement des nappes de la Montagne Noire[END_REF][START_REF] Engel | Synorogenic gravitational transport in the Carboniferous of the Montagne Noire (S-France)[END_REF][START_REF] Engel | Le Carbonifère anté-stéphanien de la Montagne Noire : rapports entre mise en place des nappes et sédimentation[END_REF][START_REF] Vachard | Mississippian (Middle Tournaisian-Late Serpukhovian) lithostratigraphic and tectonosedimentary units of the southeastern Montagne Noire (Hérault, France)[END_REF] is therefore untenable.

Structural and kinematic analysis

1. Overall structure

Our investigations led to a structural scheme that does not require a distinction between a Mont Peyroux and a Faugères nappe (Fig. 2). The Mont Peyroux overturned series and the Mont de Faugères normal series are simply part of a regional-scale, recumbent F1 east-verging recumbent syncline with an axis initially trending close to N-S, which has been refolded by the map-scale F2 ENE trending folds (Figs. 2,3a and 3b). That syncline is called hereafter the Orb syncline, for its axial trace follows the Orb River for some distance SW of Le Lau (Figs. 3a and4a). Both limbs of the F1 Orb syncline are attenuated northward as F2 folds become tighter (Figs. 3b and4a). The wildflysch belongs to the normal forelimb of the Orb syncline and is bounded to the North by the Roquessels fault [START_REF] Engel | Synorogenic gravitational transport in the Carboniferous of the Montagne Noire (S-France)[END_REF][START_REF] Engel | Le Carbonifère anté-stéphanien de la Montagne Noire : rapports entre mise en place des nappes et sédimentation[END_REF]; Fig. 2). The Orb syncline tectonically overlies in the North parautochtonous units detached from the Schistes X and is overlain to the West by the Pardailhan unit and to the East and Southeast by the Pic the Vissou and Écailles de Cabrières units (Figs. 2 and4a). The parautochtonous units and Schistes X form a corridor of steeper and more penetrative schistosity or foliation concordant with the gneissic fabric of the dome. That northern fringe of the study area is called hereafter the northern deformation belt (Fig. 4a).

Given the late exhumation of the gneissic lower crust along the northern deformation belt and the southeastward decreasing very low-grade metamorphism in the nappes [START_REF] Engel | Le Carbonifère anté-stéphanien de la Montagne Noire : rapports entre mise en place des nappes et sédimentation[END_REF][START_REF] Wiederer | Low-grade metamorphism in the Montagne Noire (S-France): Conodont Alteration Index (CAI) in Paleozoic carbonates and implications for the exhumation of a hot metamorphic core complex[END_REF][START_REF] Franke | Hot metamorphic core complex in a cold foreland[END_REF][START_REF] Doublier | The tectono-metamorphic evolution of the very low-grade hangingwall constrains two-stage gneiss dome formation in the Montagne Noire (Southern France)[END_REF], the map in Figure 2 also provides a kind of cross sectional view of the upper crust, with progressively shallower levels exposed in the south. The present work relies on extensive structural mapping based on more than 700 field stations dedicated to structural measurements, kinematic observations and logging of roadside sections.

2. Deep Upper Crust

This crustal level comprises the terrains located NNW of the Roquessels fault and Roquebrun, and West of Cabrières (Fig. 2). The area is affected by a regional, penetrative schistosity or slaty cleavage and locally by a fracture cleavage in massive sandstones collectively called S1-2 (Figs. 4c and6a). This planar fabric bears a ubiquitous, NNE-to NE-trending, shallowly plunging stretching lineation (Figs. 3c and5b) marked by quartz fibers or the elongation of quartz aggregates in siliciclatics and by calcite fibers and the elongation of nodules in carbonates (L1-2).

2. 1. Monts de Faugères

The Monts de Faugères East of 3°05'E (Fig. 2) consist in a north-facing recumbent anticlinal fold sheet of Devonian carbonates with its backlimb supporting the flysch (Fig. 4c to 4e). The schistosity of the backlimb is moderately to shallowly south dipping (Fig. 5a). The structure of the backlimb Devonian limestones may be complex in details, as exemplified by second-order, northwardly inclined to slightly overturned F2 folds (the regional S1-2 schistosity being axial planar to those folds) and stratigraphic repetitions [START_REF] Maurel | Études sur le Dévonien et le Carbonifère inférieur du versant méridional de la Montagne Noire[END_REF][START_REF] Pinna | Sur la distinction d'unités tangentielles nouvelles dans les Monts de Faugères, versant sud de la Montagne Noire (feuille à 1/50 000, Bédarieux)[END_REF][START_REF] Mattauer | Plissement hercynien synschisteux post-nappe et étirement subhorizontal dans le versant sud de la Montagne Noire (Sud du Massif Central, France)[END_REF]. But the structural envelop of the Devonian remains shallowly South dipping and local fault/fold patterns are systematically indicative of South-over-North apparent thrusting / vergence [START_REF] Maurel | Études sur le Dévonien et le Carbonifère inférieur du versant méridional de la Montagne Noire[END_REF][START_REF] Pinna | Sur la distinction d'unités tangentielles nouvelles dans les Monts de Faugères, versant sud de la Montagne Noire (feuille à 1/50 000, Bédarieux)[END_REF]present work;Fig. 4). Planar and linear D1-2 fabrics in the flysch are associated with pervasive top-to-the ENE shearing recorded by pervasive shallowly dipping shear zones (Figs. 5c). Shearing parallel to the regional stretching lineation and the recumbent fold axes as well as the common attenuation of the fold limbs along the shear zones attests to a genetic link between recumbent folding and shearing (Figs. 6a and6b). The occurrence of macroscopic sheath folds (Fig. 6c) further attests to the intensity of the simple shear component of deformation [START_REF] Cobbold | Development of sheath folds in shear regime[END_REF]. Intense LS tectonites affect the carbonates (Fig. 6d) but recrystallization into marble seems to have prevented preservation of macroscopic shear criteria. Microscopic shear criteria [START_REF] Lee | Analyse structurale du versant sud de la Montagne Noire (Hérault -France). Aspects cinématiques de la mise en place des nappes[END_REF] and calcite lattice preferential orientation [START_REF] Mattauer | Plissement hercynien synschisteux post-nappe et étirement subhorizontal dans le versant sud de la Montagne Noire (Sud du Massif Central, France)[END_REF] are however indicative of top-to-the ENE shearing too. West of Cabrières, the eastern termination of the Devonian limestones corresponds to the nose of a sheath anticline that would be compatible with the regional ENE shearing regime documented throughout the Monts de Faugères (e.g., Figs. 4 and6). Schistosity trajectories in the Monts de Faugères (Fig. 5a) delineate a series of shallowly SSE-dipping shear zones that are interpreted to have accompanied differential top-to-the ENE shearing (Fig. 5c).

The parautochtonous units display a fabric map pattern comparable to that of the overlying Monts de Faugères fold sheet although with higher dips of the planar fabric that becomes in most cases a foliation (Figs. 4b to 4d; Fig. 5). Top-to-the NE shearing is documented at the base of the Mont de Faugères fold sheet (e.g., Fig. 5c), suggesting partitioning between internal top-to-the ENE shearing deformation in the fold sheet and top-to-the NE slip at its base / northern margin. Top-to-the NE sense of shear is documented as well within and at the base of the para autochtonous units (Fig. 5c). A tectonic window exposing the flysch in the Monts de Faugères (Fig. 2) implies at least several km of transport of the fold sheet towards the ENE / NE (Figs. 4d and4e). To summarize, the structure, internal deformation and kinematics of the Monts de Faugères fold sheet and the underlying parautochthonous units are indicative of a ENE-to NE-vergent, sinistral transpressive low-angle thrust system (Fig. 4).

2. 2. Western Monts de Faugères and the rest of the deep upper crust

The western termination of the Monts de Faugères Devonian corresponds to the F2 Le Lau antiform (Figs. 2 3b and4a). The hinge of the antiform is affected by a beam of NE-trending second-order folds parallel to the regional stretching lineation (Figs. 3a and5b). These folds have no systematic asymmetry and /or complex N-S cross-sectional geometries [START_REF] Arthaud | Étude structurale de la terminaison occidentale des Monts de Faugères (Montagnes Noire, Hérault)[END_REF] that are actually mostly those of sheath folds [START_REF] Franke | Hot metamorphic core complex in a cold foreland[END_REF]. Deformation in the fold beam is associated with top-to-the ENE to NE sense of shear parallel to the regional stretching lineation (Fig. 5c). This shearing pattern -but devoid of sheath folds -also affects the overturned Mont Peyroux limb further to the West (Fig. 6d) and is richly documented upward (westward) in the structural pile, including the Pardailhan unit (Fig. 5c). Map-scale shear zones laminating the inverted Mont Peyroux limb are interpreted as recording localization of regional top-to-the ENE shearing (Figs. 2, 4a and4b). The regional schistosity wraps the Le Lau antiform, together with the overturned Mont Peyroux limb and its sub concordant shear zones (Figs. 4a and5a).

The Laurenque F2 synform affects the flysch between Roquebrun and Le Lau (Figs. 2, 3b and 4a). The fold refolds the axial plane of the F1 Orb syncline but the map axial trace of the F1 fold may not be mapped precisely (Figs. 3a and3b). The Laurenque fold is interpreted as a sheath fold with its nose pointing to the ENE. Shallowly S-dipping S1-2 appears to be axial-planar to that fold, which has undergone pervasive ENE-directed shearing and generated a schistosity triple point at its eastern termination (Figs. 2 and5). This indicates fold growth -most probably by eastward shearing -during NNW-directed shortening.

The Le Lau antiform is followed to the North by the map-scale F2 l'Aire Marty syncline refolding the F1 Orb syncline and the shear zones of its overturned and normal limbs (Figs. 3 and4a). The northern limb of that F2 fold is attenuated and taken into the northern deformation belt (Figs. 5 and4a). Top-to the ENE / sinistral shearing, comparable to that documented in the allochtonous units, prevails throughout the northern deformation belt (Figs. 5c and4a; see also [START_REF] Beaud | Étude structurale de la Zone Axiale orientale de la Montagne Noire (Sud du Massif Central français)[END_REF][START_REF] Lee | Analyse structurale du versant sud de la Montagne Noire (Hérault -France). Aspects cinématiques de la mise en place des nappes[END_REF][START_REF] Schranzhofer | La zone de cisaillement polyphasée du versant Sud de la Montagne Noire (Massif Central, France) : Un "vecteur" pour l'exhumation des dômes migmatitiques[END_REF].

3. Uppermost Crust: Wildflysch and Écailles de Cabrières

Along the cross-section of Figure 4b, the Mont Peyroux overturned fold limb exposes a continuous stratigraphy from the Devonian to the wildflysch. The eastward transition from overturned to normal bedding along that section [START_REF] Engel | Le Carbonifère anté-stéphanien de la Montagne Noire : rapports entre mise en place des nappes et sédimentation[END_REF] is interpreted as a progressive unconformity formed by eastward overturning of the Mont Peyroux limb. Higher up (eastward; Fig. 2) in the wildflysch stratigraphy, at least two main unconformities are documented (Fig. S1, supplementary material). They are deformed by map-scale F2 folds (Figs.

2, 3a and 4c). The oldest of the two unconformities passes by Lenthéric (Fig. 4b) and is taken into the steep overturned forelimb of a F2 anticline (Figs. 4c and4d). Downlaps on this unconformity (Fig. 4d) indicate northeastward progradation of the wildflysch. The youngest unconformity is a progressive unconformity passing by Laurens and La Plaine (Figs. 2 and4c) that shows a northward-fanning pattern of bedding indicative of north-or northeastward progradation / thickening of the flysch sequence. Northeastward progradation of the flysch series is consistent with syn-sedimentary NE-vergent F2 folding and thrusting (Figs. 2 and4).

The basal (western) contact of the Écailles de Cabrières unit is sub horizontal and truncates the underlying folded flysch sequence described above (Figs. 2 and4d). The Écailles de Cabrières unit is made of duplex lenses separated by low-angle S-dipping faults, most of which root into the basal contact (Figs. 4d to 4f). The South-over-North stacking pattern of the lenses (Figs. 4d to 4f) revealed by the detailed investigations of [START_REF] Gèze | Étude géologique de la Montagne Noire et des Cévennes méridionales[END_REF] and [START_REF] Maurel | Études sur le Dévonien et le Carbonifère inférieur du versant méridional de la Montagne Noire[END_REF] is consistent with the top-to-the NE to ENE reverse shear criteria we collected along the basal contact, along the internal contacts and within the flysch of the Écailles de Cabrières unit (Figs. 4,5c,7,8a and 8c). The Écailles de Cabrières unit is interpreted as a shallow NE-vergent thrust system having propagated over the folded flysch basin (e.g., Figs. 2 and4d), in agreement with North-vergent thrust folding and the unconformity patterns in the underlying wildflysch basin.

The Roquessels mass transport complex (Fig. 2) is made of a mix of pre-and syn-flysch lithologies stacked at the northwestern front of the Écailles de Cabrières unit (Fig. 4d). Low angle, top-to the WSW shearing affects the eastern portion of the mass transport complex (Fig. 8b), whereas syn-sedimentary (syn-flysch), top to the WSW normal faulting and gliding is documented near the western termination of the mass transport complex (Fig. 8c). The latter pattern may result from westward gravitational escape of the mass transport complex at the front of the northeastward propagating Écailles de Cabrières unit. The former pattern may either be related to (1) lateral escape process recorded at a lower (i.e., solid-state / ductile) structural level of the glided mass or (2) early, low angle westward detachment faulting prefiguring the Roquessels fault (see section 4.4).

Relatively low penetrative deformation of the Écailles de Cabrières unit allows for the preservation of syn-sedimentary gliding and normal faulting features within or at the base of reef carbonate massifs in the flysch series (Fig. S2, supplementary material). Senses of slip on the gliding surfaces and normal faults are mostly top-to-the South and, to a lesser extent, top-to the WSW (Fig. 5c).

Late Dextral Transtensional Fault System

Normal-dextral kinematics of the Roquessels fault [START_REF] Engel | Le Carbonifère anté-stéphanien de la Montagne Noire : rapports entre mise en place des nappes et sédimentation[END_REF] are attested to by fractures in massive vein quartz injected in the fault (Figs. 2 and4), with a mean pitch of 60° to the WSW (e.g., Vailhan dam; Fig. 2). The normal component of slip on the fault is consistent with a subtractive break in the very-low grade metamorphic map pattern [START_REF] Engel | Le Carbonifère anté-stéphanien de la Montagne Noire : rapports entre mise en place des nappes et sédimentation[END_REF] and the more penetrative schistosity affecting the flysch in its footwall than in its hangingwall. Documentation of low-angle, top-to-the WSW shear criteria in the vicinity of the Roquessels fault (Figs. 5c and8b) suggests that the fault recorded late (C' type) brittle strain localization across an earlier, lower angle detachment [START_REF] Engel | Le Carbonifère anté-stéphanien de la Montagne Noire : rapports entre mise en place des nappes et sédimentation[END_REF] 5c). South dipping faults with top-to-the SW and SSW (i.e., dextral-transtensional) slip are documented in the Pardailhan unit, especially south of the western extension of the Roquessels fault [START_REF] Lee | Analyse structurale du versant sud de la Montagne Noire (Hérault -France). Aspects cinématiques de la mise en place des nappes[END_REF][START_REF] Echtler | Geometry and kinematics of recumbent folding and low-angle detachment in the Pardailhan nappe (Montagne Noire, Southern French Massif Central)[END_REF]. Those faults reactivate ramps associated with F2 north-vergent anticlines [START_REF] Lee | Analyse structurale du versant sud de la Montagne Noire (Hérault -France). Aspects cinématiques de la mise en place des nappes[END_REF].

NW of Cabrières, the basal contact of the Écailles de Cabrières and Pic de Vissou units over the Mont de Faugères series (Figs. 2 and4f) marks a subtractive metamorphic break indicative of extensional décollement shearing after emplacement of those units [START_REF] Engel | Le Carbonifère anté-stéphanien de la Montagne Noire : rapports entre mise en place des nappes et sédimentation[END_REF]. Top-to the WSW shearing with syn-kinematic emplacement of massive quartz veins along this décollement appears to post-date eastward shearing in the Monts de Faugères and the Écailles de Cabrières unit (Fig. 5c). The décollement is interpreted to have accompanied top-tothe WSW dextral transtension along the Roquessels fault system. Localized top-to the W or SW (i.e., dextral) shearing is also documented along shear zones -often associated with quartz veins -in the northern deformation zone where top-to-the ENE shearing features are dominant (Figs.

4d, 4e and 5c; see also [START_REF] Lee | Analyse structurale du versant sud de la Montagne Noire (Hérault -France). Aspects cinématiques de la mise en place des nappes[END_REF][START_REF] Schranzhofer | La zone de cisaillement polyphasée du versant Sud de la Montagne Noire (Massif Central, France) : Un "vecteur" pour l'exhumation des dômes migmatitiques[END_REF]. Likewise, dextral top-to-the WSW shearing is documented along the basal contact of the Mont Peyroux-Monts de Faugères series West of 3°05'E as well as along the Le Lau fault (Figs. 5c). Dextral shears are also documented further to the West in the northern deformation belt and along the basal contact of the Pardailhan and Minervois nappes [START_REF] Echtler | Geometry and kinematics of recumbent folding and low-angle detachment in the Pardailhan nappe (Montagne Noire, Southern French Massif Central)[END_REF][START_REF] Cassard | Variscan crustal thickening, extension and late overstacking during the Namurian-Westphalian in the Western Montagne Noire[END_REF]Fig. 1b).

Interpretation

1. Early Left-Lateral Transpressional Fold-and-Thrust Tectonics

The strain pattern of the southeastern Montagne Noire formed by the interplay of (1) pervasive top-to-the ENE shear thrusting, map-scale recumbent folding and sinistral shearing (D1) and ( 2) N-to NE-vergent fold-and-thrust tectonics contemporaneous with wildflysch sedimentation (D2).

The two are kinematically compatible within a framework of D1-2 partitioned sinistral transpression along a ENE (i.e., Cévennes) structural trend (Fig. 1b). The consistent regional ENE trend of the stretching lineations is not perturbed by F2 folding (Figs. 2 and5b) as F2 folds, intersection lineations and stretching lineations are statistically undistinguishable (Fig. 3c) and parallel to microfold and crenulation axes [START_REF] Lee | Analyse structurale du versant sud de la Montagne Noire (Hérault -France). Aspects cinématiques de la mise en place des nappes[END_REF]. Coincidence of the macroscopic recumbent (sheath) fold axes and the stretching lineations is consistent with fold amplification / reorientation by simple shearing [START_REF] Berthé | Evolution of folds during progressive shear in the South Armorican shear zone, France[END_REF][START_REF] Cobbold | Development of sheath folds in shear regime[END_REF] further enhanced by shear-perpendicular (D2) shortening. The remaining spread in fold directions around the ENE trend would be indicative of various degrees of reorientation of F1 folds towards the shear direction (e.g., [START_REF] Franke | Hot metamorphic core complex in a cold foreland[END_REF]). S1-2 is axial-planar to the macroscopic recumbent folds but is also folded around the Le Lau antiform (Fig. 5a) and at the same time axial-planar to the Laurenque sheath synform (Figs. 3a, 4a and 5a) and to the F2 folds further to the East in the Monts de Faugères. The S1-2 triple point at the eastern termination of the Laurenque synform further argues for interference between eastward amplification of the fold and NNW-directed (D2) shortening. These considerations are indicative of an overlap in time between eastward shearing (D1) and F2-related shortening (D2) in a common D1-2 kinematic frame.

Series overturning has been achieved essentially eastwardly (Fig. 9), in agreement with eastward shear thrusting. The overall structure of the Pardailhan unit is in fact that of an ENEfacing sheath anticline underlined by the Cambrian massive series (see cross-sections of [START_REF] Echtler | Geometry and kinematics of recumbent folding and low-angle detachment in the Pardailhan nappe (Montagne Noire, Southern French Massif Central)[END_REF]. Superimposition of ENE F2 folding on regional-scale F1 ENE-verging recumbent anticlines and synclines produced east-facing sheath anticlines (the Pardailhan anticline, the Roquebrun synformal anticline and, to a lesser extend, the fold NW of Cabrières) and W-facing sheath synclines (Le Lau antiform), respectively (Fig. 3b). The present example therefore shows that transpression with a major component of longitudinal shearing (i.e., wrench dominated) can produce regional-scale, wrench-parallel recumbent sheath folds.

Early syn-flysch (D1) fold-and-thrusting is illustrated by the progressive unconformity at the northeastwardly overturned backlimb of the Orb syncline (Fig. 4b). This, together with the regional northeastward regional stratigraphic polarity of the wildflysch (Fig. 2), indicates that early NE-verging fold-and-thrusting set the first-order geometry of the wildflysch basin.

Younger progressive unconformities in the wildflysch attesting to more pronounced northward progradation (e.g., Laurens area; Figs. 2 and4c) suggest a later control of northward fold-andthrusting on flysch sedimentation. This, together with the large-scale F1/F2 interference pattern, indicates that ENE-vergent thrusting (D1) started before northward fold-and-thrust tectonics (D2).

The onset of eastward thrusting is constrained by the first occurrences of calciturbidites along the overturned limb of the Orb syncline (Fig. 4b), testifying to the destabilization of the carbonate platform topping the Mont Peyroux anticline in its early amplification stages. Vachard et al.

(2017) reported a mid-Viséan (Livian) age (∼340-336 Ma) for those calciturbidites. The late Serpukhovian age of the youngest dated olistoliths in the wildflysch (near Cabrières) indicates that northeastward fold-and-thrusting was still active or had ceased by ∼323 Ma (end Serpukhovian; [START_REF] Vachard | Mississippian (Middle Tournaisian-Late Serpukhovian) lithostratigraphic and tectonosedimentary units of the southeastern Montagne Noire (Hérault, France)[END_REF], because the flysch hosting these olistoliths is involved in the Écailles de Cabrières folds and thrusts. Left-lateral D1-2 transpressional fold-and-thrust tectonics therefore took place after 340 Ma over a ∼20 Myr period.

2. Late Right-Lateral Transtensional Tectonics

Tectonic contacts formed by sinistral transpression (D1-2) have been reactivated by dextral transtension (D3) through a system of normal-oblique faults and décollement(s) along which strain localization took place in the presence of fluids. Dextral transtension took place along shear bands and shear zones distributed in the northern deformation zone that earlier recorded pervasive sinistral shearing. In the Margal-Mons area (Fig. 2), the outer dome and Schistes X have Ar-Ar muscovite and biotite ages of 308 +/-3 Ma [START_REF] Maluski | Late Variscan tectonic evolution by thinning of earlier thickened crust -an 40Ar-39Ar study of the Montagne Noire, Southern Massif Central, France[END_REF] and K-Ar muscovite ages of 297-292 Ma [START_REF] Franke | Hot metamorphic core complex in a cold foreland[END_REF], whereas the parautochtonous unit has muscovite and biotite Ar-Ar ages of 297 +/-3 Ma [START_REF] Maluski | Late Variscan tectonic evolution by thinning of earlier thickened crust -an 40Ar-39Ar study of the Montagne Noire, Southern Massif Central, France[END_REF]. These ages are consistent with partial melting and granite emplacement contemporaneous with extensional deformation and detachment faulting in the Axial Zone as refined to 317-294 Ma by TIMS, LA-ICPMS, and SIMS U-Th-Pb dating [START_REF] Franke | Hot metamorphic core complex in a cold foreland[END_REF][START_REF] Poilvet | The Montalet granite, Montagne Noire, France: An Early Permian syn-extensional pluton as evidenced by new U-Th-Pb data on zircon and monazite[END_REF][START_REF] Pitra | Early Permian extensional shearing of an Ordovician granite: The Saint-Eutrope "C/S-like" orthogneiss (Montagne Noire, French Massif Central)[END_REF][START_REF] Roger | Timing of formation and exhumation of the Montagne Noire double dome, French Massif Central[END_REF][START_REF] Roger | Age of metamorphism and deformation in the Montagne Noire dome (French Massif Central): Tapping into the memory of fine-grained gneisses using monazite U-Th-Pb geochronology[END_REF][START_REF] Poujol | Two-stage partial melting during the Variscan extensional tectonics (Montagne Noire, France)[END_REF][START_REF] Trap | Timing and duration of partial melting and magmatism in the Variscan Montagne Noire gneiss dome (French Massif Central)[END_REF]. The shift from sinistral transpression to dextral transtension therefore took place between 323 Ma (minimum stratigraphic age of thrusting) and 317 Ma.

Discussion

1. Nappe tectonics in the Montagne Noire

Sinistral transpressive fold-and-thrust tectonics of the Southern Montagne Noire accounts at last for paleogeography. Such kinematics indeed imply a southwestern origin for the "nappes", as opposed to an elusive source north of the Axial Zone. It is also consistent with the Écailles de Cabrières being exotic in the Montagne Noire and part of a southern province including the Mouthoumet massif and the Pyrenees (Fig. 1b). The model also provides a mechanism for producing ENE recumbent folds with their axes parallel to the main direction of shearing, which is responsible for the main and only pervasive deformation pattern in the southeastern Montagne Noire. This prompts abandonment of the southward nappe emplacement paradigm and therefore also challenges models interpreting the Axial Zone as hosting a N-dipping crustal-scale thrust and/or being a stack of duplexes or pennic-like fold nappes pilled-up from the north [START_REF] Graham | Géométrie des surfaces de chevauchement[END_REF][START_REF] Soula | Thrustrelated, diapiric, and extensional doming in a frontal orogenic wedge: example of the Montagne Noire, Southern French Hercynian Belt[END_REF][START_REF] Matte | Variscan thrust nappes, detachments, and strike-slip faults in the French Massif Central: Interpretation of the lineations[END_REF][START_REF] Malavieille | Impact of erosion, sedimentation, and structural heritage on the structure and kinematics of orogenic wedges: analog models and case studies[END_REF][START_REF] Faure | Middle Carboniferous intracontinental subduction in the Outer Zone of the Variscan Belt (Montagne Noire Axial Zone, French Massif Central): multimethod geochronological approach of polyphase metamorphism[END_REF]. In the end, our results support the original model of [START_REF] Gèze | Étude géologique de la Montagne Noire et des Cévennes méridionales[END_REF] in which the northern and southern thrust belts of the Montagne Noire have opposite vergencies towards the Axial Zone. [START_REF] Lee | Mise en évidence d'un cisaillement ductile d'ouest en est dans les nappes du versant sud de la Montagne Noire (Sud du Massif Central)[END_REF] came to an interpretation comparable to ours for the deep deformation pattern of the Southeastern Montagne Noire as being possibly related to original eastward "nappe" emplacement. But they also considered the alternate possibility for this deformation to result from a "reorientation" of originally N-S nappe-related lineations. As recalled by [START_REF] Franke | Hot metamorphic core complex in a cold foreland[END_REF], such stretching lineations preexisting the penetrative deformation pattern of Figure 5 do not exist. [START_REF] Franke | Hot metamorphic core complex in a cold foreland[END_REF] proposed a post-nappe D2-D3 deformation model somehow comparable to our D1-2 model in its description. But if their D3 matches our F2-related shortening, their D2 is interpreted as ENE-directed extension. This however contradicts the dextral slip these authors evoke along the northern deformation belt at the time of that extension, for eastward shearing implies sinistral slip there, which is actually the case (Fig. 5c). ENE extension envisioned by [START_REF] Franke | Hot metamorphic core complex in a cold foreland[END_REF] was interpreted to be coeval with HT-LP metamorphism of the Axial Zone and shearing at the dome's margin at 314-306 Ma, prior to ENE (F2) folding [START_REF] Doublier | The tectono-metamorphic evolution of the very low-grade hangingwall constrains two-stage gneiss dome formation in the Montagne Noire (Southern France)[END_REF]. But as shown here, F2 folds grew during flysch sedimentation i.e., essentially before 323 Ma. Contrary to extension, sinistral transpression provides for the first time a kinematic scheme for producing recumbent folding by ENE shearing, whose pervasiveness and intensity can account for the amplitude of the overturned limbs. Sinistral transpression therefore represents the main and pervasive tectonic episode in the Southern Montagne Noire.

2. Tectonics and flysch sedimentation

The space-time sedimentology patterns of the flysch and its platform carbonate timeequivalent series have been argued to attest to, or to be consistent with, the southward emplacement of the nappes [START_REF] Engel | Synorogenic gravitational transport in the Carboniferous of the Montagne Noire (S-France)[END_REF][START_REF] Engel | Le Carbonifère anté-stéphanien de la Montagne Noire : rapports entre mise en place des nappes et sédimentation[END_REF][START_REF] Vachard | Mississippian (Middle Tournaisian-Late Serpukhovian) lithostratigraphic and tectonosedimentary units of the southeastern Montagne Noire (Hérault, France)[END_REF]. It is our opinion that these patterns are compatible with either a northern or a southern origin. But the newly documented progressive unconformities in the wildflysch are consistent with progradation in the same sense as D2 fold-and-thrust propagation. This would also be consistent with, for instance, the Monts de Faugères flysch being more distal than the Mont Peyroux -Laurens flysch (e.g., [START_REF] Engel | Le Carbonifère anté-stéphanien de la Montagne Noire : rapports entre mise en place des nappes et sédimentation[END_REF][START_REF] Vachard | Mississippian (Middle Tournaisian-Late Serpukhovian) lithostratigraphic and tectonosedimentary units of the southeastern Montagne Noire (Hérault, France)[END_REF]Figs. 2 and 4b). Syn-sedimentary gliding patterns in the wildflysch (Fig. 5c) suggest gliding on the slopes of shallowly WSW-plunging F2 synclines, consistently with WSW gliding documented in the mass transport complex (Fig. 8c). Poor preservation of northward gliding features may be explained by the fact that the northward slope forming the forelimbs of north-verging anticlines are preferentially affected by north-vergent thrust deformation that overprinted them (e.g., Figs. 7c, 8a and8c). More generally, the spatial sedimentological pattern of the flysch would have been controlled at the scale of anticline / syncline pairs, with the platform carbonates having tried to maintain on the upper backlimbs and crests of northward-verging F2 anticlines and more distal flysch in F2 synclines. Likewise, variation in the Carboniferous stratigraphy among the Écailles de Cabrières [START_REF] Engel | Le Carbonifère anté-stéphanien de la Montagne Noire : rapports entre mise en place des nappes et sédimentation[END_REF][START_REF] Aretz | The Kulm Facies of the Montagne Noire (Mississippian, southern France)[END_REF][START_REF] Vachard | Mississippian (Middle Tournaisian-Late Serpukhovian) lithostratigraphic and tectonosedimentary units of the southeastern Montagne Noire (Hérault, France)[END_REF] would be explained by the fact that they originate from folds with contrasted uplift histories.

3. Cévennes fault kinematics

The Montagne Noire represents a portion of the >500 km-long Cévennes fault [START_REF] Arthaud | Les décrochements tardi-hercyniens du Sud-Ouest de l'Europe. Géométrie et essai de reconstitution des conditions de la déformation[END_REF]; e.g., Fig. 1), which bounded the Devonian-Carboniferous sedimentary basin to the NW and must have had somehow a SE-side-down throw to allow Devonian and Tournaisian sedimentation (until ∼345 Ma) that did not take place in its northwestern hangingwall. That early fault history may tentatively be linked to late Devonian NW-directed shearing affecting the hinterland [START_REF] Duguet | Successive shearing tectonics during the Hercynian collisional evolution of the southwestern French Massif Central[END_REF] and could have recorded orogen-parallel extension at a time of back-arc basin opening in the Northeastern Massif Central [START_REF] Faure | A review of the pre-Permian geology of the Variscan French Massif Central[END_REF].

Shortly after 340 Ma and until ca. 323 Ma (stratigraphic dating of deformation), the Cévennes fault underwent sinistral transpression. It was reactivated as a dextral transtensional fault during dome exhumation after 317 Ma. The dextral releasing bend of the Cévennes fault in the Montagne Noire is therefore interpreted to result from the inversion of a preexisting sinistral restraining bend (Fig. 10).

Our investigation of the eastern part of the northern thrust belt (Monts de Lacaune; Fig. 1b) revealed a system of thrust duplexes affected by pervasive shallowly dipping shears with systematic top-to-the-SSE (N160°E) sense of slip. In the easternmost unit, the Mendic granitic pluton represents a sheet in that shear system affected by a strong fabric with the same shear sense. Ar-Ar muscovite dating in the pluton [START_REF] Costa | De la collision continentale à l'extension tardi-orogénique : 100 millions d'années d'histoire varisque dans le Massif Central français[END_REF] indicates that southward thrusting was active at 333 +/-4 Ma. But more generally, Ar-Ar and K-Ar dating constrains activity of the northern thrust belt from 342 Ma until after 328 Ma [START_REF] Costa | De la collision continentale à l'extension tardi-orogénique : 100 millions d'années d'histoire varisque dans le Massif Central français[END_REF][START_REF] Doublier | Age and grade of metamorphism in the eastern Monts de Lacaune -Implications for the collisional accretion in Variscan externides (French Massif Central)[END_REF]. SSEdirected thrust shearing implies sinistral transpression along the NE-striking thrusts of the northern thrust belt and along the Cévennes fault, even considering the 20° of counter-clockwise rotation undergone by the thrust system during transtension [START_REF] Cogné | Paleomagnetic evidence for rotation during Stephano-Permian extension in the Southern Massif Central (France)[END_REF]Fig. 9). Kinematics of the southern and northern thrust belts were therefore linked during sinistral transpression along the restraining bend of the Cévennes fault at ∼340-323 Ma.

The pervasiveness of sinistral shearing in the Caroux sub-dome of the Axial Zone [START_REF] Beaud | Étude structurale de la Zone Axiale orientale de la Montagne Noire (Sud du Massif Central français)[END_REF][START_REF] Schranzhofer | La zone de cisaillement polyphasée du versant Sud de la Montagne Noire (Massif Central, France) : Un "vecteur" pour l'exhumation des dômes migmatitiques[END_REF] and its southern envelope [START_REF] Lee | Analyse structurale du versant sud de la Montagne Noire (Hérault -France). Aspects cinématiques de la mise en place des nappes[END_REF]present study) indicates that part of the Axial Zone was involved in the sinistral Cévennes shear zone (Fig. 10).

The superimposition of dextral shearing on sinistral transpression required by the present reappraisal of thrust tectonics should open new perspectives on the disputed internal deformation of the gneiss dome [START_REF] Ellenberger | Replis de micaschistes et tectonique d'infrastructure au sein du massif gneissique du Caroux (zone axiale de la Montagne Noire)[END_REF][START_REF] Beaud | Étude structurale de la Zone Axiale orientale de la Montagne Noire (Sud du Massif Central français)[END_REF][START_REF] Matte | La zone axiale hercynienne de la Montagne Noire n'est pas un "metamorphic core complex" extensif mais un anticlinal post-nappe à coeur anatectique[END_REF][START_REF] Schranzhofer | La zone de cisaillement polyphasée du versant Sud de la Montagne Noire (Massif Central, France) : Un "vecteur" pour l'exhumation des dômes migmatitiques[END_REF][START_REF] Rey | Viscous collision in channel explains double domes in metamorphic core complexes[END_REF][START_REF] Rey | Viscous collision in channel explains double domes in metamorphic core complexes: Reply[END_REF][START_REF] Rey | The origin of contractional structures in extensional gneiss domes[END_REF][START_REF] Van Den Driessche | Viscous collision in channel explains double domes in metamorphic core complexes: Comment[END_REF][START_REF] Rabin | Strain partitioning along the anatectic front in the Variscan Montagne Noire massif (southern French Massif Central)[END_REF][START_REF] Roger | Age of metamorphism and deformation in the Montagne Noire dome (French Massif Central): Tapping into the memory of fine-grained gneisses using monazite U-Th-Pb geochronology[END_REF]. In any case, the present work provides a kinematic scheme for crustal thickening within the bend during early sinistral transpression. Eclogite boudins in the Caroux gneisses have provided two sets of geochronological ages (360 and 315 Ma), both obtained independently by two research groups [START_REF] Faure | Middle Carboniferous intracontinental subduction in the Outer Zone of the Variscan Belt (Montagne Noire Axial Zone, French Massif Central): multimethod geochronological approach of polyphase metamorphism[END_REF][START_REF] Whitney | Syn-collapse eclogite metamorphism and exhumation of deep crust in a migmatite dome: The P-T-t record of the youngest Variscan eclogite (Montagne Noire, French Massif Central)[END_REF]. The oldest age retained by [START_REF] Faure | Middle Carboniferous intracontinental subduction in the Outer Zone of the Variscan Belt (Montagne Noire Axial Zone, French Massif Central): multimethod geochronological approach of polyphase metamorphism[END_REF] as that of eclogite metamorphism is not reconcilable with the sedimentary record characterized by regionally distributed and homogeneous chert / carbonate sedimentation at the time [START_REF] Aretz | The Kulm Facies of the Montagne Noire (Mississippian, southern France)[END_REF] and the fact that thrusting took place after 340 Ma (maximum stratigraphic age of thrusting). Alternatively, if valid (but still unlikely), the 360-Ma eclogite metamorphism hypothesis would imply complete decoupling between the thickening gneissic core (Caroux) of the shear zone and the Paleozoic series. The 315 Ma age of HP metamorphism favored by [START_REF] Whitney | Syn-collapse eclogite metamorphism and exhumation of deep crust in a migmatite dome: The P-T-t record of the youngest Variscan eclogite (Montagne Noire, French Massif Central)[END_REF] would imply that the Caroux gneisses were at ∼30 km depth at the onset of transtensional exhumation of the Axial Zone (317 Ma). But burial, if any, to HP conditions by sinistral transpression would still be older (>320 Ma, the minimum age of thrusting).

4. Orogen-scale transcurrent faulting and orocline bending

Variscan convergent deformation in the southern Massif Central took place from ∼342 to 323 Ma across a >80 km wide sinistral transpressive fold-and-thrust belt centered on the Cévennes fault, forming a restraining bend in the Montagne Noire (Fig. 10a). Sinistral transpression responded to far-field (plate boundary driven) convergence. The shift to dextral transtension along the Cévennes fault after 317 Ma (Fig. 10b) responded to the amplification of the Iberain-Armorican syntax and final closure of the Cantabrian orocline in its core between 305 and 295 Ma (timing in [START_REF] Weil | New time constraints on lithospheric-scale oroclinal bending of the Ibero-Armorican Arc: a palaeomagnetic study of earliest Permian rocks from Iberia[END_REF].

Early sinistral kinematics of the Cévennes fault (and, probably, the East Variscan shear zone) between 340 and 323 Ma implies partitioning of convergence in the southern foreland between thrusts and NNE striking sinistral faults (Fig. 11). Such a partitioning requires hinterland-ward (retro) fold-and-thrust tectonics to have taken place as attested to in the Southern Montagne Noire. Besides, field reconnaissance in the Mouthoumet Massif (Fig. 1b) suggests a comparable north-verging transpressive deformation pattern. Various transpressive reliefs must therefore have been produced, at least in the strike-slip corridor formed by the Cévennes fault and the East Variscan shear zone, feeding the flysch with proximal material. This suggests a multiplicity of coeval wildflysch depocenters rather than a foreland-ward succession of younger basins formed by southward propagating pro-thrusts (see [START_REF] Martínez | Provenance, age, and tectonic evolution of Variscan flysch, southeastern France and northeastern Spain, based on zircon geochronology[END_REF]. Retro-thrusts east of the Cévennes fault may be prefiguring the growth of an orocline flanking the Eastern Massif Central and pointing toward the Bohemian massif [START_REF] Matte | The Variscan collage and orogeny (480-290 Ma) and the tectonic definition of the Armorica microplate: a review[END_REF]e.g., Fig. 1a).

Dextral transtension along the Cévennes fault from 317 to 294 Ma accompanied gravitational collapse and northeastward escape of the northern limb of the growing syntax (Fig. 11) in which convergent deformation had ceased. The Sillon houiller acted as a transfer fault between (1) orogen-parallel extrusion / extension of the wedge escaping from the syntax hinge and (2) orogen-normal extensional collapse guided by the Cévennes-trend faults [START_REF] Burg | Syn-to post-thickening extension in the Variscan belt of Western Europe: Modes and structural consequences[END_REF]. At that time (and until 290 Ma), just SW of the North Pyrenean fault, SW-vergent thrusting as well as orocline limb-parallel extension and dextral strike-slip were taking place in the Axial Zone of the Pyrenees [START_REF] Cochelin | Vertical strain partitioning in hot Variscan crust: Syn-convergence escape of the Pyrenees in the Iberian-Armorican syntax[END_REF]Figs. 1b and 11). The North Pyrenean fault is therefore a first-order transform fault in the orogen, decoupling the closing orocline from the northern syntax limb undergoing gravitational collapse.

5. Shear sense reversal and exhumation in orogen-scale transcurrent fault systems

Releasing bends along strike-slip fault systems are propitious to the formation of metamorphic core complexes [START_REF] Denèle | Strike-slip metamorphic core complexes: Gneiss domes emplaced in releasing bends[END_REF]. In the Montagne Noire, early transpressional crustal thickening within the bend would be a prerequisite to extensional exhumation in the dextral releasing bend. The restraining bend was indeed a mountain range that had the gravitational potential to spread in the dextral releasing context, further enhancing lower crust advection in the gneiss dome. This would also explain why the Montagne Noire releasing bend is not a pull-apart sedimentary basin but a gneiss dome, with syn-tectonic sediments flanking the releasing bend instead of filling it (e.g., Fig. 1b).

Shear sense reversal along long-lived, orogen-scale strike-slip fault systems should be very common, because such fault systems undergo large-magnitude vertical axis-rotation(s) and bending during collision as a consequence of indentation, escape tectonics or orocline bending [START_REF] Tapponnier | On the mechanics of the collision between India and Asia[END_REF][START_REF] Martínez-Catalán | Are the oroclines of the Variscan belt related to late Variscan strike-slip tectonics?[END_REF]. It is the case for the Cévennes fault, which was active for 50 . The fault first contributed to the partitioning of plate convergence and was later incorporated to the hinterland as a transfer fault bounding escaping orogenic domains (Fig. 11). [START_REF] Chantraine | Carte géologique de la France à 1/1 000 000[END_REF][START_REF] Faure | A review of the pre-Permian geology of the Variscan French Massif Central[END_REF]. Post-Permian cover is shown in white in (a) and (b). Nappe terminology in the Montagne Noire is that of [START_REF] Arthaud | Étude tectonique et microtectonique comparée de deux domaines hercyniens : les nappes de la Montagne Noire (France) et l'anticlinorium de l'Iglesiente (Sardaigne)[END_REF]. [START_REF] Feist | Carte géologique de la France à 1/50 000[END_REF], [START_REF] Engel | Le Carbonifère anté-stéphanien de la Montagne Noire : rapports entre mise en place des nappes et sédimentation[END_REF], Alabouvette et al. (1982aAlabouvette et al. ( , 1982b) ) and [START_REF] Bogdanoff | Carte géologique de la France à 1/50 000[END_REF]. Bedding trajectories in the wildflysch are based mostly on our measurements and those of [START_REF] Engel | Le Carbonifère anté-stéphanien de la Montagne Noire : rapports entre mise en place des nappes et sédimentation[END_REF] (see Fig. S1, supplementary material). The pic de Vissou unit is an overturned slab that has stratigraphic affinities with the Mont Peyroux overturned limb [START_REF] Engel | Le Carbonifère anté-stéphanien de la Montagne Noire : rapports entre mise en place des nappes et sédimentation[END_REF] and may be considered as one of the Écailles de Cabrières (see Fig. 4f). The inset shows the main area/units mentioned in the text and the interpretative contacts of the Mont Peyroux and Faugères nappes of [START_REF] Arthaud | Étude tectonique et microtectonique comparée de deux domaines hercyniens : les nappes de la Montagne Noire (France) et l'anticlinorium de l'Iglesiente (Sardaigne)[END_REF]. Our kinematic data in (c) are complemented by those of [START_REF] Lee | Analyse structurale du versant sud de la Montagne Noire (Hérault -France). Aspects cinématiques de la mise en place des nappes[END_REF], mostly west of 3°E, and those of [START_REF] Schranzhofer | La zone de cisaillement polyphasée du versant Sud de la Montagne Noire (Massif Central, France) : Un "vecteur" pour l'exhumation des dômes migmatitiques[END_REF] in the Mons-Margal area (Fig. 2). The insets show a simplified structural map. See Figure 2 for geological caption and locality names. Devonian-Carboniferous contact at the classical Graïs locality (western tip of section: 43.534412°N, 2.988400°E). Fold asymmetry and bedding-cleavage relationship in the marbles were used to illustrate southward nappe emplacement [START_REF] Arthaud | Étude structurale de la terminaison occidentale des Monts de Faugères (Montagnes Noire, Hérault)[END_REF]. The structural pattern argues instead for a causal kinematic link between eastward shearing and folding of the marbles that were too competent to allow for complete alignment of the fold axes with the shearing direction, contrary to the other lithologies of the section (see also [START_REF] Lee | Analyse structurale du versant sud de la Montagne Noire (Hérault -France). Aspects cinématiques de la mise en place des nappes[END_REF]. See Figures 2 and4 for locations.

Conclusion

Instead

  To summarize, eastward shearing affecting the normal limb of the F1 Orb syncline (Monts de Faugères) is also pervasive in its western overturned limb (Mont Peyroux) and the overlying Pardailhan unit. Eastward shearing is interpreted to have overturned the Mont Peyroux limb and Pardailhan series and thrust the Pardailhan unit over the Mont Peyroux inverted backlimb of the F1 Orb syncline. Eastward shearing produced shear-parallel sheath folds that are also parallel to F2 folds formed by NNW shortening, in agreement with low-angle sinistral transpressional thrusting documented in the Monts de Faugères and overlying flysch, the parautochthonous units and the northern deformation belt.

  had a comparable interpretation of strain localization, but in the hypothesis of a south-verging and south-dipping early Roquessels thrust fault). The Roquessels fault connects westward with the shear zone ramp mapped North of Roquebrun that roots into the deep overturned Mont Peyroux limb (Figs. 2, 4b and 5c), indicating that the Roquessels fault is a reactivated thrust ramp. The Roquessels fault extends further to the West to crosscut the basal contact of the Pardailhan unit (Figs 2 and

  of having glided southward, the Paleozoic nappes of the Montagne Noire were thrust northeastwardly during wrench-dominated sinistral transpression along the Cévennes fault between 340 and 323 Ma. Consequently, convergent tectonics of the southern side of the Variscides may be reconsidered, with a foreland basin being decoupled from the hinterland along orogen-scale transcurrent fault(s) trending at a high angle to the orogenic trend. These faults interacted with hinterland-ward thrust systems East of the Cévennes fault, which must have generated a variety of reliefs and adjoining depocenters. Shift to dextral transtension along the Cévennes fault after 317 Ma accompanied closure of the Iberian-Armorican syntax by accommodating northeastward escape and gravitational collapse of the northern limb of the syntax. These results have implications for orogenic-scale kinematic control on shear sense inversion and lower crust exhumation along long-lived transcurrent fault systems.

Figure Captions Figure 1 .

 Captions1 Figure Captions

Figure 2 .

 2 Figure 2. Geology of the southeastern Montagne Noire based on the present study, adapted from

Figure 3 .

 3 Figure 3. (a) Map showing the axial fold traces in the southeastern flank of the Montagne Noire. See Figure 2 for geological caption and locality names. (b) Interpretative three-dimensional fold pattern and axial planes between the western Monts de Faugères and the Mont Peyroux. (c) Synthesis of structural measurements collected east of the Pardailhan unit (equal area, lower hemisphere stereonets).

Figure 4 .

 4 Figure 4. Simplified cross-sections through the southeastern Montagne Noire. (a) Overall geometry of the F1 Orb syncline in a section perpendicular to the dominant shearing direction. (b) Overturned limb of the F1 Orb syncline (lower part of the section shows an idealized configuration for the F1 Orb syncline without considering F2 folding). (c) Wildflysch basin and Monts de Faugères. (d)-(e) Écailles de Cabrières and Monts de Faugères. (f) Écailles de Cabrières and pic de Vissou unit. The cross-sections are labeled on Figure 2 with red capital letters.

Figure 5 .

 5 Figure 5. Fabrics and kinematic map patterns of the southeastern Montagne Noire. (a) Schistosity-cleavage. (b) Stretching lineation. (c) Shear criteria and interpretative shear zones.

Figure 6 .

 6 Figure 6. Top-to the ENE shear deformation patterns in the Monts de Faugères (a-c) and the Mont Peyroux overturned limb (d). (a) Recumbent rootless folds and shear zones in the flysch (shore of Vailhan Lake; 43.564905°N, 3.303711°E). Fold axes are mostly parallel to the stretching lineation. (b) Recumbent sheath fold parallel to the ENE-trending stretching lineation in chert-carbonate associations (East of Faugères; 43.567821°N, 3.223836°E). (c) Devonian marbles West of Cabrières (43.572912°N, 3.325665°E). The ENE-trending lineation (L1-2) is marked by the stretching of carbonate nodules (aspect ratio up to 1:10) and coincides with the intersection between bedding (S0) and the subhorizontal schistosity (S1-2). (d) Overturned

Figure 7 .

 7 Figure 7. Deformation patterns in the flysch of the Écailles de Cabrières unit. (a) Top-to-the NE serial reverse shears (SW of Vailhan; 43.545366°N, 3.294435°E). (b) Olistolith SE of Vailhan (43.551666°N, 3.310578°E). (c) Line drawing of (b). (d) Slip/shear surface measurements shown in (c). Slip surfaces coincide with the layering of a sedimentary slope along which the olistolith and other flysch elements glided. Shear features may be due to syn-sedimentary gliding on a slope or, more likely, tectonic activation of the layering (bed-parallel slip) during N/NE-vergent shearing. Observations in a nearby quarry attest to syn-schistosity -post-sedimentary -top-to-the NE shearing. See Figure 2 for locations.

Figure 8 .

 8 Figure 8. Field sketches of road / railroad cuts in the flysch of the Écailles de Cabrières unit (a) and the Roquessels mass transport complex (b-c). (a) Olistolith bearing flysch sheared and thrust upon slumped flysch (Castelsec-Fos road; 43.545146°N, 3.241515°E). Northward slump / gliding features are apparently compatible with collapse at the front of the thrust system. (b) Eastern Roquessels mass transport complex (Castelsec-Fos road; southern tip of section: 43.550739°N, 3.234843°E). Low-angle, top-to-the W shearing may be interpreted as prefiguring the Roquessels fault (i.e., Roquessels detachment) or as accompanying westward gliding of the Mass transport complex documented in (c). (c) Westernmost part of the mass transport complex (Malac railroad cut; NW tip of section: 43.548767°N, 3.205925°E). Southeastern part of the section shows a flysch-on-flysch apparent north-vergent thrust comparable to that shown in (a). Rest of the section shows syn-sedimentary top-to-the WSW gliding and normal faulting features. Growth of the mudmound (identified by Vachard et al., 2017) can be shown to have overlapped in time with normal-oblique faulting during top-to-the WSW gliding. Shear measurements are shown by colored stars on the cross-sections. Sections (b) and (c) correspond to East-looking

Figure 9 .

 9 Figure 9. Structural model for the southeastern flank of the Montagne Noire before dextral transtension. The wildflysch is transported as a transpressional piggy-back basin on the Paleo-Roquessels ramp.

Figure 10 .

 10 Figure 10. Two-stage evolution of the Montagne Noire portion of the Cévennes fault showing a sinistral restraining bend (a) inverted into a dextral releasing bend (b). The structural pattern in (b) takes up and upgrades that of Echtler and Malavieille (1990) by adding, for instance, the Roquessels fault to the southern splays of the Cévennes fault dextral releasing bend. Syntranstension Stéphano-Permian sediments are omitted.

Figure 11 .

 11 Figure 11. Sketch model of two late collisional stages of the Southern Variscides showing the Cévennes fault shifting from sinistral to dextral as a consequence of the formation of the Iberian -Armorican syntax. The early stage is reconstructed by restoring the suture zone as a straight line. Fault names: SH -Sillon houiller, CF -Cévennes fault, EVSZ -East Variscan shear zone, NPF -North Pyrenean Fault. Extension directions are mostly after Malavieille (1993), Burg et al. (1994), Martínez-Catalán et al. (2014) and Cochelin et al. (2017).

Acknowledgements

We thank José R. Martínez Catalán, an anonymous referee and editor Philippe Agard for their constructive remarks. Fieldwork was partially supported by a CNRS-INSU SYSTER grant. We acknowledge Arnaud Dalbin and Mouna Nadrani for their participation in the fieldwork.