This work establishes the relative timing of pluton emplacement and regional deformation from new dating and structural data. (1) Monazite and (2) zircon dating show Tournaisian ages for the Gué ret granites [Aulon granite 352 ± 5 Ma (1), 351 ± 5 Ma (2) and Villatange tonalite 353 ± 6 Ma (1)] and ViseoNamurian ages for the north Millevaches granites [Chavanat granite 336 ± 4 Ma (1), Goutelle granite 336 ± 3 Ma (1), Royè re granite 323 ± 2 Ma (1) and 328 ± 6 Ma (2), Courcelles granite 318 ± 3 Ma (1)]. The Gué ret and Millevaches granites are separated by the N110 Arrè nes-la Courtine Shear Zone (ACSZ), composed from West to East by the Arrè nes Fault (AF), the North Millevaches Shear Zone (NMSZ) and the la Courtine Shear Zone (CSZ), respectively. Tournaisian Gué ret granites experienced a non-coaxial dextral shearing (NMSZ) recorded by the Villatange granite while the Aulon granite (Gué ret granite) cuts across this dextral shear zone which thus stopped shearing during Tournaisian time. Visean to Namurian Millevaches granites experienced a coaxial deformation. Therefore, low displacements along the NMSZ and the CSZ occurred at the emplacement time of Chavanat and Pontarion-Royè re granites (336-323 Ma). The structural analyses of Goutelle granite emphasizes a deformation related to the dextral Creuse Fault System (CFS) oriented N150-N160. From 360 to 300 Ma, the Z strain axis is always horizontal inferring a wrench setting for these granite emplacements. During this tectonic evolution, the Argentat zone acted as a minor normal fault and is related with a local Middle Visean (340-335 Ma) syn-orogenic extension on the western border of the Millevaches massif.

The Variscan continental collision has led to the development of large strike-slip shear zones in western Europe. Our study focuses on the regional deformation and shear zone patterns in the Massif Armoricain and the French Massif Central. The synthesis of granite emplacement ages associated to granite deformation fields, allow us to propose a geodynamic model for the tectonic evolution of this part of the Variscan belt between 370 Ma -320 Ma (Late Devonian -Namurian).After the first steps of the continental subduction-collision, leading to high temperature and anatexis associated with N-S shortening at 380-370 Ma (Frasnian to Famennian), the southern part of the Massif Armoricain and western part of French Massif Central underwent large dextral shearing along N100-N130 trending shear zones up to early Visean time. These large-scale displacements progressively decreased at around 350-340 Ma, during the first emplacements of biotite bearing granites (Moulins-les Aubiers-Gourgé massif and Guéret massif intrusions).During middle Visean times, the shortening axis direction rotated towards a NNE-SSW direction implying changes in the regional deformation field. The occurrence of N070-N100 sinistral and N110-N130 dextral conjugate shear zones within leucogranites are related to that time. Finally, new N150-N160 dextral shear zones appeared in middle to late Visean times: as for examples, the Parthenay and the Pradines shear zones in the SE Massif Armoricain and the Millevaches massif, respectively. These shear zones were conjugated to the sinistral N020 Sillon Houiller in the French Massif Central. They reflect large scale brittle continental indentation in the French Variscan belt during the middle to late Visean. Tectoniques transcurrentes famenno-namuriennes (370-320 Ma) enregistrées par les plutons syn-cinématiques dans la chaîne varisque française (Massifs armoricain et central) Mots-clés. -Varisque, Massif armoricain, Massif central, Zone de cisaillement, Granites, Datations.Résumé. -La collision continentale varisque évolue en Europe occidentale par le développement de zones de cisaillement d'échelle crustale jalonnées d'intrusions granitiques syn-et post-cinématiques. Cette étude se focalise sur les zones de cisaillement qui disloquent cet orogène varisque du Massif armoricain au Massif central, et sur la déformation des granites qui les jalonnent. La synthèse de nombreux âges récents obtenus sur ces granites syn-et post-cinématiques, qui ont enregistrés les différents champs de déformation, permet de proposer un modèle géodynamique pour cette partie de l'orogène entre 370-320 Ma, soit sur la période Dévonien supérieur -Carbonifère inférieur. Au Dévonien moyen-supérieur, la fin de la collision continentale varisque est marquée dans la partie méridionale du Massif armoricain (Vendée) et la partie occidentale du Massif central par une évolution métamorphique de haute température accompagnée d'une anatexie vers 380-370 Ma (Frasnien-Famennnien). Cette évolution est relayée par le développement d'une tectonique trans...

The South Armorican Shear Zone consists of a set of faults that runs across the southern Armorican Massif and extends eastwards to the Massif Central. One of its branches, the Cholet Shear Zone of South Brittany, can be correlated with the North-Millevaches-La Courtine Shear Zone in the Massif Central. It was active immediately after the regional Frasnian anatexis (372-368 Ma) as a right-lateral strike-slip fault. The horizontal offset, which can be estimated between 110 and 170 km, was achieved before the emplacement of non-deformed Late Tournaisian calc-alkaline and peraluminous granites . This newly established age of activity (Fammenian-Tournaisian) of the Cholet-La Courtine Shear Zone (CCSZ) has to be taken into account in geodynamical reconstructions of the Variscan belt of western Europe.

The Sillon Houiller is one of the main crustal discontinuities of the Variscan domain of the French Massif Central. Paradoxically, its kinematics and its tectonic significance are still a matter of debate.Since Grolier and Letourneur [1968]'s works, a Stephanian sinistral offset, inferred from the emplacement of numerous coal basins along the fault, is widely accepted.The earlier history of this accident is still debated and subject to controversies. The finite offset of the Sillon Houiller results from the superposition of 3 distinct events. The first one is a brittle/ductile accident that is probably at the origin of the main left-lateral motion. Dated granitoid intrusions and Visean tuff basins seal this accident. The later Stephanian motion is revealed by brittle faulting related to coal basin opening. Finally, a vertical offset of the fault is suggested by a few strong-dipping striations.The Visean offset of the Sillon Houiller has first order implications for the understanding of the western Europe Variscan orogeny. We suggest that the Sillon Houiller and the Paris Basin Magnetic anomaly belong to a single crustal discontinuity interpreted as the eastern boundary of the Armorican/Massif Central block. The 15 o clockwise rotation affecting this crustal block and inferred from the structural study of this domain occurred along this accident. The magnetic and gravimetric anomaly may be the result of Visean mafic intrusions, such as quartz diorites that are exposed in the northern part of the Massif Central close to the southern end of the anomaly. Le cisaillement senestre d'âge viséen le long du Sillon Houiller dans le Massif central français : implications sur la tectonique tardi-varisqueMots-clés. -Chaîne varisque, Massif central français, Sillon houiller, Viséen, Anomalie magnétique du Bassin parisien Résumé. -Le Sillon houiller est l'un des plus importants accidents du domaine varisque du Massif central français. Paradoxalement, son fonctionnement et ses implications géodynamiques restent à débattre. Depuis les travaux de Grolier et Letourneur [1968], le jeu en décrochement senestre Stéphanien de cet accident est admis par tous.Les jeux antérieurs sont débattus et sujets à controverse. Le jeu du Sillon houiller est la conséquence de 3 accidents distincts. Le premier est un accident qui s'est produit en conditions ductiles/fragiles, et qui est vraisemblablement à l'origine de la plus grande part du décrochement. Des intrusions de granitoïdes et des dépôts de tufs Viséens scellent cet accident. Le second jeu, Stéphanien, est révélé par une faille cassante jalonnée de brèches peu abondantes, qui a guidé l'ouverture de bassins houillers. Enfin, un jeu vertical du Sillon houiller est révélé par la présence de quelques rares stries à fort plongement.Le jeu viséen du Sillon houiller a des conséquences géodynamiques de tout premier ordre pour la compréhension de l'orogenèse varisque d'Europe occidentale. En effet, cet accident peut être envisagé comme lié à l'anomalie magné-tique du Bassin parisien. Les 2 accident...

Summary The Plateau d’Aigurande represents the north-westernmost part of the French Massif Central. It is overlain by the sediments of the Paris Basin to the north and bounded by the La Marche shear zone to the south. Detailed mapping, mainly from the Creuse Valley region, indicates thrust and nappe tectonics. Beginning at the base of the sequence one can recognize: (1) the Fougères unit (schists of low to medium grade) intruded by syntectonic leucogranites; (2) the Eguzon unit (medium- to high-grade schists which are partly diaphtoretic in the lower part of the unit); (3) the Gargilesse unit (high-grade schists); and (4) the Migmatitic unit. The metasediments of the Fougères, Eguzon and Gargilesse units were originally coarse grained clastics. They are interbanded with magmatic units (orthogneisses and amphibolites). The migmatites are derived from greywacke-type rocks intruded by magmatic rocks (orthogneisses and amphibolites). Following a high-pressure (Silurian?) tectonometamorphic event, the piling up of tectonostratigraphic units occurred during two periods of deformation. The main one, probably of late Caledonian (Acadian?) age, was synchronous with or slightly after the climax of metamorphism. The second, of Westphalian age, was accompanied by the emplacement of leucogranitic magma and by retrograde metamorphism. The shear-sense appears to have been from SW to NE during the Acadian phase and from NW to SE during the Westphalian. Structural and lithological studies suggest that the three lowermost units may have been derived from the same palaeogeographic domain while the migmatites have a distinctly different history.