The Variscan continental collision induced the development of large crustal melting in the western French Massif Central, accompanied by emplacement and deformation of syn- to post-tectonic granites spatially related to normal and strike slip faulting. Our study focuses on the regional deformation and shear zone patterns in the Millevaches massif, one of the largest magmatic area of the French Massif Central. In this massif, the syn-tectonic intrusions are related i) to the dextral wrenching along the Treignac-Pradines shear zones and the Creuse faults system, and ii) to the coeval extension along the N000°–N020° normal faults on the western edge of the Millevaches massif (Bourganeuf and Argentat faults). The analysis of deformation and kinematics correlated to new datations of granites allow us to propose a pull-apart model to explain the tectono-magmatic evolution of this part of the Variscan belt from 350 Ma to 325 Ma. At that time, these granites intruded a “pull-apart” system bounded by two major N140°–160° dextral strike-slip zones operating in the middle continental crust during a bulk N020° regional shortening. From 325 Ma to 320 Ma, a clockwise rotation of the regional shortening axis was responsible for the late reactivation of the N020° eastern Millevaches tectonic border as a dextral fault system (Felletin-Ambrugeat fault system). This NE-SW shortening displaced the N140°–160° Creuse fault system and induced a reverse motion along the northern border of the Millevaches massif (St-Michel-de-Veisse fault). This Visean tectono-magmatic event induced the late exhumation of the Millevaches massif with respect to surrounding units and favoured the widespread granite emplacement in this part of the Variscan belt.

The Variscan continental collision induced the development of large crustal melting in the western French Massif Central, accompanied by emplacement and deformation of syn- to post-tectonic granites spatially related to normal and strike slip faulting. Our study focuses on the regional deformation and shear zone patterns in the Millevaches massif, one of the largest magmatic area of the French Massif Central. In this massif, the syn-tectonic intrusions are related i) to the dextral wrenching along the Treignac-Pradines shear zones and the Creuse faults system, and ii) to the coeval extension along the N000 degrees-N020 degrees normal faults on the western edge of the Millevaches massif (Bourganeuf and Argentat faults). The analysis of deformation and kinematics correlated to new datations of granites allow us to propose a pull-apart model to explain the tectono-magmatic evolution of this part of the Variscan belt from 350 Ma to 325 Ma. At that time, these granites intruded a "pull-apart" system bounded by two major N140 degrees-160 degrees dextral strike-slip zones operating in the middle continental crust during a bulk N020 degrees regional shortening. From 325 Ma to 320 Ma, a clockwise rotation of the regional shortening axis was responsible for the late reactivation of the N020 degrees eastern Millevaches tectonic border as a dextral fault system (Felletin-Ambrugeat fault system). This NE-SW shortening displaced the N140 degrees-160 degrees Creuse fault system and induced a reverse motion along the northern border of the Millevaches massif (St-Michel-de-Veisse fault). This Visean tectono-magmatic event induced the late exhumation of the Millevaches massif with respect to surrounding units and favoured the widespread granite emplacement in this part of the Variscan belt.

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-Gourge massif and Gueret 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.

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° 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.

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.