POLYPHASE WRENCH TECTONICS IN THE SOUTHERN FRENCH MASSIF-CENTRAL - KINEMATIC INFERENCES FROM PRETECTONIC AND SYNTECTONIC GRANITOIDS

In the Variscan French Massif Central, the South Limousin area consist s of low- to medium-grade metamorphic rocks intruded by two granitic b odies. The structural and textural analyses of these plutons undertake n in parallel with the structural analysis of their host rocks allow u s to characterize and to date different stages in the tectonic evoluti on of this area. This study shows that the South Limousin area experie nced successivelly two strike-slip events along two geographically dis tinct shear zones, from north to south the left-lateral Estivaux and t he right-lateral South Limousin strike-slip faults, respectively. Thes e ductile faults subdivide the South Limousin into three structural un its, from north to south they are the Upper Gneiss unit, Thiviers-Payz ac unit and Genis unit. The two granitic bodies intrude the Thiviers-P ayzac unit only. The younger Estivaux granite is a syntectonic pluton which emplaced during left-lateral wrenching. Ar-40/Ar-39 dates from b iotites indicate an Early Carboniferous age (346 +/- 3 Ma). The older granite is a pretectonic body. It is the Ordovician ''Saut du Saumon'' augen orthogneiss in which detailed structural analyses show the poly phase nature of the solid-state deformation. Our microtectonic data in dicate that the right-lateral motions overprint the left-lateral ones and produce apparently symmetrical fabrics.