Successive post-Variscan stress fields in the French Massif Central and its borders (Western European plate): comparison with geodynamic data

Abstract

Structural analysis and particularly microtectonic methods have made it possible to define the different stages of brittle deformation of the Massif Central basement and the surrounding sedimentary cover from the end of the Hercynian orogeny to the end of the Tertiary. During the Stephanian a compressional tectonic regime prevailed: regional faults appeared or were react vated reactivation as a result of initial N-S compression, becoming NW then E-W. These regional strike-slip faults caused local extension which led to the formation of small coal-bearing basins. This compressional regime, which marked the end of the formation of Pangea. was followed by a series of extension episodes: Permian-Triassic extension oscillating around N-S. E-W to NW-SE extension in the Early and Middle Jurassic and finally N-S to NE-SW extension in the Late Jurassic to Cretaceous. The normal faults formed during these episodes strongly influenced the distribution of emerging continents and sedimentary basins. From the Campanian (75 Ma) to the Present, the convergence of Africa and Eurasia involved the distribut on of stresses in the West European plate. Several tectonic episodes are distinguished in the Massif Central. During the Eocene approximately N-S compression predominated. General E-W extension in the Late Eocene-Oligocene resulted in grabens with general northerly strike, mainly in the centre of the Massif Central and on its east and southeast borders. Lastly, compression, varying from NW-SE to E-W, in the north and south of the Massif Central, prevailed during the Alpine orogenic phase at the end of the Miocene. These successive stages of brittle deformation are interpreted in the context of the evolution of the West European plate and its displacement in relation to the African plate. The correspondences between the major geodynamic periods and the distribution of stresses over the West European continent are noted as well as the problems which remair to be resolved.