Reappraisal of Variscan tectonics in the southern French Massif Central

Abstract

The comprehensive kinematic analysis of the Variscan fold nappes and associated wildflysch in the Southeastern Montagne Noire shows that the nappes were thrust northeastwardly along the Cévennes fault as a result of strike-slip-dominated sinistral transpression between 340 and 323 Ma. Macro- and map-scale recumbent folding and nappe stacking were achieved by ENE-directed, strike-parallel thrust shearing. The recumbent folds evolved into sheath folds by interplay of continued strike-parallel thrust shearing and strike-normal shortening manifested by north-verging folds that grew during wildflysch sedimentation. These results call for a tectonic reassessment of the southern side of the Variscides. The foreland basin was decoupled from the hinterland along orogen-scale sinistral fault(s) trending at a high angle to the orogenic trend, which interacted with a variety of hinterland-ward thrust systems. The shift from sinistral transpression to dextral transtension along the Cévennes fault after 317 Ma accompanied the closure of the Iberian-Armorican syntax by accommodating northeastward escape and gravitational collapse of the northern limb of the syntax. These results illustrate the impact of the shift from plate convergence-controlled to escape-controlled kinematics on shear sense reversal and lower crust exhumation along long-lived strike-slip fault systems.