Post-Variscan evolution of the lithosphere in the area of the European Cenozoic Rift System

The European Cenozoic Rift System (ECRIS) transects Variscan basement, Permo-Carboniferous troughs and Late Permian to Mesozoic series, deposited in thermal sag basins, which are exposed on rift-related arches. We have analysed processes governing the transformation of the orogenically destabilized Variscan lithosphere into end-Cretaceous stabilized cratonic lithosphere, prior to its renewed Cenozoic rift-related destabilization. In the ECRIS area, crustal and lithospheric thicknesses at present are in the range of 24-35 km and 60-120 km, respectively. The Variscan orogen was characterized at the time of its end-Westphalian consolidation by 45-60 km deep crustal roots, marking major sutures. During the Stephanian-Early Permian wrench-induced collapse of the Variscan orogen, subducted lithospheric slabs were detached, causing upwelling of the asthenosphere, thermal thinning and/or partial delamination of the lithospheric mantle, and regional uplift. By mid-Permian times, the crust was thinned to 28-35 km owing to its regional erosional unroofing, localized mechanical stretching and the interaction of mantle-derived melts with its basal parts. By mid-Permian times, when the temperature of the asthenosphere returned to ambient levels, thermal subsidence of the lithosphere commenced, controlling development of a system of Late Permian and Mesozoic intracratonic basins. These experienced repeated minor subsidence accelerations, related to the build-up of far-field stresses, which did not involve renewed lithospheric destabilization. Modelling of observed subsidence curves indicates that during the mid-Permian lithospheric thicknesses ranged in the ECRIS area between 40 and 80 km, but had increased by the end of the Cretaceous to 100-120 km. Cenozoic rifting and mantle-plume activity caused renewed lithospheric thinning. © The Geological Society of London 2006.