LATE OROGENIC BASIN EVOLUTION IN THE VARISCAN INTERNIDES - THE SAAR-NAHE BASIN, SOUTHWEST GERMANY

The late Variscan evolution of the Saar-Nahe Basin in southwest Germany is closely controlled by the kinematics of the Hunsruck Boundary Fault, which also separates two main tectonostratigraphic units of the Variscides. The Saar-Nahe Basin comprises a half-graben structure, which formed due to extensional reactivation of a Variscan thrust. Between the early Westphalian and late Rotliegend, about 8.5 km of alluvial fan, fluvial and lacustrine sediments accumulated. During the Permo-Carboniferous, W-E oriented extension was accommodated by a system of NW-SE trending transfer faults and orthogonal normal faults. Balanced cross-section construction and subsidence analyses suggest a 35% extension of the previously thickened crust in the late stage of the orogeny. The subsidence analyses show discontinuous depth-dependent extension, with laterally varying extension factors in the crust and mantle. The offset between syn- and post-rift depocentres is explained by a mantle stretching zone, shifted laterally with respect to the area of maximum crustal extension. Finally, a geodynamic model for the evolution of the Saar-Nahe Basin, with special reference to the earlier Variscan development and the general evolution of Permo-Carboniferous basins in Central Europe is presented.