LATE VARISCAN EXHUMATION HISTORIES OF THE SOUTHERN RHENOHERCYNIAN ZONE AND WESTERN MID-GERMAN CRYSTALLINE RISE - RESULTS FROM THERMAL MODELING

Thermal modeling techniques constrained by published petrological and thermo-chronometric data were applied to examine late orogenic burial and exhumation at a Variscan suture zone in Central Europe. The suture separates the southern Rhenohercynian zone from the Mid-German Crysta lline Rise and traces the former site of a small oceanic basin. Closur e of this basin during Variscan subduction and subsequent collision of continental units were responsible for different tectono-metamorphic evolutions in the suture's footwall and hanging wail. Relative converg ence rates between the southern Rhenohercynian zone and western Mid-Ge rman Crystalline Rise can be inferred from the pressure-temperature-ti me evolution of the Northern Phyllite Zone. During Late Visean-Early N amurian times, horizontal thrusting velocities were at least 20 mm/a. Thermal modeling suggests that exhumation of the Mid-German Crystallin e Rise occurred temporarily at rates of more than 3 mm/a. Such rapid e xhumation cannot be produced by erosion only, but requires a substanti al contribution of extensional strain. Exhumation by upper crustal ext ension occurred con temporaneously with convergence and is explained b y continuous underplating of crustal slices and thrusting along faults with ramp-flat geometry. Finally, implications for the tectono-metamo rphic history of the study area and the thermal state of the crust dur ing late Variscan exhumation are discussed.