Thermo-Mechanical Modeling of Late-Orogenic Extension -A Study from the Variscan Orogen in Central Europe

摘要

A two-dimensional thermo-mechanical finite element model is used to study the post-thickening evolution of the Variscan orogen in Central Europe along a lithosphere-scale transect from the internal zone to the undeformed foreland. The study concentrates on a quantitative evaluation of the processes controlling late-orogenic extension and destruction of crustal roots, particularly the gravitational instability of thickened crust. Modeling results suggest that gravitational forces alone cannot reproduce the observed timing and amount of Permo-Carboniferous crustal thinning. Tensile plate boundary forces are required in addition to gravitation to restore a crustal thickness of about 30 km in the Variscan Interludes. Stresses as little as 10 MPa result already in up to 35 % extension and agood fit between model predictions and observed data. It is concluded that the Stephanian to Rotliegend evolution in the vicinity of the modeled traverse resulted not from gravitational forces inherited from Variscan crastal thickening but was related to a modification of the plate boundary stresses at the end of the Westphalian.