Did the Variscides collapse or were they torn apart?: A quantitative evaluation of the driving forces for postconvergent extension in central Europe

Extension following immediately after the end of convergence caused rapid destruction of the European Variscan orogen and resulted in the formation of numerous sedimentary basins and widespread magmatism. Possible driving forces for this phase of extension, i.e., gravitational collapse of the thickened crust or reorientation of the far‐field stress regime, are assessed quantitatively using a two‐dimensional thermomechanical finite element modeling approach. The initial model setup approximates the geometry and physical properties of a lithosphere‐scale half profile through the Variscan orogen and its foreland. Various numerical simulations and parameter studies suggest that the gravitational instability of the Variscan orogen alone was not sufficient to explain the observed amount and timing of crustal extension. Tensile plate boundary stresses of the order of 10 MPa, superposed on the gravitational forces, are required to overcome the finite strength of the crust and restore a uniform crustal thickness in the Variscan realm. Modeling results are constrained by comparison with existing data sets from the central European Variscides, for example, crustal structure, seismic reflectivity, as well as temporal and spatial distribution of magmatic activity.