Post-collisional orogen-parallel large-scale extension in the Eastern Alps

Abstract

Large-scale extension affected the Eastern Alps during post-collisional lateral tectonic extrusion in Early and Middle Miocene times. The Tauern window was mainly tectonically exhumed by the 160-km pullapart of the rigidly behaving Austroalpine basement blocks forming the tectonic lid of the Penninic contents of the window. An evaluation of the syn-extrusion fault pattern reveals displacements of several tens of kilometers along the low-angle extensional shear zones at the western and eastern margins of the window, and along the important strike-slip fault zones north and south of the window. Large-scale shear is reflected by discontinuities in mineral cooling patterns across important shear zones. The cooling histories of the tectonic blocks show that the window boundaries during exhumation coincide only partly with the classical boundaries of the window defined by thrust units. Reconstruction of the exhumation history shows an asymmetric evolution of the Tauern window. We argue that the eastern and western low-angle extensional shear zones formed in sequence, which is reflected by different evolutions of the fragmentation and uplift history of the Austraolpine tectonic blocks to the east and west of the window. In the Central and Eastern Alps, three structural domes, the Lepontin dome in the Central Alps and the Tauern and Rechnitz domes in the Eastern Alps, were formed by large-scale extension in Miocene times. Total E–W stretch amounts to more than 300 km and results in >70% extension. We propose that the Central and Eastern Alps are part of an extensional province that also includes the Pannonian basin and has a counterpart, separated by the Moesian indenter, in the Rhodope Mountains, the Aegean Sea and the Menderes Massif in Asia Minor. In these regions a number of mainly tectonically exhumed domes or deep sedimentary basins formed by Miocene large-scale extension.