Exhumation mechanisms of the Tauern Window (Eastern Alps) inferred from apatite and zircon fission track thermochronology

摘要

Orogen-parallel extension and orogen-perpendicular shortening accommodated by folding acted at the same time to exhume the Tauern Window. In order to investigate the relative contribution of upright folding and erosion and of extensional denudation for exhumation, we provide compilations in map view of previous and new zircon and apatite fission track ages. These age maps show that isoage contour lines are subparallel to the axial planes of large-scale, upright folds. On age versus distance diagrams, along a profile perpendicular to the dome axis, all thermochronometers show bell-shaped curves with younger ages in the hinge area of the dome and age differences between different chronometers decreasing from the limbs to the hinge area. All these observations suggest that folding synchronous with erosion was largely responsible for exhumation of the Tauern Window. The younger ages and the higher fold amplitudes of the western subdome compared to the eastern one are corroborated by the results of inversion of cooling ages that show higher exhumation rates in the west. These reflect one and the same shortening and folding event that affected the entire Tauern Dome synchronously, but at higher rates than that in the western subdome. Only during Pliocene time were exhumation rates slightly higher along the normal faults bordering the window; hence, extensional unroofing may have dominated exhumation in the Pliocene. The northward displacement of the Dolomites Indenter was associated to a clockwise rotation, which caused increased amounts of shortening westward, hence higher uplift and exhumation rates in the western subdome.