Footwall uplift in an orogenic wedge: the Tauern Window in the Eastern Alps of Europe

Abstract

In the Tauern Window (TW), the deepest structural units of the Eastern Alps are exposed in a 30 × 160 km antiform. European basement and cover occur under nappes of oceanic (Penninic units) and continental origin (Austroalpine nappes). The Tertiary structural history of the TW is related to a rapid uplift of 20–30 km since Oligocene times. Structural mapping revealed: (1) detachment and folding of the cover units and stacking of orthogneiss sheets; (2) constrictional folding of the entire duplex with amplitudes and half wavelengths of several kilometres; (3) backthrusting and backfolding along the northern margin of the TW; and (4) displacement along steep dip-divergent strike-slip faults. The strain history is complex and related to all these deformation phases. The most uniform structural element is a stretching parallel to the long axis of the TW and its major fold axes. Strain did not contribute to TW uplift, because ductile N-S shortening was compensated by E-W extension. Restoration of the TW shows that the exposed structures are not sufficient to explain the TW uplift. By analogy with the Engadine Window and the Western Alps, where seismic data are available, a deep-seated duplex is suspected. The TW uplift is best explained in a dextral transpressive regime.