East Tauern Detachment System: Coupled Oligocene ductile thinning and Miocene extension of the eastern European Alps

Differentiating between syn- and post-orogenic structures is critical for determining the contribution from any one mechanism toward net exhumation. In the Tauern Window of the Eastern Alps, new mapping in its northeastern region reveals significant deformation associated with W–E extension and a component of N–S shortening. Kinematic indicators reveal a clear top-to-E shear sense, and deformation is further highlighted by progressively deformed quartz-calcite-dolomite veins, whose rotation was used to quantify flow parameters, revealing an equal contribution of simple and pure shear. The ductile deformation is overprinted by E-dipping shear bands and faults, which transition into brittle-ductile faults compatible with incremental strain axes indicating vertical shortening during top-to-E extension. Raman spectroscopy data show a temperature gradient with higher structural levels exhibiting paleotemperatures <450°C, increasing to >500°C at deeper levels. White mica 40Ar/39Ar ages (25–34 Ma) in both shear veins and recrystallized fabrics confirm Oligocene deformation. At higher crustal levels, the deformation gradient progressively increases toward the newly discovered top-to-E Schuhflicker Detachment, defined by a knife-sharp fault surface of ultramylonites and cataclasites. The Schuhflicker Detachment developed at mid-crustal levels during the Oligocene, and during progressive exhumation, W–E extension was transferred to the structurally higher Katschberg Fault and Katschberg Shear Zone System during the Miocene. Collectively, these structures form the East Tauern Detachment System, which accommodated tens of kilometers of exhumation of the Tauern Window, facilitating the incipient stages of its exhumation during the Oligocene and subsequent erosion-dominated unroofing in the Miocene.