The East Tauern Detachment System and its role in the Oligo-Miocene exhumation of the Tauern Window

In the NE Tauern Window, bedrock mapping across the Penninic nappes documents substantial deformation transitioning from nappe stacking to extensional tectonics. The Oligo-Miocene deformation record is interpreted as W-E extension accompanied by a component of N-S shortening during the switch from compressional thickening to extensional exhumation. Kinematic indicators (e.g. winged inclusions, tiling, and climbing pinch-and-swell veins) consistently indicate a top-to-E shear sense, confirming progressive east-directed transport under ductile conditions. Quantitative estimates of ductile flow are derived from structurally rotated quartz-calcite-dolomite veins, highlighting that deformation is shared approximately equally between pure shear and simple shear components. Ductile folding is characterized by sub-horizontal axial planes of late structures, which imply vertical flattening during ductile flow. This ductile regime is overprinted by E-dipping shear bands and faults, which evolve into brittle-ductile faults consistent with incremental strain axes that also indicate vertical shortening during top-to-E extension. Geochronology from white mica Ar-Ar dating from both shear veins and recrystallized fabrics indicates Oligocene (c. 25-34 Ma) deformation ages. The deformation pattern suggests distributed ductile thinning in the footwall of an extensional detachment systems, motivating investigation toward higher crustal levels. At the upper limit of the Nordrahmen Zone, deformation localizes into the newly identified top-to-E Schuhflicker Detachment, a knife-sharp ultramylonite-cataclasite fault surface. The hanging wall comprises slightly deformed Lower Austroalpine quartzites and dolomites. Eleven apatite fission track ages from the Schuhflicker footwall were incorporated with apatite grain-specific chemistry for thermal history modeling, indicating c. 11-7 Ma cooling in the sub-dome core (~17°C/Myr) consistent with Miocene folding and exhumation of the eastern Tauern Window. However, earlier c. 19-13 Ma cooling (~12°C/Myr) below the detachment is interpreted as unroofing of the Schuhflicker footwall prior to and during Miocene doming. Estimated cumulative unroofing associated with this tectonic phase is 22.4 ± 4.4 km between 30 and 19 Ma, and as much as 26 km of total exhumation of the Penninic Unit since the early Oligocene. The Schuhflicker Detachment formed at mid-crustal depths during the Oligocene, after which W-E extension migrated structurally upward during the Miocene to the Katschberg Fault and Katschberg Shear Zone System. Collectively, these structures define the East Tauern Detachment System. The results support a progressive exhumation history combining tectonic unroofing and surface erosion, while accounting for the proposed >20 km of exhumation since the Oligocene that has been suggested for parts of the Tauern Window.