A four-dimensional approach to understand the Miocene deformation of the western Tauern Window (European Eastern Alps)

The nappes of the Tauern Window (TW) in the European Eastern Alps were formed by the southward subduction of the European plate beneath the Adriatic plate. These nappes were stacked during the Late Eocene and refolded during the Miocene due to the northward push of the Dolomites Indenter. This study focuses on the Miocene deformation history of the western TW using 2-D, 3-D, and 4-D approaches, while we concentrate only on the core of the western TW. We first restore a N-S oriented cross-section along the trace of the Brenner Base Tunnel using published zircon fission-track and P-T data. Restoration reveals two deformation phases: upright folding of the nappe stack began to wane around 17 Ma, followed by thrusting of the entire nappe stack along the Sub-Tauern ramp. The hanging-wall nappes experienced 25-48% thinning due to W–E extension. Subsequently, we restore the western TW in 4-D using the same method as for our 2-D reconstruction. We displace the nappe stack downwards along the Sub-Tauern ramp, followed by unfolding under high-temperature conditions. We found that 21 – 23 Ma ago, indentation began in N to NE direction, which was followed by anticlockwise rotation during the Miocene, resulting in a NNW-NW indentation direction. During indentation, the lower crust of the Dolomites Indenter probably detached in the vicinity of the TRANSALP section. Volumetric differences of the gneiss cores are most likely primary and not due to lateral extrusion.