Exhumation mechanisms of middle to lower crust in the Tertiary Eastern Alps (Tauern Window)

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Middle to lower crustal rocks (up to ~ 30 km depth) of Tertiary age in the Eastern Alps are only exposed within the metamorphic dome of the Tauern Window. Past investigations concluded that this metamorphic dome was exhumed by Miocene extensional unroofing along its western and eastern boundaries. However, several observations and recent analogue models suggest that exhumation resulted from large-scale crustal folding associated with transpressive shear zones, leading to uplift and erosion. While the geometry of gneiss domes formed by extensional unroofing may be similar to that of domes formed by folding and erosion, the spatial distribution of cooling ages and cooling rates is different. Therefore, we will test different exhumation models, by applying a combined structural - geochronological investigation. Rb/Sr cooling ages on white micas and biotites from selected sites of the western lobe of the Tauern Window, combined with compiled ages of adjacent localities will enable us to construct detailed contour maps of cooling ages. In addition, we will measure cooling rates along different traverses in order to obtain a spatial distribution of the rate of cooling. These data are diagnostic for the specific mechanism of shortening and/or extension, which resulted in exhumation of deep crustal rocks. Finally, we will date synkinematic white micas from several large-scale sinistral shear zones and from the axial planes of the large-scale upright-folds of the Tauern Window. These ages will allow us to test if the upright folds were coeval with sinistral shear zones and exhumation of the Tauern dome.