More than erosion: Oligo-Miocene tectonic unroofing of the eastern Tauern Window resolved via AFT thermal history models accounting for grain-specific annealing kinetics

In the Tauern Window of the Eastern Alps, Miocene exhumation is commonly linked to erosion driven by relatively high topography coupled to structural doming, yet erosion alone cannot account for the observed magnitude of unroofing of the once deep-seated rocks. Recent work by our group in the eastern Tauern sub-dome identified the Eastern Tauern Detachment System (ETDS), an Oligo-Miocene crustal-scale extensional fault network, but its contribution to the overall exhumation remains unresolved. We report eleven new apatite fission track (AFT) ages from a north-south transect in the footwall of the Schuhflicker Detachment that yield three distinct age domains: i) early Miocene dates in the northern limb of the sub-dome, separating younger late Miocene dates in the ii) sub-dome core and iii) the northern edge of the window. Because AFT dates can be biased by partial annealing and kinetic heterogeneity, apatite grain-specific chemistry was quantified via electron microprobe to calculate rmr0, a proxy for fission track annealing kinetics. Thermal history models incorporating rmr0 were generated for one representative sample from each of the three domains. Models yield plausible cooling rates in the sub-dome core from c. 11-7 Ma at ~17°C/Myr, whereas the northern limb cooled earlier and slightly more slowly (c. 19-13 Ma at ~12°C/Myr). Although Miocene cooling in the sub-dome core fits the tectonic model of unroofing via erosion during doming, the older AFT ages in the northern limb record cooling associated with exhumation of the footwall of the Oligocene Schuhflicker Detachment, suggesting ductile thinning and east-directed extension contributed to tectonic exhumation prior to, and synchronous with, Miocene doming. Based on this model, 19-22 km of exhumation has occurred in the eastern Tauern sub-dome between 30 Ma and 19 Ma. Our model attempts to account for the proposed >20 km of exhumation since the Oligocene that has been proposed for parts of the Tauern Window, and supports accelerated unroofing during the Oligocene to earliest Miocene. These results indicate a complex exhumation history that involves tectonic unroofing and surface processes, and demonstrate both the utility and limitations of incorporating apatite chemistry into thermal history modeling.