New insights into the deformation history of the Brenner Fault by the application of ESR thermochronometry

The Brenner Fault (BF) is an extensional low-angle fault in the eastern Alps that borders the western edge of the Tauern Window. The BF was instrumental in the exhumation of the latter, allowing the formation of the tectonic window by the uplift of the footwall. It consists of a wide shear zone, dipping to the west by an angle of 25-30°, overprinted by a brittle and steeper fault zone with a few metres thickness.  Exhumation and cooling history of its footwall has been investigated by several low temperature thermochronometry approaches, which have defined the Neogenic deformation history, using the zircon and apatite U-Th/He dating methods (Wolff et al. 2021). Because of the lack of thermochronological methods able to date the thermal history of the rocks during Quaternary, the most-recent knowledge of this fault activity has not yet been defined. New studies have shown the possible application of ESR dating on quartz as an ultralow-temperature thermochronometer, characterized by a closure temperature of 30°-90°C, and dating range of 10³-10⁷ years that is therefore a useful tool to reconstruct the tectonic deformation of the upper crust during the Quaternary. In this work, we show new structural data and the first results of ESR thermochronometry on quartz applied to rocks of BF collected across both the shear and fault zones. An en-echelon system of normal faults can be distinguished within the continuous N-S striking main fault, suggesting the probable start of brittle deformation or a following deformation phase overprinted the previous one. Moreover, ESR measurements of ten samples collected across the BF show that the ESR ages of quartz get younger toward the Tauern Window, in accordance with fission track and (U-Th)/He ages. The ESR ages indicate the Quaternary exhumation of the BF, i.e. the youngest activity of the BF. Our results promise the successful application of ESR thermochronometry in defining the youngest deformation histories of Neogenic faults in the Alpine chain.