Electron Spin Resonance Thermochronometry Indicates Quaternary Activity of the Brenner Fault (Eastern Alps)

Abstract The Brenner Fault is one of the most important normal faults in the Eastern Alps as it accommodates uplift and lateral extrusion of the Tauern Window. Consequently, understanding its kinematic history is important for studying the dynamics of the Eastern Alps, in particular the Tauern Window. However, the timing of fault activity remains debated. Based on low‐temperature thermochronometry, it has been proposed that the fault has not moved since approximately 9 Ma. However, recent seismicity suggests that it is still active. We bridge this time gap by applying electron spin resonance (ESR) dating on quartz. This ultra‐low temperature thermochronometer has a closure temperature of 80–50°C and therefore enables the study of the most recent footwall exhumation. Our ESR thermochronometric ages obtained from the Brenner area ranged from 0.38 ± 0.02 to >3.34 ± 0.63 Ma. The lateral distribution of these ages suggests that exhumation was caused by a combination of tectonic activity and glacial/fluvial erosion over the last million years. Exhumation occurred mostly within the first 500 m of the footwall of the Brenner Fault. Using 2D thermokinematic inverse modeling, constrained by the ESR data, we estimate the movement on the fault to a slip rate of 3.0 ± 0.7 mm/yr over the last million years. Our results, together with previous data, imply that the Brenner Fault has been almost constantly active for 19 Ma until the present‐day.