Unravelling the Tectonic History of an Intraplate Region: A Geochronological Study of the Danube Fault, Bavarian Forest, Germany

Deformation in the Earth’s upper crust is typically accommodated by faults, which can range from microscopic displacements to regional tectonic features. Despite being located in the continental interior of the Eurasian plate, Central Europe displays notable evidence for recent activity, including active faulting, even along fault lines previously presumed inactive. This intraplate region has experienced multiple phases of fault reactivation, which provide the basis for debate regarding the underlying causative deformation mechanisms and driving forces. Determining the timing of episodic fault activity and their deformation rates is crucial to investigating the mechanisms behind Cretaceous to Paleocene exhumation and its relationship to more recent fault activity.

An excellent region for this purpose is the Bohemian Massif, which is characterized by a complex structural and lithological architecture recording a long history of deformation. This area hosts significant fault zones, such as the NW–SE-striking Pfahl and Danube faults. Despite being one of the largest faults in Central Europe with a prominent scarp and young morphology, the ages of inception and reactivation of the Danube fault remain poorly constrained. Furthermore, therefore, seismic risks associated with these significant intraplate faults are difficult to include in earthquake hazard catalogs.

To determine the timing of fault-slip and re-activation of the intracontinental Danube fault system in the Bavarian forest, we designed a sampling strategy involving multiple radiometric geochronometers and judiciously sampled transects across minor faults exposed in numerous quarries. We are currently dating authigenic and synkinematically recrystallized minerals, including U-Pb dating of slickenfiber calcite and K-Ar dating of illite. We also employ ⁴⁰Ar/³⁹Ar thermochronology and multi-domain diffusion modeling of potassium-bearing minerals of the granitoid host rocks to determine the timing of exhumation and re-setting of this system due to fault activity.

The earliest time constraint for the initiation of the Danube fault was established by using published U-Pb zircon ages of deformed granites (310 to 342 Ma) (Klein et al. 2008 Lithos 102). We anticipate the K–Ar ages of illite and U–Pb ages of calcite to be significantly younger, which would confirm potential phases of reactivation accompanied by fluid alteration during cataclastic deformation. These fluid-infiltration events could potentially serve as markers for dating various phases of fault reactivation, which, along with information from frictional resetting, offer insights into the dynamic evolution of the Danube fault over time.