Brittle deformation of continental lithosphere due to high strain rates is often associated with the abrupt failure of rocks and the release of seismic energy, which results in the occurrence of earthquakes. This process is associated with a rapid increase in frictional heat and can produce frictional melts that are instantly quenched to form pseudotachylites. Such structures help to understand the interplay between brittle deformation and hydrothermal and fault activity. This is particularly important with respect to nuclear waste disposal and production of deep geothermal eneregy.
We document pseudotachylites from the Mid-German Crystalline Zone, which is represented by the NW-SE trending Thüringer Wald basesment-high. It is composed of syn- and postvariscan, partially deformed crystalline rocks that are overlain by volcanic- and volcaniclastic rocks of the Rotliegend (Permian Redbeds). The Thüringer Wald is fault bound to the Mesozoic cover in the NE and SW and was uplifted during Mesozoic to Cenozoic times (e.g., Thieme et al., 2023).
Pseudotachylites were recovered in syn- to post-Variscan granitoids and successions of quartz-porphyric pyroclastic rocks of the Lower Rotliegend. Here, cataclastic zones host cm-sized black veins of glass-like material that crosscut the sample and carry cataclasts of host rock material. Inclination of the pseudotachylite veins is approx. 60°, which suggests that formation of the veins was associated with normal rather than reverse displacement. This could either represent direct evidence for post-variscan extension or volcanic activity related to Rotliegend-volcanism.