Late to post-Variscan differential uplift and basement segmentation along the SW Bohemian Massif, Central Europe

Abstract

Abstract. The exposed Variscan basement in Central Europe is well-known for its complex structural and lithological architecture resulting from multiple deformation phases. We study the southwestern margin of the Bohemian Massif, which is characterized by major and long-lived shear zones, such as the Pfahl and Danube shear zones, extending over > 100 km and initiated during Variscan tectonics. We integrate Bouguer gravity anomaly and LiDAR topographic data analyses and combine our results with available data and observations from low-temperature thermochronology, metamorphic grades, and granite intrusion depths to detect patterns of basement block segmentation and differential uplift. Three NW-SE striking basement blocks are bordered by the Runding, Pfahl, and Danube shear zones from the northeast to the southwest. Basement block boundaries are indicated by abrupt changes in measured gravity patterns and metamorphic grades. By applying high-pass filters to gravity data in combination with lineament analysis, we identified a new NNW-SSE striking tectonic structure (Cham Fault), which further segments known basement blocks. Basement blocks that are segmented by the Cham Fault differ in the abundance and spatial distribution of exposed late Variscan granites and are further characterized by variations of apparent thermochronological age data. Based on our observations and analyses, a differential uplift and tectonic tilt model is proposed to explain the juxtaposition of different crustal levels exposed at the surface. Block segmentation along the NW-SE striking Pfahl and Runding shear zones most likely occurred prior, during, and after late-orogenic granite emplacement at ca. 320 ± 10 Ma, as some of the granites are cross-cut by the shear zones while others utilized these structures during magma ascent and emplacement. In contrast, activity and block segmentation along the Cham Fault occurred after granite emplacement as the fault sharply truncates the granite inventory. Our study provides evidence for intense and continuous fault activity during late and early post-orogenic times and highlights the importance of tectonic structures in the juxtaposition of different crustal levels and the creation of complex lithological patterns in orogenic terrains.