Late to post-Variscan basement segmentation and differential exhumation 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 studied 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 integrated Bouguer gravity anomaly and lidar topographic data analyses and combined our results with available data and observations from low-temperature thermochronology, metamorphic grades, and the exposed granite inventory to detect patterns of basement block segmentation and differential exhumation. 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 in apparent thermochronological age data. Based on our observations and analyses, a differential exhumation and tectonic tilt model is proposed to explain the juxtaposition of different crustal levels. 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 of intense and continuous fault activities during late and post-orogenic times and highlights the importance of tectonic structures in the exhumation and juxtaposition of different crustal levels and the creation of complex lithological patterns in orogenic terrains.

Timanian Fold-and-Thrust Belt and Caledonian Overprint in the Selis Ridge Imaged by New 3D Seismic Attributes and Spectral Decomposition

“…A major argument to support this interpretation is the higher reflectivity character (higher amplitude) and planar aspect of mylonite and tilted dykes on seismic data generated respectively by preferred mineral orientation along foliation and shear surfaces (Christensen, 1965(Christensen, , 1966Fountain et al, 1984;Hurich et al, 1985) and by density contrast of igneous rocks (especially if mafic) with adjacent mylonite and metasedimentary rocks (e.g., Phillips et al, 2018;Koehl et al, 2018Koehl et al, , 2022a. Positive relief is commonly created by mineral precipitation along shear zones and magmatic intrusions more resistant to erosion (e.g., Eberts et al, 2021, their Figure 2b), which typically produces rugose subcrops with numerous asperities and protuberances (e.g., Phillips et al, 2016, 2018, their Figures 14 and1c, respectively). In addition to their ductile character, it is highly probable that the faults are (at least) partly brittle as suggested by their disruptive and offsetting character.…”

Variscan structures and their control on latest to post-Variscan basin architecture: insights from the westernmost Bohemian Massif and southeastern Germany

“…A third deformation phase (D3) records latest Variscan tectonics at ∼ 320 Ma and is represented by the folding of synorogenic deposits during general NW-SE to NNW-SSE shortening (Hahn et al, 2010). The latest stages of D3 and the early post-Variscan are dominated by a wrench tectonic phase and the collapse of thickened crust, resulting in the development of dextral strike-slip faults initiating fault-bounded graben and halfgraben basins in central Europe, including the study area in SE Germany (Schröder, 1987;Arthaud and Matte, 1977;Krohe, 1996;Stephan et al, 2016;Ziegler, 1990;Eberts et al, 2021). Detailed and comprehensive overviews of the geodynamic and tectonostratigraphic evolution of the mid-European Variscides have been presented by and .…”