From late-Variscan localised folding to post-Variscan brittle tectonics: structural evolution of the Glinno Graben, Góry Sowie Massif, SW Poland (NE Bohemian Massif)

Abstract

We have combined traditional geological field mapping, LiDAR-based digital elevation model (DEM) analysis, and shallow 2D Electrical Resistivity Tomography (ERT) to investigate the syn- to late-orogenic Mississippian (‘Culm’) succession preserved in the Glinno Graben (NE Bohemian Massif, SW Poland), and to propose a new model for its multistage tectonic evolution. The Glinno Graben, situated in the Góry Sowie Massif (GSM) southwest of the Sudetic Boundary Fault, is ~7.5 km long, up to 1.5 km wide, and has a markedly asymmetrical internal structure. Structural and geophysical data, supported by regional evidence from the nearby Kamionki Graben, suggest that the main boundary faults of the graben originated during a late Carboniferous to early Permian extensional or transtensional phase, following folding of the Mississippian strata, likely during the Namurian. A subsequent compressional episode during the Late Cretaceous to early Paleogene interval reactivated pre-existing faults and produced broad, gentle folds within the Carboniferous graben fill. Although direct structural evidence is sparse due to limited exposure, this event is supported by regional tectonic correlations. The final tectonic phase, possibly of Neogene to Quaternary age, was marked by NE–SW extension and resulted in the development of high-angle normal faults and internal compartmentalization of the graben. This phase also controlled the development of structurally induced landslides and the formation of Ostrzew Hill as a resistant erosional outlier in the southern part of the graben. Despite poor bedrock exposure, ERT and DEM analyses consistently delineated boundary faults and internal segmentation of the graben. This integrated approach provides the first detailed structural characterization of the Glinno Graben atop the GSM and highlights the long-term reactivation of inherited basement discontinuities.