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Multistage structural evolution of the end-Cretaceous–Cenozoic Wleń Graben (the Sudetes, NE Bohemian Massif) : a contribution to the post-Variscan tectonic history of SW Poland

Kowalski Aleksander

Annales Societatis Geologorum Poloniae

2021

Vol. 91, No. 1

37--66

Results of a new mapping and structural field study of the Wleń Graben (North Sudetic Synclinorium, SW Poland), made up of a post-Variscan volcano-sedimentary succession, were used to set up a new model of its multiphase tectonic evolution. The Wleń Graben constitutes a narrow tectonic trough, ca. 17.5 km long and up to 3.5 km wide, superimposed on the low-grade metamorphic rocks of the Kaczawa Metamorphic Unit and bounded by steep, NW−SE-oriented, normal and reverse faults. Previously, a simple, one-stage evolution of the graben was considered, with a single Alpine age intraplate compressional event responsible for the formation of the unit. The present study shows that the Late Cretaceous (post-Santonian?) evolution of the Wleń Graben was dominated by NW−SE-oriented, normal faults during the first, extensional stage of its formation. The central and southern parts of the graben were strongly affected by NW−SE-trending reverse faults and overthrusts, which reflect the second, probably latest Cretaceous to early Palaeogene(?) compressional event of tectonic deformation. Moreover, the whole area of the graben is dissected by sinistral strike-slip faults oriented perpendicular to the graben margins, representing the third stage of deformation (late Palaeogene–Neogene). The latest stage of evolution of the Wleń Graben includes a possible Neogene to Quaternary development of normal faults, interpreted here as gravitational collapse structures related to present-day morphology, rather than tectonically induced ones.

Fault geometry and evidence of depocentre migration within a transtensional intra-basinal high : a case study from the Łączna Anticline (Intrasudetic Synclinorium, SW Poland)

Kowalski A.

Geological Quarterly

2017

Vol. 61, No. 4

779--794

The paper presents the results of geological mapping and a detailed structural analysis carried out in the Łączna Anticline. This elevated region coincides with the Zawory (Cz. Závora) mountain range in the Central Sudetes (SW Poland). The Łączna Anticline separates two minor geological units (depressions) within the northwestern part of the Intrasudetic Synclinorium – the Krzeszów and the Police brachysynclines. In numerous exposures of Triassic and Upper Cretaceous sedimentary rocks, several brittle and a few soft-sediment deformation structures have been recognized. Their orientation and spatial distribution suggest that the Łączna Anticline is a horst-like, intra-basinal high, formed due to permanent extension, dextral strike-slip movements within fault zones, and negative flower structures. The studies did not confirm the occurrence of continuous deformations such as anticlinal bends and flexures. The results show that the preservation of some lithological varieties of sedimentary rocks within modern morphological and structural elevations reflects the migration of centres of maximum subsidence within a pull-apart basin system. A new structural and geodynamic interpretation for the Łączna Anticline area is proposed.