The Variscan overthrust of the Lower Palaeozoic gneiss unit on the Cadomian basement in the Strzelin and Lipowe Hills massifs, Fore-Sudetic Block, SW Poland: is this part of the East-West Sudetes boundary?

Teresa Oberc-Dziedzic, Stanisław Madej


The problem of the position of the boundary between the geological structures of the West and the East Sudetes has been a topic of discussion since 1912, when F.E. Suess developed the concept of the Moldanubian overthrust as a boundary between the Moldanubian and Moravo-Silesian zones. The West Sudetes comprise gneisses of Cambro-Ordovician protolith age with inclusions of high pressure metamorphic rocks. The Cadomian basement, referred to as the Brunovistulian and overlain by Devonian rocks, is characteristic of the East Sudetes. The location of the East-West Sudetes boundary is well-defined in the mountainous part of the Sudetes but still a matter of debate in the Fore-Sudetic Block. This paper puts forward a new approach to this problem.
The Proterozoic Strzelin gneiss with its Proterozoic (the older schist series) and Devonian envelope (the Jegłowa beds) are tectonically overlain by the Early Palaeozoic Gościęcice gneiss and the light Stachów gneiss with its envelope. The former occurs in the footwall and the latter in the hanging wall rocks of the Strzelin Thrust. This juxtaposition resembles the situation along the East-West Sudetes boundary separating two domains with contrasting protolith ages. Consequently, the Strzelin Thrust is considered part of the border zone between the East and West Sudetes, i.e. the northern continuation of the Ramzova/Nyznerov thrust to the Fore-Sudetic Block. At the present erosion level, the hanging wall rocks of the Strzelin Thrust are separated from their roots and form klippen. The minimum transport distance along the thrust is estimated at 10 km. The Strzelin Thrust forms a generally shallowly dipping domed surface. It becomes steeper east of the Strzelin massif, where it is hidden beneath Cenozoic sediments, and west of the Lipowe Hills, where it follows the eastern border of the Kamieniec Ząbkowicki Metamorphic Complex. The hanging wall is probably rooted in the strongly mylonitised mica schists exposed along the Mała Ślęza river. The thrust zone is a wide mylonitic belt carrying relatively HT and HP garnet-bearing amphibolites in the northern part of the Strzelin massif and the strongly mylonitised Henryków gneiss and quartzites in the southern part at the Lipowe Hills.
This paper discusses the problem of the East-West Sudetes boundary, mainly in the framework of the Strzelin massif. The attitude of this boundary in other parts of the Fore-Sudetic Block is still unclear because of poor exposure and numerous faults of E-W and NW-SE orientation that displace it from its original position.


Moravo-Silesian zone, East-West Sudetes boundary, Fore-Sudetic Block, Cadomian basement, Strzelin Thrust.

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