Gneiss protolith ages and tectonic boundaries in the NE part of the Bohemian Massif (Fore-Sudetic Block, SW Poland)

Abstract

Published geochronological data, petrology, geochemistry and geological context of orthogneisses in the Strzelin and the Stachów complexes (NE-part of the Fore-Sudetic Block), together with structural observations help to locate the northern extension of the boundary between the East and West Sudetes within the poorly exposed NE margin of the Bohemian Massif. The Strzelin complex, in the east, comprises the Strzelin gneiss, with zircon ages of 600ą7 and 568ą7 Ma, and the Nowolesie gneiss with a mean zircon age of 1020ą 1 Ma. The Stachów complex to the west, which forms several tectonic klippen in the Strzelin Massif and in the Lipowe Hills Massif, contains the Gooecięcice gneiss and pale Stachów gneiss, both yielding Late Cambrian zircon ages (~500ą5 Ma). The orthogneisses in both complexes correspond to peraluminous S-type granites, but have different inherited zircon ages and display contrasting trace element characteristics, indicating different sources and petrogenetic histories. Based on the ages, petrology and overall geological context, the Strzelin orthogneiss is similar to the Keprník orthogneiss of the East Sudetes, whereas the orthogneisses of the Stachów complex correspond to rocks known from the West Sudetes (e.g. the Izera and OEnieżnik orthogneisses). The Stachów and the Strzelin complexes are separated by the Strzelin Thrust, which may be interpreted as the northern extension of the boundary between the East and West Sudetes, i.e. part of the boundary between the Brunovistulian and Moldanubian terranes of the NE part of the Bohemian Massif.