Structural, metamorphic and geochronological record in the Goszow quartzites of the Orlica-nienik Dome (SW Poland): implications for the polyphase Variscan tectonometamorphism of the Saxothuringian terrane

摘要

This integrated study on the pressure-temperature-deformation-time record of the Goszow light quartzites from the Mynowiec-Stronie Group (Sudety Mts., SW Poland) provides new data that improve our understanding of the structure and geodynamic development of the Orlica-nienik Dome (OSD) as a Gondwana-derived unit involved in the formation of the Variscan orogen. The structural and metamorphic record of the Goszow light quartzites, when compared to the under- and overlying rock formations, indicates that the whole Mynowiec-Stronie Group in the eastern part of the Saxothuringian terrane functioned as a single, integral lithotectonic unit with no visible structural or metamorphic discontinuities. The sequence of structures and thermodynamic modelling indicate that the light quartzites underwent the same polyphase tectonometamorphic evolution as the adjacent rocks belonging to the Mynowiec-Stronie Group. The development of tight, N-S-trending folds and axial penetrative metamorphic foliation was related to metamorphic progression from 500 degrees C to 640 degrees C at 6-7kbar. Subsequently, under the retrogressive conditions below 540 degrees C, the foliation was reactivated as a result of subsequent N-S-directed ductile shearing and extension. Therefore, the study of the light quartzites exemplifies the penetrative structures in the OSD, and the metamorphic foliation and N-S-trending lineation are composite structures. The monazite metamorphic ages of ca. 364Ma and 335Ma may be related to the approximately E-W- and N-S-oriented tectonic movements, respectively, which occurred during the amalgamation of the Saxothuringian terrane with Brunovistulia. In contrast, the previously unknown early Palaeozoic monazite age of ca. 494Ma is interpreted as the protolith age of the light quartzites. Copyright (c) 2015 John Wiley & Sons, Ltd.