Cambro-Ordovician vs Devono-Carboniferous geodynamic evolution of the Bohemian Massif: evidence from P-T-t studies in the Orlica-snie(z) over dotnik Dome, SW Poland

The pressure-temperature-deformation-time (P-T-d-t) record of metagranitic rocks and adjacent diverse rocks of the metavolcano-sedimentary group from the Orlica-snie(z) over dotnik Dome (OSD) in SW Poland is examined. The study aims to better understand the course of the break-up of northern Gondwana and the overprinting Variscan tectonometamorphism in the NE Bohemian Massif. We test the existing hypotheses that explain the Cambro-Ordovician thermal event recorded in the meta-supracrustal group by (i) syn-deformational regional metamorphism or (ii) the contact metamorphism of the (meta)sedimentary rocks around the intruding similar to 490-500 Ma granitic magmas. In addition, we check the extent and timing of the Variscan prograde and retrograde medium-pressure metamorphism in the OSD. The results imply that Early Palaeozoic monazites, rarely preserved in both rock groups, document similar to 490-500 Ma volcanic and plutonic events related to the Gondwana's break-up and following disturbance of the Th-U-Pb system during younger, Variscan events. The monazite geochronology reveals no distinct Cambro-Ordovician thermal aureole around the post-granitic orthogneisses. However, no large-scale Variscan juxtaposition is evident between the two main OSD rock groups or within the meta-supracrustal rocks. Consistent P-T-d-t results for the meta-supracrustal rocks and the orthogneisses suggest that their precursors contacted before the Variscan tectonometamorphism. The directly contiguous ortho- and paragneisses together experienced tectonometamorphic processes at maximum depths that correspond to 7.5-8.0 kbar and maximum temperatures of similar to 600-620 degrees C, as a result of the Variscan collision of Gondwana and Euramerica. The continental collision-related events intensified at similar to 360 Ma and similar to 330-340 Ma.