Geochemistry, zircon U‒Pb and Hf isotopic compositions of lower crustal rocks from the Góry Sowie Massif (Central Sudetes, SW Poland): New insights on the sedimentary origin and tectono-thermal evolution

Abstract

Devonian HP-UHP lithotectonic associations represent a pivotal element of Paleozoic evolution of the European Variscan belt across the continent from Portugal to Poland. The Góry Sowie Massif (GSM), located in the Central Sudetes, represents one of the best preserved outcrops of lower crustal rocks that experienced a protracted Devonian tectono-metamorphic history at the easternmost extremity of the belt. The area is surrounded by Devonian ophiolite remnants and Devonian to Carboniferous sedimentary basins in the northern and southern part, respectively. The GSM is mainly composed of paragneisses and subordinate orthogneisses, metabasites and granulite. The dominantly sedimentary association and the overall geotectonic setting contrast with the other km-scale granulite complexes in the Bohemian Massif that are dominated by felsic granulites and late Cambrian orthogneisses that experienced 340 Ma HP metamorphism. Weak Carboniferous overprint makes the GSM a key locality to better understand the Devonian stages of formation of HP granulites and provenance of the whole pre-Devonian lithological association. New U-Pb and Lu/Hf analyses were carried out on zircons from 4 migmatitic paragneisses, 3 felsic biotite-poor granulites and 2 biotite-rich granulites in the northern part of the GSM, and combined with geochemical analyses in order to constrain a source provenance and tectono-thermal history of the area. The paragneisses dominated by stromatic migmatite and felsic granulites occur as hundred meter-scale bodies associated with metric lenses of amphibolites, mafic and ultramafic rocks in the northern part of the massif.