THE METABASITES FROM THE KOPAONIK METAMORPHIC COMPLEX, VARDAR ZONE, SOUTHERN SERBIA: REMNANTS OF THE RIFTING-RELATED MAGMATISM OF THE MESOTETHYAN DOMAIN OR EVIDENCE FOR PALEOTETHYS CLOSURE IN THE DINARIC-HELLENIC BELT?

摘要

The Kopaonik area belongs to the Vardar Zone, regarded as the eastermost terrane of the Dinaric-Hellenic belt. This area is characterized by a pile of tectonic units that includes, from bottom to top: the Kopaonik metamorphic complex, the Brzece Unit, the Ophiolite Unit and the Bras Unit. During Early Oligocene, the nappe pile was intruded by the I-type Kopaonik intrusive complex. The Kopaonik metamorphic complex mainly includes metasedimentary rocks consisting of Upper Triassic metalimestones, metarenites, metapelites and metadolomites. In addition, this complex is characterized by metabasites that occur as up to 200 m thick bodies folded together with the metasedimentary rocks of Late Triassic age. Their original stratigraphic position is here interpreted at the base of the metasedimentary succession. These rocks show a complex deformation history that includes two phases developed under upper greenschist-upper amphibolite conditions followed by subsequent two phases characterized by very-low grade metamorphism. The geochemical affinity of the igneous protoliths of the studied rocks, evaluated using discrimination diagrams based on the relative distributions of several immobile elements, indicates basaltic magmas generated at continental arc settings. Two different, alternative geodynamic hypotheses about the origin of these rocks are proposed in this paper. The first hypothesis suggests an origin during the Lower Triassic rifting phase by partial melting from small areas of enriched hydrous mantle, probably a consequence of preexisting subduction. By contrast, an origin of the metabasites from Kopaonik metamorphic complex as remnants of the Upper Permian-Middle Triassic calc-alkaline magmatism related to Cimmerian orogenesis is provided by the second hypothesis.