Gondwana-derived terranes in the northern Hellenides

Abstract

The Hellenides constitute an integral part of the Alpine orogenic system in southeast Europe. Despite the recognition of several subparallel zones, which are interpreted as terranes separated by ophiolitic sutures (e.g., Pindos and Vardar sutures), the classical view of an orogen with a foreland fold-and-thrust belt, a central crystalline zone, and a rather undeformed hinterland is still under discussion. This paper concentrates on basement terranes of exotic provenance in two of the internal zones of the Hellenides that support the interpretation of the Hellenides as an accretionary orogen formed by amalgamation of crustal segments during the subduction of Tethyan oceanic basins. The oldest of these terranes, the Florina terrane in the Pelagonian zone, is composed of Neoproterozoic arc-related orthogneisses. Two other exotic terranes occur east of the Vardar zone within the Serbo-Macedonian Massif. The Pirgadikia terrane is a microterrane in the southern Chalkidiki Peninsula that consists of PanAfrican mylonitic orthogneisses with volcanic arc–related trace-element geochemistry and Sr isotopic composition. The Vertiskos terrane occupies the northwestern part of the Serbo-Macedonian Massif and is primarily composed of coarse-grained, volcanic arc–related peraluminous orthogneisses of Silurian age. These terranes are exotic in relation to the other parts of the Hellenides. The provenance of the late Proterozoic Pan-African Florina and Pirgadikia terranes is assumed to be Gondwanan, whereas the Silurian Vertiskos terrane may have been part of the so-called Hun terrane, which formed at the northern active continental margin of Gondwana in the early Paleozoic.