NEW EVIDENCE FOR SUPRA-SUBDUCTION ZONE OPHIOLITES IN THE VARDAR ZONE FROM THE VERMION MASSIF (NORTHERN GREECE): IMPLICATION FOR THE TECTONO-MAGMATIC EVOLUTION OF THE VARDAR OCEANIC BASIN

The Vardar zone represents a main Tethyan suture, which testifies for the existence of a Mesozoic oceanic basin between the Pelagonian and the Serbo-Macedonian continental realms. The Vardar zone in the Greek sector is subdivided into three sub-zones: the Almopias (including the western, central, and eastern Almopias ophiolites), the Paikon (continental volcanic arc), and the Guevgueli (ensialic backarc basin). The Vermion massif consists of three tectonic units belonging to the Pelagonian domain, which are tectonically overlain by three tectonic units associated with the Almopias sub-zone. All these units include ophiolitic rocks (mantle harzburgites and ophiolitic mélanges) referred to the western and central Almopias ophiolites. Mantle harzburgites have a very depleted nature and represent portion of the supra-subduction (SSZ) mantle developed in an intra-oceanic arc setting. The Pelagonian mélange formations display intense ductile and pervasive metamorphism and mainly include materials derived from the Pelagonian margin (calc-alkaline rocks and Triassic marbles) and materials derived from the Vardar oceanic basin (MORBs and alkaline within-plate rocks), as well as minor material derived from the intra-oceanic arc setting (very low-Ti boninites). The Almopias units mainly include intra-oceanic arc materials, such as low-Ti island arc tholeiitic and boninitic rocks associated with minor MORBs. The new evidence from the Vermion massif compared with literature data on other magmatic rocks within the Vardar zone suggests a much more complex scenario than previously depicted for the tectono-magmatic evolution of the Vardar ocean and provides new constraints for its possible evolution as follows. (1) In the Late Permian-Early Triassic the rifting of the continental lithosphere between the future Pelagonian and Serbo-Macedonian continental margins was associated with calc-alkaline and alkaline within-plate (WPB) magmatic events. (2) From the Mid Triassic, the continuous extension between the Pelagonian and Serbo-Macedonian continental margins led to the generation of the oceanic crust of the Vardar ocean in which E- and N-MORB, as well as alkaline WPB (seamounts) were erupted. (3) In the Early-Mid Jurassic, the Vardar oceanic basin was affected by convergence with development of an intra-oceanic arc characterized by tectonic extension trigged by slab-rollback. During this phase typical SSZ ophiolites, such as low-Ti IAT and very low-Ti boninitic rocks, as well as very depleted mantle harzburgites were produced. (4) The Mid-Late Jurassic closure of the Vardar ocean was characterized by the formation of the mélange successions of the Vermion ophiolites, which is associated with the emplacement of the ophiolitic sequences onto the Pelagonian continental margin. (5) Meanwhile, the extension tectonics moved eastward to the backarc in consequence of the continuing slab-rollback. This led to the Late Jurassic formation of a new spreading centre (Almopias ocean) with generation of MORB crust now represented by the Eastern Almopias ophiolites. Afterwards, the plate margin moved eastward in consequence of the continuing convergence between the Adria and Eurasia plates and a new subduction started in the eastern part of the Almopias ocean beneath the Serbo-Macedonian continent leading to the formation of the Late Jurassic (-Early Cretaceous?) Paikon volcanic arc and Guevgueli backarc basin. (6) The final emplacement of the Pelagonian, Western-,Central-, and Eastern- Almopias ophiolites, Paikon arc, and Guevgueli complex occurred from the Early Cretaceous to Tertiary.