ZIRCON GEOCHRONOLOGY OF BASEMENT ROCKS FROM THE PELAGONIAN ZONE, GREECE: CONSTRAINTS ON THE PRE-ALPINE EVOLUTION OF THE WESTERNMOST INTERNAL HELLENIDES

Abstract

The Pelagonian Zone of Greece is the westernmost segment of the Internal Hellenides comprising widespread crystalline basement exposures of granites and orthogneisses. We dated these basement rocks in order to identify the major crust-forming episodes and to understand the evolutionary history of the area. In our study we investigated granites, gneisses, meta-rhyolites and mylonites from the major occurrences of the Pelagonian Zone. We applied single-zircon dating techniques such as Pb–Pb evaporation, conventional U–Pb and SHRIMP. The majority of the basement rocks gave Permo-Carboniferous intrusion ages, thus emphasizing the importance of this crust-forming event for the Internal Hellenides of Greece. Triassic intrusion ages were obtained, however, for a meta-rhyolite from the western Pelagonian Zone and two mylonites from the eastern Pelagonian Zone. These ages are interpreted to reflect magmatism accompanying early rifting that led to the subsequent opening of the Pindos Ocean to the west and the Meliata Ocean to the east of the Pelagonian Zone. The geochronological results demonstrate that the magmatic episodes during which most of the Pelagonian Zone crystalline basement formed are predominantly pre-Alpine in age.