Petrology and geotectonic significance of salic rocks preceding ophiolites in the Eastern Vardar Zone, Greece

Abstract

In the eastern Vardar Zone of Greece, Na-dominant salic rocks are intimately associated with ophiolites, constituting a NW-trending, about 8 km thick belt along the western margin of the Serbomacedonian Massif. Though of different ages and metamorphic histories, both contrasted lithologic units display similar lateral variations. The salic rocks vary from a hypabyssal tonalite-trondhjemite series in the NW into granophyres and submarine volcanics in the SE. The juxtaposed ophiolites change in the same direction from tectonite peridotites overlain or intruded by mafic-ultramafic cumulates into sheeted dykes and submarine volcanics. The salic rocks were formed by multi-staged fractional melting of a mafic source and correspond chemically to the low-K andensite rhyolite series. The geological and chemical evidence points at an immature island-are setting for the salic rocks above a NE-dipping subduction zone. The lateral variations in their mode of occurrences probably reflect progressive attenuation of the continental crust. The corresponding variations displayed by the juxtaposed ophiolites may have resulted from a change in the plate motion from conservative in the NW to constructive in the SE.