Metamorphosed ophiolitic rocks from the Serbo-Macedonian Massif, near Lake Volvi, North-east Greece

Abstract

Summary The paper describes preliminary results from the 120 sq km Volvi mafic complex within the Greek Serbo-Macedonian Massif. We conclude from published information and isotopic ages that the central and eastern part of the Massif (basement and Triassic/Jurassic cover) were affected by an amphibolite-facies regional metamorphic and deformational event in the Late Jurassic-Early Cretaceous. Delayed uplift from this same event may explain Tertiary ages from Kerdilion migmatites. The Volvi complex may thus be A: pre-Mesozoic ‘basement’, or B: an in situ Mesozoic rift complex or C: a Mesozoic collisional suture remnant. Field, microprobe and XRF data appear to fit model B best. Though deformed, the complex has recognisable 100% sheeted-dyke tracts and substantial areas of undeformed gabbro at lower structural levels. Deformation began before the end of magmatic activity: late sheets of pegmatic gabbro cut deformed dykes; late dykes cut sheared gabbro. Assemblages are of high-grade amphibolite facies and give garnet-hornblende temperatures of 750°C, significantly higher than inferred for staurolite-garnet schists outside the complex. Geochemically, the basaltic rocks show LIL enrichment and are intermediate between ‘alkalic’ and ‘above-subduction-zone’ in character. The complex may relate to Mesozoic rift-basins identified in E. Serbia, but is not thought to be a Palaeotethyan remnant.