Geochemistry of the Osnitsk-Mikashevichy volcanoplutonic complex of the Ukrainian shield

Abstract

This paper addresses the geochemistry of intrusive (Osinitsk complex) and volcanic (Klesov Group) rocks of the Osnitsk-Mikashevichy volcanoplutonic belt (OMVPB) of the Ukrainian shield, which is an active continental margin existing approximately 1980–2000 Ma ago. The Osnitsk complex comprises a wide range of rocks, from ultrabasics to granitoids, and the Klesov Group is dominated by extrusive rocks of basaltic and rhyolitic compositions metamorphosed under epidote-amphibolite facies conditions. The Sr-Nd-Hf isotopic systematics (ɛSr1990 from −4 to +10, ɛNd1990 from −0.6 to +2.3, and ɛHf1990 from 0.1 to 1.4) indicates a juvenile source for the OMVPB rocks. Geochemical data suggest independent origin of the rocks of gabbroid (SiO2 60 wt %) series. The gabbroids are subdivided into pre- and post-granite groups on the basis of the higher contents of incompatible trace elements and lower contents of compatible elements in the post-granite rocks. The geochemical characteristics of the two groups of basic rocks indicate their formation in a convergent tectonic setting. The origin of the granitoid melts is attributed to the low-degree (eutectoid) melting of basic rocks at relatively low temperatures.