Title

S. B. Lobach-Zhuchenko, N. A. Arestova, A. B. Vrevsky, Yu. S. Egorova, S. K. Baltybaev, V. V. Balagansky, E. S. Bogomolov, L. M. Stepanyuk, A. V. Yurchenko

The origin of the pyroxene granulites of the Bug granulite complex of the Ukrainian Shield

Mafic and ultramafic granulites of the oldest Dniestr-Bug sequence located at the Dniestr-Bug province of the western Ukrainian Shield were derived from the volcanic rocks such as: iron-, high-magnesium, aluminous and tholeitic basalts and komatiites. Processes which were responsible for the variations of compositions of the rocks include: contamination (up to 4%) of the ancient crustal component providing disequilibrium of Sm-Nd systems; fluid activities resulted in increasing of LIL, LREE, while small REE enrichment of all rocks suggest enriched mantle sources. Basalts of all greenstone belts of the Ukrainian Shield are derived from the deep level and were originated from a plume. Based on CaO/Al₂O₃, CaO/TiO₂, Gd/Yb ratios characterizing Al-content in komatiites it was suggested different conditions of their formation in the Ukrainian Shield and the Kaapvaal craton compared to komatiites of the Baltic Shield and most of those from the Pilbara craton.
Key words: Ukrainian Shield, Bug granulite complex, pyroxene granulites, basalts, komatiites, geochemistry.