Title

S. K. Baltybaev, S. B. Lobach-Zhuchenko, V. V. Balagansky, A. V. Yurchenko, Yu. S. Egorova, E. S. Bogomolov

Age and metamorphism of mafic and ultramafic rocks of the bug granulite unit within the Ukrainian Shield – the oldest volcanic rocks of the East-European Platform

Metamorphosed mafic and ultramafic rocks of the Dniestr-Bug sequence located at the the Dniestr-Bug province were studied in the western Ukrainian shield. The most part of the basic metamorphic rocks consists of garnet-clinopyroxene-orthopyroxene and two-pyroxene assemblages of granulite facies. An age of 3 Ga or older of the volcanic rocks suggested as a protholite of the studied rocks imply the oldest greenstone association of the East-European platform. The mafic metamorphic rocks have been suffered several deformations and polymetamorphism, the main metamorphic mineral assemblages were occurred or their main and isotope elements were totally re-equilibrated during Early Proterozoic time as it follows from U-Pb data of zircon and Sm-Nd age of garnet. The peak conditions of the Proterozoic stage of metamor- phism recorded in the rocks were estimated as P = 7–9 kb and T = 780–900 °C, while the regressive path is characterized by a coherent decreasing of P and T down to 4–6 kb and 600–650 °C.
Key words: Ukrainian shield, mafic metamorphic rocks, mineral assamblages, granulate facies, zircon, Sm-Nd age of garnet.