S. K. BALTYBAEV, S. B. LOBACH-ZHUCHENKO (ИГГД РАН), V. V. BALAGANSKY (ГИ КНЦ), A. V. YURCHENKO, YU. S. EGOROVA, E. S. BOGOMOLOV (ИГГД РАН)

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 metamorphism 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.

Keywords: Ukrainian shield, mafic metamorphic rocks, mineral assamblages, granulate facies, zircon, Sm-Nd age of garnet