CONDITIONS OF PETROGENESIS OF BONINITES IN OPHIOLITES OF THE DZHIDA ZONE, NORTHERN MONGOLIA

Abstract

Based on new data on melt inclusions in clinopyroxenes, we have established the physicochemical conditions (magma compositions, temperature, and pressure) of formation of boninites in ophiolites of the Dzhida zone (northern Mongolia) and have determined the parameters of generation of primary magmas (T = 1400-1500 °C, P = 10-30 kbar, depth 30-90 km) and the crystallization temperatures of boninite melts (T = 1170-1250 °C). Ion microprobing of Vendian-Cambrian boninites helped to investigate the trace and rare-earth element patterns of their melt inclusions. The patterns of the host clinopyroxenes agree with the data on inclusions and show that the crystallizing minerals were in equilibrium with the melt. The melt compositions evidence the existence of at least two types of primary melts that produced ophiolites of the Dzhida zone: boninite and calc-alkalic andesite-basalt.