FEATURES OF THE STRUCTURE AND EVOLUTION OF THE LOWER PARTS OF THE CONTINENTAL CRUST OF THE YAKUTIAN DIAMONDIFEROUS PROVINCE IN THE AREA OF THE UPPER-MUNA KIMBERLITE FIELD

Abstract

Upper Muna kimberlite field) showed that the crust at different levels is composed of pyroxene, garnet-pyroxene crystalline schists and garnet-pyroxene gneisses. Exsolution textures in pyroxenes and amphiboles, granat rims around grains of ilmenite and pyroxenes indicate that the mineral associations of crystalline schists were formed during cooling at constant pressure. Р–Т equilibrium parameters indicate that garnet-pyroxene crystalline schists are present in the middle crust (P = 7–8 kbar), while garnet-pyroxene gneisses can be considered as rocks of the lower crust (P = 9–10.1 kbar). For the first time, sodalite was found in xenoliths of crystalline schists, which indicates the presence of brines with a high concentration of NaCl at the final stages of rock cooling. The determination of the U–Pb age of zircons testifies to the Neoarchean (2.7 Ma) tectono-thermal event, accompanied by the melting of the crust. In the garnet–pyroxene gneisses, the 1.9 stage is weakly manifistated. The obtained data confirm the earlier conclusion about the vertical and lateral heterogeneity of the crust of the Yakutsk diamondiferous province and the absence of dependence between the degree of crust reworking and spatial location relative to the main collision zones of the Siberian craton.