Features of the Structures and Evolution of the Lower Part of the Continental Crust of the Yakutian Diamondiferous Province within the Upper Muna Kimberlite Field

Study of xenoliths of crustal rocks from the Novinka kimberlite pipe (Upper Muna kimberlite field) showed that the crust at different levels is composed of pyroxene and garnet–pyroxene crystal schists and garnet–pyroxene gneisses. The exsolution structures in pyroxenes and amphiboles and the garnet rims around ilmenite and pyroxene grains indicate that the mineral assemblages of crystal schists formed upon cooling of rocks at a constant pressure. The PT equilibrium conditions indicate that garnet–pyroxene crystal schists are present in the middle crust ( P = 7–8 kbar), whereas garnet–pyroxene gneisses could be constituent rocks of the lower crust ( P = 9–10.1 kbar). Sodalite is identified for the first time in xenoliths of the crystal schists, which is evidence of the presence of highly saline brines at the final stages of cooling of rocks. The U–Pb age of zircons indicates a Neoarchean (2.7 Ga) tectono-thermal event, which was accompanied by partial melting of the crust. The stage of 1.9 Ga is weakly manifested in garnet–pyroxene gneisses. Our data support an earlier conclusion on vertical and lateral crustal heterogeneity of the Yakutsk diamondiferous province and the absence of a correlation between the reworking degree of the crust and its spatial location relatively to the main collision zones of the Siberian Craton.