Xenoliths of Mafic Granulites from the Udachnaya-East Kimbelite Pipe: Evidence of Metamorphic Evolution

The paper presents data on petrography, bulk chemical composition, and composition of coexisting minerals for 12 crustal xenoliths from the Udachnaya-East kimberlite pipe. According to the mineral composition, the xenoliths are mostly garnet–clinopyroxene–plagioclase (±orthopyroxene, quartz, and Fe–Ti oxides) mafic granulites. The compositions of 5 of 12 studied samples fall into uncertainty range between metaigneous and metasedimentary rocks. Estimations of РТ-parameters of mineral equilibria, which take into account compositional heterogeneity of coexisting minerals, yielded ~860‒910°C/10–14 kbar and 560–800°C/4–8 kbar for metamorphic peak and retrograde stage, respectively. These results indicate that the mafic granuliltes, represented by the xenoliths of Udachnaya-East kimberlite pipe, were tectonically exhumed to the higher crustal horizons during an ancient metamorphic event rather than were mechanically coupled with to the underlying ultramafic upper mantle up untill Late Devonian kimberlite eruption.