Mineralogy of Peridotite Xenoliths from the Komsomol'skaya–Magnitnaya Kimberlite Pipe (Upper Muna Field, Siberian Craton).

Novel data from mineralogical studies of the peridotite xenoliths from the Komsomol'skaya–Magnitnaya kimberlite pipe, Upper Muna field, Siberian craton, are presented. The mineral composition of 170 peridotite xenoliths (dunites, harzburgites, and lherzolites) is investigated. Based on these studies, it has been established that the lithospheric mantle beneath the Upper Muna kimberlite field is composed mainly of garnet and chromite-bearing dunites, harzburgites, and subordinate amounts of granular garnet lherzolites. The high proportion of peridotites with high-Mg olivines (Fo > 93 mol %) indicates the highly depleted nature of the lithospheric mantle peridotites. Based on the geochemical studies of the garnets, it has been found that the diamondiferous lithospheric keel underwent a low degree of metasomatic modification, mainly with the participation of carbonatite fluids/melts. Using the data on clinopyroxene monomineral geothermobarometry, it has been established that the thickness of the lithosphere in the area of the Upper Muna field at the time of kimberlite magmatism (~360 Ma) was about 220 km and the interval of the diamond window was about 95 km (from 125 to 220 km). [ABSTRACT FROM AUTHOR]