Composition of the Kimberlite Melt of the Komsomolskaya-Magnitnaya Pipe (upper Muna Field, Siberian Craton)

Reconstruction of kimberlite melt composition is especially important to understand the processes of mantle-derived magmatism and the Earth’s mantle evolution. This task seems to be very complicated because mantle melts during ascent and emplacement changed their initial characteristics due to degassing and contamination by both mantle and crustal xenogenic materials. Moreover, mantle magmatic rocks are often subjected to secondary alteration. Melt inclusions in minerals of mantle xenoliths can preserve information about the initial characteristics of mantle melts.Here, we present the results of a study on secondary crystallized melt inclusions in olivines in two partially serpentinized xenoliths of sheared peridotites (AKM-42n and AKM-56) from the Komsomolskaya-Magnitnaya pipe (Upper Muna field, Siberian craton). The mantle residence P–T conditions of AKM-42n and AKM-56 are 6.4 GPa and 1380°C, and 6.7 GPa and 1395°C, respectively.We identified twenty-one daughter minerals in the melt inclusions using confocal Raman spectroscopy and scanning electron microscopy coupled with energy-dispersive X-ray microanalysis. The minerals within the inclusions are presented by chlorides (sylvite KCl and halite NaCl), silicates (tetraferriphlogopite KMg3Fe3+Si3O10(OH,F)2, phlogopite KMg3AlSi3O10(OH,F)2, olivine (Mg,Fe)2SiO4, clinopyroxene (Ca,Mg,Fe)2Si2O6, and monticellite Ca(Mg,Fe)SiO4), carbonates (nyerereite (Na,K)2Ca(CO3)2, shortite Na2Ca2(CO3)3, eitelite Na2Mg(CO3)2, dolomite CaMg(CO3)2, calcite CaCO3, and magnesite MgCO3), carbonates with additional anions (burkeite Na6CO3(SO4)2 and tychite Na6Mg2(CO3)4(SO4)), sulphates (aphthitalite K3Na(SO4)2 and thenardite Na2SO4), fluorapatite Ca5(PO4)3F, sulfides (pyrrhotite Fe1-xS and djerfisherite K6(Fe,Ni,Cu)25S26Cl) and magnetite FeFe2O4.The studied melt inclusions are considered to be relics of a near‐primary or primitive kimberlite melt that formed the Komsomolskaya-Magnitnaya pipe. The assemblage of the daughter minerals indicates that the melt had an alkali-carbonatitic composition and was enriched in Cl and S.This work was supported by the Russian Foundation for Basic Research (grant No. 20-35-70058) and the Russian Science Foundation (grant No 18-77-10062).