Vol 31, No 2 (2023)

This work is a comprehensive review of existing data on melt inclusions entrapped in minerals of kimberlite rocks emplaced in different cratonic settings at different times. The crystallized melt inclusions represent snapshots of kimberlite melts at different stages of their evolution. All inclusions are composed of daughter minerals and shrinkage bubbles, but no aqueous fluids and quenched silicate glasses have been so far found. More than 60 mineral species were identified among the daughter phases in the inclusions, however, such diverse phase assemblages are typical of all kimberlites studied to date. Daughter minerals are represented by various Na-K-Ca-, Na-Ca-, Na-Mg-, K-Ca-, Ca-Mg-, Ca-, Mg-, Na-carbonates, Na-Mg- and Na-carbonates with additional anions Сl^–, \({\text{SO}}_{4}^{{2 - }},\) \({\text{PO}}_{4}^{{3 - }},\) alkali- sulfates, chlorides, phosphates, sulfides, oxides and silicates. Alkali carbonates, sulfates, and chlorides are usually absent among groundmass minerals the majority of kimberlites in the world, except the Udachnaya-East kimberlite in Siberia. On the other hand, this paragenesis in association with traditional kimberlite minerals, such as olivine, micas, monticellite, spinel group minerals, perovskite, rutile, ilmenite, calcite, and dolomite, is common in the crystallized melt inclusions in all studied kimberlites. Carbonates (~30 to 85 vol. %) always dominate over silicates (only up to 18 vol. %) within inclusions. All inclusions also contain variable (2 to 55 vol. %.) amounts of chlorides (halite and sylvite). When relatively low abundances of carbonate minerals (30–50 vol. %) are observed in the inclusions, chlorides (18–55 vol. %) appear to take over other minerals, including silicates that are traditionally considered as main components of “ultramafic” kimberlite parental melts. The published results on melt inclusions in the kimberlite minerals strongly imply that parental kimberlite melts were generated and further evolved within the Na₂O-K₂O-CaO-MgO-CO₂-Cl system, that is, they were alkali-rich carbonatite/carbonatite-chloride liquids. According to various estimates, the SiO₂ content in kimberlite melts at different stages of their evolution could have varied from the first to 19 wt. %. Obviously, during and after of а kimberlite bodies formation, interaction with external waters leads to serpentinization of kimberlite olivine and dissolution of a significant part of kimberlite igneous minerals, such as alkaline carbonates, sulfates, and chlorides. In the traditional approach to studying kimberlites, the role of components such as Na₂O, CO₂, Cl, and to a lesser extent K₂O and S, F in the petrogenesis of kimberlite magmas and rocks have been largely underestimated, while olivine- and serpentine-forming components, such as of SiO₂, MgO and H₂O are still overestimated in contemporaneous literature.

The paper presents geochemical and isotopic characteristics of Neoarchean (2.7–2.66 Ga) mafic granulites of the Sharyzhalgay uplift in the southwestern Siberian craton. Mafic and predominant felsic granulites compose fragments of the metamorphic complex among the Neoarchean and Paleoproterozoic granitoids. Mafic granulites are characterized by the mineral association Cpx + Pl ± Hbl ± Opx ± Qz and include two types with different major and immobile trace element contents. The dominant rocks of the first type have a wide range of Mg# and concetrations of TiO₂ and immobile trace elements (REE, Zr, Nb, and most positive ε_Nd(Т) va-lues. The first type of mafic granulites show elevated (La/Sm)_n and enrichment in Th and LREE relative Nb which is typical of basalts of subduction origin or crustal contaminated basalts. The absence of negative correlation between (La/Sm)_n and ε_Nd(Т) and a clear positive correlation of TiO₂ with Nb testify against the effect of crustal contamination on the composition of the mafic granulites. The magmatic protoliths of first type of mafic granulites are suggested to form by the melting of depleted peridotites of the subcontinental mantle which metasomatized by melts formed from basalts or terrigenous sediments of the subducting plate. Mafic granulites of the second type have a narrower range of Mg#, TiO₂ content, positive ε_Nd(Т), flat rare earth patterns and no subduction signatures, which indicates an asthenospheric depleted mantle source. Ma-fic granulites contaminated by the Paleoarchean crust are characterized by increased (La/Sm)_n, depletion of Nb relative to Th and LREE, and negative ε_Nd(Т) values. Post magmatic influence of granitoids lead to the enrichment of mafic granulites in biotite and apatite, an increased in concentrations of K₂O, P₂O₅, a signi-ficant enrichment of Zr, Nb, Th, LREE, and negative ε_Nd(Т) values. The difference between mafic granulites of the first and second types is not resulted from crustal contamination, but is due to the melting of two types of sources: asthenospheric and subcontinental lithospheric mantle. The subcontinental lithospheric mantle of the Irkut block was isotopically depleted for the Neoarchean time (∼2.7 Ga), and its enrichment in incompatible trace elements, presumably by felsic melts generated from the rocks of subducting plate, immediately preceded mafic magmatism.