ИСТИНА

In the study at 6 GPa model approximations of mineral phases, significant in compositions of probable metasomatic agents, the upper mantle peridotites, and also syngenetic inclusions in diamonds were used: starting mixtures were model peridotite with composition Ol48Opx16Cpx16Grt20, close to model compositions of the primitive mantle and real mantle xsenolithes, complex carbonate with composition (CaCO3)20(Na2CO3)20(FeCO3)20(Na2CO3)20(K2CO3)20, which model fluid inclusions in natural diamonds, and spectral pure graphite as a source of carbon in the system. Pressure and temperature were reached using apparatus of toroidal type “anvil-with-hole”. Electron microprobe and SEM researches were carried out on the polished surfaces with carbon covering at IEM RAS. Phase relations of end-member binary systems carbonatite-carbon, peridotite-carbon and complex peridotite-carbonatite were studied at 6 GPa and 1100 - 1750°C. Carbonatite-carbon and peridotite-carbonatite systems are characterized by euthectic type of melting and are responsible for the formation of diamond and paragenetic minerals. We also carried out test experiments proving diamond-forming effectiveness of carbonate-carbon melts oversaturated with dissolved carbon. A solubility curve on the diagram carbonatite-carbon controls the conditions of nucleation and crystallization of diamond. At the same time it conjugated with phase areas of formation of associations of paragenetic carbonate minerals. End-member system peridotite – carbon is notable for complete immiscibility by peridotite components (olivine, orthopyroxene, clynopyroxene, garnet and peridotite melt) in solid and liquid state and is a supplier with components providing syngenesis of diamond and peridotite minerals within a base triple system peridotite-carbonatite-diamond. Experimentally proved thermodynamic and kinetic points and boundaries (concentration barrier of diamond nucleation, diamond solubility in peridotite-carbonatite melts, fields of metastable and labile oversaturation) are plotted on a projection of liquidus surface of the system. The plotted diagrams characterize physico-chemical conditions of syngenesis of diamond and paragenetic peridotitic and carbonatitic minerals.