V.S. Shkodzinsky (DPАMGI SB RAS)

THE NATURE OF THE DISTRIBUTION FEATURES OF DIAMOND-BEARING KIMBERLITES

The evidence obtained for hot heterogeneous accretion of the Earth indicates the formation of the lithosphere of ancient platforms, kimberlites, and diamonds as a result of the fractionation of a layered global magma ocean, which arose due to the massive impact heat release during accretion. This explains the confinement of diamond-bearing kimberlites only to ancient platforms. The worldwide distribution of the magma ocean determined the presence of kimberlites on all ancient platforms. Their bottom residual magmatic origin is the reason for the small volume of kimberlite bodies and their relatively late formation. Diamonds crystallized as a result of the accumulation of carbon in residual melts. Extremely low viscosity of the bottom peridotite layer of the magma ocean determined the low rate of carbon diffusion in them and the formation of early octahedral diamonds through layer-by-layer tangential growth. The accumulation of multivalent elements in residual melts during fractionation led to an increase in the viscosity of the melts by thousands of times and to the formation of diamond rhombic dodecahedrons and cubes as a result of radial growth. A decrease in the rate of carbon diffusion with an increase in the viscosity of the melts caused a reduction in the area of the formed layers on diamonds and the appearance of their rounded crystals. A slow decrease in temperature in the early magma ocean led to the long-term crystallization of giant diamonds and their predominantly octahedral cut.
Keywords: magma ocean, origin of kimberlites and diamonds.