Hot spots of mantle and experiment to 10 GPa: Alkaline reactions, lithosphere carbonatization, and new diamond-generating systems

The peculiarities of the interaction of chemically active alkaline-fluid pl ume components with major minerals of the lithosphere (the situation of hot spots of mantle) were experimentally studied at a pressure as high as 10 G Pa. Active interaction of model alkaline-carbonate component K2CO3 With for sterite and enstatite results in formation of carbonates Mg2CO3 and K2Mg(CO 3)(2). At 3.7 GPa, the phase equilibria of the forsterite - K2CO3-K2SiO3 - system are represented by periclase- and forsterite-bearing subsolidus mine ral associations with participation of MgCO3, K2Mg(CO3)(2), and K2CO3. Thes e facts may point to intense carbonatization of the lithosphere. At pressur e above 4.0 GPa, alkaline reactions of aluminosilicate plume components NaA lSi2O6 (jadeite) and NaAlSiO4 (nepheline) with forsterite and enstatite giv e rise to silicate Na2Mg2Si2O7 (which may be a new mantle mineral) and pyro pic garnet Mg3Al2Si3O12. The phase equilibrium in the forsterite-jadeite an d enstatite-nepheline pseudobinary systems on their melting at 6 GPa are co ntrolled by invariant peritectics. High-pressure interaction of alkaline-ca rbonate plume components with forsterite results in formation of a series o f carbonates with mixed Na, K, and Mg cations. The carbonate melts were tes ted as media for diamond crystallization. The experiments at 8-10 GPa have shown that diamond efficiently crystallizes in the carbonate-carbon melts o f the Na2Mg(CO3)(2)-K2Mg(CO3)(2)-C (graphite) system in the cases of both s pontaneous and seed-stimulated kinds of nucleation.