Ya. Litvin, Hot spots of mantle and experiment to 10 GPa: Alkaline reactions, lithosphere carbonatization, and new diamond-generating systems, GEOL GEOFIZ, 39(12), 1998, pp. 1772-1779
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.