The high-pressure stability of majority garnet will be experimentally determined at 165-230 kbar pressures, 1650and higher temperatures, with the split-sphere anvil apparatus in Stony Brook (USSA-2000). The study would include: 1. The determination of the equilibrium compositions of enstatite- jadeite garnet coexisting with MgSiO3 ilmenite, and NaAlSiO4 (calcium ferrite structure) + stishovite; 2. The determination of the compositions of diopside-jadeite garnet coexisting with pyroxene, CaSiO3 perovskite, and NaAlSiO4 + stishovite. The compositions of enstatite-pyrope garnet coexisting with MgSiO3- Al2O3 perovskite would be determined at 220-280 kbar, 2000oC, If new developments are successful in reaching those pressures. The results of the proposed experiments would place new constraints on the nature of the 650 km discontinuity, and on the cause of the high-velocity gradients in the vicinity of the 650 km discontinuity. The results would also allow to evaluate the effect of sodium on the CMAS phase relations, which would lead to a better understanding of the Earth Mantle mineralogy. Supplementary projects could include: 1. The determination of the melting curves of simple compounds at 165-230 kbar, e.g. Mg4Si4O12 garnet, beta phase, diopside, CaSiO3 perovskite, grossular, jadeite; 2. The extension of the CMAS melting relations to the superphase B - Mg10Si3O14 (OH,F,Cl).4
