This project involves the experimental determination of the phase relations of coexisting clinopyroxenes and (majorite) garnet at very high pressures (150-250 kbar) and temperatures (1300-2200 C) in the system Na2O-CaO-MgO-Al2O3-SiO2. Equilibrium compositions of coexisting C2/c clinopyroxene, majorite garnet, and P21/c clinoenstatite will be determined, as will the high pressure stability limit of the diopside- jadeite-enstatite C2/c clinopyroxene solid solution. The results of these experiments will provide information on the phase relations in sodium bearing systems at very high pressures and temperatures, on the mixing properties of the C2/c clinopyroxene solution near its high pressure stability limit, on the mixing properties of majorite garnet, and potentially on the breakdown products of clinopyroxene (perovskite phases). This information will test the feasibility of explaining the high seismic velocity gradients in the transition zone of the earth's mantle by dissolution of C2/c clinopyroxene in majorite garnet, and if confirmed, would place narrow constraints on the bulk chemistry of the mantle in the transition zone.
