Phase equilibria and thermodynamic, properties of granulite facies minerals.

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1. The theoretical and experimental investigations were carried out on the Ca-Fe-Mg partitioning between olivine and clinopyroxene and on the miscibility of Ca-Mg olivine. Both olivine and clinopyroxene can be approximated as the two-site asymmetric regular solution cooperating intracrystalline exchange equilibria. The Fe-Mg distribution coefficient increases with the Ca content, Fe/(Fe+Mg) of the system and h pressure, but the increase with pressure is very small. The solvus of the Ca-Mg olivine becomes narrow with pressure due to the negative excess volume of this solid solution.2. The high pressure experiments were carried out to constrain the phase relations in the Mg_3Al_2Si_3O_<12>(pyrope composition) and (Mg_<0.75>, Fe_<0.25>)_3Al_2Si_3O_<12>(Prp_<75> composition) systems. The system equivalent to the Mg-rich garnet composition never directly break down to the low-pressure phase assemblages without any garnet phases, and has an intermediate P-T field including garnet + orthopyroxene + sillimanite + quartz, as well as garnet + orthopyroxene + sapphirine + quartz as decreasing pressure.3. High pressure experiments reveals that an orthopyroxene granulite from McIntyre Island, Enderby Land, East Antarctica experienced retrograde metamorphism at 11.2 kbar and 895℃ and subsequently passed at a certain pressure between 10.9 kbar and 11.4 kbar at 873℃.