Phase Equilibria in the Systems Consisting of Px, Ol and Gt.

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The results of the present study show that the high pressure minerals having the compositions of pyroxenes, garnet, olivine are indicepensable in elucidating the structure of the Earth's mantle.The results obtained in the present study are as follows :I.The system Fo (Mg_2SiO_4) -Py (Mg_3Al_2Si_3O_<12>) ; The experiments have performed at 8 and 13.5 GPa and 2025-2200ﾟC.An eutectic point (Fo+Py+liquid) and a peritectic point (Fo*periclase+liquid) are present.II.The system Fo-Di (CaMgSi_2O_6) ; The experiments have made at 8-15 GPa. An eutectic point (Fo+Px+liquid) is present and moves towards Fo with increasing pressure. Pressure depencdence of Di were also determined up to 22 GPa with the Saimon equation P=[(T/1664.5) ^<5.17(]SY.+-.])0.04>-1].III.The system Fo-Py-En (MgSiO_3) ; An entectic point at 15 GPa lies at 2200(]SY.+-.])20ﾟC and Fo_<54>Py_<13>En_<33>.IV.The system Fo-Py-Di ; An eutectic point at 7 GPa lies at 1170(]SY.+-.])20ﾟC and Fo_<30>Py_<25>Di_<45> and moves towards Fo with increasing pressure.V.The system Fo-Fa (Fe_2SiO_4) ; Phese equilibrium diagam at 8 GPa has been studied. Olivine (Fo_<90>Fa_<10>) melts incongruently into "phase B "+liquid and modified spinel into wustite+liquid at 18-23 GPa.IV.The system MgO-SiO_2-H_2O ; The experiments have been made at 11-23 GPa. The results obtained suggest that phase E is a candidate of H_2O reservior in the subducting sulab and the superphase B,the phase F,and the brucite in the lower part of the transion zone and the upper part of the lower mantle.