Abstract
The phase equilibria of the system MgO-FeO-SiO2 at pressures higher than 20 GPa studied in our laboratory were summarized. The signs of the phase boundary curves were found to be negative for the transformations of ilmenite-perovskite in MgSiO3 and spinel-perovskite+periclase in Mg2SiO4. The phase boundaries are very close each other. The Fe-component does not affect significantly on these features. The stability fields of spinel, ilmenite and perovskite solutions were specified up to 26 GPa. The stabilization of the perovskite-bearing assemblage was demonstrated to bethe dominant cause of the 670km discontinuity, which is completed within a quite narrow pressure interval, less than 1 GPa. The phase relations including the Fe-Mg partitioning between perovskite and magnesiowustite and the density consideration suggest suggest an assebbage of (Mg0.96Fe0.04)SiO3 perovskite and (Mg0.76Fe0.24) O magnesiowustite to be the major constituent of the lower mantle.
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