P-T-oxygen fugacity relations in the system Fe-O-MgO-SiO 2

The T-oxygen fugacity equilibrium for the system has been developed for a semi-quantitative T-oxygen fugacity petrogenic grid applicable to both basic igneous rocks and to meteorites. Olivine-silica-pyroxene-metallic iron-liquid exist at 1305 degrees C and 10 (super -11.8) atm (1 atm total), and in the system Fe-O-SiO ~2~ at 17.5 kb, 1280 degrees C, and 10 (super -10.8) atm oxygen fugacity. Subsolidus Mg enrichment of the silicate phases occurs with decreasing T and increasing oxygen fugacity in the magnetite-bearing assemblages at 1 atm. For iron-bearing assemblages, a T increase and oxygen fugacity decrease leads to Mg enrichment of the silicate phase. These phases can be divided by a region in which neither Mg nor metallic iron are stable, and transition between the two is unlikely.