MELTING RELATION OF Fe2SiO4 UP TO ABOUT 20Okbar

Abstract

The melting relations in fayalite Fe₂SiO₄ and its high pressure modification γ-Fe₂SiO₄ have been experimentally studied at pressures up to about 200kbar. Fayalite melts congruently up to the triple point, 70±5kbar and 1, 520±25°C, of fayalite, γ-Fe₂SiO₄, and liquid. The initial slope of γ-Fe2siO4 is about 12°/kbar. γ-Fe₂siO₄ melts congruently up to about 130 kbar, above which it melts incongruently into stishovite SiO2 and liquid. The incongruent melting in γ-Fe₂SiO₄ terminates at about 170kbar and 2, 200°C. Above this pressure, the melting mode switches to the eutectic melting between wustite Fe_1-xO and stishovite SiO₂, which are the post γ-Fe₂SiO₄ assembly. The present data suggest a possibility of incongruent melting of γ-(Mg, Fe)₂SiO₄ at high pressure. Possible roles of the change in melting mode on the chemical fractionation of the earth's mantle are discussed.