Melting relation of Fe2SiO4 up to about 200 kbar.

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 Fe1-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.