Effect of high pressure on the melting relation of the Fe₂SiO₄-FeSiO₃ system

The melting relation of the Fe₂SiO₄(Fa)-FeSiO₃(Fs) system has been studied at pressures of 5, 6, and 9 GPa. This pseudo-binary system shows an eutectic melting between fayalite and ferrosilite, and ferrosilite is observed to melt in-congruently into coesite plus melt at all pressures studied. The eutectic point of this system is determined as Fa74Fs26 and 1,335±15°C at 6 GPa, and Fa55Fs45 and 1,530±20°C at 9 GPa, where spinel phase emerges in place of fayalite as a liquidus phase of the Fe2SiO4-rich portion of the system. The peritectic point, where the liquidus surface of ferrosilite intersects with that of coesite, is determined as Fa35Fs65 and 1,435 ±35°C at 6 GPa, and Fa15Fs85 and 1,610±30°C at 9 GPa. On the basis of the melting curves for iron silicate minerals, the liquidus relation of the FeO-SiO2 system is extrapolated to higher pressures. The result demonstrates the large influence of phase transitions in the constituent minerals on the melting relation.