EFFECT OF HIGH PRESSURE ON THE MELTING RELATION OF THE Fe₂SiO₄-FeSiO₃ SYSTEM

抄録

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 incongruently 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.