The phase relations in the FeO-MgO-Al2O3-SiO2 system: assessment of thermodynamic properties and phase equilibria at pressures up to 30 GPa

Thermodynamic parameters for minerals in the FeO-MgO-Al2O3-SiO2 (FMAS) syst em have been assessed from phase equilibria at pressures up to 30 GPa. All solid solution phases except orthopyroxene have been described by the subla ttice model. Calculated phase diagrams of end member systems, exchange reac tions in the FMAS system, phase equilibria for fixed compositions at pressu res up to 30 GPa are in a reasonable agreement with the experimental data. The most critical data in the MgO-Al2O3-Sio(2) (MAS) system were compositio ns of garnet in equilibrium with Mg-rich ilmenite at 1273 K. To reproduce t he experimentally observed Fe-Mg partition between perovskite and magnesiow ustite, it is necessary to take into account the presence of Fe+3 ions in p erovskite. The phase diagram of the FMAS system for pyrolite composition ha s been calculated in the temperature range of 1500 to 2400 K at pressures b etween 12 to 32 GPa.