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) system have been assessed from phase equilibria at pressures up to 30 GPa. All solid solution phases except orthopyroxene have been described by the sublattice model. Calculated phase diagrams of end member systems, exchange reactions in the FMAS system, phase equilibria for fixed compositions at pressures up to 30 GPa are in a reasonable agreement with the experimental data. The most critical data in the MgO-Al2O3-SiO2 (MAS) system were compositions of garnet in equilibrium with Mg-rich ilmenite at 1273 K. To reproduce the experimentally observed Fe-Mg partition between perovskite and magnesiowustite, it is necessary to take into account the presence of Fe3+ ions in perovskite. The phase diagram of the FMAS system for pyrolite composition has been calculated in the temperature range of 1500 to 2400 K at pressures between 12 to 32 GPa.