The assessment of thermodynamic parameters for solid phases in the Fe-Mg-O and Fe-Mg-Si-O systems

Thermodynamic data for solid phases in the Fe-Mg-Si-O system have been assessed using phase equilibrium data, oxygen fugacity measurements, calorimetric data and equation of state parameter measurements. The sublattice solid solution model has been applied to magnesiowustite; the other phases are described by the regular solution model. Mixing properties of magnesiowustite have been obtained from phase equilibria: the reaction magnesiowustite + metallic iron, oxygen fugacity data in the magnesiowustite stability field, and data on the magnesiowustite+olivine exchange equilibrium. Phase equilibria at high pressures and temperatures in the Fe-Mg-Si-O system have been used to calculate thermodynamic data for the phases (β-, γ- spinel, phases with ilmenite and perovskite structure and majorite) stable in the mantle transition zone.