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 su blattice solid solution model has been applied to magnesiowustite; the other phases are described by the regular solution model. Mixing prop erties of magnesiowustite have been obtained from phase equilibria: th e reaction magnesiowustite + metallic iron, oxygen fugacity data in th e magnesiowustite stability field, and data on the magnesiowustite+oli vine exchange equilibrium. Phase equilibria at high pressures and temp eratures in the Fe-Mg-Si-O system have been used to calculate thermody namic data for the phases (beta-, gamma- spinel, phases with ilmenite and perovskite structure and majorite) stable in the mantle transition zone.