CONSTITUTION OF THE MOON .1. ASSESSMENT OF THERMODYNAMIC PROPERTIES AND RELIABILITY OF PHASE RELATION CALCULATIONS IN THE FEO-MGO-AL2O3-SIO2 SYSTEM

The thermodynamic functions of minerals in the FeO-MgO-Al2O3-SiO2 (FMA S) system have been assessed using phase equilibria, equations of stat e and calorimetric data. Phase equilibria in this system have been cal culated using ideal, symmetric and asymmetric models of solid solution for minerals to obtain K(D) of exchange reactions consistent with exp erimental data. A symmetric model for olivine (W(ol) = 10800 J mol-1), spinel (W(sp) = 1300 J mol-1) and pyroxene(W(FeAl)opx = W(AlFe)opx = -3383 - 2.35T - 0.4723P) and an asymmetric model for garnet (W(FeMg)gr = 230 + 0.01 P, W(MgFe)gr = 3720 + 0.06P) were recommended, as these mixing parameters provide a better agreement for the calculated phase equilibria with the totality of experimental data. The THERMOSEISM dat abase which includes experimental and assessed data on thermodynamic a nd thermoelastic properties (bulk modulus and its pressure derivative, thermal expansion, heat capacity, volume, Debye temperature, enthalpy of formation, entropy and mixing parameters of solid solutions), has been obtained for calculation of mineral assemblages at high pressure and temperature and for the further application to the modelling of th e mineral composition of the lunar mantle.