AN INTERNALLY CONSISTENT THERMODYNAMIC DATA SET FOR PHASES OF PETROLOGICAL INTEREST

The thermodynamic properties of 154 mineral end-members, 13 silicate l iquid end-members and 22 aqueous fluid species are presented in a revi sed and updated data set. The use of a temperature-dependent thermal e xpansion and bulk modulus, and the use of high-pressure equations of s tate for solids and fluids, allows calculation of mineral-fluid equili bria to 100 kbar pressure or higher. A pressure-dependent Landau model for order-disorder permits extension of disordering transitions to hi gh pressures, and, in particular, allows the alpha-beta quartz transit ion to be handled more satisfactorily. Several melt end-members have b een included to enable calculation of simple phase equilibria and as a first stage in developing melt mixing models in NCKFMASH. The simple aqueous species density model has been extended to enable speciation c alculations and mineral solubility determination involving minerals an d aqueous species at high temperatures and pressures. The data set has also been improved by incorporation of many new phase equilibrium con straints, calorimetric studies and new measurements of molar volume, t hermal expansion and compressibility. This has led to a significant im provement in the level of agreement with the available experimental ph ase equilibria, and to greater flexibility in calculation of complex m ineral equilibria. It is also shown that there is very good agreement between the data set and the most recent available calorimetric data.