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The system albite–H2O–CO2: a model for melting and activities of water at high pressures

1982; Mineralogical Society of America; Volume: 67; Linguagem: Inglês

1945-3027

Steven R. Bohlen, A. L. Boettcher, V. J. Wall,

Phase Equilibria and Thermodynamics

The melting of albite in the presence of H2O-CO2 v?por has been determined in pistoncylinder apparatus from 5 to 25 kbar for mole fractions of HzO in the vapor (Xfir6) from 1.0 to 0.0. Albite in the presence of CO2-rich vapor melts as much as 150-300'C lower than indicated by previous theoretical and experimental studies. The albite-CO2 melting curve is indistinguishable from the vapor-absent melting curve up to l5 kbar, but it is significantly lower above 15 kbar as a result of a substantial increase in the Solubility of COz in the liquid. Calculated activity coefficients (y) for water in H2O-CO2 vapor in the range 7001000C, 5-15 kbar are everywhere greater than unity and increase isobarically and isothermally toward COz-rich compositions. For Xfir6 < 0.3 calculated lffro are significantly greater than those predicted by the modified Redlich-Kwong equation.