A general model for predicting the solubility behavior of H2O–CO2 fluids in silicate melts over a wide range of pressure, temperature and compositions

Abstract

In this study, a general thermodynamically-based model is presented for the solubility of H2O–CO2 in silicate melts over a wide range of temperatures (from 933K to 2003K), pressures (up to 30kbar) and melt compositions (from ultramafic to silicic, from metaluminous to peraluminous, and from subalkaline to peralkaline). Using an equation of state for the fluid phase that differs from previous models and deriving activity coefficients of species in silicate melts based on a specific interaction theory, this model can not only reproduce the data used for calibrations, but also predict the solubility well beyond the data range. The accuracies of solubilities predicted from this model are shown to be 7.2% for H2O and 9.7% for CO2, respectively, which are well within the experimental uncertainty. In addition, this model can be applied to the determination of equilibrium saturation pressure at which silicate melts are saturated with a fluid phase, modeling the evolution of ascending magmas through degassing processes, and elucidating the fluid-melt partitioning behavior of CO2 and H2O. An online version of this model is available at the website: http://calc.geochem-model.org/Test/Services/WebForm1.aspx and the program can be downloaded at: www.geochem-model.org/archives/programs.htm.