Carbon dioxide and water in the crust. Part 2: Solubility in silicate melts

The solubility of H2O and CO2 in silicate melts is crucial in understanding the geological phenomena occurring in a fluid–melt system. Although several recent solubility models are used in petrological studies, the model of Duan (2014) has rarely been used and has been evaluated less thoroughly, despite its potentially high applicability, mainly because calculation software is unavailable. This paper reviews the Duan (2014) solubility model and its calculation procedure for H2O–CO2 solubility. It was found that the Duan (2014) model uses a special protocol to calculate the fluid partial fugacity coefficient, for which no explanation is given in the original paper, thereby limiting the general use of the model. Therefore, I present an appropriate calculation procedure and provide a C-language code for convenience. The predictability of the model was evaluated by comparison with experimental solubility data. It was shown that the Duan (2014) model reproduces well the data for rhyolitic melts, whereas predictability is somewhat weak for other melts, including dacitic, andesitic, and basaltic melts. Caution is thus required when applying the Duan (2014) model to SiO2-poor melts.