SUMMARY
The effect of pressure, temperature, and melt composition on CO2 and H2O solubilities in aluminosilicatemelts, coexisting with CO2-H2O fluids, is discussed on the basis of previously published and new experimentaldata. The datasets have been chosen so that CO2 and H2O are the main fluid components and the conclusionsare only valid for relatively oxidizing conditions. The most important parameters controlling the solubilitiesof H2O and CO2 are pressure and composition of melt and fluid. On the other hand, the effect of temperatureon volatile solubilities is relatively small. At pressures up to 200 MPa, intermediate compositionssuch as dacite, in which both molecular CO2 and carbonate species can be dissolved, show higher volatilesolubilities than rhyolite and basalt. At higher pressures (0.5 to 1 GPa), basaltic melts can incorporate higheramounts of carbon dioxide (by a factor of 2 to 3) than rhyolitic and dacitic melts. Henrian behavior is observedonly for CO2 solubility in equilibrium with H2O-CO2 fluids at pressures <100 MPa, whereas at higherpressures CO2 solubility varies nonlinearly with CO2 fugacity. The positive deviation from linearity withalmost constant CO2 solubility at low water activity indicates that dissolved water strongly enhances the solubilityof CO2. Water always shows non-Henrian solubility behavior because of its complex dissolutionmechanism (incorporation of OH-groups and H2O molecules in the melt). The model of Newman and Lowenstern(2002), in which ideal mixing between volatiles in both fluid and melt phases is assumed, reproducesadequately the experimental data for rhyolitic and basaltic compositions at pressures below 200 MPa butshows noticeable disagreement at higher pressures, especially for basalt. The empirical model of Liu et al.(2004) is applicable to rhyolitic melts in a wide range of pressure (0-500 MPa) and temperature (700-1200°C) but cannot be used for other melt compositions. The thermodynamic approach of Papale (1999) allowsto calculate the effect of melt composition on volatile solubilities but needs an update to account formore recent experimental data. A disadvantage of this model is that it is not available as a program code. Thereview indicates a crucial need of new experimental data for scarcely investigated field of pressures and fluidcompositions and new models describing evident non-ideality of H-C-O fluid solubility in silicate meltsat high pressures.