The effect of CO2 on the solubility of aqueous chloride fluid in dacite, phonolite, and rhyolite melts

Abstract

The solubility of H₂O–CO₂–Cl-containing fluids of various concentrations (0, 3, 10, and 23 wt % of HCl and from 0 to ~8–15 wt % of CO₂) in dacite, phonolite, and rhyolite melts at 1000°C and 200 MPa was studied in experiments. It was shown that the Cl concentration in the melt increased substantially from rhyolite to phonolite and dacite (up to 0.25, 0.85, and 1.2 wt %, respectively). The introduction of CO₂ into the system resulted in an increase in the Cl content in the melt composition by 20–25%. One may suppose that Cl reactivity in a fluid increases in the presence of CO₂ to cause growth of the Cl content in the melt. The introduction of CO₂ into the system considerably affects the content of H₂O in aluminosilicate melts as well. Thus, the addition of CO₂ decreases the H₂O content in the melt by ~0.5–1.0 wt %. The decrease in the H₂O content in an aluminosilicate melt is probably caused by fluid dilution with CO₂ resulting in a decrease in the H₂O mole fraction and fugacity in the fluid.