The effect of CO (sub 2) on the solubility of H (sub 2) O-Cl fluids in andesitic melt
The effect of CO (sub 2) on the solubility of H (sub 2) O-Cl fluids in andesitic melt (in EMPG XI; Experimental mineralogy, petrology and geochemistry symposium, Jonathan D. Bundy (editor), Simon C. Kohn (editor) and Michael J. Walter (editor))
European Journal of Mineralogy (October 2007) 19 (5): 671-680
The solubility of C-O-H-Cl-bearing fluids in andesitic melt was investigated experimentally at temperatures of 1050 and 1200 degrees C and pressure of 200 MPa. The CO (sub 2) -free andesitic melts produced experimentally contained up to 5.5-6 wt.% H (sub 2) O and up to 2.5 wt.% Cl at the investigated conditions. The complex non-linear relationship between the concentrations of H (sub 2) O and Cl in the melt indicates a strong non-ideality of the H (sub 2) O-salt-bearing fluid phase(s), presumably resulting in the formation of two immiscible fluids. The addition of CO (sub 2) to the system (80-800 ppm dissolved CO (sub 2) in the melt) has two effects: a simple dilution of the fluid at low bulk Cl concentration and a significant influence on the mixing properties of the H (sub 2) O- and Cl-bearing fluids related to the enlargement of the immiscibility gap in the fluid at higher bulk Cl content. The first effect results in lower H (sub 2) O (by approximately 1 wt.%) and almost constant Cl concentrations in the melt, while the second effect causes an increase in activity coefficients of both H (sub 2) O and Cl. This effect of CO (sub 2) is expected to be most pronounced at low pressures and high CO (sub 2) concentrations in Cl-bearing mafic melts due to an enlargement of the immiscibility gap in fluids with decreasing pressure and an increase in proportions of divalent cations.