C-O-H-Cl-S-F Volatile Solubilities, Partitioning, and Mixing in Phonolitic-Trachytic Melts and Aqueous-Carbonic Vapor Saline Liquid at 200 MPa

Abstract

Hydrothermal experiments were conducted at 200MPa and 900^10188C to determine the solubilities, fluid(s)^melt partitioning, and mixing properties of H2O, CO2, S, Cl, and F in phonolitic^trachytic melts saturated in vapor, vapor plus saline liquid, or saline liquid.The bulk compositions and S, Cl, and F concentrations of the run-product glasses were determined by electron microprobe and the H2O and CO2 contents by Fourier-transform infrared spectroscopy (FTIR). A new parameterization was developed to calculate molar absorption coefficients for FTIR analysis of carbonate in glasses and applied to the run-product glasses.The concentrations of volatiles in the fluid(s) were determined by mass-balance calculations and checked with chloridometer analysis and gravimetry.The range in oxygen fugacity of these experiments is NNO to NNOþ 2 (where NNO is nickel^nickel oxide buffer).The phonolitic^trachytic melts dissolved up to 7 5 wt % H2O, 0 94 wt % Cl, 0 73 wt % CO2, 0 75 wt % F, and 0 16 wt % S, and the integrated bulk fluid(s) contained up to 99 mol % H2O, 34 mol % Cl, 82 mol % CO2, 1 7 mol % F, and 3 7 mol % S.The mixing relationships of H2O, CO2, and Cl in melt versus fluid(s) are complex and strongly non-ideal at these pressure^temperature conditions, particularly with two fluid phases stable. The concentrations of H2O and CO2 in melt change with the addition of Cl S to the system, and the solubility of Cl in melt varies with S.The reductions in H2O and CO2 solubility in melt exceed those resulting from simple dilution of the coexisting fluid(s) owing to addition of other volatiles.The partitioning of H2O and CO2 between fluid(s) and melt varies as a function of fluid(s) and melt composition.The experimental data are applied to phonolitic and related magmas of Mt. Somma^ Vesuvius, Italy, Mt. Erebus, Antarctica, and Cripple Creek, USA, to better interpret processes of fluid(s) exsolution in eruptive and mineralizing systems. Application of the experimental results also provides constraints on eruptive and mineralizing fluid(s) compositions.