Pressure and temperature dependence of CO2 solubility in hydrous rhyolitic melt: implications for carbon transfer to mantle source of volcanic arcs via partial melt of subducting crustal lithologies
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We conducted high pressure and temperature experiments to determine pressure and temperature dependence of CO2 solubility in natural hydrous rhyolitic melts. The goal was to constrain the limit of CO2 transfer via hydrous silicic melt derived from subducting crust at sub-arc depths. We performed two sets of experiments: (1) to determine the FTIR absorption coefficients CO2 species (CO 2 mol. and CO3 2−) for natural rhyolitic glass and (2) to constrain the effect of temperature on CO2 solubility in rhyolitic melts. The values of ε and ε*, linear and integrated absorption coefficients, for CO 2 mol. matched previous studies, and values for CO3 2− had not been previously calculated for rhyolitic compositions. The use of the new ε values leads to lower total CO2 solubility for rhyolitic glasses compared to those obtained using ε values determined from albitic compositions. Further, we assessed the uncertainty of our fluid compositions and the quench effects on carbon speciation in glasses and constrained the pressure [ΔV and ln(K 0)] and temperature (ΔH) dependence of the CO2 dissolution reactions with the updated ε values. The calculated values of ΔV, ln(K 0) and ΔH were used to calculate total CO2 in rhyolitic melts as a function of pressure and temperature. Finally, our model was applied to calculate CO2 carrying capacity of rhyolitic slab melts for any given subduction zones.
KeywordsCO2 solubility CO2 speciation Rhyolite FTIR absorption coefficient Carbon cycle Subduction zones
We gratefully acknowledge the thorough and critical reviews by Roman Botcharnikov and an anonymous reviewer as well as comments by the journal associate editor Mark Ghiorso. We also thank Mark Ghiorso for making the CO2–H2O solubility model of Ghiorso and Gualda (2015) available to us prior to formal publication. Cin-Ty Lee is thanked for giving us access to the FTIR laboratory. This work received funding from NSF Grant OCE-1338842 and Deep Carbon Observatory.
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