Megan S. Duncan

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

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 (CO2mol. and CO32−) 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 CO2mol. matched previous studies, and values for CO32− 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(K0)] and temperature (ΔH) dependence of the CO2 dissolution reactions with the updated ε values. The calculated values of ΔV, ln(K0) 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.