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Published November 1987 | public
Journal Article

Solubility of carbon dioxide in albitic melt


Infrared spectroscopy has been used to measure the concentrations of molecular CO_2, and carbonate in albitic (NaAlSi_3O_8) glasses quenched from melts equilibrated with CO_2, vapor at high pressures (15-30 kbar) and temperatures (1450-1625 °C). At constant temperature, the concentrations of carbonate and molecular CO_2, as well as the CO^2_3/CO_2, ratio increase with increasing pressure under vapor-saturated conditions. The second derivative of these species concentrations with respect to pressure under vapor-saturated conditions at constant temperature is positive over the range of conditions studied. At constant pressure under vapor-saturated conditions, the solubility of molecular CO_2, decreases with increasing temperature, but the concentration of carbonate increases. The net effect is that total CO_2, solubility is nearly independent of temperature. According to our results, CO_2 solubility and speciation change gradually over the range of conditions that we have studied and do not indicate major or abrupt structural changes in albitic melts in this P-Z range. Our results can be described thermodynamically in terms of two reactions. The first, CO_2(vapor) = CO_2,molecular(melt), describes the heterogeneous equilibrium between melt and vapor. The second, CO_2,molecular(melt) + O^2-(melt) = CO^2_3-(melt), models the homogeneous equilibrium between melt species. Volume and enthalpy changes of these two reactions have been constrained by our solubility and speciation data. We emphasize that the solubilities of volatile components that dissolve in melts in several different forms must be treated by such coupled heterogeneous and homogeneous equilibria and that spectroscopic methods provide direct insights into them.

Additional Information

© 1987 Mineralogical Society of America. Manuscript received November 25, 1985. Manuscript accepted July 2, 1987. We thank George Rossman for his cooperation and Paula Rosener for her help with the FTIR. The interest and assistance of A. Boettcher, J. T. Cheney, and J. R. Holloway are appreciated. Ian Hutcheon generously helped us with SEM examination of our glasses. This work was began under an Undergraduate Summer Internship (to T.J.) in the Division of Geological and Planetary Sciences, Caltech, and was the basis of an honors thesis submitted to Amherst College. The research was supported by NSF Grants EAR-8212765 and EAR-8417434, Caltech Division of Geological and Planetary Sciences Contribution Number 4274.

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October 18, 2023