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Published August 1993 | public
Journal Article

Solubilities of carbon dioxide and water in rhyolitic melt at 850°C and 750 bars


Concentrations of carbon dioxide and water dissolved in glasses quenched from rhyolitic melts equilibrated with H_2O-CO_2 fluids at 850°C and 750 bar were measured using infrared spectroscopy; concentrations of H_2O and CO_2 in the quenched fluids were measured manometrically. The mole fraction of CO_2 in the quenched fluid ranged from 0.06 to 0.91. Concentrations of CO_2 in the coexisting rhyolitic melt increased from 23(±6) ppm for the sample equilibrated with the most CO_2-poor fluid to 515(±16) ppm for that equilibrated with the most CO_2-rich fluid. The water content of the melt varied from 0.51(±0.06) to 3.34(±0.08) wt%. Our results show that concentrations of molecular CO_2 and H_2O in the glasses obey Henry's Law; i.e., the mole fractions of molecular CO_2 and molecular H_2O in the quenched melts are proportional to their fugacities in the coexisting vapor. CO_2 contents of vapor-saturated melts are not enhanced by addition of water to CO_2-rich vapor, contrary to previous reports for silicate melts at higher pressures. The Henrian behavior of CO_2 and H_2O at low pressure considerably simplifies modeling of the degassing of silicic magmas.

Additional Information

© 1993 Elsevier B.V. Received 26 October 1992. Accepted 11 June 1993. Available online 23 October 2002. We thank T. Gerlach, M. Rutherford, T. Sisson and T. Trull for their careful reviews. This work was funded by NASA grant NGT-50501, by NSF grants EAR89-16707 and 92-19899, and by DOE grant DE-FG03-85ER13445. This is Division of Geological and Planetary Sciences contribution 5157.

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