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Published December 1993 | public
Journal Article

Noble gas solubilities in silicate melts and glasses: New experimental results for argon and the relationship between solubility and ionic porosity


New measurements of the solubility of Ar in basaltic, rhyolitic, orthoclasic, and albitic melts and glasses ar Ar pressures of 250–10,000 bar and temperatures of 400–1300°C are presented and combined with other solubility measurements for a wider range of melt compositions to parameterize the effects of pressure, temperature, and melt composition on Ar solubility. Argon solubility in melts and glasses is roughly linear with Ar pressure under these conditions. At near-liquidus temperatures, solubility in melts is approximately independent (within ∼ 10%) of temperature, while some results below 600–700°C show an increase in solubility with decreasing temperature, perhaps reflecting differences in the nature of Ar solubility in glasses and melts. There is also a positive, linear correlation between the "ionic porosity" of melt and the logarithm of Ar solubility. This correlation is better than previously noted correlations between inert gas solubility and melt density and volume, and provides a useful means of predicting how Ar solubility varies with melt composition. The solubilities of He, Ne, Kr, and Xe are also positively correlated with ionic porosity, but are increasingly sensitive to ionic porosity as the size of the gas atom increases, suggesting that with more efficient packing of the melt structure the availability of sites that can incorporate inert gas atoms decreases more rapidly for larger atoms than for smaller atoms. Comparison of inert gas solubilities with those of molecular CO_2 and molecular H_2O in rhyolitic melts shows that solubilities decrease in the order H_2O_(mol) ⪢ He > Ne > Ar > CO_(2,mol) ≈ Kr > Xe. The much higher solubility of molecular H_2O compared to the other neutral gas species (and molecular CO_2) suggests that it is not merely passively occupying interstitial "holes" in the melt structure as is thought to be the case for the rare gases (and likely for molecular CO_2), but rather it is stabilized in the melt structure by chemical bonds (e.g., by hydrating cations or through hydrogen bonds).

Additional Information

© 1993 Pergamon Press. Received 29 October 1992. Accepted 10 June 1993. We thank Dr. G. Brent Dalrymple of the USGS, Menlo Park, for mass spectrometric analysis of Ar in material used for microprobe standards. Additional material used for standardization was analyzed by Rutherford backscattering spectrometry with help from D. Jamieson and M. Thouillard in the laboratory of Professor M. Nicolet at Caltech. Prof. M. J. Rutherford of Brown University is thanked for making available his internally heated pressure vessel for the BU series of experiments. Dr. M. Fisk is thanked for supplying the four RE basalt samples from experiments he did at Edinburgh University. Prof. J. R. Holloway kindly provided a program for Redlich-Kwong fugacity calculations. Some of the experiments were conducted at the Bayerisches Geoinstitut, Bayreuth and the help of K. Klasinski and G. Herrnannsdorfer is much appreciated. Reviews by A. Jambon, B. Fogel, and an anonymous reviewer helped to improve the manuscript. MRC acknowledges the hospitality of Prof. A. Mottana and the Department of Geology, Universitl di Roma "La Sapienza" during completion of this manuscript. Financial support provided by NATO grant 0339/88, NERC grant GR3/7776, and NSF grants EAR8916707 and EAR9219899. Division of Geological and Planetary Sciences Contribution #5213.

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