XE AND AR IN HIGH-PRESSURE SILICATE LIQUIDS

We investigated the solubility of Xe in liquids of NaAlSi3O8, KAlSi3O8 , K2Si4O9, and plagioclase (Ab80An20) compositions to pressures of 25 kbar and to temperatures of 1600-degrees-C, complementing our previous study of Ar in a wide range of mafic and felsic silicate liquids (Whi te et al., 1989). The solubility of Xe is about one-third that of the smaller Ar atom on an atomic basis, ranging up to 1.45 wt% in KAISi3O8 liquid at 25 kbar and 1600-degrees-C As with Ar, the solubility of Xe increases with pressure, is independent of temperature except in K2Si 4O9 liquid, where it has a positive temperature dependence, and is str ongly dependent upon the composition of the liquid, being most soluble in polymerized liquids with a high Si/Al ratio. These results shed li ght on the solubility mechanisms of molecular species, such as CO2, an d they reveal that the noble gases dissolve in specific sites in the l iquid, presumably as do CO2, and some other molecular species, and not simply as microbubbles indiscriminantly sequestered in interstitial s ites. Our range of calculated molar volumes for Xe at 15 kbar is 28.0- 29.4 cm3/mol, which is similar to that of solid Xe, 32-29 cm3/mol at 8 9-degrees-C between 10 and 20 kbar (Lahr and Eversole, 1962). Calculat ions using the Redlich-Kwong equation and corresponding states theory yield values for the volume of the vapor of 32.5 cm3/mol for Ar and 39 .4 cm3/mol for Xe. Our calculated enthalpies of solution for Ar and Xe are within the range for Ar and Xe in magmas at 1 bar (Lux, 1987) and for CO2 in NaAlSi3O8 at high pressures (Stolper et al., 1987).