Solubility and solution mechanism of H2O in alkali silicate melts and glasses at high pressure and temperature

The solubility behavior of H2O in melts in the system Na2O-SiO2-H2O was determined by locating the univariant phase boundary, melt = melt + vapor in the 0.8-2 GPa and 1000degrees-1300degreesC pressure, and temperature range, respectively. The NBO/Si-range of the melts (0.25-1) was chosen to cover that of most natural magmatic liquids. The H2O solubility in melts in the system Na2O-SiO2-H2O (X-H2O) ranges between 18 and 45 mol% (O = 1) with (partial derivativeX(H2O)/partial derivativeP)(T)similar to14-18 mol% H2O/GPa. The (partial derivativeX(H2O)/partial derivativeP)(T) is negatively correlated with NBO/Si (= Na/Si) of the melt. The (partial derivativeX(H2O)/partial derivativeT)(P) is in the -0.03 to +0.05 mol% H2O/degreesC range, and is negatively correlated with NBO/Si. The [partial derivativeX(H2O)/partial derivative(NBO/Si)](P,T) is in the -3 to -8 mol% H2O/(NBO/Si) range. Melts with NBO/Si similar to basaltic liquids (similar to0.6-similar to1.0) show (partial derivativeX(H2O)/partial derivativeT)(P)<0, whereas more polymerized melts exhibit (partial derivativeX(H2O)/partial derivativeT)(P)>0. Complete miscibility between hydrous melt and aqueous fluid occurs in the 0.8-2 GPa pressure range for melts with NBO/Si less than or equal to0.5 at T >1100degreesC. Miscibility occurs at lower pressure the more polymerized the melt. Copyright (C) 2004 Elsevier Ltd.