Rutile solubility in supercritical NaAlSi3O8-H2O fluids

Rutile solubility was measured in the supercritical NaAlSi3O8-H2O system using hydrothermal piston-cylinder methods at 900 degrees C. Solubility in intermediate albite-H2O fluids varies as a function of both pressure (P) and fluid composition (X). Rutile solubility increases with increased albite content of the fluid, and is on the order of similar to 1000 to similar to 5000 ppm for all P-X conditions investigated here. The relationship between solubility and pressure is complex, and solubility decreases with increasing pressure for intermediate fluid compositions (35-75 wt.% H2O). Ti contents of glasses indicate that, with rising pressure at 900 degrees C, the liquid-vapor miscibility gap in the albite-H2O system closes at 0.9-1.0 GPa. A single supercritical fluid is stable above this pressure, to 2.0-2.2 GPa when further compression induces a return to a subcritical state. Supercritical fluids could be plausible transfer agents for Ti and other HFSE in high-P metasomatic environments, but the results show that their stability may be more limited than previously recognized. (C) 2011 Elsevier B.V. All rights reserved.