WATER SOLUBILITY IN ALBITE-ORTHOCLASE JOIN AND JR-1 RHYOLITE MELTS AT1000-DEGREES-C AND 500 TO 2000 BARS, DETERMINED BY MICROANALYSIS WITHSIMS

Water solubilities in albite (Ab)-orthoclase (Or) join and JR-1 rhyoli te melts at 1000 degrees C and up to 2000 bars were determined by the ''excess of water'' method using an internally heated pressure vessel (IHPV) with rapid quenching and a secondary ion microprobe mass spectr ometer (SIMS). We have found that secondary hydration of run product g lass with coexisting aqueous fluid occurs during quenching. The hydrat ion is significant in sodium-rich glass. The bulk analysis of such sec ondary hydrated run-products will cause overestimation of the water so lubility, while the true water solubility can be obtained by microanal ysis on non-attacked portion of the glass. The apparent compositional dependence in the published water solubility data could be due to the secondary hydration of run product glass. Newly determined water solub ility for the Ab-Or join and rhyolite melts is expressed as H2O (mol%) = 0.19 root P-H2O (bar), at 1000 degrees C.