Determination of water solubilities in high-viscosity melts; an experimental study on NaAlSi (sub 3) O (sub 8) and KAlSi (sub 3) O (sub 8) melts

The solubility of water in melts of albitic and orthoclasic compositions was re-investigated at 1100 degrees C and 0.5-5.0 kbar. The lowest solubilities were found for samples of stoichiometric feldspar composition; an excess of several wt.% of SiO (sub 2) has a negligible effect, but an excess of Na (sub 2) O or Al (sub 2) O (sub 3) relative to NaAlSi (sub 3) O (sub 8) increases the solubility by approximately 3 % relative per wt.% of excess oxide. At 5 kbar, significantly higher solubilities than those previously reported were obtained (11.60 wt.% H (sub 2) O for Ab and 10.32 wt.% H (sub 2) O for Or); this is attributed to the drying of run products at 105 degrees C in previous studies. At 2 kbar, experiments using single pieces of glass, crystal plates or pieces of glass embedded in glass powder as starting materials gave a water solubility of 5.95 wt.% for Ab melts, which is less than the solubilities determined in previous studies. The water solubility in Ab melts at 5 kbar apparently increases with the ratio of fluid to melt; this effect is probably caused by formation of strongly hydrated quench products on the melt body and diffusional exchange between both during cooling.