Abstract

We present 16 new manometric determinations of H 2 O solubility for a range of natural silicate liquid compositions equilibrated up to 3 kbar of H 2 O pressure. As the threshold temperature of dehydration of the quenched glasses during measurements of the H 2 O content becomes lower as a function both of bulk silicate composition and the dissolved H 2 O content, we measured the H 2 O released on heating over a range of temperature intervals. For example, alkali-rich samples having a dissolved H 2 O content greater than approximately 6 wt% start to evolve H 2 O at temperatures less than 150 degrees C, whereas more mafic samples and silicic samples with less than 6 wt% H 2 O begin to dehydrate at temperatures greater than 200 degrees C. This behavior is consistent with the concept that alkali-rich liquids can have their glass transition temperatures lowered substantially by dissolved H 2 O and that H 2 O is released only significantly on heating in the supercooled liquid region, rather than in the glass region. Using these new data, in conjunction with previous data from the literature, we refined and extended the empirical H 2 O solubility model of Moore et al. (1995b). The new model works well (2sigma = + or -0.5 wt%) between 700-1200 degrees C and 1-3000 bar and can be applied to any natural silicate liquid in that range. The model may also be used for systems where X H2O <1 in the vapor phase.

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