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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 ϳ6 wt% start to evolve H 2 O at temperatures less than 150 ЊC, whereas more mafic samples and silicic samples with less than 6 wt% H 2 O begin to dehydrate at temperatures greater than 200 ЊC. 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 (2 ϭ Ϯ 0.5 wt%) between 700-1200 ЊC 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 Ͻ 1 in the vapor phase.

We present new thermometers and barometers based on clinopyroxene-liquid equilibria specific to 37 alkaline differentiated magmas. The new models were calibrated through regression analyses of 38 experimental datasets obtained by merging phase equilibria experiments from literature with new 39 experiments performed by using trachytic and phonolitic starting compositions. The regression 40 strategy was twofold: i) we have tested previous thermometric and barometric equations and 41 recalibrated these models using the new datasets; ii) we have calibrated a new thermometer and a 42 new barometer including only regression parameters that closely describe the compositional 43 variability of the datasets. The new models yield more precise estimates than previous 44 thermometers and barometers when used to predict temperatures and pressures of alkaline 45 differentiated magmas. We have tested the reliability of the new equations by using clinopyroxene-46 liquid pairs from trachytes and phonolites erupted during major explosive eruptions at the Phlegrean 47 Fields and Mt. Vesuvius (central Italy). The test yielded crystallization conditions comparable to 48 those determined by means of melt and fluid inclusion analyses and phase equilibria studies; this 49 validates the use of the proposed models for precise estimates of crystallization temperatures and 50 pressures in differentiated alkaline magmas. Because these magmas feed some of the most 51 voluminous, explosive, and threatening volcanic eruptions in the world, a better understanding of 52 the environmental conditions of their reservoirs is mandatory and this is now possible with the new 53 models provided here. 54 55 56 table 2 Click here to download table: Table 2.doc

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