The H2O solubility of alkali basaltic melts: an experimental study

Abstract

The H2O solubility of alkali basaltic melts: an experimental study. Contributions to Mineralogy and Petrology, Springer Verlag, 2011, 162 (1) Our results show that at pressures above 1 kbar, alkali basalts dissolve more water than typical mid-ocean ridge basalts (MORB). Combination of our data with those from previous studies allows the following simple empirical model for the water solubility of basalts of varying alkalinity and fO 2 to be derived:where H 2 O MORB is the water solubility at the calculated P, using the model of Dixon et al. (1995). This equation reproduces the existing database on water solubilities in basaltic melts to within 5%. Interpretation of the speciation data in the context of the glass transition theory shows that water speciation in basalt melts is severely modified during quench. At magmatic temperatures, more than 90% of dissolved water forms hydroxyl groups at all water contents, whilst in natural or synthetic glasses, the amount of molecular water is much larger. A regular solution model with an explicit temperature dependence reproduces well-observed water species. Derivation of the partial molar volume of molecular water using standard thermodynamic considerations yields values close to previous findings if room temperature water species are used. When high temperature species proportions are used, a negative partial molar volume is obtained for molecular water. Calculation of the partial molar volume of total water using H 2 O solubility data on basaltic melts at pressures above 1 kbar yields a value of 19 cm 3 /mol in reasonable agreement with estimates obtained from density measurements.

Solubility of water in lunar basalt at low pH2O

“…With further increases in total water content, molecular water becomes the dominant species and the hydroxyl content levels off or may even decrease. The observed concentrations of hydroxyl and molecular water at different total water concentrations are well described by equations (1)- (3), although the appropriate solution model to describe the mixing of OH, H 2 O mol and O 0 in the melt is still not completely resolved (Silver and Stolper 1989;Silver et al 1990;Dixon et al 1995;Chertkova and Yamashita 2015), and the effect of quenching on the speciation of water in glasses versus high temperature melts is still debated (Stolper 1989;Dingwell and Webb 1990;Silver et al 1990;Dixon et al 1995;Sowerby and Keppler 1999;Withers et al 1999;Nowak and Behrens 2001;Lesne et al 2010). …”

“…The solubility of water in silicate melts is known to be strongly dependent on pressure (e.g., Goranson 1931;Hamilton et al 1964;Orlova 1964;McMillan 1994;Dixon et al 1995;Liu et al 2005;Moore 2008;Lesne et al 2010;Shishkina et al 2014). At sufficiently low pressures, only small quantities of water dissolve in the melt; consequently, because the reaction of molecular water with oxygen in the melt to produce hydroxyl groups causes a negligible reduction of the large number of reactive oxygens in the melt (whether bridging, non-bridging, or free), it can be assumed that [O ,௧ ] is approximately constant.…”

“…, Stolper 1982a;McMillan 1994;Dixon et al 1995;Moore et al 1998;Berndt et al 2002;Benne and Behrens 2003;Zhang et al 2007;Behrens et al 2009;Lesne et al 2010;Morizet et al 2010;Persikov et al 2010;Zhang and Ni 2010;Iacono-Marziano et al 2012;Shishkina et al 2014), water solubility and diffusion have not been studied for melts approaching the high iron contents of lunar magmas, and at the low fO 2 's and relatively low pH 2 O conditions of the Moon. Another source of uncertainty in lunar volcanic degassing models is the role of molecular hydrogen (Elkins-Tanton and Grove 2011;Zhang 2011;Hirschmann et al 2012;Sharp et al 2013;McCubbin et al 2015), with some authors suggesting that molecular hydrogen may be the main propellant of the lunar fire-fountain eruptions (Sharp et al 2013;McCubbin et al 2015), while other authors argue that the low solubility of molecular hydrogen in silicate melts at low pressures and low total H contents precludes a significant role for molecular hydrogen dissolution under low-pressure near-surface lunar conditions (Hirschmann et al 2012).…”

Heat capacity, configurational heat capacity and fragility of hydrous magmas

“…Molar absorption coefficients for the combination band of OH_ at 4500 cm_1 and H2Om at 5200 cm_1: PS (Behrens and Zhang, 2009), AMSB1 (Misiti et al, 2006) and ETN (Lesne et al, 2011). The duration of each experiment is 24 h. a Water content (mol%) measured by Infrared spectroscopy.…”

Amphibole and apatite insights into the evolution and mass balance of Cl and S in magmas associated with porphyry copper deposits

“…The speciation of water is controlled by the dissociation reaction (Stolper 1982;Zhang 1999;Zhang and Ni 2010 Lesne et al (2011) whereas for the porphyries (of dacitic to rhyodacitic compositions) we use the K 2 temperature-dependent dacite calibration of Liu et al (2004) recommended by Zhang and Ni (2010). In both cases, we have used the amphibole crystallization temperatures obtained by Chelle-Michou et al (2015a) to calculate the K 2 relevant to each amphibole analyses.…”