Water solubility in aluminosilicate melts of haplogranite composition at 2 kbar

Holtz, F., Behrens, H., Dingwell, D.B. and Taylor, R.P., 1992. Water solubility in aluminosilicate melts of haplogranite composition at 2 kbar. In: Y. Bottinga, D.B. Dingwell and P. Richet (Guest-Editors), Silicate Melts. Chem. Geol., 96: 289-302. The compositional dependence of H20 solubility was investigated at 2 kbar and 800 °C in haplogranite melts (system SiO2-NaAISi3Os-KA1Si308 or Qz-Ab-Or) . The sixteen investigated compositions contained 25, 35 or 45 wt.% normative Qz and various Ab/ (Ab + Or ) ratios (0.15-0.92 ). Starting solid materials were anhydrous bubble-free glasses to which 10 wt.% H20 was added. The H20 contents of the isobarically quenched melts (glasses) were measured by Karl-Fischer titration. The results show that H20 solubility in aluminosilicate melts depends significantly upon anhydrous composition. The highest solubility values are obtained for the most Ab-rich melts. At a constant normative quartz content, the solubility of water decreases from 6.49 _+ 0.20 wt.% H20 for a composition Qz35AbroOro5 (normative composition expressed in wt.%) to 5.50 4-_ 0.15 wt.% H20 for a composition QzasAbloOr55. Along this join, the most significant changes are observed for Ab-rich melts whereas H20 solubility in Or-rich melts remains almost constant. The H20 solubility data imply that H20 is preferentially associated with the Ab component in aluminosilicate melts. Application of the results to natural granitic melts suggests that Na-rich, H20-saturated melts may be significantly less viscous than H20-saturated, K-rich melts. The temperature dependence of H20 solubility, investigated for composition Qz28Ab38Or34 at 2 kbar, is low. Increasing temperature from 750 ° to 1150 °C only causes a decrease in H20 solubility from 6.00 to 5.41 wt.% H20. These data are in agreement with previous data obtained for albite melts.