Effects of F, B20 a and P205 on the solubility of water in haplogranite melts compared to natural silicate melts

The effects of F, B203 and P205 on the H 2 0 solubility in a haplogranite liquid (36wt .% SiO2, 39 wt. % NaA1Si3Os, 25 wt. % KAISi3Os) have been determined at 0.5, 1, 2, and 3 kb and 800, 850, and 900 ~ The H20 solubility increases with increasing F and B content of the melt. The H 2 0 solubility increase is more important at high pressure (2 and 3 kb) than at low pressure (0.5 kb). At 2 kb and 800 ~ the HzO solubility increases from 5.94 to 8.22 wt. % H 2 0 with increasing F content in the melt from 0 to 4.55 wt. %, corresponding to a linear H20 solubility increase of 0.53 tool H20 /mol F. With addition of 4.35 wt. % BzO 3, the HzO solubility increases up to 6.86 wt. % H 2 0 at 2 kb and 800 ~ corresponding to a linear increase of 1.05 mol HzO/mol B203. The results allow to define the individual effects of fluorine and boron on H20 solubility in haplogranitic melts with compositions close to that of HzO-saturated thermal minima (at 0.5-3 kb). Although P has a dramatic effect on the phase relations in the haplogranite system, its effect on the H 2 0 solubility was found to be negligible in natural melt compositions. The concomitant increase in H 2 0 solubility and F can not be interpreted on the basis of the available spectroscopic data (existence of hydrated aluminofluoride complexes or not). In contrast, hydrated borates or more probably boroxol complexes have been demonstrated in B-bearing hydrous melts.