Melt densities for leucogranites and granitic pegmatites: Partial molar volumes for SiO 2, Al 2O 3, Na 2O, K 2O, Li 2O, Rb 2O, Cs 2O, MgO, CaO, SrO, BaO, B 2O 3, P 2O 5, F 2O −1, TiO 2, Nb 2O 5, Ta 2O 5, and WO 3

Abstract

The densities and thermal expansivities of thirty-eight haplogranitic silicate melts have been experimentally determined. The compositions represent the additions of approximately 5, 10, and 20 wt% of selected oxide components Al 2O 3, Na 2O, K 2O, Li 2O, Rb 2O, Cs 2O, MgO, CaO, SrO, BaO, TiO 2, Nb 2O 5, Ta 2O 5, and WO 3 to a base melt of haplogranitic (HPG8) composition. The densities of melts have been obtained by a combination of scanning dilatometry and room temperature Archimedean density determinations together with scanning calorimetry. The thermal expansivities were obtained by a combination of scanning calorimetry and scanning dilatometry. The results of the density and expansivity determinations for the melts are fit to a multicomponent linear least squares regression of molar volume vs. molar composition. The resulting partial molar volumes of the molten oxides are reported for a reference temperature of 750°C. The multicomponent linear least squares regression yields a description of the database with a root mean squared deviation of 0.3%. The fit to these new partial molar volume data includes our previous data for B 2O 3, P 2O 5, and F 2O −1-bearing haplogranitic melts. The partial molar volumes of the oxides vary from 10.53 ± 0.29 cm 3 mole −1 for MgO to 69.09 ± 1.82 cm 3 mol −1 for P 2O 5. Compared on the basis of one oxygen per mole they range from 10.53 ± 0.29 cm 3 mol −1 (MgO) to 55.38 ± 1.69 cm 3 mol −1 (Cs 2O). The present data, taken together with an estimate of the partial molar volume of water in these melts (13.1 ± 1.3 cm 3 mol −1) are recommended to be used to calculate the low pressure densities of leucogranitic and pegmatitic melts.