MELT DENSITIES FOR LEUCOGRANITES AND GRANITIC PEGMATITES: PARTIAL MOLAR VOLUMES FOR SIO2, AL2O3, NA2O, K2O, LI2O, RB2O, CS2O, MGO, CAO, SRO, BAO, B2O3, P2O5, F2O-1, TIO2, NB2O5, TA2O5, AND WO3

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 Al2O3, Na2O, K2O, Li2O, Rb2O, Cs2O, MgO, CaO, SrO, BaO, TiO2, Nb2O5, Ta2O5, and WO3 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 B2O3, P2O5, and F2O-1-bearing haplogranitic melts. The partial molar volumes of the oxides vary from 10.53 +/- 0.29 cm3 mole-1 for MgO to 69.09 +/- 1.82 cm3 mol-1 for P2O5. Compared on the basis of one oxygen per mole they range from 10.53 +/- 0.29 cm3 mol-1 (MgO) to 55.38 +/- 1.69 cm3 mol-1 (Cs2O).The present data, taken together with an estimate of the partial molar volume of water in these melts (13.1 +/- 1.3 cm3 mol-1) are recommended to be used to calculate the low pressure densities of leucogranitic and pegmatitic melts.