Abstract

Experimental brackets on the melting temperature of high albite (NaAlSi3O8) were determined at 2.33 ± 0.03 GPa (1360–1370 °C) and 2.79 ± 0.03 GPa (1370–1389 °C) in a piston-cylinder apparatus. All run products that quenched to a glass were analyzed by Fourier-transform infrared spectroscopy and found to contain ≤500 ppm H2O. In addition, new X-ray diffraction experiments on fully disordered albite are reported to 7.6 GPa; the fitted results lead to a zero-pressure bulk modulus (K0) of 56.4 ± 0.7 and a pressure derivative (K0) of 3.9 ± 0.3 in a third-order Birch-Murnaghan equation of state. Revised values for the enthalpy and entropy of fusion of high albite at one bar and 1100 °C [ΔHTf = 64.5 ± 2.1 kJ/mol and ΔSTf = 47.0 J/(mol·K)] are recommended on the basis of improved heat capacity equations for NaAlSi3O8 glass and liquid. On the basis of these new results on the fusion curve and thermodynamic data for high albite, the pressure dependence of the NaAlSi3O8 liquid compressibility (K0) is constrained to be 10.8 ± 1.5 in a third-order Birch-Murnaghan equation of state. The uncertainty in K0 of ±1.5 contributes an error to melt density at 3 GPa (2.543 ± 0.010 g/cm3 at 1500 °C) of ±0.4%.

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