Abstract

The 1bar, thermodynamic properties of crystalline and liquid NaAlSi3O8 are used to calculate the fusion curve of albite to 10 kbar. The calculated temperatures (±2σ) of the melting reaction are 1152 (±7) °C at 3 kbar and 1247 (±24) °C at 10 kbar. The location of the calculated fusion curve to 10 kbar is in excellent agreement with phase-equilibrium constraints on the maximum and minimum temperatures of the fusion curve at 3 and 15 kbar, respectively. Calculation of the melting reaction at pressures >10 kbar requires that the pressure dependence of the liquid compressibility (K0′ = dKT,0/dP, where KT,0 = 1/βT,0) be known. On the basis of five half-reversal, crystallization experiments in the literature, which collectively provide minimum temperatures of the fusion curve between 12 and 32 kbar, K0′ (derived from the Birch-Murnaghan relation) is constrained to be ≥10 for liquid NaAlSi3O8. A comparison with other silicate liquids shows that there is a strong, positive correlation between the compressibility at one bar (βT,0) and K0′. In addition, data on the water-saturated fusion curve of albite are used to quantify the effect of small amounts of H2O (≤1 wt%) on lowering the melting temperature of albite (≤68 degrees).

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