The fusion curve of albite revisited and the compressibility of NaAlSi3O8 liquid with pressure

The 1 bar, thermodynamic properties of crystalline and liquid NaAlSi3O8 are used to calculate the fusion curve of albite to 10 kbar. The calculated temperatures (+/-2sigma) of the melting reaction are 1152 (+/-7) degreesC at 3 kbar and 1247 (+/-24) degreesC 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 (K-0' = dK(T,0/dP), dP, where K-T,K-0 = 1/beta(T,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, K-0' (derived from the Birch-Murnaghan relation) is constrained to be greater than or equal to10 for liquid NaAlSi3O8. comparison with other silicate liquids shows that there is a strong, positive correlation between the compressibility at one bar (beta(T,0)) and K-0'. In addition, data on the water-saturated fusion curve of albite are used to quantify the effect of small amounts of H2O (less than or equal to1 wt%) on lowering the melting temperature of albite (less than or equal to68 degrees).