Dry melting of high albite

The properties of albitic melts are central to thermodynamic models for syn thetic and natural granitic liquids. We have analyzed published phase-equil ibrium and thermodynamic data for the dry fusion of high albite to develop a more accurate equation for the Gibbs free energy of this reaction to 30 k bar and 1400 degrees C. Strict criteria for reaction reversal were used to evaluate the phase-equilibrium data, and the thermodynamic properties of so lid and liquid albite were evaluated using the published uncertainties in t he original measurements. Results suggest that neither available phase-equi librium experiments nor thermodynamic data tightly constrain the location o f the reaction. Experimental solidus temperatures at 1 atm range from 1100 to 1120 degrees C. High-pressure experiments were not reversed completely a nd may have been affected by several sources of error, but the apparent inc onsistencies among the results of the various experimentalists are eliminat ed when only half-reversal data are considered. Uncertainties in thermodyna mic data yield large variations in permissible reaction slopes. Disparities between experimental and calculated melting curves are, therefore, largely attributable to these difficulties, and there is no fundamental disagreeme nt between the available phase-equilibrium and thermodynamic data for the d ry melting of albite. Consequently, complex speciation models for albitic m elts, based on the assumption that these discrepancies represent a real cha racteristic of the system, are unjustified at this time.