Zircon solubility in silicate melts: New empirical models and thermodynamics

Published experimental data on zircon (Zrn) solubility in silicate melts are critically evaluated to conclude that H₂O dissolved in the melts has no to minor effect on the Zrn solubility. The effect of pressure is small but resolvable. A new empirical equation describing zircon solubility in silicate melts as a function of temperature, pressure and melt composition, is derived based on the published experimental data. The new equation predicts log Zr (ppm) in the melts with a standard error of 0.087, which is equivalent to ca. 22 % error in the range from 178 to 61,370 ppm Zr, 750-1500 °C, and 0.001–25 kbar covered by the experiments. A new equation describing the relatively low-temperature range 750-1200 °C, more appropriate for application to natural magmatic rocks, is also suggested.

The new equation for temperature dependence of the standard Gibbs free energy of zircon melting reaction is derived for the first time. The equation is consistent with the high temperature phase diagram of the ZrO₂-SiO₂ system and predicts metastable zircon fusion temperature at T_fus = 2232 K. This equation is silicate melt model independent. Thermodynamic mixing properties of the zircon species in silicate melts consistent with the MELTS thermodynamic model retrieved by fitting 186 experimental data points, agree qualitatively with the empirical formulation and simple equations suggested by Bruce Watson and co-workers.