Based on experimental data for reactions involving sapphirine in the system MgO–Al2O3–SiO2 (MAS), thermodynamic properties of the sapphirine solid solution end-members have been optimized for both ideal and non-ideal models, and internally consistent P–T grids are proposed. According to the calculated P–T relationships in MAS, the sapphirine + quartz assemblage, which is widely recognized as indicative of ultrahigh-temperature metamorphism, can be stable down to 840 ° C and 0.67 GPa, i.e., at temperatures up to 150 ° C lower than estimated by Kelsey et al. (2004). The sapphirine + kyanite assemblage has been found stable at temperatures below 860 ° C and 1.13 GPa, whereas the sapphirine + forsterite assemblage may be stable below 800 ° C only under specific conditions of a very low activity of water. Calculations of P–T relationships involving sapphirine using the Thermocalc dataset revealed its inconsistency with both experimental and natural assemblages.

You do not currently have access to this article.