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Sapphirine-bearing assemblages in the system MgO–Al₂O₃–SiO₂: a continuing ambiguity

¹ Institute of Experimental Mineralogy, Russian Academy of Sciences, 142432 Chernogolovka, Moscow, Russia
² Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry (IGEM), Russian Academy of Sciences, Staromonetny per. 35, 119017 Moscow, Russia
³ Institute of Geophysics, Department of Geosciences, Swiss Federal Institute of Technology (ETH – Zürich), ETH – Hönggerberg, HPP, 8093 Zürich, Switzerland

^* Corresponding author, e-mail: kkp{at}iem.ac.ru

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.

Key-words: sapphirine, MgO–Al₂O₃–SiO₂, thermodynamic data, ultrahigh-temperature metamorphism.

This article has been cited by other articles:

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