Sapphirine-bearing assemblages in the system MgOAl2O3SiO2: a continuing ambiguity
Podlesskii, Konstantin K.; Aranovich, Leonid Y.; Gerya, Taras V.; Kosyakova, Natalia A.
European Journal of Mineralogy Volume 20 Number 5 (2008), p. 721 - 734
published: Nov 5, 2008
ArtNo. ESP147052005004, Price: 29.00 €
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.