| Abstract: | Consistent thermodynamic data on the properties of pure mineral end members and the mixing properties of solid solutions in
the system FeO-MgO-Al2O3-SiO2 were employed to simulate phase relations of sapphirine, garnet, spinel, orthopyroxene, cordierite, quartz, Al silicates,
and corundum. Compositional variations of the solid solutions with temperature notably modify the topology of the P-T diagrams, which differ from the petrogenetic grids widely used in the literature. It is worth noting that the evaluation
of P-T metamorphic conditions based on reaction relations in sapphirine-bearing assemblages cannot be so far considered reliable
enough. The lower stability limit of the sapphirine + quartz assemblage in the system in question is possibly located at much
lower P-T parameters: at least 835°C and ∼6 kbar. The sapphirine + kyanite assemblage can be stable at temperatures below 860°C and
a pressure of ∼11 kbar, and the stability field of the sapphirine + olivine assemblage is narrow and constrained to temperatures
no higher than ∼800°C. |
