Abstract
Summary Experimental data on equilibria involving rock-forming minerals in high-grade metapelites (garnet, orthopyroxene, cordierite and plagioclase) have been used to derive an internally consistent system of mineralogical thermometers and barometers based on component reactions and excess mixing properties of solid solutions. Application of these data to a granulite-facies metapelite sample reveals that compositional inhomogeneity of minerals on a thin-section scale is likely to be a result of several reactions opening simultaneously at the retrograde stage of metamorphic evolution. The widely accepted practice of estimating pressure and temperature from separate reactions may thus lead to errors and misinterpretation of P-T paths.
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