Using calculated chemical potential relationships to account for replacement of kyanite by symplectite in high pressure granulites

Abstract

Calculated mineral equilibria are used to account for the formation of sapphirine-plagioclase, spinel-plagioclase and corundum-plagioclase symplectites replacing kyanite in quartz-plagioclase-garnet-kyanite granulite facies gneisses from the Southern Domain of the Athabasca granulite terrane, a segment of the Snowbird tectonic zone in northern Saskatchewan, Canada. Metamorphic conditions of >14 kbar and 800 °C are established for the high pressure, garnet-kyanite assemblage using constraints from P-T pseudosections and Zr-in-rutile thermometry. Replacement of kyanite by symplectites reflects the reaction of kyanite with the matrix following near-isothermal decompression to <10 kbar. The chem..