Pages: 283 - 293
Abstract: Cordierite, as a product of Variscan regional metamorphism and exhumation, has been recognized in the migmatitic metapelites of the Western Tatra Mountains, Western Carpathians. The following cordierite-producing reactions have been deduced from reaction textures and phase equilibria in the system KFMASH: a) garnet decomposition according to the reaction garnet + sillimanite + quartz + fluid = cordierite during decompression at a temperature of ~700 °C down to a pressure of ~5 kbar; b) dehydration-melting of biotite by the reaction biotite + sillimanite + quartz = cordierite + K-feldspar + melt due to further pressure drop to ~4 kbar at a constant, or increasing temperature to ~750 °C; c) melt crystallization in the leucosomes according to the reaction melt = cordierite + quartz + K-feldspar + biotite + fluid, during cooling. Cordierite pinitization and its replacement by fine grained phengitic white mica and pale green Mg-rich biotite according to the reactions cordierite + sillimanite + K-feldspar + fluid = phengitic muscovite + quartz and cordierite + K-feldspar + fluid = biotite + sillimanite + quartz took place during subsolius retrogression at a temperature of ~ 600 °C and pressure of ~3 kbar. The origin of cordierite was also controlled by the local, more magnesian bulk composition of cordierite-bearing metapelites. The presence of cordierite is indicative of a high-temperature/low-pressure stage during the Variscan orogenic collapse in the pre-Alpine basement of the Western Carpathians.
Keywords: Variscan orogen, Western Tatra Mountains, dehydration-melting, migmatites, cordieriteDownload PDF document Show Text Version