STABILITY FIELD OF ALUMINIUM SILICATE POLYMORPHS*

Abstract – Andalusite, kyanite and sillimanite occur in well-defined zones in the Ardara aureole, NW Ireland. Temperature and pressure conditions of the Al2SiO5-bearing pelites in this aureole were estimated using ten different calibrations of garnet-biotite thermometry and five calibrations of garnet-plagioclase-Al2SiO5-quartz barometry. The different calibrations provide different estimates of temperature and pressure. However, using the most recent, and the best reversed experimental data give temperatures varying from 510 to 605 ºC, and a pressure of around 4 kbar across the Ardara aureole. The calculated temperatures for the analyzed samples are compared with published andalusite=sillimanite equilibria, and these equilibria are evaluated in the Ardara aureole