Al zoning in pyroxene and plagioclase: window on late prograde to early retrograde P-T paths in granulite terranes

Al-zoning data may be used to examine that part of the granulite P-T path along which pyroxene grew. The slope of the log K curves for the reaction CaTs + quartz = anorthite is negative below 20 kbar whereas that for jadeite + quartz = albite is positive, and the two may be combined to yield both pressure and temperature. A subregular quaternary activity model for the system CaTs-jadeite-diopside-hedenbergite was fitted for these calculations. Data for the following four granulite terranes were examined: the Grenville Province, Ontario; the Furua Complex, Tanzania; the Fiordland complex; the Pikwitonei area, Manitoba. -from Author