Abstract
Abstract Late Archaean orthogneisses and aluminous and iron‐rich metasedimentary rocks intruded by anorthosite and a ferrodiorite‐granite suite were completely recrystallized during Proterozoic granulite facies metamorphism. Geobarometry and geothermometry indicate P‐T conditions of around 7.5kbar. 700°C, with a CO2‐rich fluid phase and logfO2 at or below ‐16. A two‐stage high‐grade history of near isochemical corona growth is preserved in metasediments with the reaction cycle opx + plag + H2O → hbl+gar+SiO2→ opx+plag+H2O. End product compositions resemble those of the initial phases, and the only mobile components were SiO2 and/or H2O. The coronas reflect shortlived fluctuations in chemical activity at essentially constant P and T, contrary to simple progressive change in equilibrium parameters recorded by most corona‐bearing textures.
Published Version
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