Two‐stage corona growth during Precambrian granulite facies metamorphism of Smitbson Bjerge, north‐west Greenland

• Published in: Journal of Metamorphic Geology
• Main Authors: GARDE, ADAM A., GLASSLEY, WILLIAM E., NUTMAN, ALLEN P.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1984
• Subjects: Gar’; Greenland
• Online Access: http://dx.doi.org/10.1111/j.1525-1314.1984.tb00298.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1525-1314.1984.tb00298.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1525-1314.1984.tb00298.x

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 CO 2 ‐rich fluid phase and logfO 2 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 + H 2 O → hbl+gar+SiO 2 → opx+plag+H 2 O. End product compositions resemble those of the initial phases, and the only mobile components were SiO 2 and/or H 2 O. 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.