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Two‐stage corona growth during Precambrian granulite facies metamorphism of Smitbson Bjerge, north‐west Greenland
Author(s) -
GARDE ADAM A.,
GLASSLEY WILLIAM E.,
NUTMAN ALLEN P.
Publication year - 1984
Publication title -
journal of metamorphic geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.639
H-Index - 114
eISSN - 1525-1314
pISSN - 0263-4929
DOI - 10.1111/j.1525-1314.1984.tb00298.x
Subject(s) - granulite , geology , metamorphism , geochemistry , proterozoic , precambrian , facies , archean , metamorphic facies , anorthosite , petrology , geomorphology , paleontology , structural basin , quartz , plagioclase , tectonics
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.