Two-stage corona growth during Precambrian granulite facies metamorphism of Smitbson Bjerge, north-west Greenland |
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| Authors: | ADAM A GARDE WILLIAM E GLASSLEY ALLEN P NUTMAN |
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| Institution: | Geological Survey of Greenland. Oster Voldgade 10, 1350 Kohenhavn K, Denmark; Middlebury College, Middlebury, VT 05753. USA; Geological Survey of Greenland. Θster Voldgade 10, 1350 Kobenhavn K. Denmark |
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| 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. |
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| Keywords: | Key-words: coronas fluctuation in chemical activity geothermobarometry granulite facies metamorphism north-west Greenland overprinting |
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