Recalibration of the Garnet-Muscovite (GM) Geothermometer and the Garnet-Muscovite-Plagioclase-Quartz (GMPQ) Geobarometer for Metapelitic Assemblages |
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Authors: | WU CHUN-MING; ZHAO GUOCHUN |
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Institution: | 1 LABORATORY OF COMPUTATIONAL GEODYNAMICS, THE GRADUATE SCHOOL CHINESE ACADEMY OF SCIENCES, P.O. BOX 4588, BEIJING 100049, CHINA
2 DEPARTMENT OF EARTH SCIENCES, THE UNIVERSITY OF HONG KONG POKFULAM ROAD, HONG KONG, CHINA |
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Abstract: | The garnetmuscovite (GM) geothermometer and the garnetmuscoviteplagioclasequartz(GMPQ) geobarometer have been simultaneously calibrated underconditions of T = 450760°C and P = 0·811·1kbar, using a large number of metapelitic samples in the compositionalranges = 0·530·81, = 0·050·24, = 0·030·23 in garnet, = 0·170·74 in plagioclase, and Fe = 0·040·16, Mg =0·040·13, AlVI = 1·741·96in muscovite on the basis of 11 oxygens. The resulting GM thermometeryielded similar temperature estimates (mostly within ±50°C)to that of the garnetbiotite thermometer, and successfullydiscerned the expected systematic temperature change of progradesequences, thermal contact zones and an inverted metamorphiczone. The resulting GMPQ barometer yielded similar pressureestimates (mostly within ±1·0 kbar) to the garnetaluminumsilicateplagioclasequartz (GASP) barometer andplaced the aluminosilicate-bearing samples in the appropriatealuminosilicate stability fields. Application of the GMPQ barometerto thermal contact aureoles or rocks within limited geographicalareas confirmed the expected constant pressures that shouldexist in these settings. The random errors of the GM thermometerand the GMPQ barometer are estimated to be ±16°Cand ±1·5 kbar, respectively. When biotite or aluminosilicateis absent in metapelites, metamorphic PT conditions maybe determined by simultaneously applying the GM thermometerand the GMPQ barometer. KEY WORDS: application; calibration; geobarometer; geothermometer; metapelite |
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Keywords: | : application calibration geobarometer geothermometer metapelite |
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