Journal of Petrology Advance Access originally published online on September 21, 2006
Journal of Petrology 2006 47(12):2357-2368; doi:10.1093/petrology/egl047
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Recalibration of the GarnetMuscovite (GM) Geothermometer and the GarnetMuscovitePlagioclaseQuartz (GMPQ) Geobarometer for Metapelitic Assemblages
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
RECEIVED NOVEMBER 27, 2005; ACCEPTED AUGUST 15, 2006
| Abstract |
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The garnetmuscovite (GM) geothermometer and the garnetmuscoviteplagioclasequartz (GMPQ) geobarometer have been simultaneously calibrated under conditions of T = 450760°C and P = 0·811·1 kbar, using a large number of metapelitic samples in the compositional ranges
= 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 = 1·741·96 in muscovite on the basis of 11 oxygens. The resulting GM thermometer yielded similar temperature estimates (mostly within ±50°C) to that of the garnetbiotite thermometer, and successfully discerned the expected systematic temperature change of prograde sequences, thermal contact zones and an inverted metamorphic zone. The resulting GMPQ barometer yielded similar pressure estimates (mostly within ±1·0 kbar) to the garnetaluminum silicateplagioclasequartz (GASP) barometer and placed the aluminosilicate-bearing samples in the appropriate aluminosilicate stability fields. Application of the GMPQ barometer to thermal contact aureoles or rocks within limited geographical areas confirmed the expected constant pressures that should exist in these settings. The random errors of the GM thermometer and the GMPQ barometer are estimated to be ±16°C and ±1·5 kbar, respectively. When biotite or aluminosilicate is absent in metapelites, metamorphic PT conditions may be determined by simultaneously applying the GM thermometer and the GMPQ barometer.
KEY WORDS: application; calibration; geobarometer; geothermometer; metapelite
*Corresponding author. Telephone: +86-10-8825-6312. Fax: +86-10-8825-6012. E-mail: wucm{at}gucas.ac.cn
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