Journal Article

Recalibration of the Garnet–Muscovite (GM) Geothermometer and the Garnet–Muscovite–Plagioclase–Quartz (GMPQ) Geobarometer for Metapelitic Assemblages

CHUN-MING WU and GUOCHUN ZHAO

in Journal of Petrology

Volume 47, issue 12, pages 2357-2368
ISSN: 0022-3530
Published online September 2006 | e-ISSN: 1460-2415 | DOI: http://dx.doi.org/10.1093/petrology/egl047
Recalibration of the Garnet–Muscovite (GM) Geothermometer and the Garnet–Muscovite–Plagioclase–Quartz (GMPQ) Geobarometer for Metapelitic Assemblages

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The garnet–muscovite (GM) geothermometer and the garnet–muscovite–plagioclase–quartz (GMPQ) geobarometer have been simultaneously calibrated under conditions of T = 450–760°C and P = 0·8–11·1 kbar, using a large number of metapelitic samples in the compositional ranges [math] = 0·53–0·81, [math] = 0·05–0·24, [math] = 0·03–0·23 in garnet, [math] = 0·17–0·74 in plagioclase, and Fe = 0·04–0·16, Mg = 0·04–0·13, AlVI = 1·74–1·96 in muscovite on the basis of 11 oxygens. The resulting GM thermometer yielded similar temperature estimates (mostly within ±50°C) to that of the garnet–biotite 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 garnet–aluminum silicate–plagioclase–quartz (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 P–T conditions may be determined by simultaneously applying the GM thermometer and the GMPQ barometer.

Keywords: application; calibration; geobarometer; geothermometer; metapelite

Journal Article.  5094 words.  Illustrated.

Subjects: Petrology

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