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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 相似文献
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High-Pressure Granulites (Retrograded Eclogites) from the Hengshan Complex, North China Craton: Petrology and Tectonic Implications 总被引:55,自引:1,他引:55
ZHAO GUOCHUN; CAWOOD PETER A.; WILDE SIMON A.; LU LIANGZHAO 《Journal of Petrology》2001,42(6):1141-1170
Both high- and medium-pressure granulites have been found asenclaves and boudins in tonalitictrondhjemiticgranodioriticgneisses in the Hengshan Complex. Petrological evidence fromthese rocks indicates four distinct metamorphic assemblages.The early prograde assemblage (M1) is preserved only in thehigh-pressure granulites and represented by quartz and rutileinclusions within the cores of garnet porphyroblasts, and omphacitepseudomorphs that are indicated by clinopyroxene + sodic plagioclasesymplectic intergrowths. The peak assemblage (M2) consists ofclinopyroxene + garnet + sodic plagioclase + quartz ±hornblende in the high-pressure granulites and orthopyroxene+ clinopyroxene + garnet + plagioclase + quartz in the medium-pressuregranulites. Peak metamorphism was followed by near-isothermaldecompression (M3), which resulted in the development of orthopyroxene+ clinopyroxene + plagioclase symplectites and coronas surroundingembayed garnet grains, and decompression-cooling (M4), representedby hornblende + plagioclase symplectites on garnet. The THERMOCALCprogram yielded peak (M2) PT conditions of 13·415·5kbar and 770840°C for the high-pressure granulitesand 911 kbar and 820870°C for the medium-pressuregranulites, based on the core compositions of garnet, matrixpyroxene and plagioclase. The PT conditions of pyroxene+ plagioclase symplectite and corona (M3) were estimated at 相似文献
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