Permo-Triassic ultrahigh-temperature metamorphism in the Kontum massif, central Vietnam
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Accession number;04A0874351
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| Title;Permo-Triassic ultrahigh-temperature metamorphism in the Kontum massif, central Vietnam |
| Author;
OSANAI Y
(Kyushu Univ., Fukuoka, Jpn)
NAKANO N
(Kyushu Univ., Fukuoka, Jpn)
OWADA M
(Yamaguchi Univ., Yamaguchi, Jpn)
NAM T N
(Hue Univ. Sci., Hue, Vnm)
TOYOSHIMA T
(Niigata Univ., Niigata, Jpn)
TSUNOGAE T
(Univ. Tsukuba, Tsukuba, Jpn)
BINH P
(Res. Inst. Geology And Mineral Resources, Hanoi, Vnm)
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Journal Title;J Mineral Petrol Sci
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Journal Code:G0150B
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ISSN:1345-6296
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VOL.99;NO.4;PAGE.225-241(2004)
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| Figure&Table&Reference;FIG.9, TBL.3, REF.48 |
| Pub. Country;Japan |
| Language;English |
| Abstract;The Kontum massif in central Vietnam consists of low-grade schists and amphibolite- to granulite-facies metamorphic rocks, that have been intruded by S-type and I-type granites. This terrane was formerly considered to be composed mainly of Archean granulites (the Kannak Complex), Proterozoic amphibolite-facies metamorphic rocks (the Ngoc Linh Complex) and low-grade schists (the Kham Duc Complex). They were thought to be the basement of the indochina Craton in south-east Asia. The Kannak Complex is dominated by pelitic-semipelitic gneisses metamorphosed under high- to ultrahigh-temperature (UHT) conditions into granulite-facies. A minor amount of mafic and calc-silicate rocks are also intercalated within the gneisses. The major types of ultrahigh-temperature pelitic metamorphic rocks in this complex are garnet-orthopyroxene-sillimanite-cordierite gneiss, orthopyroxene-bearing garnet-cordierite-silliamnite-biotite gneiss and garnet-orthopyroxene charnockitic gneiss. The highest-grade metamorphic condition is determined from garnet -orthopyroxene-sillimanite-cordierite gneiss, which indicates that multi-stage symplectite formation during retrograde stage started from isothermal decompression in UHT condition (1000.DEG.C.<). Because of the high amount of pyrope (up to 59 mole%) in garnet and high-Al2O3 in orthopyroxene (up to 10wt%), these minerals were unstable in the P-T conditions during the retrograde stage. On the other hand, the newly found garnet-clinopyroxene-orthopyroxene granulites (eclogitic ultrahigh-temperature mafic granulite) from the Ngoc Linh Complex shows a series of changes in divariant assemblages from garnet-clinopyroxene-quartz to hornblende-quartz through clinopyroxene-orthopyroxene-plagioclase-(garnet). It was identified that these rocks were formed as a result of their metamorphic evolution of isothermal decompression followed by nearly isobaric cooling.... (author abst.) |
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