| Project/Area Number |
14340150
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Geology
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| Research Institution | Kyushu University (2004)
Okayama University (2002-2003) |
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Principal Investigator |
OSANAI Yasuhito Kyushu University, Graduate School of Social and Cultural Studies, Professor, 大学院・比較社会文化研究院, 教授 (80183771)
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| Co-Investigator(Kenkyū-buntansha) |
ITAYA Tetsumaru Okayama University of Science, Research Inst Natural Sc., Professor, 自然科学研究所, 教授 (60148682)
OWADA Masaaki Yamaguchi University, Faculty of Science, Associate Professor, 理学部, 助教授 (50213905)
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| Project Period (FY) |
2002 – 2004
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| Project Status |
Completed (Fiscal Year 2004)
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| Budget Amount *help |
¥13,500,000 (Direct Cost: ¥13,500,000)
Fiscal Year 2004: ¥3,700,000 (Direct Cost: ¥3,700,000)
Fiscal Year 2003: ¥3,400,000 (Direct Cost: ¥3,400,000)
Fiscal Year 2002: ¥6,400,000 (Direct Cost: ¥6,400,000)
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| Keywords | Vitnam / Kontum Massif / ultrahigh-temperature metamorphism / ultrahigh-pressure metamorphism / metamorphic evolution / precise geochronology / collision metamorphism / super-continent formation / SHRIMP年代測定 / 衝突型変成作用 / 超高温泥質グラニュライト / 苦鉄質エクロジャイト / 時計回りの変成履歴 / スリランカ / ゴンドワナ超大陸 / 超高温変成岩 / 等温減圧過程 / エクロジャイロ相 / グラニュライト相 / 衝突帯型変成作用 / 同位体年代 |
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| Research 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 calcsilicate rocks are also intercalated within the gneisses. 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 ℃<). On the other hand,
… More
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.
The ultrahigh-temperature metamorphic rocks in the Kontum massif, which are exposed along the Dac To Kan shear zone, show a clockwise pressure-temperature path with the peak metamorphic condition of ca. 1.2 GPa and ca. 1050 ℃ (M1 metamorphism). High-pressure M0 metamorphism (ca. 1.7 GPa<, ca. 1000 ℃) as part of the prograde metamorphism and low-pressure (but still ultrahigh-temperature) M2 metamorphism (0.9-1.0 GPa,ca. 1000 ℃) as part of the retrograde metamorphism during the clockwise pressure-temperature evolution are also recognized. The widely reported Permo-Triassic metamorphic event (ca. 240-260 Ma) from the ultrahigh-temperature metamorphic rocks would indicate a rapid metamorphic evolution from M0 stage to low-pressure and low-temperature retrograde stage (later M2 stage) during the continents collision in eastern Asia. The newly determined Sm-Nd internal isochron and SHRIMP ages from the Kannak and Ngoc Linh Complexes would also indicate that the Kontum massif had also undergone the Pan African metamorphic event (ca. 2.5,1.0 and 0.5 Ga). The present results of the metamorphic evolution of the Kontum massif including 41 journal papers indicate a strong constraint to consider the coninental evolution process in Eastern Asia. Less
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