Triassic eclogite from northern Vietnam: Inferences and geological significance

Nobuhiko Nakano, Yasuhito Osanai, K. Sajeev, Y. Hayasaka, Tomoharu Miyamoto, N. T. Minh, M. Owada, B. Windley

研究成果: ジャーナルへの寄稿記事

72 引用 (Scopus)

抄録

The first finding of low-temperature eclogites from the Indochina region is reported. The eclogites occur along the Song Ma Suture zone in northern Vietnam, which is widely regarded as the boundary between the South China and Indochina cratons. The major lithology of the area is pelitic schist that contains garnet and phengite with or without biotite, chloritoid, staurolite and kyanite, and which encloses blocks and lenses of eclogite and amphibolite. The eclogites commonly consist of garnet, omphacite, phengite, rutile, quartz and/or epidote with secondary barroisite. Omphacite is commonly surrounded by a symplectite of Na-poor omphacite and Na-rich plagioclase. In highly retrograded domains, diopside + tremolite + plagioclase symplectites replace the primary phases. Estimated peak-pressure metamorphic conditions based on isochemical phase diagrams for the eclogites are 2.1-2.2 GPa and 600-620 °C, even though thermobarometric results yield higher pressure and temperature conditions (2.6-2.8 GPa and 620-680 °C). The eclogites underwent a clockwise P-T trajectory with a post-peak-pressure increase of temperature to a maximum of >750 °C at 1.7 GPa and a subsequent cooling during decompression to 650 °C and 1.3 GPa, which was followed by additional cooling before close-to-isothermal decompression to ∼530 °C at 0.5 GPa. The surrounding pelitic schist (garnet-chloritoid-phengite) records similar metamorphic conditions (580-600 °C at 1.9-2.3 GPa) and a monazite chemical age of 243 ± 4 Ma. A few monazite inclusions within garnet and the cores of some zoned monazite in garnet-phengite schist record an older thermal event (424 ± 15 Ma). The present results indicate that the Indochina craton was deeply (>70 km) subducted beneath the South China craton in the Triassic. The Silurian cores of monazite grains may relate to an older non-collisional event in the Indochina craton.

元の言語英語
ページ(範囲)59-76
ページ数18
ジャーナルJournal of Metamorphic Geology
28
発行部数1
DOI
出版物ステータス出版済み - 1 1 2010

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Garnets
eclogite
phengite
monazite
garnet
Triassic
omphacite
craton
schist
chloritoid
decompression
plagioclase
symplectite
Cooling
cooling
tremolite
Quartz
staurolite
Lithology
kyanite

All Science Journal Classification (ASJC) codes

  • Geology
  • Geochemistry and Petrology

これを引用

Triassic eclogite from northern Vietnam : Inferences and geological significance. / Nakano, Nobuhiko; Osanai, Yasuhito; Sajeev, K.; Hayasaka, Y.; Miyamoto, Tomoharu; Minh, N. T.; Owada, M.; Windley, B.

:: Journal of Metamorphic Geology, 巻 28, 番号 1, 01.01.2010, p. 59-76.

研究成果: ジャーナルへの寄稿記事

Nakano, Nobuhiko ; Osanai, Yasuhito ; Sajeev, K. ; Hayasaka, Y. ; Miyamoto, Tomoharu ; Minh, N. T. ; Owada, M. ; Windley, B. / Triassic eclogite from northern Vietnam : Inferences and geological significance. :: Journal of Metamorphic Geology. 2010 ; 巻 28, 番号 1. pp. 59-76.
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AU - Nakano, Nobuhiko

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AU - Owada, M.

AU - Windley, B.

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N2 - The first finding of low-temperature eclogites from the Indochina region is reported. The eclogites occur along the Song Ma Suture zone in northern Vietnam, which is widely regarded as the boundary between the South China and Indochina cratons. The major lithology of the area is pelitic schist that contains garnet and phengite with or without biotite, chloritoid, staurolite and kyanite, and which encloses blocks and lenses of eclogite and amphibolite. The eclogites commonly consist of garnet, omphacite, phengite, rutile, quartz and/or epidote with secondary barroisite. Omphacite is commonly surrounded by a symplectite of Na-poor omphacite and Na-rich plagioclase. In highly retrograded domains, diopside + tremolite + plagioclase symplectites replace the primary phases. Estimated peak-pressure metamorphic conditions based on isochemical phase diagrams for the eclogites are 2.1-2.2 GPa and 600-620 °C, even though thermobarometric results yield higher pressure and temperature conditions (2.6-2.8 GPa and 620-680 °C). The eclogites underwent a clockwise P-T trajectory with a post-peak-pressure increase of temperature to a maximum of >750 °C at 1.7 GPa and a subsequent cooling during decompression to 650 °C and 1.3 GPa, which was followed by additional cooling before close-to-isothermal decompression to ∼530 °C at 0.5 GPa. The surrounding pelitic schist (garnet-chloritoid-phengite) records similar metamorphic conditions (580-600 °C at 1.9-2.3 GPa) and a monazite chemical age of 243 ± 4 Ma. A few monazite inclusions within garnet and the cores of some zoned monazite in garnet-phengite schist record an older thermal event (424 ± 15 Ma). The present results indicate that the Indochina craton was deeply (>70 km) subducted beneath the South China craton in the Triassic. The Silurian cores of monazite grains may relate to an older non-collisional event in the Indochina craton.

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