Bauxite to eclogite

Evidence for late Permian supracontinental subduction at the Red River shear zone, northern Vietnam

Nobuhiko Nakano, Yasuhito Osanai, Nguyen Van Nam, Tran Van Tri

研究成果: ジャーナルへの寄稿記事

3 引用 (Scopus)

抄録

We have investigated the geological processes recorded in aluminous granulites from the Red River shear zone in northern Vietnam using mineral and whole-rock chemistries, fluid inclusions, metamorphic pressure–temperature paths, and geochronology. The granulites are extremely rich in Al2O3 (36.3–50.9 wt%), TiO2, and total Fe2O3, and poor in SiO2 (7.9–24.1 wt%), MgO, CaO, Na2O, and K2O. The granulites are enriched in high-field-strength elements and rare earth elements, and severely depleted in large-ion lithophile elements. These features strongly suggest the protolith was lateritic bauxite. Moreover, the other elemental concentrations and the Zr/Ti ratios point to basaltic rock as the precursor of the bauxite. Some of the aluminous granulites contain high-pressure mineral inclusions of kyanite, staurolite, siderite, and rutile, none of which are observed in the matrix. Abundant primary carbonic fluid inclusions are observed in garnet, corundum, and staurolite, but are rare in quartz and zircon. The average densities of fluid inclusions in garnet, corundum, staurolite, quartz, and zircon are 1.00 ± 0.06, 1.07 ± 0.04, 1.09 ± 0.03, 0.29 ± 0.07, and 1.15 ± 0.05 g/cm3, respectively. The mineral features not only in the matrix and but also in garnet from all rock types, isochemical phase diagrams obtained for each bulk rock composition, and Zr-in-rutile thermometry indicate an early eclogite-facies metamorphism (~ 2.5 GPa at 650 °C) and a subsequent nearly isothermal decompression. Zircons yield a wide range of U–Pb ages from 265 to 36 Ma, whereas the dark luminescent cores of the zircons, which contain high-density CO2 inclusions, yield a concordia age of 257 ± 8 Ma. These observations suggest that the dark luminescent zircon cores were formed at the same time as the garnet, corundum, and staurolite that contain high-density CO2 fluid inclusions. Based on the carbonic fluid inclusion isochore and the densities as well as calculated phase diagram, the concordia age can be regarded as recording a prograde stage of metamorphism under conditions lower than 600 °C and 0.7 GPa. Our new data provide the following geological and tectonic constraints: 1) the eruption of basalt occurred before the Permian, possibly related to subduction of the Paleo-Tethys Plate beneath the Indochina craton near the paleo-equator in the Devonian–Carboniferous; 2) strong weathering transformed the basalt to bauxite before the late Permian; 3) the uppermost continental crust, including the bauxites, was subducted in the late Permian due to the collision of the Indochina and South China cratons, leading to eclogite-facies metamorphism; 4) the rocks were then exhumed; and 5) shearing-related thermal events took place until the Paleogene.

元の言語英語
ページ(範囲)37-49
ページ数13
ジャーナルLithos
302-303
DOI
出版物ステータス出版済み - 3 1 2018

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Aluminum Oxide
bauxite
eclogite
staurolite
fluid inclusion
shear zone
Permian
zircon
subduction
Rivers
corundum
garnet
Garnets
Rocks
river
metamorphism
rock
Fluids
rutile
Minerals

All Science Journal Classification (ASJC) codes

  • Geochemistry and Petrology

これを引用

Bauxite to eclogite : Evidence for late Permian supracontinental subduction at the Red River shear zone, northern Vietnam. / Nakano, Nobuhiko; Osanai, Yasuhito; Nam, Nguyen Van; Tri, Tran Van.

:: Lithos, 巻 302-303, 01.03.2018, p. 37-49.

研究成果: ジャーナルへの寄稿記事

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title = "Bauxite to eclogite: Evidence for late Permian supracontinental subduction at the Red River shear zone, northern Vietnam",
abstract = "We have investigated the geological processes recorded in aluminous granulites from the Red River shear zone in northern Vietnam using mineral and whole-rock chemistries, fluid inclusions, metamorphic pressure–temperature paths, and geochronology. The granulites are extremely rich in Al2O3 (36.3–50.9 wt{\%}), TiO2, and total Fe2O3, and poor in SiO2 (7.9–24.1 wt{\%}), MgO, CaO, Na2O, and K2O. The granulites are enriched in high-field-strength elements and rare earth elements, and severely depleted in large-ion lithophile elements. These features strongly suggest the protolith was lateritic bauxite. Moreover, the other elemental concentrations and the Zr/Ti ratios point to basaltic rock as the precursor of the bauxite. Some of the aluminous granulites contain high-pressure mineral inclusions of kyanite, staurolite, siderite, and rutile, none of which are observed in the matrix. Abundant primary carbonic fluid inclusions are observed in garnet, corundum, and staurolite, but are rare in quartz and zircon. The average densities of fluid inclusions in garnet, corundum, staurolite, quartz, and zircon are 1.00 ± 0.06, 1.07 ± 0.04, 1.09 ± 0.03, 0.29 ± 0.07, and 1.15 ± 0.05 g/cm3, respectively. The mineral features not only in the matrix and but also in garnet from all rock types, isochemical phase diagrams obtained for each bulk rock composition, and Zr-in-rutile thermometry indicate an early eclogite-facies metamorphism (~ 2.5 GPa at 650 °C) and a subsequent nearly isothermal decompression. Zircons yield a wide range of U–Pb ages from 265 to 36 Ma, whereas the dark luminescent cores of the zircons, which contain high-density CO2 inclusions, yield a concordia age of 257 ± 8 Ma. These observations suggest that the dark luminescent zircon cores were formed at the same time as the garnet, corundum, and staurolite that contain high-density CO2 fluid inclusions. Based on the carbonic fluid inclusion isochore and the densities as well as calculated phase diagram, the concordia age can be regarded as recording a prograde stage of metamorphism under conditions lower than 600 °C and 0.7 GPa. Our new data provide the following geological and tectonic constraints: 1) the eruption of basalt occurred before the Permian, possibly related to subduction of the Paleo-Tethys Plate beneath the Indochina craton near the paleo-equator in the Devonian–Carboniferous; 2) strong weathering transformed the basalt to bauxite before the late Permian; 3) the uppermost continental crust, including the bauxites, was subducted in the late Permian due to the collision of the Indochina and South China cratons, leading to eclogite-facies metamorphism; 4) the rocks were then exhumed; and 5) shearing-related thermal events took place until the Paleogene.",
author = "Nobuhiko Nakano and Yasuhito Osanai and Nam, {Nguyen Van} and Tri, {Tran Van}",
year = "2018",
month = "3",
day = "1",
doi = "10.1016/j.lithos.2017.12.023",
language = "English",
volume = "302-303",
pages = "37--49",
journal = "Lithos",
issn = "0024-4937",
publisher = "Elsevier",

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TY - JOUR

T1 - Bauxite to eclogite

T2 - Evidence for late Permian supracontinental subduction at the Red River shear zone, northern Vietnam

AU - Nakano, Nobuhiko

AU - Osanai, Yasuhito

AU - Nam, Nguyen Van

AU - Tri, Tran Van

PY - 2018/3/1

Y1 - 2018/3/1

N2 - We have investigated the geological processes recorded in aluminous granulites from the Red River shear zone in northern Vietnam using mineral and whole-rock chemistries, fluid inclusions, metamorphic pressure–temperature paths, and geochronology. The granulites are extremely rich in Al2O3 (36.3–50.9 wt%), TiO2, and total Fe2O3, and poor in SiO2 (7.9–24.1 wt%), MgO, CaO, Na2O, and K2O. The granulites are enriched in high-field-strength elements and rare earth elements, and severely depleted in large-ion lithophile elements. These features strongly suggest the protolith was lateritic bauxite. Moreover, the other elemental concentrations and the Zr/Ti ratios point to basaltic rock as the precursor of the bauxite. Some of the aluminous granulites contain high-pressure mineral inclusions of kyanite, staurolite, siderite, and rutile, none of which are observed in the matrix. Abundant primary carbonic fluid inclusions are observed in garnet, corundum, and staurolite, but are rare in quartz and zircon. The average densities of fluid inclusions in garnet, corundum, staurolite, quartz, and zircon are 1.00 ± 0.06, 1.07 ± 0.04, 1.09 ± 0.03, 0.29 ± 0.07, and 1.15 ± 0.05 g/cm3, respectively. The mineral features not only in the matrix and but also in garnet from all rock types, isochemical phase diagrams obtained for each bulk rock composition, and Zr-in-rutile thermometry indicate an early eclogite-facies metamorphism (~ 2.5 GPa at 650 °C) and a subsequent nearly isothermal decompression. Zircons yield a wide range of U–Pb ages from 265 to 36 Ma, whereas the dark luminescent cores of the zircons, which contain high-density CO2 inclusions, yield a concordia age of 257 ± 8 Ma. These observations suggest that the dark luminescent zircon cores were formed at the same time as the garnet, corundum, and staurolite that contain high-density CO2 fluid inclusions. Based on the carbonic fluid inclusion isochore and the densities as well as calculated phase diagram, the concordia age can be regarded as recording a prograde stage of metamorphism under conditions lower than 600 °C and 0.7 GPa. Our new data provide the following geological and tectonic constraints: 1) the eruption of basalt occurred before the Permian, possibly related to subduction of the Paleo-Tethys Plate beneath the Indochina craton near the paleo-equator in the Devonian–Carboniferous; 2) strong weathering transformed the basalt to bauxite before the late Permian; 3) the uppermost continental crust, including the bauxites, was subducted in the late Permian due to the collision of the Indochina and South China cratons, leading to eclogite-facies metamorphism; 4) the rocks were then exhumed; and 5) shearing-related thermal events took place until the Paleogene.

AB - We have investigated the geological processes recorded in aluminous granulites from the Red River shear zone in northern Vietnam using mineral and whole-rock chemistries, fluid inclusions, metamorphic pressure–temperature paths, and geochronology. The granulites are extremely rich in Al2O3 (36.3–50.9 wt%), TiO2, and total Fe2O3, and poor in SiO2 (7.9–24.1 wt%), MgO, CaO, Na2O, and K2O. The granulites are enriched in high-field-strength elements and rare earth elements, and severely depleted in large-ion lithophile elements. These features strongly suggest the protolith was lateritic bauxite. Moreover, the other elemental concentrations and the Zr/Ti ratios point to basaltic rock as the precursor of the bauxite. Some of the aluminous granulites contain high-pressure mineral inclusions of kyanite, staurolite, siderite, and rutile, none of which are observed in the matrix. Abundant primary carbonic fluid inclusions are observed in garnet, corundum, and staurolite, but are rare in quartz and zircon. The average densities of fluid inclusions in garnet, corundum, staurolite, quartz, and zircon are 1.00 ± 0.06, 1.07 ± 0.04, 1.09 ± 0.03, 0.29 ± 0.07, and 1.15 ± 0.05 g/cm3, respectively. The mineral features not only in the matrix and but also in garnet from all rock types, isochemical phase diagrams obtained for each bulk rock composition, and Zr-in-rutile thermometry indicate an early eclogite-facies metamorphism (~ 2.5 GPa at 650 °C) and a subsequent nearly isothermal decompression. Zircons yield a wide range of U–Pb ages from 265 to 36 Ma, whereas the dark luminescent cores of the zircons, which contain high-density CO2 inclusions, yield a concordia age of 257 ± 8 Ma. These observations suggest that the dark luminescent zircon cores were formed at the same time as the garnet, corundum, and staurolite that contain high-density CO2 fluid inclusions. Based on the carbonic fluid inclusion isochore and the densities as well as calculated phase diagram, the concordia age can be regarded as recording a prograde stage of metamorphism under conditions lower than 600 °C and 0.7 GPa. Our new data provide the following geological and tectonic constraints: 1) the eruption of basalt occurred before the Permian, possibly related to subduction of the Paleo-Tethys Plate beneath the Indochina craton near the paleo-equator in the Devonian–Carboniferous; 2) strong weathering transformed the basalt to bauxite before the late Permian; 3) the uppermost continental crust, including the bauxites, was subducted in the late Permian due to the collision of the Indochina and South China cratons, leading to eclogite-facies metamorphism; 4) the rocks were then exhumed; and 5) shearing-related thermal events took place until the Paleogene.

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