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Geochemical Distinction Between Altered Oceanic Basalt- and Seafloor Sediment-Derived Fluids in the Mantle Source of Mafic Igneous Rocks in Southwestern Tianshan, Western China.

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Title: Geochemical Distinction Between Altered Oceanic Basalt- and Seafloor Sediment-Derived Fluids in the Mantle Source of Mafic Igneous Rocks in Southwestern Tianshan, Western China.
Authors: Ma, Li-Tao1 (AUTHOR), Dai, Li-Qun1,2 (AUTHOR) lqdai@ustc.edu.cn, Zheng, Yong-Fei1,2 (AUTHOR), Zhao, Zi-Fu1,2 (AUTHOR), Fang, Wei1 (AUTHOR), Zhao, Kai1 (AUTHOR), Xiao, Yilin1,2 (AUTHOR), Tong, Fengtai1 (AUTHOR)
Source: Journal of Petrology. Jan2021, Vol. 62 Issue 1, p1-23. 23p.
Subjects: Mafic rocks, Igneous rocks, Metasomatism, Trace elements, Strontium, Strontium isotopes, Subduction zones, Uranium-lead dating, Oceanic crust
Geographic Terms: China
Abstract: The role of subducting oceanic crust-derived fluids in generating mafic arc magmatism has been widely documented. However, the subducting oceanic crust is generally composed of basaltic igneous crust and seafloor sediment, which may give rise to different compositions of liquid phases causing metasomatism of the mantle wedge. Because of the similarity in enrichment of fluid-mobile incompatible elements in the two sources of subduction zone fluids, it has been a challenge to distinguish between them when studying the products of mafic arc magmatism. This difficulty is overcome by a combined study of whole-rock Li isotopes and zircon O isotopes in addition to whole-rock major-trace elements and Sr–Nd–Hf isotopes in Late Paleozoic mafic igneous rocks from southwestern Tianshan in western China. Zircon U–Pb dating yields consistent ages of 313 ± 3 Ma to 305 ± 1 Ma for magma crystallization. The mafic igneous rocks exhibit arc-like trace element distribution patterns and depleted whole-rock Nd–Hf isotopes but slightly high (87Sr/86Sr)i ratios of 0·7039– 0·7057. They also show positive zircon εHf(t) values and slightly higher zircon δ18O values of 5·2–7·6‰. There are covariations of whole-rock Sr isotopes with Th/La and Rb/Nb ratios, indicating a contribution from terrigenous sediment-derived fluids to their mantle source in addition to basaltic igneous crust-derived fluids. Based on the slightly higher zircon δ18O values but variably lower whole-rock δ7Li values of -0·8 to 3·5‰ for the target rocks than those of mantle respectively, both altered oceanic basalt- and terrigenous sediment-derived fluids are identified in the mantle source of these mafic igneous rocks. Model calculations for trace elements and Sr–Nd–Li isotopes further confirm that the geochemical compositions of these mafic igneous rocks can be explained by chemical reaction of depleted MORB mantle peridotite with the mixed fluids to generate ultramafic metasomatites at subarc depths. Therefore, chemical metasomatism of the mantle wedge is a key mechanism for the incorporation of crustal components into the source of arc-like mafic igneous rocks above oceanic subduction zones. [ABSTRACT FROM AUTHOR]
Copyright of Journal of Petrology is the property of Oxford University Press / USA and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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DbLabel: Engineering Source
An: 150148481
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PubTypeId: academicJournal
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  Data: Geochemical Distinction Between Altered Oceanic Basalt- and Seafloor Sediment-Derived Fluids in the Mantle Source of Mafic Igneous Rocks in Southwestern Tianshan, Western China.
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  Data: <searchLink fieldCode="DE" term="%22Mafic+rocks%22">Mafic rocks</searchLink><br /><searchLink fieldCode="DE" term="%22Igneous+rocks%22">Igneous rocks</searchLink><br /><searchLink fieldCode="DE" term="%22Metasomatism%22">Metasomatism</searchLink><br /><searchLink fieldCode="DE" term="%22Trace+elements%22">Trace elements</searchLink><br /><searchLink fieldCode="DE" term="%22Strontium%22">Strontium</searchLink><br /><searchLink fieldCode="DE" term="%22Strontium+isotopes%22">Strontium isotopes</searchLink><br /><searchLink fieldCode="DE" term="%22Subduction+zones%22">Subduction zones</searchLink><br /><searchLink fieldCode="DE" term="%22Uranium-lead+dating%22">Uranium-lead dating</searchLink><br /><searchLink fieldCode="DE" term="%22Oceanic+crust%22">Oceanic crust</searchLink>
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– Name: Abstract
  Label: Abstract
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  Data: The role of subducting oceanic crust-derived fluids in generating mafic arc magmatism has been widely documented. However, the subducting oceanic crust is generally composed of basaltic igneous crust and seafloor sediment, which may give rise to different compositions of liquid phases causing metasomatism of the mantle wedge. Because of the similarity in enrichment of fluid-mobile incompatible elements in the two sources of subduction zone fluids, it has been a challenge to distinguish between them when studying the products of mafic arc magmatism. This difficulty is overcome by a combined study of whole-rock Li isotopes and zircon O isotopes in addition to whole-rock major-trace elements and Sr–Nd–Hf isotopes in Late Paleozoic mafic igneous rocks from southwestern Tianshan in western China. Zircon U–Pb dating yields consistent ages of 313 ± 3 Ma to 305 ± 1 Ma for magma crystallization. The mafic igneous rocks exhibit arc-like trace element distribution patterns and depleted whole-rock Nd–Hf isotopes but slightly high (87Sr/86Sr)i ratios of 0·7039– 0·7057. They also show positive zircon εHf(t) values and slightly higher zircon δ18O values of 5·2–7·6‰. There are covariations of whole-rock Sr isotopes with Th/La and Rb/Nb ratios, indicating a contribution from terrigenous sediment-derived fluids to their mantle source in addition to basaltic igneous crust-derived fluids. Based on the slightly higher zircon δ18O values but variably lower whole-rock δ7Li values of -0·8 to 3·5‰ for the target rocks than those of mantle respectively, both altered oceanic basalt- and terrigenous sediment-derived fluids are identified in the mantle source of these mafic igneous rocks. Model calculations for trace elements and Sr–Nd–Li isotopes further confirm that the geochemical compositions of these mafic igneous rocks can be explained by chemical reaction of depleted MORB mantle peridotite with the mixed fluids to generate ultramafic metasomatites at subarc depths. Therefore, chemical metasomatism of the mantle wedge is a key mechanism for the incorporation of crustal components into the source of arc-like mafic igneous rocks above oceanic subduction zones. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
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  Data: <i>Copyright of Journal of Petrology is the property of Oxford University Press / USA and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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RecordInfo BibRecord:
  BibEntity:
    Identifiers:
      – Type: doi
        Value: 10.1093/petrology/egab014
    Languages:
      – Code: eng
        Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 23
        StartPage: 1
    Subjects:
      – SubjectFull: Mafic rocks
        Type: general
      – SubjectFull: Igneous rocks
        Type: general
      – SubjectFull: Metasomatism
        Type: general
      – SubjectFull: Trace elements
        Type: general
      – SubjectFull: Strontium
        Type: general
      – SubjectFull: Strontium isotopes
        Type: general
      – SubjectFull: Subduction zones
        Type: general
      – SubjectFull: Uranium-lead dating
        Type: general
      – SubjectFull: Oceanic crust
        Type: general
      – SubjectFull: China
        Type: general
    Titles:
      – TitleFull: Geochemical Distinction Between Altered Oceanic Basalt- and Seafloor Sediment-Derived Fluids in the Mantle Source of Mafic Igneous Rocks in Southwestern Tianshan, Western China.
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            NameFull: Ma, Li-Tao
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            NameFull: Dai, Li-Qun
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            NameFull: Zheng, Yong-Fei
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            NameFull: Zhao, Kai
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            – D: 01
              M: 01
              Text: Jan2021
              Type: published
              Y: 2021
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