A mafic intrusion of "arc affinity" in a post-orogenic extensional setting: A case study from Ganluogou gabbro in the northern Yidun Arc Belt, eastern Tibetan Plateau

T. Wu, L. Xiao, C. Ma, Franco Pirajno, Y. Sun, Q. Zhan

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    Abstract

    © 2014 Elsevier Ltd. Generally, arc-related or subduction-related mafic magmas are formed during or slightly postdate subduction, and characterized by depletion in high field strength elements (HFSEs) relative to the large ion lithophile elements (LILEs) and light rare-earth elements (LREEs). Combining with mineral chemistry and Sr-Nd isotopes, these geochemical characteristics were usually used to define an arc setting, especially for some ancient arcs that had been strongly modified by later tectonic activities. However, we report an exceptional case from the northern part of the Triassic Yidun Arc Belt, eastern Tibetan Plateau. The Ganluogou gabbro (~152Ma) occurs as several intrusive bodies. Its mineral assemblage is olivine (chrysolite), plagioclase (anorthite), clinopyroxene (diopside), amphibole (edenite and pargasite) and phlogopite. Whole rock geochemistry shows low SiO2 (42.87-46.99wt.%), total rear earth elements (σREE=22.8-28.4ppm), Na2O+K2O (0.92-1.34wt.%), and high Al2O3, MgO and FeO contents. It has small variations of initial 87Sr/86Sr ((87Sr/86Sr)i=0.7053-0.7055) and εNd(t) values (-4.8 to -1.8). All the samples exhibit enrichment in LILEs including Th and U, but strongly depleted in HFSEs, including Nb, Ta, Zr and Hf. For the mineral chemistry, there are two type amphiboles. Amp(I) show higher V, Sc, Cr, Sr, Nb and Zr contents, but lower Th and U contents than those of Amp(II). Their REE patterns range from convex shape without Eu anomaly to LREE-enriched pattern with weak positive Eu anomaly. We suggest that Amp(I) was crystallized from a liquid that was mainly buffered by olivine, clinopyroxene and plagioclase, while Amp(II) crystallized from later melt that was mainly buffered by olivine. Based on clinopyroxene chemistry, compositions of coexisting olivine and plagioclase, and whole rock Sr-Nd isotopes, the parental magma of the Ganluogou gabbro is interpreted as a tholeiitic arc-affinity magma, which might be derived from an N-MORB mantle that had been metasomatised by slab-derived melts in the late Triassic (237-206Ma). Thus, the Ganluogou gabbro provides an example that magmas exhibiting arc-affinity could in fact be formed in a post-orogenic extensional setting.
    Original languageEnglish
    Pages (from-to)139-156
    JournalJournal of Asian Earth Sciences
    Volume94
    DOIs
    Publication statusPublished - 2014

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    gabbro
    olivine
    rare earth element
    plateau
    clinopyroxene
    plagioclase
    amphibole
    Triassic
    mineral
    subduction
    magma
    edenite
    melt
    isotope
    pargasite
    anomaly
    anorthite
    ion
    phlogopite
    diopside

    Cite this

    @article{39484d58fe1b414aabb224809770df18,
    title = "A mafic intrusion of {"}arc affinity{"} in a post-orogenic extensional setting: A case study from Ganluogou gabbro in the northern Yidun Arc Belt, eastern Tibetan Plateau",
    abstract = "{\circledC} 2014 Elsevier Ltd. Generally, arc-related or subduction-related mafic magmas are formed during or slightly postdate subduction, and characterized by depletion in high field strength elements (HFSEs) relative to the large ion lithophile elements (LILEs) and light rare-earth elements (LREEs). Combining with mineral chemistry and Sr-Nd isotopes, these geochemical characteristics were usually used to define an arc setting, especially for some ancient arcs that had been strongly modified by later tectonic activities. However, we report an exceptional case from the northern part of the Triassic Yidun Arc Belt, eastern Tibetan Plateau. The Ganluogou gabbro (~152Ma) occurs as several intrusive bodies. Its mineral assemblage is olivine (chrysolite), plagioclase (anorthite), clinopyroxene (diopside), amphibole (edenite and pargasite) and phlogopite. Whole rock geochemistry shows low SiO2 (42.87-46.99wt.{\%}), total rear earth elements (σREE=22.8-28.4ppm), Na2O+K2O (0.92-1.34wt.{\%}), and high Al2O3, MgO and FeO contents. It has small variations of initial 87Sr/86Sr ((87Sr/86Sr)i=0.7053-0.7055) and εNd(t) values (-4.8 to -1.8). All the samples exhibit enrichment in LILEs including Th and U, but strongly depleted in HFSEs, including Nb, Ta, Zr and Hf. For the mineral chemistry, there are two type amphiboles. Amp(I) show higher V, Sc, Cr, Sr, Nb and Zr contents, but lower Th and U contents than those of Amp(II). Their REE patterns range from convex shape without Eu anomaly to LREE-enriched pattern with weak positive Eu anomaly. We suggest that Amp(I) was crystallized from a liquid that was mainly buffered by olivine, clinopyroxene and plagioclase, while Amp(II) crystallized from later melt that was mainly buffered by olivine. Based on clinopyroxene chemistry, compositions of coexisting olivine and plagioclase, and whole rock Sr-Nd isotopes, the parental magma of the Ganluogou gabbro is interpreted as a tholeiitic arc-affinity magma, which might be derived from an N-MORB mantle that had been metasomatised by slab-derived melts in the late Triassic (237-206Ma). Thus, the Ganluogou gabbro provides an example that magmas exhibiting arc-affinity could in fact be formed in a post-orogenic extensional setting.",
    author = "T. Wu and L. Xiao and C. Ma and Franco Pirajno and Y. Sun and Q. Zhan",
    year = "2014",
    doi = "10.1016/j.jseaes.2014.08.026",
    language = "English",
    volume = "94",
    pages = "139--156",
    journal = "Journal of Asian Earth Sciences",
    issn = "1367-9120",
    publisher = "Elsevier",

    }

    TY - JOUR

    T1 - A mafic intrusion of "arc affinity" in a post-orogenic extensional setting: A case study from Ganluogou gabbro in the northern Yidun Arc Belt, eastern Tibetan Plateau

    AU - Wu, T.

    AU - Xiao, L.

    AU - Ma, C.

    AU - Pirajno, Franco

    AU - Sun, Y.

    AU - Zhan, Q.

    PY - 2014

    Y1 - 2014

    N2 - © 2014 Elsevier Ltd. Generally, arc-related or subduction-related mafic magmas are formed during or slightly postdate subduction, and characterized by depletion in high field strength elements (HFSEs) relative to the large ion lithophile elements (LILEs) and light rare-earth elements (LREEs). Combining with mineral chemistry and Sr-Nd isotopes, these geochemical characteristics were usually used to define an arc setting, especially for some ancient arcs that had been strongly modified by later tectonic activities. However, we report an exceptional case from the northern part of the Triassic Yidun Arc Belt, eastern Tibetan Plateau. The Ganluogou gabbro (~152Ma) occurs as several intrusive bodies. Its mineral assemblage is olivine (chrysolite), plagioclase (anorthite), clinopyroxene (diopside), amphibole (edenite and pargasite) and phlogopite. Whole rock geochemistry shows low SiO2 (42.87-46.99wt.%), total rear earth elements (σREE=22.8-28.4ppm), Na2O+K2O (0.92-1.34wt.%), and high Al2O3, MgO and FeO contents. It has small variations of initial 87Sr/86Sr ((87Sr/86Sr)i=0.7053-0.7055) and εNd(t) values (-4.8 to -1.8). All the samples exhibit enrichment in LILEs including Th and U, but strongly depleted in HFSEs, including Nb, Ta, Zr and Hf. For the mineral chemistry, there are two type amphiboles. Amp(I) show higher V, Sc, Cr, Sr, Nb and Zr contents, but lower Th and U contents than those of Amp(II). Their REE patterns range from convex shape without Eu anomaly to LREE-enriched pattern with weak positive Eu anomaly. We suggest that Amp(I) was crystallized from a liquid that was mainly buffered by olivine, clinopyroxene and plagioclase, while Amp(II) crystallized from later melt that was mainly buffered by olivine. Based on clinopyroxene chemistry, compositions of coexisting olivine and plagioclase, and whole rock Sr-Nd isotopes, the parental magma of the Ganluogou gabbro is interpreted as a tholeiitic arc-affinity magma, which might be derived from an N-MORB mantle that had been metasomatised by slab-derived melts in the late Triassic (237-206Ma). Thus, the Ganluogou gabbro provides an example that magmas exhibiting arc-affinity could in fact be formed in a post-orogenic extensional setting.

    AB - © 2014 Elsevier Ltd. Generally, arc-related or subduction-related mafic magmas are formed during or slightly postdate subduction, and characterized by depletion in high field strength elements (HFSEs) relative to the large ion lithophile elements (LILEs) and light rare-earth elements (LREEs). Combining with mineral chemistry and Sr-Nd isotopes, these geochemical characteristics were usually used to define an arc setting, especially for some ancient arcs that had been strongly modified by later tectonic activities. However, we report an exceptional case from the northern part of the Triassic Yidun Arc Belt, eastern Tibetan Plateau. The Ganluogou gabbro (~152Ma) occurs as several intrusive bodies. Its mineral assemblage is olivine (chrysolite), plagioclase (anorthite), clinopyroxene (diopside), amphibole (edenite and pargasite) and phlogopite. Whole rock geochemistry shows low SiO2 (42.87-46.99wt.%), total rear earth elements (σREE=22.8-28.4ppm), Na2O+K2O (0.92-1.34wt.%), and high Al2O3, MgO and FeO contents. It has small variations of initial 87Sr/86Sr ((87Sr/86Sr)i=0.7053-0.7055) and εNd(t) values (-4.8 to -1.8). All the samples exhibit enrichment in LILEs including Th and U, but strongly depleted in HFSEs, including Nb, Ta, Zr and Hf. For the mineral chemistry, there are two type amphiboles. Amp(I) show higher V, Sc, Cr, Sr, Nb and Zr contents, but lower Th and U contents than those of Amp(II). Their REE patterns range from convex shape without Eu anomaly to LREE-enriched pattern with weak positive Eu anomaly. We suggest that Amp(I) was crystallized from a liquid that was mainly buffered by olivine, clinopyroxene and plagioclase, while Amp(II) crystallized from later melt that was mainly buffered by olivine. Based on clinopyroxene chemistry, compositions of coexisting olivine and plagioclase, and whole rock Sr-Nd isotopes, the parental magma of the Ganluogou gabbro is interpreted as a tholeiitic arc-affinity magma, which might be derived from an N-MORB mantle that had been metasomatised by slab-derived melts in the late Triassic (237-206Ma). Thus, the Ganluogou gabbro provides an example that magmas exhibiting arc-affinity could in fact be formed in a post-orogenic extensional setting.

    U2 - 10.1016/j.jseaes.2014.08.026

    DO - 10.1016/j.jseaes.2014.08.026

    M3 - Article

    VL - 94

    SP - 139

    EP - 156

    JO - Journal of Asian Earth Sciences

    JF - Journal of Asian Earth Sciences

    SN - 1367-9120

    ER -