Petrology and U-Pb SHRIMP Geochronology of a Garnet Peridotite, Sulu UHP Terrane, East-Central China

Ruixuan Zhao, Juhn G. Liou, Tatsuki Tsujimori, Ru Y. Zhang

    Research output: Contribution to journalArticle

    14 Citations (Scopus)

    Abstract

    Garnet clinopyroxenite at Rizhao occurs as a lens 100 × 225 m2 within a serpentinized peridotite body, in fault contact with felsic gneiss. Minor dunite also occurs within the same peridotite. The clinopyroxenite consists of porphyroblastic Grt-bearing (type 1), megacrystic Grt-bearing (type 2), porphyroblastic Cpx-bearing (type 3), and equigranular (type 4) garnet clinopyroxenite. Lamellaerich, coarse-grained Cpx occurs as inclusions in megacrystic Grt from type 2 clinopyroxenite, and as porphyroblasts in a matrix of Cpx + Grt + Ilm from type 3 clinopyroxenite; these clinopyroxenes contain abundant exsolution lamellae of Grt (PrP16-19Grs62 Alm19-21SpS1) + Ilm± Mag ± Amp (Mg#: 0.88-0.98; Na2O: 0.5-3.3 wt%; K2O: 0.7-1.0 wt%; TiO2: 0.1-0.2 wt%). Megacrystic and porphyroblastic garnet (Prp35-42Grs34-45Alm19-24 SpS1) also occurs in a matrix of fine-grained Cpx + Grt + Ilm; spinel (Mg#: 0.60-0.62) is present as inclusions in both porphyroblastic Grt and lamellae-rich Cpx. Petrochemical data support a mantle origin involving crystallization of majoritic garnet. We propose that the protolith of the Rizhao clinopyroxenite initially was a spinel clinopyroxenite, and was convected to great depths (>450 km) to form a majoritic garnet that contains high CaO and considerable amounts of FeO and TiO2. During later decompression, the majoritic garnet broke down to form intergrowths of Cpx + Grt + Ilm ± Mag ± Amp at T = 700-300°C, P ≤ 3 GPa. It was then emplaced into a subduction zone and experienced UHP metamorphism at 620-880°C, 3 GPa during Triassic continental collision. Megacrystic /porphyroblastic garnet formed during this stage, and lamellae-rich Cpx recrystallized to the matrix assemblage of Cpx + Grt + Ilm subsequently. The clinopyroxenite also experienced later retrogression during exhumation. Zircon U-Pb geochronology yields 215 ± 2 Ma for the Rizhao garnet clinopyroxenite, occurrence of garnet and clinopyroxene inclusions in zircon suggests that this age reflects the UHP metamorphism.

    Original languageEnglish
    Pages (from-to)732-752
    Number of pages21
    JournalInternational Geology Review
    Volume49
    Issue number8
    DOIs
    Publication statusPublished - Aug 2007

    Fingerprint

    peridotite
    petrology
    geochronology
    terrane
    garnet
    spinel
    matrix
    zircon
    metamorphism
    porphyroblast
    retrogression
    dunite
    continental collision
    exsolution
    decompression
    protolith
    exhumation
    gneiss
    clinopyroxene
    subduction zone

    ASJC Scopus subject areas

    • Geology

    Cite this

    Petrology and U-Pb SHRIMP Geochronology of a Garnet Peridotite, Sulu UHP Terrane, East-Central China. / Zhao, Ruixuan; Liou, Juhn G.; Tsujimori, Tatsuki; Zhang, Ru Y.

    In: International Geology Review, Vol. 49, No. 8, 08.2007, p. 732-752.

    Research output: Contribution to journalArticle

    Zhao, Ruixuan ; Liou, Juhn G. ; Tsujimori, Tatsuki ; Zhang, Ru Y. / Petrology and U-Pb SHRIMP Geochronology of a Garnet Peridotite, Sulu UHP Terrane, East-Central China. In: International Geology Review. 2007 ; Vol. 49, No. 8. pp. 732-752.
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    abstract = "Garnet clinopyroxenite at Rizhao occurs as a lens 100 × 225 m2 within a serpentinized peridotite body, in fault contact with felsic gneiss. Minor dunite also occurs within the same peridotite. The clinopyroxenite consists of porphyroblastic Grt-bearing (type 1), megacrystic Grt-bearing (type 2), porphyroblastic Cpx-bearing (type 3), and equigranular (type 4) garnet clinopyroxenite. Lamellaerich, coarse-grained Cpx occurs as inclusions in megacrystic Grt from type 2 clinopyroxenite, and as porphyroblasts in a matrix of Cpx + Grt + Ilm from type 3 clinopyroxenite; these clinopyroxenes contain abundant exsolution lamellae of Grt (PrP16-19Grs62 Alm19-21SpS1) + Ilm± Mag ± Amp (Mg#: 0.88-0.98; Na2O: 0.5-3.3 wt{\%}; K2O: 0.7-1.0 wt{\%}; TiO2: 0.1-0.2 wt{\%}). Megacrystic and porphyroblastic garnet (Prp35-42Grs34-45Alm19-24 SpS1) also occurs in a matrix of fine-grained Cpx + Grt + Ilm; spinel (Mg#: 0.60-0.62) is present as inclusions in both porphyroblastic Grt and lamellae-rich Cpx. Petrochemical data support a mantle origin involving crystallization of majoritic garnet. We propose that the protolith of the Rizhao clinopyroxenite initially was a spinel clinopyroxenite, and was convected to great depths (>450 km) to form a majoritic garnet that contains high CaO and considerable amounts of FeO and TiO2. During later decompression, the majoritic garnet broke down to form intergrowths of Cpx + Grt + Ilm ± Mag ± Amp at T = 700-300°C, P ≤ 3 GPa. It was then emplaced into a subduction zone and experienced UHP metamorphism at 620-880°C, 3 GPa during Triassic continental collision. Megacrystic /porphyroblastic garnet formed during this stage, and lamellae-rich Cpx recrystallized to the matrix assemblage of Cpx + Grt + Ilm subsequently. The clinopyroxenite also experienced later retrogression during exhumation. Zircon U-Pb geochronology yields 215 ± 2 Ma for the Rizhao garnet clinopyroxenite, occurrence of garnet and clinopyroxene inclusions in zircon suggests that this age reflects the UHP metamorphism.",
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