Progressive changes in lithological association of the Sanbagawa metamorphic complex, Southwest Japan: Relict clinopyroxene and detrital zircon perspectives

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  • Shunsuke Endo
    Department of Earth Science Shimane University Matsue 690‐8504 Japan
  • Kazuhiro Miyazaki
    Geological Survey of Japan AIST 1‐1‐1 Higashi, Tsukuba 305‐8567 Japan
  • Tohru Danhara
    Kyoto Fission‐Track Co., Ltd. Kita‐ku, Kyoto 603‐8832 Japan
  • Hideki Iwano
    Kyoto Fission‐Track Co., Ltd. Kita‐ku, Kyoto 603‐8832 Japan
  • Takafumi Hirata
    Geochemical Research Center The University of Tokyo Bunkyo‐ku, Tokyo 113‐0033 Japan

書誌事項

公開日
2018-07-15
資源種別
journal article
権利情報
  • http://onlinelibrary.wiley.com/termsAndConditions#vor
DOI
  • 10.1111/iar.12261
公開者
Wiley

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説明

<jats:title>Abstract</jats:title><jats:p>The main tectono‐stratigraphic unit (Shirataki unit) of the Sanbagawa metamorphic complex in central Shikoku is characterized by abundant mafic schist layers that show the mid‐ocean ridge basalt (MORB) affinity. These MORB‐derived schist layers are absent in a southern (structurally lower) domain within the unit. Instead, sporadic occurrences of small metabasite lenses that contain relict igneous minerals (Ti‐rich augite and kaersutite) indicative of alkali basalt magmatism are newly recognized in the southern domain. Compositions of relict clinopyroxene in metabasalt are useful to identify the tectonic setting and origin of the protolith basalt, and those in each unit of the Sanbagawa metamorphic complex are presented. The metamorphic grade of the Shirataki unit generally increases structurally upwards in the southern side of the highest‐grade zone, and metamorphic zonation is subparallel to lithostratigraphic succession. The protolith assemblage of the Shirataki unit shows a distinct change from the southern low‐grade domain (lower Shirataki subunit) composed of terrigenous sedimentary rocks (mudstone and sandstone) with minor alkali basalt to the northern higher‐grade domain (upper Shirataki subunit) consisting of terrigenous and pelagic sedimentary rocks with abundant MORB. The youngest detrital zircon U–Pb ages (<jats:italic>ca</jats:italic> 95–90 Ma) suggest that both domains have Late Cretaceous depositional ages at the trench. Progressive peeling of oceanic plate stratigraphy during subduction can account for the observed change of lithological association in the Shirataki unit.</jats:p>

収録刊行物

  • Island Arc

    Island Arc 27 (5), e12261-, 2018-07-15

    Wiley

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