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Geological history of the Southwest Japan from the triple junction of the Shimanto, Chichibu, and Sanbagawa belts

Research Project

Project/Area Number 19K04013
Research Category

Grant-in-Aid for Scientific Research (C)

Allocation TypeMulti-year Fund
Section一般
Review Section Basic Section 17040:Solid earth sciences-related
Research InstitutionShinshu University

Principal Investigator

Tokiwa Tetsuya  信州大学, 学術研究院理学系, 准教授 (50649241)

Co-Investigator(Kenkyū-buntansha) 森 宏  信州大学, 学術研究院理学系, 助教 (80788183)
Project Period (FY) 2019-04-01 – 2024-03-31
Project Status Completed (Fiscal Year 2023)
Budget Amount *help
¥4,290,000 (Direct Cost: ¥3,300,000、Indirect Cost: ¥990,000)
Fiscal Year 2023: ¥520,000 (Direct Cost: ¥400,000、Indirect Cost: ¥120,000)
Fiscal Year 2022: ¥910,000 (Direct Cost: ¥700,000、Indirect Cost: ¥210,000)
Fiscal Year 2021: ¥910,000 (Direct Cost: ¥700,000、Indirect Cost: ¥210,000)
Fiscal Year 2020: ¥780,000 (Direct Cost: ¥600,000、Indirect Cost: ¥180,000)
Fiscal Year 2019: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000)
Keywords西南日本 / 地質構造発達史 / ジルコンU-Pb年代 / ラマン分光分析 / 広域地質構造
Outline of Research at the Start

西南日本の形成史については,ナップ説と横ずれ説の二つの説が提案されているが,未だ解決されておらず,地質学における大きな課題の一つである.紀伊半島は,四万十帯・秩父帯・三波川帯が唯一直接接しており,両説の検証を行うことができる.本研究は,広域地質調査や変形構造解析に加え,最新の手法(ジルコンU-Pb年代,ラマン分光分析,帯磁率異方性測定)を用いることにより,広域地質構造・年代・被熱温度・変形から,地質構造発達史を明らかにし,ナップ説や横ずれ説の間で論争のあるジュラ紀~白亜紀における西南日本の形成史(地質構造発達史)を解明するものである.

Outline of Final Research Achievements

Geological survey, structure analysis, zircon U-Pb dating and Raman spectra of carbonaceous-material thermometry were carried out on the Shimanto, Chichibu and Sambagawa belts. The results confirm that these belts consist of several thrust sheets and that there is a geological unit with peak temperature of about 300°C, which is the boundary region between accretionary and metamorphic rocks. Detrital zircon U-Pb ages for Cretaceous trench-fill deposits show no significant age gap between their youngest zircon ages and true depositional age inferred from fossils. In addition, Cretaceous zircons dramatically increased during the mid-Cretaceous, and this large amount of Cretaceous zircons were most likely supplied by Ryoke Granitoids and Abukuma Granitoids.

Academic Significance and Societal Importance of the Research Achievements

紀伊半島には付加体と変成岩の境界領域である約300℃の被熱温度を受けた地質体が存在することが明らかになり,今後の付加体・変成岩の境界領域の研究場を提供することになった.また,ジュラ紀から白亜紀の海溝充填堆積物の砕屑性ジルコンU-Pb年代の最若年代が示準化石から求めた堆積年代と大きな差がないことが分かり,ジルコン年代による堆積年代の制約能力の可能性を見出した.加えて,海溝充填堆積物のジルコン年代構成は,東西で違いが認められるものの,その原因は近接する内帯の火成岩の分布状況で説明できる.このことは,大規模な左ずれを必要とせず,西南日本の地質構造発達史の解釈において重要な情報を提供する.

Report

(6 results)
  • 2023 Annual Research Report   Final Research Report ( PDF )
  • 2022 Research-status Report
  • 2021 Research-status Report
  • 2020 Research-status Report
  • 2019 Research-status Report
  • Research Products

    (4 results)

All 2022 2021 2020

All Journal Article (3 results) (of which Int'l Joint Research: 1 results,  Peer Reviewed: 3 results) Presentation (1 results)

  • [Journal Article] Structural analyses and peak-temperature estimations for the Sanbagawa Metamorphic and Shimanto Accretionary complexes on the central Kii Peninsula, SW Japan: Implications for the tectonic development of Cretaceous subduction complexes Journal of Asian Earth Sciences2021

    • Author(s)
      Shimura, Y., Tokiwa, T., Mori, H., Takeuchi, M., and Kouketsu, Y.
    • Journal Title

      Journal of Asian Earth Sciences

      Volume: - Pages: 1-16

    • DOI

      10.1016/j.jseaes.2021.104791

    • Related Report
      2021 Research-status Report
    • Peer Reviewed / Int'l Joint Research
  • [Journal Article] Use of detrital zircon U-Pb ages to assess the timing of deposition of Cretaceous trench-fill deposits in the active continental arc along the East Asian margin2021

    • Author(s)
      Tokiwa Tetsuya、Shimura Yusuke、Takeuchi Makoto、Mori Hiroshi
    • Journal Title

      Journal of Asian Earth Sciences

      Volume: 207 Pages: 104657-104657

    • DOI

      10.1016/j.jseaes.2020.104657

    • Related Report
      2020 Research-status Report
    • Peer Reviewed
  • [Journal Article] Chert-clastic sequence in the Cretaceous Shimanto Accretionary Complex on the central Kii Peninsula, SW Japan2020

    • Author(s)
      Shimura Yusuke、Takeuchi Makoto、Tokiwa Tetsuya
    • Journal Title

      Island Arc

      Volume: 29 Issue: 1

    • DOI

      10.1111/iar.12345

    • Related Report
      2019 Research-status Report
    • Peer Reviewed
  • [Presentation] 紀伊半島中央部・香肌地域における三波川帯低変成度岩の歪解析2022

    • Author(s)
      森宏,友岡洋介,野部勇貴,山岡健,常盤哲也,纐纈佑衣
    • Organizer
      日本地質学会第129年学術大会
    • Related Report
      2022 Research-status Report

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Published: 2019-04-18   Modified: 2025-01-30  

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