Continental basement beneath the oceanic arcs: Do oceanic arcs form on the oceanic plate?

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K04140
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17040:Solid earth sciences-related
• Research Institution: National Museum of Nature and Science, Tokyo
• Principal Investigator: Tani Kenichiro 独立行政法人国立科学博物館, 地学研究部, 研究主幹 (70359206)
• Co-Investigator(Kenkyū-buntansha): 山口 飛鳥 東京大学, 大気海洋研究所, 准教授 (30570634) ; 石塚 治 国立研究開発法人産業技術総合研究所, 地質調査総合センター, 首席研究員 (90356444)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 伊豆小笠原マリアナ弧 / 南サンドイッチ弧 / スコチア海 / 大陸性基盤 / ジルコン年代測定

Outline of Final Research Achievements

We focused on the basement of the Izu-Bonin-Mariana Arc and the South Sandwich Arc, which have been considered to be typical oceanic island arcs formed by the subduction of oceanic plates. We aimed to understand the crustal structure and tectonic environment of the upper plate during the subduction initiation by combining research cruises and land-based surveys for comparative studies.
Travel restrictions due to COVID-19 pandemic had a major impact on the originally planned research cruises and land-based surveys. However, we were able to constrain the presence of Mesozoic continental basement on the upper plate prior to the formation of both island arcs by conducting surveys in alternative areas. We were also successful in constraining the geochemical, geochronological, and petrological characteristics of these continental basement rocks.

Free Research Field

地質学

Academic Significance and Societal Importance of the Research Achievements

海洋性島弧に存在する大陸性基盤岩の起源を解明し、プレート沈み込み開始過程との因果関係を検証する試みは、プレートの沈み込みがどのような地質学的条件で発生するのかを明らかにするという、プレートテクトニクス理論で未解明の問いに対して重要な知見をもたらす。
また海洋性島弧が既存の大陸性基盤の上に形成されているという我々の仮説が正しければ、そのような既存大陸地殻の影響がないという前提で従来解釈されてきた様々なアプローチからの海洋性島弧研究が再検討を迫られる事態となり、今後の研究に大きな方向性を与える成果となる。