Understanding of the style of plate spreading and the governing factors of oceanic crustal architecture

• Project/Area Number: 20K04103
• 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: Kanazawa University
• Principal Investigator: Umino Susumu 金沢大学, 地球社会基盤学系, 教授 (30192511)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Project Status: Completed (Fiscal Year 2022)
• Budget Amount: ¥4,290,000 (Direct Cost: ¥3,300,000、Indirect Cost: ¥990,000); Fiscal Year 2022: ¥910,000 (Direct Cost: ¥700,000、Indirect Cost: ¥210,000); Fiscal Year 2021: ¥1,560,000 (Direct Cost: ¥1,200,000、Indirect Cost: ¥360,000); Fiscal Year 2020: ¥1,820,000 (Direct Cost: ¥1,400,000、Indirect Cost: ¥420,000)
• Keywords: プレート拡大 / 海洋地殻構造 / 海嶺軸セグメント / オマーンオフィオライト / シート状岩脈群 / 中央海嶺 / マグマ供給系 / モホール計画 / 高速拡大地殻 / マグマ組成 / プレート拡大様式 / ハワイ沖掘削計画

Outline of Research at the Start

中・高速拡大海嶺における地殻の拡大はマグマ量／歪み量の比(M)と地殻の密度構造によって規制され，高マグマ供給率(M=1)の高速拡大軸ではマグマ貫入・付加のみで拡大し，低マグマ供給率(M<1)の中速拡大軸はマグマ貫入と断層で拡大する。その結果，マグマ供給率が低いほど，岩脈群は厚く，噴出岩・下部地殻は薄くなると予想される。そこで，初生的な海洋地殻構造が世界で最もよく保存されているオマーンオフィオライトについて地質調査を行い，海洋地殻構造（噴出岩層，岩脈群，ハンレイ岩層の厚さ，シート溶岩／枕状溶岩比）を復元し，地震波速度構造から予想される“地殻構造とマグマ供給率の関係”が成立するかを検証する。

Outline of Final Research Achievements

We reconstructed the primary crustal structure of the secondary paleoridge segment in the northern Oman ophiolite, and discussed the genetic conditions of the sheeted dike magmas based on their geochemical characteristics. The sheeted dikes are divided into four segments 10-15 km long by the bending of strike. Based on chondrite-normalized patterns, the dikes are classified as whale-back type 1; slightly LREE-depleted type 2; and severely LREE-depleted type 3. Type 2, the most common type, is distributed throughout the segment and is similar to the MORB of the East Pacific Rise. Types 2 and 3 are distributed near the segment boundaries. Model calculations could reproduce Type 3 by batch melting of the mantle and Type 2 by a mixture of melts generated at low and high pressures.

Academic Significance and Societal Importance of the Research Achievements

中央海嶺におけるプレートの形成・拡大プロセスの理解には，海嶺軸下で生じるマグマ組成と海洋地殻構造の解明が不可欠である。現在の海嶺下の地殻構造を直接調べるのは困難であるため，本研究では世界最大で最も保存状態のよいオマーンオフィオライトにおいて，高速拡大した古海嶺軸セグメントの詳細な地殻構造を明らかにした。本代表者はわが国が擁する地球深部探査船「ちきゅう」によって，人類史上初めて海洋地殻を貫通し，マントル物質を回収する国際科学掘削計画「M2Mモホール計画」を推進している。モホールサイトの選定や掘削結果をプレート形成プロセスの中で正しく位置づけて理解し，一般化する上で本知見の寄与は大きい。

Research Products

• [Int'l Joint Research] Ministry of Energy and Minerals(オマーン)
• [Int'l Joint Research] Wigner Research Center for Physics(ハンガリー)
• [Int'l Joint Research] University of Hawaii/University of Rhode Island/Lamont-Doherty Earth Observatory(米国)
• [Int'l Joint Research] University of Southampton/University of Plymouth(英国)
• [Int'l Joint Research] University of Genova(イタリア)
• [Int'l Joint Research] CNRS(フランス)
• [Journal Article] ハワイ沖海洋地殻掘削調査：マントル掘削パイロットホールプロジェクト (2022)
  • Author(s): 海野 進・デーモンティーグル・スティーブンドント・グレッグムーア・ブノアイルドフォンス
  • Journal Title: 月刊地球号外 Volume: 72 Pages: 22-29
  • Open Access / Int'l Joint Research
• [Journal Article] 海洋地殻の構造と進化：高速拡大海嶺系 (2022)
  • Author(s): 海野 進・草野有紀・宮下純夫・足立佳子
  • Journal Title: 月刊地球号外 Volume: 72 Pages: 40-47
  • Open Access
• [Journal Article] Understanding the Spreading and Formation of Oceanic Plates by Drilling in the Upper Crust off Hawaii (2021)
  • Author(s): 海野 進・草野有紀
  • Journal Title: Journal of Geography (Chigaku Zasshi) Volume: 130 Issue: 4 Pages: 599-614
  • DOI: 10.5026/jgeography.130.599
  • NAID: 130008091270
  • ISSN: 0022-135X, 1884-0884
  • Year and Date: 2021-08-25
  • Peer Reviewed / Open Access
• [Journal Article] Workshop report: Exploring deep oceanic crust off Hawai`i (2021)
  • Author(s): Umino, S., Moore, G. F., Boston, B., Coggon, R., Crispini, L., D’Hondt, S., Garcia, M. O., Hanyu, T., Klein, F., Seama, N., Teagle, D. A. H., Tominaga, M., Yamashita, M., Harris, M., Ildefonse, B., Katayama, I., Kusano, Y., Suzuki, Y., Trembath-Reichert, E., Yamada, Y., Abe, N., Xiao, N., and Inagaki, F.
  • Journal Title: Scientific Drilling Volume: 29 Pages: 69-82
  • DOI: 10.5194/sd-29-69-2021
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Presentation] Muographic study of the oceanic crust-mantle structure of the Oman Ophiolite. (2022)
  • Author(s): Umino, S.
  • Organizer: Muographers 2022 General Assembly
  • Int'l Joint Research / Invited
• [Presentation] Frontiers of sampling the mantle by drilling to the Moho. International Symposium (2022)
  • Author(s): Abe, N. and Umino, S.
  • Organizer: International Symposium, Frontier of Understanding Earth's Interior and Dynamics, Tohoku Univ.
  • Int'l Joint Research / Invited
• [Presentation] Along-axis Magmatic/tectonic Phase Variation on the Spreading Ridge Inferred From the Northern Oman Ophiolite (2022)
  • Author(s): Kusano, Y., Miyashita, S., Adachi, Y., and Umino, S.
  • Organizer: AOGS 2022, Honolulu
• [Presentation] Understanding the Spreading and Formation of Oceanic Plates by Drilling in the Upper Crust Off Hawaii. (2022)
  • Author(s): Umino, S., and Kusano, Y.
  • Organizer: AOGS 2022, Honolulu
• [Presentation] The Chemical compositions and textures for magma series at the “Green Tuff” Formation in the Katakai region, Niigata, Japan. (2022)
  • Author(s): Nonaka, M., and Umino, S.
  • Organizer: Goldschmidt 2022, Honolulu
• [Presentation] The structure of magma chamber below a fast-spreading ridge based on field and core analyses of the Oman ICDP drilling (2021)
  • Author(s): Umino, S., Kusano, Y., Ishizuka, O., Fudai, T., Tamura, A., and Morishita, T.
  • Organizer: 2021 Japan Earth Planet. Sci. Joint Meeting, Yokohama (Online)
  • Int'l Joint Research
• [Presentation] Mohole to Mantle M2M Drilling Project and 951-Full Proposal: Drilling Mature Oceanic Crust on North Arch Off-Hawaii (2021)
  • Author(s): Umino, S., Inagaki, F., Teagle, D.H.A., Yamashita, M., Moore, G.F., Ildefonse, B., D'Hondt, S., Crispini, L., Hanyu, T., Garcia, M.O., and Morishita, T.
  • Organizer: 2021 Japan Earth Planet. Sci. Joint Meeting, Yokohama (Online)
  • Int'l Joint Research / Invited
• [Presentation] Understanding the spreading and formation of oceanic plates by drilling in the upper crust off Hawaii (2021)
  • Author(s): Umino, S.
  • Organizer: Virtual GEOSEA XVI and GeoCon 2021, Geological society of the Philippines
  • Int'l Joint Research / Invited
• [Presentation] Drilling Mature Oceanic Crust on North Arch off Hawaii (951-Full: Chikyu) (2021)
  • Author(s): 海野 進
  • Organizer: J-DESC主催ワークショップ「Post-IODP時代へ向けた科学海洋掘削の展望」
  • Invited
• [Presentation] How does the style of plate spreading govern the architecture of oceanic crust. (2020)
  • Author(s): Umino, S., Morishita, T., and Kusano, Y.
  • Organizer: 2020 JpGU-AGU Joint Meeting
  • Int'l Joint Research / Invited
• [Presentation] Microstructures, bulk and mineral chemistry of the gabbro cores of Holes GT1A and GT2A drilled in the Oman Drilling Project - Melt distribution in the subaxial lower crust. (2020)
  • Author(s): Umino, S., Fudai, T., Ishizuka, O., and Kusano, Y.
  • Organizer: 2020 JpGU-AGU Joint Meeting
  • Int'l Joint Research
• [Presentation] Current State of Off-Hawaii Oceanic Crust-Mantle Drilling Project. (2020)
  • Author(s): Umino, S.
  • Organizer: 2020 JpGU-AGU Joint Meeting
  • Int'l Joint Research / Invited
• [Presentation] 高速拡大海嶺の下部地殻マグマ溜まり構造―オマーン国際陸上科学掘削孔GT1A・GT2A のコア試料解析結果より (2020)
  • Author(s): 海野進・普代貴大・草野有紀・石塚治・田村明弘・森下知晃
  • Organizer: 日本鉱物科学会2020年オンライン年会
• [Presentation] ハワイ沖ノースアーチ上部地殻掘削計画 (2020)
  • Author(s): 海野 進
  • Organizer: ハードロック掘削科学ワークショップ Autumn2020
  • Invited