2021 Fiscal Year Final Research Report

Oceanic plateau-origin rocks in orogenic belts: Towards understanding the genesis of oceanic LIP

Research Project

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Project/Area Number	19H01986
Research Category	Grant-in-Aid for Scientific Research (B)
Allocation Type	Single-year Grants
Section	一般
Review Section	Basic Section 17040:Solid earth sciences-related
Research Institution	Chiba University
Principal Investigator	Ichiyama Yuji 千葉大学, 大学院理学研究院, 准教授 (90625469)
Co-Investigator(Kenkyū-buntansha)	熊谷英憲国立研究開発法人海洋研究開発機構, 海洋機能利用部門(海底資源センター), グループリーダー (10344285) 伊藤久敏一般財団法人電力中央研究所, 地球工学研究所, 上席研究員 (50371406) 田村明弘金沢大学, 地球社会基盤学系, 博士研究員 (80401884) 木村純一国立研究開発法人海洋研究開発機構, 海域地震火山部門(火山・地球内部研究センター), 上席技術研究員(シニア) (30241730)
Project Period (FY)	2019-04-01 – 2022-03-31
Keywords	みかぶ帯 / 空知ー蝦夷帯 / 三波川帯 / ジルコンU-Pb年代 / Nd-Hf同位体 / 白金族元素
Outline of Final Research Achievements	In this study, we investigated igneous rocks accreted into an orogenic belt to reveal the details of mantle plume activities in a paleo-oceanic region. Igneous rocks from the Mikabu and Sorachi-Yezo belts yield Late Jurassic to Early Cretaceous radiometric ages and show the geochemical signatures of mantle plume-origin. Their　isotopic trend is different from that of a Jurassic oceanic plateau in the Pacific but is more similar to that of Cretaceous plateaus. The field occurrence and mineral compositions of ultramafic plutons in the Sambagawa belt indicate that they are cumulates formed by crystal settling and accumulation. Ultramafic plutons in pelitic schists probably originated from mantle plume magmatism, but those in the Eclogite unit might have been formed from island-arc magmas.
Free Research Field	岩石学
Academic Significance and Societal Importance of the Research Achievements	本研究によって、ジュラ紀～白亜紀にかけての海洋地域におけるマントルプルーム活動や沈み込み帯火成活動の痕跡を突き止めることに成功した。本研究の成果は、顕生代以降の古太平洋での火成活動履歴や沈み込み帯でのテクトニクスの解明に重要な束縛条件を与えると考えられる。