Formation history of granitic batholiths in the Eastern Asian continental margin based on zicron geochemistry

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K14005
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 17040:Solid earth sciences-related
• Research Institution: Akita University
• Principal Investigator: Aoki Shogo 秋田大学, 国際資源学研究科, 助教 (60801967)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 砕屑性ジルコン / 太平洋型造山運動 / 古地理学 / 花崗岩バソリス

Outline of Final Research Achievements

The eastern margin of the Asian continent, including the Japanese Islands, is characterized by accretionary complexes, high P/T-type metamorphic belts, and granitic batholiths formed by Pacific-type orogeny over the past 500 million years. However, the older granite records have been lost by weathering and erosion, making it difficult to infer past igneous history and tectonics.
In this study, I focused on the detrital zircons of the Phanerozoic accretionary complexes that constitute the basement rocks of the Japanese Islands, and analyzed their U-Pb ages and geochemistry to constrain the age of the accretionary complexes over 500 million years and to estimate the formation and extinction history of the granite batholiths that once constituted the upper continental crust of the eastern margin of the Asian continent.

Free Research Field

地質学

Academic Significance and Societal Importance of the Research Achievements

本研究によって、変形・変成作用が激しく示準化石による形成年代の制約が難しかった付加体の形成年代を砕屑性ジルコンのU-Pb年代測定から制約することができ、付加体が成長した時期や一度形成された付加体が二次的に消失するイベントが後背地のアジア大陸縁辺部で過去に起きたことを明らかにした。
また、ジルコンのU-Pb年代に微量元素やHf同位体比のデータを組み合わせることで、アジア大陸東縁部の古地理学的な変化や、スラブの沈み込み角度の変化、上部地殻の消滅・若返りイベントのタイミングを制約することができた。