Deciphering the evolution of continental crust using monazite

2020 Fiscal Year Final Research Report

• Project/Area Number: 18H01301
• 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: The University of Tokyo
• Principal Investigator: Iizuka Tsuyoshi 東京大学, 大学院理学系研究科(理学部), 准教授 (70614569)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: 大陸地殻 / モナザイト / 超大陸 / ウランー鉛年代 / ネオジム同位体 / 微量元素

Outline of Final Research Achievements

Understanding the evolution of granitic continental crust is central to deciphering the evolution of the solid Earth and surface environments. In this study, we have studied crustal evolution by using monazite. Monazite is a phosphate that can crystallize under a wide range of metamorphic conditions and from low-Ca granitic magma. Considering that monazite can retain its primary chemical and isotopic signatures during sedimentary processes, we measured U-Pb ages of detrital monazite grains from major world rivers. Furthermore, we determined trace element and Nd isotope compositions of the dated monazite grains. The data allow us to determine the precise timing and nature of orogenic events in the drainage areas. These results provide new constraints on the timing of major metamorphic events in the continental crust.

Free Research Field

宇宙地球化学

Academic Significance and Societal Importance of the Research Achievements

花崗岩質な大陸地殻の存在は地球の主要な特徴の一つであり，大陸地殻がどのように今の姿に至ったのかを知ることは，固体地球の熱史・化学進化や表層環境の変遷を理解する上で重要となる．本研究では，大陸地殻の進化過程を明らかにすることを目的として，世界の巨大河川川砂に含まれるモナザイト鉱物のウランー鉛年代測定および微量元素・ネオジム同位体分析を実施した．これにより，プレートテクトニクスの稼働に伴って進む大陸衝突が，いつ・どのような温度圧力条件下で進んだのかについて，制約を与えることができた．