Development of high precision chronological method for the determination of volcanic eruption

2018 Fiscal Year Final Research Report

• Project/Area Number: 16K05578
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Geology
• Research Institution: Okayama University
• Principal Investigator: Tanaka Ryoji 岡山大学, 惑星物質研究所, 教授 (00379819)
• Research Collaborator: Zhou Xiaoyu ; Getachew Belay Iyasu
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: 火山噴火 / 揮発性成分 / 238U-230Th放射非平衡 / 軽元素安定同位体

Outline of Final Research Achievements

To apply the high-precision chronological method for the determination of volcanic eruption using the 238U-230Th isochron method, it is necessary to make it clear that the 238U-230Th disequilibria was triggered solely by the eruption process. The elemental fractionation in magma during or after the volcanic eruption can be caused by melt-fluid-gas fractionation and crystallization of matrix elements. To analyse these processes from the natural samples, the analytical method for the elemental and isotopic compositions of volatile (H, C, N, O) and highly siderophile elements were developed. By analysing the U-Th fractionation process by vapour exsolution and crystal fractionation during the solidifying the groundmass minerals, the eruption age of young volcanics could have been determined. This results infer that the 238U-230Th isochron method can be applied for the determination of volcanic eruption younger than 300 ka

Free Research Field

地球惑星科学

Academic Significance and Societal Importance of the Research Achievements

火山噴火年代測定には、主にK-Ar法および14C法が用いられてきた。しかしながらこれらの方法は、約５～３０万年前の高精度年代測定には適していない。238U-230Th 放射非平衡を用いた年代測定法は、原理的には３０万年以内の高精度年代測定に適しているものの、噴火以前の様々なプロセスによる元素分別との判別を行う必要があり、実際には応用されていなかった。本研究で得られた手法を発展させることにより、様々な組成の火山岩の高精度噴火年代を求めることが可能となり、火山形成履歴の解析や長期的な火山噴火予知に関する重要は指標を得られることが期待される。