Ar/Ar chronology considering heterogeneous shock metamorphism in meteorites

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K14543
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 17010:Space and planetary sciences-related
• Research Institution: Kyoto University (2021-2022); National Institute of Polar Research (2020)
• Principal Investigator: Takenouchi Atsushi 京都大学, 総合博物館, 助教 (60865426)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 隕石 / 衝撃変成作用 / 希ガス年代

Outline of Final Research Achievements

We conducted detailed observations and part-by-part argon-argon dating of meteorites with various degrees of impact metamorphism, including those containing impact melt veins and high-pressure minerals, those that have been brecciated, and those that have not undergone strong impact metamorphism. The meteorites with heterogeneous impact metamorphism show different ages, especially in the low-temperature fraction, depending on the location of the analysis. On the other hand, the age of the high-temperature fractions of the breccia is uniform, indicating that the strong thermal events are independent of the microstructures. The results indicate that it is necessary to select a tissue that is consistent with the event of interest when dating because the events that can be recorded vary depending on the analysis location.

Free Research Field

隕石学

Academic Significance and Societal Importance of the Research Achievements

隕石の年代学と岩石組織学はそれぞれ専門性が高いため，別々に行われることがしばしばある。しかし，隕石の成因などを議論する際は両者を組み合わせることが多く，年代と組織が実際に対応しているか不明瞭なまま議論されてしまうことが多くある。本研究では，分析する箇所によっては同一の隕石でも異なる年代を示すことを明示し，議論の目的のイベントが記録されているであろう組織を選択して年代測定をすることの重要性を改めて示した。本研究は，今後精確な分析を行っていく上での足がかりと成る研究である。