Development of zircon indicators to reveal behaviors of zirconium in the Earth's surface environment

2022 Fiscal Year Final Research Report

• Project/Area Number: 18K05020
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 31020:Earth resource engineering, Energy sciences-related
• Research Institution: National Institute of Polar Research
• Principal Investigator: Takehara Mami 国立極地研究所, 先端研究推進系, 特任助教 (70792448)
• Co-Investigator(Kenkyū-buntansha): 福山 繭子 秋田大学, 理工学研究科, 准教授 (40630687) ; 外田 智千 国立極地研究所, 先端研究推進系, 教授 (60370095)
• Project Period (FY): 2018-04-01 – 2023-03-31
• Keywords: ジルコン / 二次イオン質量分析

Outline of Final Research Achievements

Zircon is a physicochemically stable zirconium (Zr) silicate mineral, but it is well known that zircon can be damaged in its crystal structure by radiative modification of uranium and thorium. Moreover, there have been cases of zircon reacting with hydrothermal fluids and being altered, thereby modifying its crystal structure and chemical composition. Here, we investigated the stability of Zr in the Earth's surface environment and its behavior in underground magma reservoirs and collected information to develop chemical indicators (zircon index) to evaluate the behavior of Zr. Analyses of hydrothermally altered zircons indicated that the contents of elements such as lithium and potassium, which are monovalent cations, may be a more sensitive zircon alteration index than calcium. The oxygen isotope ratios of zircon collected from a compositionally zoned pluton indicate that they may provide a Zr fractionation index that reflects the crystal differentiation process in magma reservoirs.

Free Research Field

地質学

Academic Significance and Societal Importance of the Research Achievements

ジルコンの安定性を示す指標によって長期的な時間スケールにおけるジルコンの変質作用の程度の系統的な評価が進むことで、地球表層環境におけるジルコニウムの安定性の評価とウランやトリウム等の放射性同位体の流出や濃集の推定も可能となる。こうした情報は原子力発電所における原子炉のメルトダウン中のソースターム評価とシビアアクシデント解析コードのさらなる改善への貢献が期待される。また、ジルコニウムの分別を示す指標を組み合わせることでジルコン中のジルコニウム・ハフニウムの主原料としての評価への貢献が期待される。