Development of new geothermometer and cooling speed-meter for extraterrestrial materials based upon phase transitions of silica minerals

2022 Fiscal Year Final Research Report

• Project/Area Number: 21K18645
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 17:Earth and planetary science and related fields
• Research Institution: The University of Tokyo
• Principal Investigator: Mikouchi Takashi 東京大学, 総合研究博物館, 教授 (30272462)
• Co-Investigator(Kenkyū-buntansha): 杉山 和正 東北大学, 金属材料研究所, 教授 (40196762)
• Project Period (FY): 2021-07-09 – 2023-03-31
• Keywords: シリカ鉱物 / 相転移 / トリディマイト

Outline of Final Research Achievements

We have analyzed silica minerals in diverse extraterrestrial materials. Among them, we especially analyzed lunar meteorites in particular. As with Martian meteorites, many silica phases were amorphous, suggesting that they were affected by strong shock metamorphism. In fact, many of the samples we analyzed were brecciated, further indicating the strong influence of shock metamorphism. Heating and cooling experiments using an electric furnace are continuing under various conditions, and it will take some more time to obtain comprehensive results. The results of X-ray diffraction experiments on tridymite in both terrestrial and extraterrestrial samples did not reveal any differences between "terrestrial" and "meteoritic" types, as has been suggested, but suggested that it may be only a matter of differences in crystallinity.

Free Research Field

惑星物質科学

Academic Significance and Societal Importance of the Research Achievements

これまでに地球外物質中ではあまり注目を集めることの無かったシリカ鉱物であるが、多様な多形が存在し、重要な熱履歴・衝撃履歴の情報を含んでいることが示唆されることが、本研究を通じてあらためて示された。特にトリディマイトにおいては、複雑な多形、ポリタイプ、双晶組織を示すことからX線回折データの解釈が容易ではないが、地球型・隕石型とこれまでは区別して分けられていたものが、必ずしもそのような必要が無い可能性があることが分かって来た。