[B-BG02] Geo-Bio Interactions and its Applications

[BBG02-08] Revisiting the clay mineral compositions in carbonaceous chondrites

*Reon Okumura¹, Keisuke Fukushi², Tomohiro OHNO³, Yoko Kebukawa⁴, Yoshio Takahashi⁵ (1.School of Geosciences and Civil Engineering, College of Science and Engineering, Kanazawa University, 2.Institute of Nature and Environmental Technology, Kanazawa University, 3.Department of Earth and Planetary Environmental Science, Faculty of Science, The University of Tokyo, 4.Department of Earth and Planetary Science, School of Science, Institute of Science Tokyo, 5.Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo)

Keywords:Carbonaceous Chondrite, XAFS, Hydrous Magnesium Silicate

Chondrites are meteorites believed to originate from undifferentiated small bodies. Since carbonaceous chondrite meteorite samples contain minerals with water in their crystal structure, it is believed that liquid water once existed on their parent bodies (Brearley, 2006). This liquid water is thought to have been responsible for the synthesis, decomposition, and alteration of life's building blocks through reactions with volatile substances and rocks contained in the small bodies. Therefore, if we can determine the physicochemical conditions of the liquid water that once existed on these small bodies, we may be able to understand the physicochemical origins of life's building blocks contained within them. Fukushi et al. (2019) developed a method to precisely reconstruct the water quality - that is, the types and concentrations of dissolved components - of past water by utilizing the physicochemical properties of authigenic minerals formed by water activity in solar system bodies. To apply this method to extraterrestrial materials, accurate understanding of the authigenic minerals' characteristics is necessary. The main component of carbonaceous chondrite meteorite samples is hydrous Mg-silicate. Based on X-ray diffraction and electron microscopies, this hydrous Mg-silicate has traditionally been considered to be a nanoscale mixture of serpentine and saponite, both of which are layered silicates (Blinova et al., 2014; King et al., 2015). Both serpentine and saponite are clay minerals that form through reactions between Mg-bearing rocks and water, and their formation is ubiquitous on Earth. However, the environmental conditions under which each clay mineral forms are typically different, and geological occurrences where serpentine and saponite coexist at the nanoscale are rarely reported on Earth. To reconstruct the water quality of undifferentiated small bodies, it is necessary to elucidate the mineralogical nature of the "serpentine/saponite" nano-mixture observed in chondrite matrices. Recently, in the field of cement engineering, a material called "Magnesium Silicate Hydrate" (M-S-H) has paid attention. M-S-H is formed by the reaction between seawater and cement, and its engineering characteristics have been studied (Roosz et al., 2015; Bernard et al., 2024, etc.). Additionally, M-S-H is thought to be mineralogically similar to poorly crystalline Mg-silicates that form naturally in alkaline lakes or during early diagenesis of modern lake sediments (Zeyan et al., 2021; Nishiki et al., 2023). M-S-H is a metastable phase composed of nanoscale serpentine and talc (or saponite) layers, has an intermediate composition between serpentine and saponite, and exhibits cation exchange capacity (Bernard et al., 2019). M-S-H shares mineralogical characteristics with carbonaceous chondrite meteorite matrix materials, leading to the hypothesis that Earth-observed M-S-H may be involved in what has traditionally been considered a "serpentine/saponite" nano-mixture. This study aims to determine which model is more plausible - the traditional view of composition solely of saponite and serpentine, or our hypothesis involving M-S-H - by examining the hydrous silicates in Ivuna, Orgail and Tagish Lake meteorite using local chemical analysis and X-ray absorption spectroscopy.