¹Jun Sakuma, ^2,3Hisashi Asanuma, ²Naoto Takahata, ^4,5Akira Yamaguchi, ¹Tsuyoshi Iizuka
American Mineralogist, 111, 1683–1692
Link to Article [https://msaweb.org/MSA/AmMin/TOC/2026/Abstracts/AM111P1683.pdf]
¹Department of Earth and Planetary Science, The University of Tokyo, Bunkyo, Tokyo 113-0033, Japan
²Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba 277-0882, Japan
³Graduate School of Human and Environmental Studies, Kyoto University, Sakyo, Kyoto 606-8501, Japan
⁴National Institute of Polar Research, Tokyo 190-8518, Japan
⁵Department of Polar Science, School of Multidisciplinary Science, SOKENDAI, Tokyo 190-8518, Japan

Copyright: The Mineralogical Society of America

Precise and accurate ages of asteroidal crusts are fundamental for reconstructing the timeline of magmatic, metamorphic, and impact events in the early Solar System. Zirconolite (CaZrTi2O7) is an accessory mineral found in a wide range of crustal rocks on both the Earth and Moon and has proven to be a potentially useful U-Pb chronometer. However, this mineral is rare in asteroidal meteorites, and its use for early Solar System chronology has been limited.

We present the in situ occurrence, U-Pb chronology, and chemistry of zirconolite in the andesitic meteorite Erg Chech 002, which represents a sample of the oldest known asteroidal crust. Zirconolite occurs as needle- and fiber-shaped and stubby crystals with widths of ∼3 μm and lengths up to ∼30 μm. Electron and ion microprobe analyses yielded concordant U-Pb data with a weighted mean 207Pb/206Pb age of 4557.9 ± 4.3 Ma (2σ), rendering it the Solar System’s oldest known zirconolite. Yet, this age is distinctly younger than reported high-precision 207Pb/206Pb ages varying from 4565.6 to 4566.2 Ma, which were obtained by acid leaching of pyroxene and whole-rock samples of the meteorite.

From its mineralogical and REE–(U Th)–(Nb Ta) characteristics, we argue that the zirconolite age represents the timing of a shock metamorphism of the parent asteroid’s crust. Our results suggest that 207Pb/206Pb dating for acid-leached samples can be affected by including even a tiny amount of metamorphic zirconolite, calling for caution in interpreting the high-precision 207Pb/206Pb age data. On the basis of thermodynamic and geochemical considerations, we infer further occurrences of zirconolite in alkali-silica-rich asteroidal rocks that rapidly cooled from high temperatures.

^1,2Xiaorong Qin, ^1,3,4Jianxi Zhu, ^1,3,4Hongping He, ⁵Yiliang Li
American Mineralogist, 111, 1537–1546
Link to Article [https://msaweb.org/MSA/AmMin/TOC/2026/Abstracts/AM111P1537.pdf]
¹State Key Laboratory of Deep Earth Processes and Resources, Guangzhou Institute of Geochemistry/Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
²National Key Laboratory of Deep Space Exploration/School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China
³Center for Advanced Planetary Science (CAPS), Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
⁴University of Chinese Academy of Sciences, Beijing 100049, China
⁵Department of Earth & Planetary Sciences, the University of Hong Kong, Hong Kong 999077, China
Copyright: The Mineralogical Society of America

In Gale crater, the Curiosity rover has documented a sequence of ∼3500 million year old sedimentary rocks containing smectite, indicating the presence of liquid water. However, the paleoenvironment in Gale crater, particularly the question of whether a paleolake ever existed, remains hotly debated.

Here, we compare the interlayer cations of smectite from terrestrial basalt weathering sequences and marine environments. Marine smectites are considered key analogs for smectites detected in martian paleolakes due to perceived similarities in formation processes and geochemical contexts between terrestrial marine settings and ancient lacustrine environments on Mars. Numerous observations show that K/Na-rich smectite is associated with marine environments, whereas Ca2-rich smectite is typical of terrestrial basalt weathering sequences.

We find that the basal spacings of K- and Na-smectite are ∼10.0 Å, whereas the basal spacings of Ca2- and Mg2-smectite range from 13.1 to 13.8 Å at a relative humidity (<1%) equivalent to that of the Curiosity rover on Mars. The XRD profiles measured by Curiosity in Gale crater show a basal spacing of ∼10.0 Å, which is attributed to K/Na-rich smectites. Our results support the idea that the presence of K/Na-rich smectites from Yellowknife Bay to Glen Torridon indicates that a lake existed in the 3500 million-year-old Gale crater, confirming that the habitable state lasted longer than previously thought.