^1,2Liying Huang et al. (>10)
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2023JE007955]
¹State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing, China
²College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, China
Published by arrangement wth John Wiley & Sons

Baddeleyite (ZrO2) is widespread in lunar basalts and frequently used for U-Pb geochronology of magmatic and impact events. The formation of baddeleyite involves two primary mechanisms: (a) crystallization from late-stage magma, and (b) decomposition of zircon under high-temperature (high-T) conditions. Baddeleyite with distinct formation mechanisms commonly displays different morphologies. In a Chang’e-5 lunar basalt, we report baddeleyite with two different morphologies, termed “singular type” and “aggregate type.” Petrographic and crystallographic analyses were conducted on both types of baddeleyite to understand their formation conditions and evolution processes. Despite the similarity in the morphology and mineral assemblages between the aggregate type baddeleyite and zircon decomposition products, the petrographic characteristics and the rarity of zircon in lunar basalts tend to suggest that both types of baddeleyite are derived from magma crystallization. Crystallographic relationships observed in both types indicate a phase transformation from the precursor tetragonal-ZrO2/cubic-ZrO2 or orthorhombic-ZrO2 phase. Two potential scenarios are proposed for the formation of these microstructures: (a) direct crystallization of high symmetry ZrO2 from magma, and (b) crystallization of baddeleyite from magma followed by a high-pressure (high-P) event causing its phase transition. However, due to unresolved scientific issues in both scenarios, an accurate evolutionary process cannot currently be determined. Therefore, extensive thermodynamic experiments are necessary to enhance our understanding of baddeleyite microstructures as indicators of P-T processes, providing insights into magmatism and the impact history of planetary bodies.

¹Toshihiro Tada,^2,3Kosuke Kurosawa,⁴Naotaka Tomioka,^5,6Takayoshi Nagaya,³Junko Isa,⁷Christopher Hamann,⁸Haruka Ono,⁹Takafumi Niihara,³Takaya Okamoto,^1,3Takafumi Matsui
Journal of Geophysical Research (Planets) (in Press) Open Access Link to Article [https://doi.org/10.1029/2024JE008409]
¹Institute for Geo-Cosmology, Chiba Institute of Technology, Chiba, Japan
²Department of Human Environmental Science, Graduate School of Human Development and Environment, Kobe University, Hyogo, Japan
³Planetary Exploration Research Center, Chiba Institute of Technology, Chiba, Japan
⁴Kochi Institute for Core Sample Research, X-star, Japan Agency for Marine-Earth Science and Technology, Kochi, Japan
⁵Department of Environmental Science, Tokyo Gakgei University, Tokyo, Japan
⁶Department of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan
⁷Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, Germany
⁸Research Organization of Science and Technology, Ritsumeikan University, Kyoto, Japan
⁹Department of Applied Science, Okayama University of Science, Okayama, Japan
Published by arrangement with John Wiley & Sons

Feather features (FFs) in quartz consist of a planar fracture (PF) and associated fine lamellae (FF lamellae; FFL) and have been observed in various natural impact structures. However, the mechanisms and conditions of FF formation are poorly understood. We conducted shock recovery experiments on granite using decaying compressive pulses to investigate the formation conditions of FFs. We characterized the recovered samples using an optical microscope equipped with a universal stage, a scanning electron microscope combined with an electron back-scattered diffraction detector, and a transmission electron microscope. We found that FFs are formed over a wide range of peak pressures (2–18 GPa) and that FFs can be divided into at least three types (I–III) based on the crystallographic orientation of the PFs and FFL, the angle between the orientation of the FFL and the propagation direction of the compression wave, and the presence/absence of amorphous silica in the FFL. The peak pressures that produce type I–III FFs are estimated to be <12, 12–14, and >16 GPa, respectively. We propose that FFs can be used as a shock barometer for quartz-bearing rocks.