¹Lang Zhang, ¹Ai-Cheng Zhang, ¹Xiao-Wen Liu, ²Yan-Jun Guo, ¹Jia-Ni Chen, ³Yuan-Yun Wen, ⁴Qiu-Li Li, ⁴Yu Liu, ⁴Xiao-Xiao Ling, ⁵Jin S. Zhang
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2025.06.032]
¹State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
²CAS Key Laboratory of Standardization and Measurement for Nanotechnology, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing, China
³Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
⁴State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
⁵Department of Geology and Geophysics, Texas A&M University, College Station, TX 77843, USA
Copyright Elsevier

Mineralogical records of strong shock metamorphism (around or above 20 GPa) are common in L-group chondrites, Martian meteorites, and lunar meteorites, but rarely reported in Howardite-Eucrite-Diogenite (HED) meteorites. Here, we report detailed mineralogical observations of shock-induced features and ion-microprobe merrillite U-Pb ages from the pigeonite cumulate eucrite Northwest Africa (NWA) 8326. Shock-induced mineralogical features in NWA 8326 contain: (i) planar fractures in pyroxene and partial maskelynitization of plagioclase; (ii) presence of high-pressure minerals such as tissintite, stishovite, vacancy-rich augite, super-silicic garnets within melt veins, and xieite, tuite, and reidite in the host rock outside melt veins. We also observed fine-grained clinoenstatite and pigeonite at the edges of shock melt and propose they formed through metastable crystallization. Our study indicates that NWA 8326 experienced shock metamorphism of at least 20 GPa, comparable to those observed in L-group chondrites, Martian meteorites, and lunar meteorites. We propose that the relatively low shock pressures inferred for shocked eucrites in previous investigations could be due to the absence of suitable high-pressure mineralogical indicators. The ion-microprobe 207Pb/206Pb age of merrillite in NWA 8326 is 4238 ± 32 Ma (95 % confidence) and represents the timing of the shock metamorphism. The similarity of the impact ages across NWA 8326, some eucrites, lunar samples/meteorites, and chondrites suggests that there were probably widespread impact events at ∼4.2 Ga in the Solar System.

¹Fabio Joseph,²Igor Drozdovsky,^1,3Malte Junge,¹Joanna Brau,^1,3Melanie Kaliwoda
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14381]
¹Department of Earth and Environmental Sciences, Ludwig-Maximilians-University, Munich, Germany
²Directorate of Human and Robotics Exploration, European Astronaut Centre (EAC)—European Space Agency (ESA), Troisdorf, Germany
³Mineralogical State Collection, SNSB, Bavarian State Collections of Natural History, Munich, Germany
Published by arrangement with John Wiley & Sons

Chondrules are one of the oldest objects in our solar system. Therefore, they play an important role as messengers, offering new insights into the early stage of the solar system processes and potential understanding of formation. Therefore, the investigation of all detailed structures, especially not well-known inversely zoned chondrules (IZ chondrules), is crucial. In this paper, we describe the chemical as well as the structural composition of inversely zoned chondrules with EDX, light microscopy, BSE, and Raman spectroscopy, which reveal a new process in the early solar system. Inversely zoned chondrules consist of a pyroxene core surrounded by an olivine rim. The olivines have a higher Fe content (Fa, 39%–41%) compared to those found in most other chondrules. The core displays a radial pyroxene chondrule with sometimes olivines (Fa34). These IZ chondrules have originated during the early stages of our solar system and do not show the typical known forming process of chondrules. Minor fluctuations in the SiO₂ content of chondritic melts can lead to SiO₂ depletion of the residual melt at a constant temperature due to crystallization of pyroxene, which shifts the phase equilibrium in favor of fayalite-enriched olivine, which forms a rim.