¹S. A. Singerling,²A. J. Brearley
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70061]
¹Schwiete Cosmochemistry Laboratory, Goethe University, Frankfurt, Germany
²Department of Earth and Planetary Sciences, MSC-03 2040, 1 University of New Mexico, Albuquerque, New Mexico, USA
Published by arrangement with John Wiley & Sons

We conducted a scanning electron microscopy (SEM) and transmission electron microscopy (TEM) study of sulfide–metal assemblages (SMAs) in minimally to moderately altered CR2 chondrites. The assemblages occur on chondrule rims and consist of kamacite cores rimmed by pyrrhotite. The kamacite and pyrrhotite share orientation relationships, arguing for a genetic link. The SMAs contain secondary alteration products, including nanoscale magnetite at the sulfide–metal interface (minimally altered SMAs) and magnetite, serpentine, nanoscale Ni-rich metal at metal–magnetite interfaces, and Ni,S-bearing reaction fronts within magnetite (moderately altered SMAs). We argue the SMAs initially formed in the solar nebula from the separation of immiscible metal and silicate melts followed by sulfidization of the metal. Aqueous alteration on the asteroidal parent body caused the kamacite to transform into magnetite and the magnetite to transform into serpentine. Alteration of kamacite to magnetite occurred under oxidizing and alkaline conditions, whereas alteration of magnetite to serpentine occurred under reducing, alkaline, and higher aSiO2 conditions. Serpentinization of magnetite appears to be a relatively common process in some carbonaceous chondrites. Additionally, theoretical and experimental studies are needed that simulate the oxidation of metal by H2O gas and water and also serpentinization of magnetite to form serpentine with variable Mg-Fe contents.

¹Gabriel Zachén,¹Carl Alwmark,¹Sanna Alwmark,^2,3Ludovic Ferrière,^4,5Roger H. Hewins
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70051]
¹Department of Geology, Lund University, Lund, Sweden
²Natural History Museum Vienna, Vienna, Austria
³Natural History Museum Abu Dhabi, Abu Dhabi, United Arab Emirates
⁴IMPMC, MNHN, UMR CNRS 7590, Sorbonne Université, Paris, France
⁵Earth and Planetary Sciences, Rutgers University, Piscataway, New Jersey, USA
Published by arrangement with John Wiley & Sons

Mesosiderites are rare, differentiated meteorites, so-called stony-iron meteorites—they are impact breccias composed of an unusual mix of crustal basalt and pyroxenite, core-derived metal, but no mantle materials. This odd mixture makes their origin enigmatic and has inspired many different formation theories over the last several decades. Some of the outstanding questions have regarded the origin of the metal, whether it came from another celestial body or from within the main parent body, and the puzzlingly low abundance, or absence, of mantle material in mesosiderites. The role of impacts has been central to most of the suggested theories, but mesosiderites show little to no evidence of shock metamorphism. The mystery of the origin of mesosiderites is further compounded by the relatively limited amount of published data, as well as the restricted number of samples available for research. With the detailed investigation and reclassification of the mesosiderites Lamont, Acfer 265, Queen Alexandra Range 86900 (QUE 86900), and MacAlpine Hills 88102 (MAC 88102) presented herein, our new observations shine some much-needed light on this meteorite group. Based on their petrologic and metamorphic characteristics, Lamont is classified as a B3/4, Acfer 265 and QUE 86900 as A1, and MAC 88102 as an A4 mesosiderite. The observation of multiple sets of parallel thin lamellae in high-Ca plagioclase and cristobalite in Lamont, and a silicate emulsion in QUE 86900 is proposed to be shock-related features. In both Lamont and QUE 86900, these features are interpreted to be subsequent to the initial impact, which mixed crustal and core material, and prior to deep burial. No shock-related features were noted in Acfer 265 and MAC 88102.

^1,2C. S. Harrison,¹A. J. King,²R. H. Jones,³L. Piani
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70052]
¹Planetary Materials Group, Natural History Museum, London, UK
²Department of Earth and Environmental Sciences, The University of Manchester, Manchester, UK
³Centre de Recherches Pétrographiques et Géochemiques CNRS, Université de Lorraine, Metz, France
Published by arrangement with John Wiley & Sons

Phosphate minerals are significant carriers of volatiles (e.g., OH) and halogens in chondritic material; however, their origin in most groups of carbonaceous chondrites remains poorly characterized. We have determined the abundance, morphology, texture, and composition of phosphate grains in aqueously altered CI chondrites and in hydrated and thermally metamorphosed Antarctic CY chondrites using scanning electron microscopy and electron probe microanalysis. Phosphates include apatite (formula Ca5(PO4)3X, where X = F-, Cl-, OH- or other anions) and sodium-bearing magnesium phosphate, both of which formed during episodes of aqueous alteration on the CI and CY parent bodies. Apatite grains in the CI chondrites range up to 40 μm in size with a modal abundance of ~0.10 area%, while in the CYs, the largest grains are ~50 μm in size and the modal abundance is ≤0.70 area%. Analysis by secondary ion mass spectrometry (SIMS) indicates that apatite in the CYs contains ~1.0–1.8 wt% H2O, with δD values of −84‰ to 393‰ likely reflecting aqueous and thermal processing. Apatite in both the CI and CY chondrites is rich in fluorine, with fluorine abundances that range from 20 to 80 mole% of the X (anion) site. This contrasts with apatite in other chondrite groups, which is predominantly Cl-rich. Estimated bulk chondrite F abundances based on F abundance in apatite are 12–21 ppm F for the CI chondrites and 61 ppm F for the CY chondrites. This is comparable to bulk CI chondrite F abundances in the literature, suggesting that most fluorine is hosted in apatite. However, the chlorine content of CI chondrite apatite (<0.05 wt%) is too low to account for the bulk chondrite Cl abundance, indicating that Cl is hosted in other phases. Mg,Na-phosphate, a rare extraterrestrial mineral, has a modal abundance of ~0.02 area% in both the CI and CY chondrites. Mg,Na-phosphates in the CI and CY chondrites are halogen-poor (<0.15 wt%) and are typically hydrated in the CIs (analytical totals as low as 67 wt%) and dehydrated in the CYs (analytical totals >96.0 wt%). The occurrence of Mg,Na-phosphates in the CI and Antarctic CY chondrites is indicative of brines on their respective parent bodies. Similarities between the two groups, as well as with the phosphate mineral assemblage in asteroids Ryugu and Bennu, indicate that comparable fluid compositions and environmental conditions were prevalent on numerous parent bodies in the early Solar System.

¹Christopher D.K. Herd, ¹Sophie Benaroya
Geochimica et Cosmochimica Acta (in Press) (Open Access) Link to Article [https://doi.org/10.1016/j.gca.2025.10.001]
¹Department of Earth and Atmospheric Sciences, 1-26 Earth Sciences Building, University of Alberta, Edmonton, AB T6G 2E3, Canada
Copyright Elsevier

We provide an updated compilation of oxygen fugacity (fO₂) estimates for martian meteorites, with a specific focus on the shergottites. The compilation includes estimates from over 70 distinct lithologies from the martian meteorite suite, calculated from olivine-pyroxene-spinel and Fe-Ti oxide oxybarometers. Olivine-pyroxene-spinel oxybarometry was recalculated from original data sources using an updated model. Results from V- in-olivine and Eu/Gd oxybarometry from the literature are provided for comparison. Oxygen fugacity data are plotted against chondrite-normalized La/Yb ratio to critically examine the correlation between fO₂ and incompatible trace element (ITE) enrichment previously postulated. We find that the correlation holds, when factors including differences in petrogenetic histories, distinctions between shergottite petrologic types, and early vs. late crystallizing assemblages, are taken into consideration. We model the degassing of H, C and S species from primitive martian magmas using the MAGEC model (Sun and Lee, 2022) and successfully reproduce the 2–3 log unit increase recorded within olivine-phyric shergottites between early and late crystallizing assemblages. We find that volatile degassing can account for most of the fO₂ increase in the olivine-phyric shergottites, without requiring extensive auto-oxidation, as long as their fO₂ remains at or below a value equivalent to the fayalite-magnetite-quartz (FMQ) equilibrium throughout their crystallization. With these considerations in mind, we propose a martian mantle redox-ITE trend defined by shergottite sources: a depleted source (La/Yb ∼ 0.1) with fO₂ = FMQ-4 ± 0.7, an intermediate source (La/Yb ∼ 0.5) at fO₂ = FMQ-3 ± 0.75 and an enriched source (Lab/Yb ∼ 1) at fO₂ = FMQ-2 ± 0.75. The depleted/reduced source is likely graphite saturated.

Comparisons with compilations of fO₂ from basaltic eruptives on Earth highlight fundamental differences between the two planets ultimately attributable to differences in degree of mantle convective mixing throughout their histories: terrestrial mantle sources produce basaltic eruptives with a relatively limited range of fO₂, within ±1 log unit of FMQ; any degassing from these magmas results in reduction, not oxidation. The mantle sources of the shergottites – while represented by a similarly limited range of fO₂, ∼FMQ-4 to FMQ-2 – produce basaltic eruptives with a range of low initial (magmatic) fO₂; the more reduced nature of these magmas make them more susceptible to overprinting by degassing of H-C-S species during eruption and emplacement. Whether the mantle sources inferred from the shergottites apply to other martian meteorites (or other martian igneous rocks) remains to be tested; however, post-magma ocean crystallization processes would have acted to oxidize and overprint initial mantle sources defined by the shergottite fO₂-ITE trend.

^1,2Zhiming Chen et al. (>10)
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2025JE008976]
¹State Key Laboratory of Deep Earth Processes and Resources, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China
²College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, China
Published by arrangement with John Wiley & Sons

Lunar regolith contains not only materials derived from the local rock unit, but also materials transferred from remote craters, which are crucial for investigating the lithological diversity of the lunar surface. In this study, we conducted detailed petrography and geochemical analyses and measured the cross-sectional area of plagioclase fragments and impact glass particles selected from the Chang’e 6 (CE-6) regolith, the first lunar far-side returned sample. Statistics of plagioclase fragments and impact glass are used to estimate the proportion of the diverse components in the CE-6 regolith. The results reveal 35.7 vol% and 28.2 vol% exotic components in CE-6 plagioclase and impact glass fractions, respectively. As plagioclase, pyroxene and glass particles are the three dominant phases (>95 vol%) in the CE-6 regolith, together with previously reported pyroxene compositions, we estimate that the abundance of the exotic materials is 23.5–33.5 vol%. These exogeneous components include very-low-Ti (VLT) basalt (2%–3%), ferroan anorthosite (5%–9%), Mg-suite (15%–20%), KREEP-related (∼0.1%), and highlands-mare-mixed materials (∼1%). The VLT-basalt component is most likely from the mare basalt unit to the east of the landing site or beneath the local mare layer. Based on the ejecta orientations and model age of impact craters, ferroan anorthite, Mg-suite and KREEP-related materials are likely transferred from Vavilov/Pythagoras (highland anorthosite), Chaffee S/White’ (rich in mafic minerals), and Birkeland (high Th contents) craters, respectively. The abundant non-mare components in the CE-6 regolith contrast to the very scarce exotic materials in the CE-5 lunar regolith, potentially providing valuable insights into the composition of the lunar far-side.

¹Garima Sodha,¹Deepak Dhingra
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2024JE008809]
¹Department of Earth Sciences, Indian Institute of Technology Kanpur (IITK), Kanpur, Uttar Pradesh, India
Published by arrangement with John Wiley & Sons

The spatial distribution of Mg-spinel lithology at South Pole-Aitken (SPA) basin is revealed by systematic mineralogical survey along the basin rings. We report Ingenii-Thomson region as a Mg-spinel anomaly, having the largest number of exposures based on newly identified and previously reported occurrences on the Moon. The timing of Mg-spinel formation is constrained by using SPA impact as a key geological time marker. Post-SPA origin of this lithology is favored in this region due to the general lack of pervasive Mg-spinel occurrences along basin rings, being the deepest exposures of the pre-SPA crust. Our detailed mineralogical analyses also highlight several detections of Mg-spinel lithology exhibiting weak 1,000 nm absorption band, emphasizing the need for a detailed analysis of such locations. Collectively, these salient findings have important implications for understanding the compositional diversity of Mg-spinel lithology, refinement of the formation models and determining the role of Mg-spinel lithology in the lunar crustal evolution.

^1,2,3Qing Zhang et al. (>10)
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2025JE009196]
¹Key Laboratory of Lunar and Deep Space Exploration, National Astronomical Observatories, Chinese Academy of Sciences, Beijing, China
²Institut d’Astrophysique Spatiale, CNRS, Université Paris-Saclay, Orsay, France
³School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing, China
Published by arrangement with John Wiley & Sons

The Zhurong rover conducted in situ spectral investigations of southern Utopia Planitia, where the bedrock composition remains relatively unknown due to dust cover. Here we identify some spectrally distinct dark patches sporadically occurring on rocks by combining the Multispectral Camera and Short-Wave Infrared data. These dark patches represent relatively dust-free surfaces and exhibit concave-up blue slopes in the near-infrared not identified in that area from orbital data. This spectral signature is most consistent with silica-enriched leached rinds on basaltic glass. The presence of such weathering rinds could imply leaching in an acidic aqueous environment of igneous rocks previously transported to the landing site as impact ejecta or pyroclastic deposits by explosive volcanism. In situ observations link the dark patches to the northern low-albedo regions, suggesting that the surficial acidic weathering may be more widespread and occurred in the northern lowlands under Amazonian climatic conditions.

¹Huaqing Cao,¹Jing Li,¹Chang Zhang,¹Lige Bai
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2024JE008884]
¹State Key Laboratory of Deep Earth Exploration and Imaging, College of GeoExploration Science and Technology, Jilin University, Changchun, China
Published by arrangement with John Wiley & Sons

The Chang’e-4 Lunar Penetrating Radar (LPR) has proven instrumental in uncovering the structure and composition of the Von Kármán crater on the lunar farside. Utilizing high-frequency (HF) LPR data collected during the first 53 lunar days, this study employs Least Squares Migration to achieve high-resolution imaging of shallow subsurface structures. Additionally, the peak frequency shift method is applied to estimate the loss tangent and the TiO2 + FeO content of the shallow regolith. The average loss tangent of the shallow regolith ranges from 4.3 × 10−3 to 5.5 × 10−3, corresponding to an iron-titanium content of 11.2 wt% to 14.7 wt%. Along the Yutu-2 rover’s traverse (300–500 m and 1,000–1,150 m), the regolith exhibits high TiO2 + FeO content, suggesting that these materials may originate from deeper basalt layers. By integrating radar profiles with estimates of TiO2 + FeO content, this study provides a detailed geological interpretation of subsurface layers and unique structures. These findings reconstruct critical geological events in the shallow subsurface at the landing site, offering new insights into the geological evolution of this region.

^1,2Zhan Zhou et al. (>10)
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025JE009052]
¹Key Laboratory of Planetary Science and Frontier Technology, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
²University of Chinese Academy of Sciences, Beijing, China
Published by arrangement with John Wiley & Sons

The Moon has been highly shocked as evidenced by numerous impact craters on its surface. High-pressure minerals are expected to form during these shock events and can be used to unravel the pressure and temperature conditions for the shock events. However, high-pressure minerals are rarely reported in the lunar returned samples, yielding a discrepancy with the prediction. The lunar soils returned by the Chang’e-6 (CE6) mission from the South Pole-Aitken (SPA) basin provide new opportunities to investigate the shock metamorphism of the lunar samples and the shock events on the Moon. Here, we reported the discovery of coesite in a shock-induced melt pocket from a CE6 mare basalt, which could have experienced a shock event with a peak pressure of ∼24 GPa. The coesite exhibits two types of occurrences, a polycrystalline aggregate in the center and a ring along the margin of a silica clast. The coesite could have been formed by solid-state transformation followed by partial conversion to silica glass during decompression. The coesite has a higher survival temperature and a slower back-transformation rate than most other high-pressure minerals, which are favorable for its preservation under high-temperature conditions of lunar soils induced by impacts. These findings provide new insights for the preservation of coesite in natural shock events and indicate that more thermal-resistant high-pressure minerals could have been formed and preserved in lunar samples than previously thought, providing new targets for studying the shock events on the Moon.

¹Jessika L. Valenciano,¹Clive R. Neal,²Scott A. Eckley,³Charles K. Shearer, the ANGSA Science Team
Journal of Geophysical research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2024JE008580]
¹Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, IN, USA
²Amentum—JETS2, Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, Houston, TX, USA
³Institute of Meteoritics, University of New Mexico, Albuquerque, NM, USA
Published by arrangement with John Wiley & Sons

Double drive tubes 73002 (upper) and 73001 (lower) were collected during Apollo 17 from a landslide deposit at the base of the South Massif in the Taurus-Littrow valley. The drive tubes were opened for the first time as part of the Apollo Next Generation Sample Analysis (ANGSA) project, representing “new” samples from the Moon. Many lithic fragments (>1 mm in size) were extracted from the core during core dissection and preliminary examination (PE), including high-Ti mare basalt clasts. Those >4 mm fragments were three-dimensionally imaged using X-ray computed tomography (XCT). The crystal size distributions of ilmenite were measured in 10 high-Ti mare basalts and within the matrix of an impact melt breccia from drive tube 73002 using thin section “slices” from the 3D XCT scans. Residence times (of the crystals in the melt from which they grew) were estimated using experimental growth rates for each sample with all but 73002,2015 being relatively short (<1 year). Linear (constant) cooling rates were determined, expanding upon data already obtained from other Apollo 17 high-Ti basalts showing that these ANGSA basalt clasts had similar cooling histories to those previously studied. Comparison with ilmenite cooling rate experiments estimated cooling rates of <10°C/h for each clast.