¹Eleanor C. McIntosh, ¹James M.D. Day
Geochimics et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.12.059]
¹Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, USA
Copyright Elsevier

The Apollo 17 high-Ti orange (74220) and Apollo 15 low-Ti green (15426) lunar pyroclastic glasses are some of the most primitive igneous samples from the Moon and are considered critical for understanding the volatile content of the lunar interior. The orange and green glass deposits are petrologically distinct, containing both holohyaline (glassy) and crystallized beads. In this study, edge and center analyses on holohyaline beads representative of the deposits were conducted by laser ablation inductively coupled plasma mass spectrometry to constrain the distribution of moderately volatile elements (MVE: K, Cu, Zn, Cs, Ga, Ge, Rb, Cd, and Pb), and trace element images were produced of the beads in 74220. Bead edges have elevated MVE abundances compared to centers in the larger (107 µm average diameter) low-Ti Apollo 15 green glasses, likely resulting from syn-eruptive processes. Leaching experiments of 15,426 bulk beads support a large fraction of Na, K, Zn, Cd, Cd and Pb on their outer surfaces. The smaller (42 µm average diameter) high-Ti Apollo 17 orange glasses have a greater extent of overlap in MVE contents between bead edges and centers. Orange and green glass bead centers offer approximations of melt MVE abundances, indicating ∼500 µg/g K, ≤20 µg/g Zn, ∼6 µg/g Cu, <4 µg/g Ga and ≤ 1 µg/g Rb and <0.1 µg/g Pb and ≤ 100 µg/g K, ≤1 µg/g Zn, ≤2.5 µg/g Cu, <2 µg/g Ga and ≤ 0.5 µg/g Rb and Pb, respectively. These estimates are as much as ten times lower than bulk bead abundances for these and other MVE within the pyroclastic glass deposits, are depleted compared to terrestrial mid-ocean ridge basalts, and are similar, or lower than, bulk silicate Earth (BSE) concentration estimates. Partial melting estimates for the source of the pyroclastic glass beads indicate similarities with tholeiitic and komatiite lavas on Earth and between ∼10 and 30 % melting of their mantle source, consistent with high mantle potential temperatures at ∼3.5 billion years ago in the Moon. The estimated MVE composition of the orange glass bead mantle source is marginally higher than the green glass mantle source, and both are within or lower than bulk silicate Moon estimates. More shallowly derived mare basalts have been shown to be yet more MVE depleted, indicating that the lunar interior had a heterogeneous distribution of volatile elements, with a deep interior with volatile abundances ∼10 times lower than BSE, volatile-poor upper magma ocean cumulates, and an incompatible volatile-enriched KREEP reservoir.

^1,2Marine Paquet, ¹James M.D. Day, ³Arya Udry
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.12.019]
¹Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92037, USA
²Université de Lorraine, CNRS, CRPG F-54000 Nancy, France
³Department of Geoscience, University of Nevada, Las Vegas, 4505 S. Maryland Parkway, NV 89154, USA
Copyright Elsevier

The nakhlite and chassignite meteorites are the only confirmed group of rocks derived from a single volcanic system on Mars, offering a unique opportunity to investigate the composition of the martian mantle and magmatic differentiation mechanisms. Nakhlites and chassignites are thought to result from low-degree partial melting of a hydrated and metasomatized depleted mantle lithosphere, unlike shergottites that predominantly sample deeper mantle reservoirs. This study presents the first comprehensive dataset on highly siderophile element (HSE: Au, Re, Pd, Rh, Pt, Ru, Ir, Os) abundances in sulfide assemblages from twelve nakhlites and two chassignites, together with siderophile (Ni, Co, W) and chalcophile (Cu, Se, Zn, Pb) element abundance data. Sulfides in chassignites exhibit relatively high total HSE abundances at ∼ 5 × carbonaceous (CI) chondrite abundances, with patterns that are generally flat, apart from notable enrichments in Pt and/or Ru. Conversely, nakhlite sulfides display more fractionated HSE patterns with total HSE abundances ∼ 1.6 × CI, characterized by lower overall abundances and enrichment in Re, Pt and Pd relative to Ru, Ir and Os. These results confirm that sulfides are the principal reservoirs of HSE in chassignites and nakhlites. Fractionation modeling suggests that the nakhlite compositions can be reproduced following up to 15 % fractional crystallization through the removal of an olivine (+Cr-spinel)-dominated cumulate, while chassignites experienced between 20 to 30 % of fractionation. The preservation of magmatic signatures in sulfide HSE compositions allows for an in-depth reconstruction of the evolution of the nakhlite-chassignite parental melt composition.

¹Martin R. Lee, ¹Sammy Griffin, ^2,2Ross Findlay, ³Xuchao Zhao, ³Ian A. Franchi
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.12.051]
¹School of Geographical and Earth Sciences, University of Glasgow, Glasgow G12 8QQ, UK
²Department of Earth Sciences, University of Cambridge, Downing St., Cambridge CB2 3EQ, UK
³School of Physical Sciences, Open University, Milton Keynes MK7 6AA, UK
Copyright Elsevier

The CM2 meteorites Grove Mountains (GRV) 021536, Murchison, and Shidian, contain anhydrous lithic clasts that have been interpreted as fragments of a planetesimal linked to CM or CV group carbonaceous chondrites. Here we describe 57 lithic clasts in Cold Bokkeveld (CM2) that are strikingly similar to those in the other three CMs in their petrography, mineralogy, and chemical and isotopic compositions. The Cold Bokkeveld clasts are dominated by equilibrated olivine, with subordinate plagioclase feldspar (andesine), clinopyroxene (diopside), nepheline, a spinel-group oxide (ferrian chromite), pentlandite, pyrrhotite, troilite and merrillite. Their bulk chemical composition is chondritic, and olivine oxygen isotope values span a wide range, from δ18O 3.6 ‰ Δ17O −3.9 ‰ to δ18O 20.3 ‰ Δ17O 1.1 ‰. Two clusters of clasts can potentially be distinguished from the chemical composition of their olivine: Fa38 and Fa41. The Fa38 cluster includes most of Cold Bokkeveld’s clasts and is close in chemical composition to those described from GRV 021526 and Murchison. The Fa41 cluster is represented by the largest Cold Bokkeveld clast, and its olivine is compositionally comparable to that in Shidian. Anhydrous lithic clasts that occur in all four of the CM meteorites are likely to have been derived from a large planetesimal with CM and CY affinities that had undergone thermal metamorphism and metasomatism. The CV3 breccias Mokoia and Yamato 86009 contain anhydrous lithic clasts that are close in mineralogy and oxygen isotopic composition to those in the four CMs and so are likely to have been sourced from the same carbonaceous planetesimal or one with a similar geological history. The oxygen isotopic compositions of olivine in clasts from GRV 021536, Murchison, Shidian, Cold Bokkeveld, Mokoia and Yamato 86009 plot on a shared trendline in 3-oxygen isotope space that connects the CV-CK-CO, CM, and CY fields thus suggesting genetic or evolutionary links between the five carbonaceous chondrite groups. The occurrence of these distinctive clasts in four CM2 meteorites could indicate that their parent body was the same rubble pile asteroid that had been built from aqueously altered and thermally metamorphosed lithologies.

¹Bennett J.K. Wilson, ²Kazuhide Nagashima, ^3,4Thomas J. Barrett, ⁵Veronica E. Di Cecco, ^5,6Kimberly T. Tait, ¹Michael G. Daly
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2025.12.046]
¹Center for Research in Earth and Space Science, York University, Toronto, ON, Canada
²Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, 1680 East-West Road, POST602, Honolulu HI96822, USA
³Department of Earth and Environmental Sciences, The University of Manchester, UK
⁴Center for Lunar Science and Exploration, Lunar and Planetary Institute, Houston, TX, USA
⁵Department of Natural History, Center for Applied Planetary Mineralogy, Royal Ontario Museum, Toronto, ON, Canada
⁶Department of Earth Science, University of Toronto, ON, Canada
Copyright Elsevier

The Tarda meteorite is a recently recovered C2-ungrouped carbonaceous chondrite that preserves evidence of early Solar System aqueous alteration. Tarda was found to share reflectance spectra with P-type asteroids, possibly enabling these elusive asteroids to be studied in the laboratory for the first time. Furthermore, Tarda has been shown to share many petrological and isotopic affinities with Tagish Lake – a pristine C2-ungrouped chondrite that is widely considered to source a D-type asteroid. Thus Tarda, Tagish Lake, and their respective spectral classes are probably genetically related, and potentially source a shared parent body. Despite their similarities, however, Tagish Lake hosts different lithologies and carbonate species than Tarda, suggesting distinct aqueous alteration histories between the two meteorites. Here, we present in-situ oxygen, carbon, and 53Mn–53Cr isotopic analyses of dolomite and magnetite in Tarda using Secondary Ion Mass Spectrometry to (i) investigate the conditions associated with aqueous alteration on the early Tarda parent body, and to (ii) compare our findings with Tagish Lake to assess heterogeneous aqueous alteration of their unique and likely shared parent body. For dolomite, we found that δ13C ranged from 55.8 ‰ to 72.9 ‰, while δ18O ranged from 23.3 ‰ to 28.8 ‰ with an average Δ17O of 0.1 ± 1.6. Dolomite additionally contained widespread 53Cr excesses that, if interpreted to have chronological significance, corresponds to a live [(53Mn/55Mn)0] value of (
. For magnetite, the δ18O values ranged from −5.5 ‰ to 5.8 ‰ with an average Δ17O of 2.4 ‰ ± 1.7. Oxygen isotope thermometry of a co-precipitating dolomite–magnetite pair indicates alteration temperatures of
°C. Compared to carbonates in Tagish Lake, dolomite in Tarda exhibits systematically lower δ17O, δ18O, and Δ17O signatures, but similar δ13C signatures. Temporally, the carbonates in both meteorites have identical ages within uncertainty. We conclude that Tarda has experienced greater aqueous alteration than Tagish Lake, likely due to increased water–rock interaction and/or higher temperatures.

¹L.J. Riches, ^1,2M.D. Suttle, ¹I.A. Franchi, ¹X. Zhao, ^1,2M.M. Grady
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.12.035]
¹School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, United Kingdom
²Planetary Materials Group, Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom
Copyright Elsevier

Analysis of carbonate minerals in ungrouped carbonaceous chondrites offer valuable insights into the geological activity on a diverse range of early-formed, hydrated planetesimals in the outer Solar System. Essebi is a C2-ung chondrite, which originated from a water-rich asteroid with close affinities to the CM chondrites group. We performed a detailed geochemical, petrographic and isotopic study of Essebi. Modal mineralogy demonstrates that Essebi is dominated by a poorly crystalline, fine-grained phyllosilicate matrix (mostly a mix of saponite and serpentine ∼63 vol%) with a modest quantity of anhydrous silicates (20 vol%) and accessory magnetite (7.5 vol%), Fe-sulphides (5.5 vol%) and carbonates (2 vol%). Its bulk O-isotope composition (2.71 ‰ δ17O (± 0.018 1σ), 8.11 ‰ δ18O (± 0.002 1σ) and −1.53 ‰ Δ17O (± 0.017 1σ) and 2.56 ‰ δ17O (± 0.040 1σ), 7.65 ‰ δ18O (± 0.009 1σ) and −1.42 ‰ Δ17O (± 0.039 1σ)) places Essebi as part of the “CM field”, although overlapping with the “CR field”. Petrographic observations reveal multiple generations of carbonate that formed both before and after brecciation, exhibiting distinct characteristics that differ from the carbonates found in established groups (CMs). Essebi’s carbonate generations have distinct morphologies and C- and O- isotope compositions and, based on these data, are interpreted as two main generations and a series of other localised carbonate expressions.
The first generation (GA) carbonates formed prior to phyllosilicate growth, and have inferred maximum formation temperatures of +45 °C. They formed under high water-to-rock (W/R) ratios. The second generation (GB) carbonates show lower W/R ratios and at higher, although unquantified temperatures. They formed near the end of the alteration sequence from a residual fluid containing abundant dissolved cations. In addition to the two main generations, we identified a third population of vein carbonates (GC) that partially infilled fractures generated by brecciation. We also identified dolomite (GD) grains found exclusively within an xenolithic clast. This clast displays a more advanced stage of alteration (C1-ung) and shows evidence of fluid leaching after being embedded, resulting in the formation of a localized ring of calcites, referred to as GE, that remain distinct from all other carbonates in this sample.
Despite textural differences, the isotopic trends observed in these Essebi carbonates closely resemble the sequence described by T1 and T2 calcites in CM chondrites, suggesting that multiple distinct episodes of carbonate precipitation, aqueous alteration along a prograde metasomatic sequence, and isotopic evolution from 16O-poor to 16O-rich trajectories were common across several water-rich planetesimals that formed in the outer Solar System.

¹Neil R. Bennett,¹Jessica D. Verschoor,²Josh Wimpenny,^1,2Corliss K. Sio
American Mineralogist 111, 118-127 Link to Article [https://doi.org/10.2138/am-2025-9765]
¹Department of Earth Science, University of Toronto, Toronto, Ontario M5S 1L1, Canada
²Lawrence Livermore National Laboratory, Livermore, California 94550, U.S.A.
Copyright: The Mineralogical Sociwety of America

Iron meteorites record a range of Fe isotope compositions that hold valuable information regarding the evolution of their parent bodies. Interpreting this isotopic variability, however, requires experimental constraints on the equilibrium isotope fractionation between phases. It is thought that the cores of many iron meteorite parent bodies experienced fractional crystallization, during which crystallization of solid iron-nickel occurs from an increasingly non-metal-rich liquid alloy. Phosphorus is one component of this alloy, and this study provides the first constraints on Fe-isotope fractionation between solid and liquid alloys in the Fe-Ni-P system. Experiments comprising Fe and P show a clear enrichment in the light isotopes of Fe in the liquid phase, which increases with the amount of phosphorus. Nickel-bearing samples are offset from the trend defined by Ni-free experiments, which is accounted for by the change in the solid alloy phase from a body-centered cubic to face-centered cubic structure upon the addition of Ni. The increasing light isotope enrichment of the liquid with increasing P content suggests interstitial solution of P, which is known to lengthen Fe-Fe bonds in Fe-P liquids (Waseda and Shiraishi 1977). Results suggest a negligible effect of P on Fe isotope fractionation during planetesimal core crystallization. Iron isotopes may, however, prove useful for identifying the petrogenesis of schreibersite in pallasites and iron meteorites.

¹W. M. Lawrence,¹B. L. Ehlmann
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2025JE009377]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
Published by arrangement with John Wiley & Sons

CM (Mighei‐type) carbonaceous chondrites host abundant OH/H2O‐bearing phyllosilicatesformed from water‐rock reactions in primitive planetesimals. Their infrared (IR) spectral features resemblethose of C‐type asteroids, making laboratory analyses of CMs essential for interpreting asteroid observations.However, CM chondrites are often breccias composed of lithologies with variable degrees of aqueousalteration, complicating their interpretation. Here we use in situ analytical techniques to characterize spectral‐compositional relationships for phyllosilicates in 8 CM lithologies across two meteorite samples. Micro‐Fourier Transform Infrared (μ‐FTIR) spectra collected from phyllosilicate‐rich matrix regions show that bandpositions of the 3‐μm feature and Si‐O stretch Reststrahlen band (RB) systematically vary with alteration.Additional data from spatially correlated electron microprobe and μ‐FTIR measurements tie spectral variationsto specific cation substitutions in serpentines: the 3‐μm feature shifts from 2.78 to 2.70 μm with increased Mg/Fe in octahedral sites, and the Si‐O stretch RB shifts from 10.8 to 9.8 μm with increased Si/Fe3+ in tetrahedralsites. Co‐variation of these features across the studied CM lithologies defines two successive alteration stages:(1) the Si‐O stretch RB and 3‐μm feature shift to longer and shorter wavelengths, respectively, as Mg‐ andcronstedtite‐rich phyllosilicates form from incipient chondrule alteration; (2) Si‐O stretch RB shifts to shorterwavelengths as Mg‐serpentines replace cronstedtite and Mg‐rich chondrules. These patterns align with inferredchanges in composition and redox state for altering fluids on the CM parent body. Similar features in thespectra of C‐type asteroids may reveal information about conditions of aqueous alteration and constrain modelsof their evolution.

^1,2C. P. Haupt,³A. N. Stojic,³A. Morlok,³I. Weber,¹S. Klemme,³H. Hiesinger,^1,4C. J. Renggli
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2024JE008895]
¹Institut für Mineralogie, Universität Münster, Münster, Germany
²ISTO, UMR 7327, University of Orléans, CNRS, BRGM, OSUC, Orléans, France
³Institut für Planetologie, Universität Münster, Münster, Germany
⁴Max-Planck-Institute for Solar System Research, Göttingen, Germany
Published by arrangement with John Wiley & Sons

Laboratory-based mid-infrared (MIR) spectroscopy of terrestrial and planetary analogue materials, combined with chemical and spectral insights from mission-derived data, provides critical tools for advancing our knowledge of planetary surfaces. The returned lunar samples provide information on the chemical variability of the lunar surface. Lunar basalts are notably enriched in TiO2 when compared to their terrestrial equivalents, and are ideal candidates to study the influence of composition on MIR spectral features. We characterized 25 synthetic lunar glasses with variable TiO2 (0.6–18.7 wt%) and SiO2 (35.6–52.1 wt%) in the thermal infrared range using micro-Fourier Transform Infrared Spectrometry (μ-FTIR). Our data reveal a strong linear relationship between the intensity of a spectral shoulder at 14.25 μm (702 cm−1) and the TiO2 content of the analyzed glasses. We suggest that the relationship in our samples reflects an increased distortion of the silicate network with increasing TiO2 concentrations. We observe that TiO2 acts as a network former in specific concentration intervals, thereby affecting the intensity of the observed spectral features in the MIR. This linear relationship is virtually nonexistent in samples that are developing stages of short-range order in the glasses and those samples that show only moderate to low amounts of TiO2. Comparison with data sets from Earth and Mercury analogue materials confirms that the Christiansen Feature (CF) consistently correlates with the SiO2 content, underscoring its robustness as a proxy for glass polymerization across planetary compositions. Finally, we emphasize that incipient crystal nucleation in glassy surfaces affects spectral features in the MIR range.

During the last days of this year, Cosmochemistry Papers will be on Christmas break. Normal service will commence on January, 5th, 2024 .

Merry Christmas & Happy New Year to everyone!

¹Abdelmadjid Seddiki, ²Bertrand Moine, ³Jérôme Bascou, ¹Ratiba Kared, ³Jean Yves Cottin, ⁴Marguerite Godard, ⁵François Faure, ⁶Richard C. Greenwood, ¹Ian A. Franchi
Chemie der Erde (Geochemistry) (in Press) Link to Article [https://doi.org/10.1016/j.chemer.2025.126363]
¹Laboratoire Géoressources, Environnement et Risques Naturels (GEOREN), Université d’Oran2, BP: 1510, Oran, 31000, Algeria
²Laboratoire Magmas et Volcans, F-63000, CNRS, IRD, OPGC, Université Clermont Auvergne, Clermont-Ferrand, France
³Université Jean Monnet, CNRS, LGL-TPE, UMR5276, F-42023, Saint-Etienne, France
⁴Géosciences Montpellier, Université Montpellier II, Place Eugène Bataillon, 34095, Montpellier, cedex5, France
⁵CRPG, Université Henri Poincaré de Nancy, 15, rue Notre-Dame des Pauvres, B.P. 20, 54501, Vandoeuvre-lès-Nancy, France
⁶Planetary and Space Sciences Research Institute, Open University, Milton Keynes, MK7 6AA, UK
Copyright Elsvier

Northwest Africa (NWA) 4269 is an anomalous monomict eucrite that is characterized by a very high content of metallic iron (~ 3 %). It shows various textures (relict magmatic sub-ophitic, granulitic areas as coarse and fine-grained). NWA 4269 also shows petrographic evidence of secondary sub-solidus reheating events. Pyroxenes have homogeneous compositions and are iron-rich. NWA 4269 is metamorphosed type 5. It has a normal HED oxygen isotope composition. The chemical composition of NWA 4269 has characteristics similar to that of Nuevo-Laredo trend eucrites. Metal is extremely abundant in the fine-grained areas (~ 10 %). Metal also has a very low Ni content (Ni < 0.1 %) that excludes a direct origin from a chondrite-like impactor. Origin of the pure-Fe groundmass metal remains enigmatic. The high metal content in NWA 4269 can be interpreted as having formed via the reduction of FeO and probably also by desulfidation of pre-existing troilite. Iron metal could have formed by deposition from a Fe-rich fluid that, probably after an event that triggered sudden reduction. NWA 4269 has normal HED oxygen isotope compositions and interpreted as belonging to the 4-Vesta asteroid.