^1,2A.P. Singh, ³S.S. Pillai, ¹K.K. Marhas, ⁴K.V.N.G. Vikram, ⁴S. Bhattacharya
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2026.117045]
¹Physical Research Laboratory, Ahmedabad, Gujarat, India
²Department of Earth Science, Gujarat University, Ahmedabad, Gujarat, India
³University of Kerala, Thiruvananthapuram, Kerala, India
⁴Space Applications Centre, Ahmedabad, Gujarat, India
Copyright Elsevier

This study investigates the mid-infrared spectral correlation between four Carbonaceous Vigarano (CV) chondrites (Allende, Grosnaja, Efremovka and Leoville) and ten asteroids of Xk, L, & Ld types (Bus- Binzel taxonomy). It leverages the mid-infrared region of the electromagnetic spectrum, which is characterised by prominent peaks indicative of crystalline bond vibrations of silicates and ionic oxides. A novel statistical methodology, integrating four distinct similarity assessment techniques (normalised local change method, covariance, Euclidean distance, and cosine similarity), was employed to determine the spectral similarity coefficient (Z) between the CV chondrites and the chosen asteroids. The highest similarity is observed between the asteroids of L type, i.e., Cantillo et al. (2023) (Cantillo et al., 2023) Victoria, (1284) Kassandra, and (1702) Latvia and the CV chondrites studied here, followed by the Xk type (114) Kassandra. The Z value between Ld asteroids (234) Barbara, (269) Justitia and CVs exhibit low similarities. This study establishes a framework for the statistical comparison of mid-infrared spectra of meteorites and asteroids by accounting for compositional variability within CV chondrites, thereby providing a basis for more detailed investigations into the parent-body association of these meteorites.

^1,2Mark Nestmeyer, ^1,3Alex J. McCoy-West
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2026.03.022]
¹IsoTropics Geochemistry Laboratory, Earth and Environmental Science, James Cook University, Townsville, QLD 4811, Australia
²CSIRO Mineral Resources, Kensington, WA 6151, Australia
³Economic Geology Research Centre, James Cook University, Townsville, QLD 4811, Australia
Copyright Elsevier

The application of rare Earth element stable isotope compositions has become of increasing interest in geochemistry. Recently, studies have begun exploring variations in the stable 146Nd/144Nd isotope ratio in geological samples, with limited isotope fractionation observed in igneous rocks but significantly larger fractionations seen in low temperature systems. Experimental and theoretical studies on the equilibrium isotope fractionation of Nd are widely missing which can support understanding the fractionation of Nd isotopes among Earth’s major reservoirs. Here, we have modelled the isotope fractionation factors for 15 common rock forming and accessory minerals to help understand equilibrium stable isotope fractionation during medium to high temperature processes.
We estimate that mantle melting will produce minimal isotope fractionation while the residual peridotite ought to retain heavier Nd isotopes which could explain a potentially superchondritic composition of the depleted mantle. This can be predicted because in mantle minerals with Mg sites (e.g. olivine, orthopyroxene) substitution of isotopically heavier Nd is preferred compared to minerals with Ca sites (e.g. clinopyroxene), with the latter being the major contributor to basaltic melts. The Earth’s outer core (i.e. sulfide matte) is a potential host of lighter Nd isotopes which we demonstrate favours sulfides over silicates. However, the low partition coefficients of rare Earth elements into the core leads to a composition of the bulk silicate Earth that is indistinguishable from chondrites. A better understanding of the δ146/144Nd composition of the mantle is warranted to elucidate the isotope fractionation of Nd between Earth’s major geochemical reservoirs.
As Nd condenses from the solar nebular gas into primitive material, the mass-independent nuclear field shift effect dominates equilibrium isotope fractionation and produces significant fractionation in δ146/144Nd even at high temperatures (>1000 °C) with the condensed material enriched in lighter Nd isotopes. However, the isotopic compositions reported for refractory inclusions (–1.86 to 2.20 ‰; Hu et al. (2021)) cannot be solely explained by equilibrium isotope fractionation and other mechanisms are required

¹Daniel R. Dunlap, ¹Julia A. Cartwright, ²Piers Koefoed, ⁴Evgenii Krestianinov, ¹Stephen J. Romaniello, ³Carl Agee, ²Yuri Amelin, ¹Meenakshi Wadhwa
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2026.03.014]
¹Arizona State University, School of Earth and Space Exploration, 781 Terrace Mall, Tempe, AZ 85287, USA
²Australian National University, Research School of Earth Sciences, 142 Mills Rd, Acton ACT 2601, Australia
³University of New Mexico, Institute of Meteoritics, 1 University of New Mexico, MSC03 2050, Albuquerque, NM 871312, USA
⁴Department of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ 08854 USA
Copyright Elsevier

The chronology of ungrouped achondrites provides key insights into the timeline of igneous activity in the early Solar System. Two ungrouped achondrites – Northwest Africa (NWA) 11119 (andesite-dacite) and NWA 8486 and its pair NWA 7325 (olivine gabbro) – are the focus of this study, where their chronologies are investigated using multiple high-resolution techniques. Here we report the lead-lead (207Pb-206Pb) and manganese-chromium (53Mn-53Cr) systematics of NWA 11119, as well as the 207Pb-206Pb systematics of NWA 8486 alongside aluminum-magnesium (26Al-26Mg) systematics for NWA 7325. The U-corrected 207Pb-206Pb ages of NWA 11119 and the combined ages of NWA 7325/8486 are 4566.4 ± 0.8 Ma and 4563.8 ± 1.9 Ma, respectively. Additionally, we report the 53Mn-53Cr age of NWA 11119 to be 4564.4 ± 2.5 Ma and the 26Al-26Mg age of NWA 7325/8486 to be 4563.1 ± 0.3 Ma.
The formation of NWA 11119 requires partial melting of a (likely chondritic) source reservoir leading to eruption of Si rich, alkali depleted magmas, while NWA 7325/8486 likely formed from a chemically fractionated reservoir with superchondritic Al/Mg. The clear geochemical and isotopic similarities of these achondrites, combined with the chronology reported here, is suggestive of formation of these two ungrouped achondrites on a common parent body which likely formed in the inner Solar System and experienced early differentiation under reducing conditions. If these achondrites did share a parent body, it would suggest that primary asteroids in the early Solar System commonly produced mineralogically and geochemically heterogeneous crusts. While mineralogical and geochemical heterogeneity is known to exist in the (mostly mafic) crust of asteroid Vesta, our findings show that even more significant crustal heterogeneity (representing felsic and mafic compositions) may exist on other asteroids.

¹Bianka Babrián, ²Queenie H.S. Chan, ³Jens Najorka, ¹James Malley, ⁴Lee F. White, ^1,3Martin D. Suttle
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2026.03.020]
¹School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
²Department of Earth Sciences, Royal Holloway, University of London, Egham TW20 0EX, UK
³Planetary Materials Group, Natural History Museum, Cromwell Road, London SW7 5BD, UK
⁴Electron Microscopy Suite, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
Copyright Elsevier

We performed a series of low temperature hydrothermal alteration experiments using the highly primitive CO3.00 chondrite DOM 08006 as the protolith to investigate aqueous alteration conditions on carbonaceous planetesimals. Our experiments employed a range of water-to-rock (W/R) ratios by mass (0.2, 0.4, 1.0) and a heating duration of 100 days at 80°C. We also used a short-duration experiment terminated on day 12 to investigate the earliest stages of aqueous alteration. We used isotopically doped 17O-rich water to track isotopic behaviour during alteration and ascertain the effective molar W/R ratios (i.e., the proportion of reacted water) in the experiments. Bulk O-isotope data suggest that the effective W/R ratio achieved by the experimental samples was capped at ∼0.2 at the end of the experiments. This reflects low alteration extents, which we attribute to low matrix permeability that results from the early and continuous precipitation of Fe-bearing phases, likely dominated by Fe-sulphides, into pore spaces, restricting fluid flow and hindering the progression of alteration at these short timescales. Conversely, early hydrothermal fracturing was observed which may lead to “runaway” alteration at longer timescales. Initial W/R ratio had little effect on the style of alteration, except for allowing Mg-serpentine (chrysotile) to form in addition to Fe-serpentine (cronstedtite) in the high W/R (1.0) experiment. Phyllosilicate production doubled over one order of magnitude longer durations, from 12 to 100 days, at similar effective W/R ratios. One sample (Exp-2) experienced initially oxidising conditions, which led to a marked distinction in alteration style dominated by Fe-oxides and Fe-(oxy)hydroxides. This sample also formed framboidal magnetite, showing that this morphology is possible under oxidising conditions and that the presence of ammonia may not be required, as previously suggested. This work is a strong step forward in experimentally recreating a “generic” hydrated chondrite in the nascent stages of aqueous alteration.

¹Zachary A. Torrano, ²Michelle K. Jordan, ²Lori N. Willhite, ²Richard W. Carlson
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2026.03.015]
¹Los Alamos National Laboratory, Nuclear and Radiochemistry Group, Los Alamos, NM, USA
²Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC, USA
Copyright Elsevier

We report Nd and Sm isotopic compositions of a sample returned from asteroid (101955) Bennu by the NASA OSIRIS-REx mission to evaluate potential genetic relationships between Bennu, known meteorite groups, and returned samples from asteroid Ryugu, and to track the cosmic ray exposure history of Bennu. We measured Nd and Sm isotopic compositions via thermal ionization mass spectrometry using 1013 Ω amplifiers. We also explore the constraints that determine the sample sizes where such high-gain amplifiers can be expected to provide improved analytical precision to that of 1011 Ω amplifiers. Bennu exhibits negative µ142Nd and µ144Sm isotopic compositions, both consistent with the nucleosynthetic anomalies previously documented for carbonaceous chondrites and Ryugu. Bennu also exhibits a resolvable deficit in 149Sm that is the result of exposure to galactic cosmic rays as demonstrated by the correlation between 150Sm/152Sm and 149Sm/152Sm ratios that fall along the expected neutron capture correlation line. The 149Sm deficit is consistent with an exposure age of 4.4 ± 1.2 Myr assuming sampling of near surface material, which overlaps with the CRE ages inferred for Bennu from other parameters.

¹Himela Moitra, ¹Sujoy Ghosh, ¹Tamalkanti Mukherjee, ¹Saibal Gupta, ²Kuljeet Kaur Marhas
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2026.03.008]
¹Department of Geology & Geophysics, Indian Institute of Technology Kharagpur, Kharagpur 721302, India
²Planetary Science Division, Physical Research Laboratory Navrangpura, Ahmedabad 380009, India
Copyright Elsevier

High-pressure layered and mixed experiments were performed at pressures of 1–3 GPa and temperatures of 1075–1500 °C in a piston cylinder apparatus to study the interaction between a novel (fayalite-rich) ilmenite-bearing cumulate (IBC) composition and ambient lunar mantle (represented by San Carlos olivine with XMg of 0.91), to investigate the origin of intermediate- and high-Ti mare basalts (6–18 wt% TiO2). The partial melts generated in the layered experiments show TiO2 contents (9–19 wt%) similar to high-Ti mare basalts, but low MgO (<6 wt%). Thermodynamic modelling shows that high-temperature, moderately Ti-rich partial melts (6–8 wt% TiO2) of the IBC layer can directly fractionate to generate intermediate-Ti lunar basalts. Lower-temperature, high-Ti partial melts (11–19 wt% TiO2) may first fractionate to more Ti-rich, Mg-poor compositions, then mix with ascending low-Ti, picritic magmas and undergo subsequent fractionation during ascent to generate high-Ti basalt compositions. Our model successfully reproduces the observed evolution of MgO, TiO2, SiO2, and FeO in high-Ti basalts, although it underestimates their Al2O3 and CaO contents. Incorporation of pockets of plagioclase-rich melts from the mantle may resolve this discrepancy. High-pressure density calculations suggest that at 1 GPa, high-Ti partial melts can ascend to the lunar surface. At 2–3 GPa, some partial melts may ascend to the surface after fractionation and assimilation, while some may sink through the lunar mantle. These findings provide new insights on the role of lunar mantle overturn, IBC melting and mantle interactions in the formation of lunar high-Ti basalts and offer a viable mechanism for their generation throughout the history of mare volcanism.

¹Katarzyna J. Gajewska,¹Sanna Alwmark,¹Mikael Calner,¹Sylvain Richoz,²Jens Ormö,³Erik Sturkell,¹Carl Alwmark
Meteoritics & Planetary Science (in Press) Free Access Link to Article [https://doi.org/10.1111/maps.70128]
¹Department of Earth and Environmental Sciences, Lund University, Lund, Sweden
²Centro de Astrobiología (CAB), CSIC-INTA, Madrid, Spain
³Earth Sciences Centre, Gothenburg University, Gothenburg, Sweden
Published by arrangement with John Wiley & Sons

The Tvären structure in southeastern Sweden has been listed as a confirmed marine-target impact structure for decades. However, to date, no measurements and/or indexed data of planar deformation features in quartz grains from the structure have been published or any other unequivocal evidence of impact. Here, we present an investigation aimed at searching for shocked quartz in the 224 m deep Tvären-2 drill core. We confirm that the rocks of this core contain, on average, about 5% of shocked quartz, either displaying up to 10 sets of planar deformation features, planar fractures, or both. Petrographic investigation resulted in a division of the core into four main stratigraphic units: (i) lithic impact breccia; (ii) coarse melt-bearing resurge deposit; (iii) finer melt-bearing resurge deposit; and (iv) post-impact deposit. Studying sedimentary facies and structures as well as using petrographic and textural characteristics of the material made it possible to recreate the process of crater formation. We describe a sequence of excavation stage-generated crystalline breccia overlain by early modification stage polymictic breccia with crystalline and limestone clasts formed when the collapse of the crater rim and walls had begun. This breccia is, in turn, overlain by a resurge deposit comprised of material brought into the crater as the water returned. Hence, studying macro- and microstructures is yet another approach to better understand the mechanisms involved in the formation of small impact craters and their associated deposits in marine environments.

^1,2Pierre-Marie Zanetta,²Pierre Rochette,¹Anne-Magali Seydoux-Guillaume,²Valérie Andrieu,¹Colette Guilbaud
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70116]
¹CNRS, LGL-TPE, UMR5276, Universite Jean Monnet, Saint-Etienne, France
²CNRS, IRD, INRAE, CEREGE, UMR 7330, Aix-Marseille Universite, Aix-en-Provence, France
Published by arrangement with John Wiley & Sons

Australasian tektites (AAT) contain grains from the impact surface that survivedthe tektite formation process. Muong Nong-type (MN) tektites, in particular, preservenumerous inclusions that provide insights into the thermal history of the material duringejection and deposition. Here, we present the first analysis of organic matter residues inMN-AAT, found adjacent to a mineral exhibiting Fe reduction within its crystallinestructure. We propose that this organic matter represents the residue of target biomass thatwas trapped in the impact glass during melting and was preserved due to its compositionand the rapid quenching of the melt, which prevented complete decomposition. Thepresence and composition of this organic matter may be linked to the ecosystem that oncecovered the impacted area and allow us to discuss the nature of this potential biomassreservoir. Moreover, carbon derived from this material appears to have influenced ironspeciation, as evidenced by the nearby dendritic oxide showing a gradient in Fe oxidationstate. These observations suggest that organic matter from soil and biomass may havecontributed to the geochemical evolution of tektites.

^1,2David A. Kring,³Charles S. Cockell
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70126]
¹Lunar and Planetary Institute, Universities Space Research Association, Houston, Texas, USA
²Radcliffe Institute for Advanced Study, Harvard University, Cambridge, Massachusetts, USA
³UK Centre for Astrobiology, University of Edinburgh, Edinburgh, UK
Published by arrangement with John Wiley & Sons

Postimpact recovery and evolution in response to climate changes produced amodern ecosystem at Meteor Crater dominated by a grassland and woodland of pi~non andjuniper, which has been used to evaluate floral and megafaunal consequences of impactcratering during the Phanerozoic Eon of complex life. Here, we describe a postimpactendolithic community that illustrates a potential habitat for micro-ecosystems aroundimpact craters in both Proterozoic and Phanerozoic times. Phototrophs withinimpact-ejected carbonate are dominated by eukaryotic green algae that affiliate withTrebouxiophycaea (Trebouxia and Stichococcus spp.). Eukaryotic fungi are dominated byAscomycota, including Hydropisphaera, Trichoderma, Acremonium, and Stanjemonium spp.,and representatives of Basidiomycota including Agaricomycetes and Clitopilus spp. Theprokaryotic community is dominated by Actinobacteria and Proteobacteria, the latterdominated by Alphaproteobacteria. At a genus level, the bacterial community containstypical representatives of soil and rock environments, including Promicromonospora,Lentzea, Streptomyces, Kribella, Rubrobacter, Deinococcus, Sphingomonas, Belnapia, andMethylobacterium spp. These data show that impact crater rocks host taxonomically diversecommunities potentially involved in carbon cycling in the early stages of colonization.

¹M. Barthez, ¹J. Flahaut, ²M. Guitreau, ¹R. Pik, ¹G. Ito, ³C. Delangle, ³J.-P. Gremilliet, ¹B. Luais, ¹F. Faure
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2026.117027]
¹Université de Lorraine, CNRS, CRPG, Nancy F-54000, France
²Laboratoire Magmas et Volcans, Université Clermont Auvergne, OPGC, CNRS UMR-6524, IRD UMR-163, F-63173 Clermont-Ferrand, France
³Centre Terrae Genesis, F-88120 Le Syndicat, France
Copyright Elsevier

Visible Near-InfraRed (VNIR) spectroscopy is a powerful tool to assess the mineralogical composition of planetary surfaces remotely. Despite decades of investigation with the Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité (OMEGA) and the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instruments, new detections are still being made on Mars. Plagioclase signatures were reported on the surface of Mars with CRISM, and it could be indicative of uncommon lithologies, as plagioclase is known to be difficult to detect with VNIR spectroscopy, except for plagioclase-pure rocks (i.e., anorthosite).
The present study investigates the VNIR spectra of 67 plagioclase-bearing terrestrial igneous rocks of various nature (e.g., granite, anorthosite, gabbro, tonalite, syenite and their volcanic equivalents) that were kept uncrushed as Mars candidate analog rocks. Total rock spectra were measured with a point spectrometer, while the spectra of their plagioclase constituents are extracted from hyperspectral camera analyses. In parallel, the petrology of rocks and the chemical compositions of feldspar minerals are evaluated with optical microscopy and electron probe microanalyzer (EPMA) respectively.
Most plagioclase crystals in our sample collection exhibit diagnostic absorption features centered between 1.15 μm and 1.40 μm at the mineral level, unless the mineral is altered and/or weathered. Both physical and spectral evidence for alteration products, such as muscovite and prehnite, are observed. Still, plagioclase signatures are often masked on the total rock spectra (44 out of 67 samples). We found that the main factors that control the spectral signature of plagioclase in the total rock spectra are its chemical composition and grain size, as well as the associated minerals and the rock albedo. Plagioclase spectral signatures are observed in total rock spectra of samples containing as little as 18% plagioclase, challenging previously published estimates and interpretations based on studies of powders and grain mixtures. Diagnostic plagioclase signatures are visible in the spectra of rocks of various natures and textures, including plagioclase-phyric basalt, anorthosite, granite and granodiorite, opening up a range of possibilities for the nature of the lithologies involved in Mars detections.