^1,2Swarna Prava Das,³Alessandro Maturilli,³Aurélie Van den Neucker,⁴Markus Patzek,⁵Dipak Kumar Panda,⁶Gopal K. Pradhan,^1,2Guneshwar Thangjam,^1,2,7Surya Snata Rout
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70183]
¹School of Earth and Planetary Sciences, National Institute of Science Education and Research (NISER), Khordha, Odisha,752050, India
²Homi Bhabha National Institute, Training School Complex, Mumbai, 400094, India
³Institute of Space Research, German Aerospace Centre (DLR), Berlin, 12489, Germany
⁴Institut für Planetologie (IfP), Universität Münster, Münster, 48149, Germany
⁵Planetary Science Division, Physical Research Laboratory, Ahmedabad, Gujarat, 380009, India
⁶Department of Physics, School of Applied Sciences, KIIT Deemed to be University, Bhubaneswar, 751024, India
⁷Center for Interdisciplinary Sciences (CIS), NISER Bhubaneswar, Khordha, Odisha, 752050, India
Published by arrangement with John Wiley & Sons

Volatile-rich xenolithic clasts in different types of brecciated meteorites represent unique pristine solar system material. This study investigates the maturity and thermal history of organic matter using Raman spectroscopy and aqueous alteration effects using infrared spectroscopy in the matrix of 15 volatile-rich clasts (C1 and CM-like) present in a polymict eucrite (NWA 7542) and a howardite (Sarıçiçek). Most of the studied C1 and CM-like clasts show similar maturity of organic matter as CI chondrites and CM chondrites, respectively. One CM-like clast from the polymict eucrite NWA 7542 shows Raman spectral signatures of heating after aqueous alteration, and another C1 and a CM-like clast from the howardite Sarıçiçek exhibit unique Raman spectral properties probably related to differences in accreted precursor organics compared to CI and CM-chondrites. One olivine-rich, unclassified clast has a high concentration of fayalitic olivine in its matrix, similar to oxidized CV chondrites and other features similar to CM- or C2 chondrites. Various evidence shows that this clast was heated up to 700–800 °C post aqueous alteration followed by the formation of fayalitic olivine during a metasomatic alteration process. Peak metamorphic temperature (PMT) estimated using different thermometric approaches does not provide reliable data for clasts altered at low temperatures (<200 °C).

^1,2Olga Ageeva,³Cyril Lorenz,¹Gerlinde Habler,⁴Lutz Nasdala,²Leonid Aranovich,²Olga Zhilicheva,²Sergey Borisovsky,¹Rainer Abart
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70185]
¹Department of Lithospheric Research, University of Vienna, Josef-Holaubek-Platz 2, Wien, 1090, Austria
²Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences(IGEM RAS), Staromonetny Per. 35, Moscow, 119017, Russia
³Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences (GEOHI RAS),Kosygin Street 19, Moscow, 119991, Russia
⁴Department of Mineralogy and Crystallography, University of Vienna, Josef-Holaubek-Platz 2, Wien, 1090, Austria
Published by arrangement with John Wiley & Sons

Two samples of the meteorite Northwest Africa 8741 (NWA 8741) were investigated using petrographic, mineral chemical, and crystal orientation analysis to reconstruct its evolution. NWA 8741 is an A4 mesosiderite composed of lithic clasts of pyroxenite and single-grain porphyroclasts of olivine and orthopyroxene as well as aggregates of Ni-rich metallic iron embedded in a medium-grained matrix of plagioclase, orthopyroxene, cristobalite, tridymite, minor chromite, clinopyroxene, and small grains of metallic iron with low Ni-contents. The mesosiderite NWA 8741 formed by a collision event, which led to the ejection of silicate and metal melts and of solid fragments from a differentiated parent body and the projectile. The matrix minerals crystallized from the silicate melt, while the metallic melt forming the Ni-rich metallic iron aggregates, and the silicate clasts were incorporated by mechanical mixing. The crystallization of the matrix phases proceeded at low oxygen fugacity, ensuring the stability of metallic iron. Interaction between the metallic and silicate melt caused partial oxidation of phosphorus and chromium originally dissolved in the metallic melt, leading to the formation of merrillite and Cr-rich spinel. The melt was out of equilibrium with the inherited olivine and orthopyroxene clasts, and a series of mineral-melt reactions led to the partial replacement of the inherited olivine by aggregates of orthopyroxene and Cr-spinel and to the partial replacement of the inherited orthopyroxene by aggregates of cristobalite, Cr-spinel, and plagioclase. During the subsequent sub-solidus evolution, the oxygen fugacity was still low, allowing the formation of Ni-poor iron grains and silica by the partial reduction of ferrous iron from the Fe-Mg silicates, and the partial replacement of olivine by symplectic orthopyroxene-metallic iron intergrowth. Finally, the replacement of olivine by troilite-orthopyroxene and of orthopyroxene by troilite-tridymite aggregates and the partial transformation of Ni-poor metallic iron to troilite indicate an elevated sulfur fugacity during the late sub-solidus evolutionary stages of mesosiderite NWA 8741. Overall, NWA 8741 records a multistage history of impact-induced mixing, melt-rock interaction, and subsequent sub-solidus metamorphism during the evolution of the mesosiderite parent body.

^1,2M. L. Gray,^1,2,3M. K. Weisberg,⁴C. M. O’D. Alexander,⁴J. Wang,⁴D. I. Foustoukos,^1,2,5D. S. Ebel
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70192]
¹Department of Earth and Environmental Sciences, CUNY Graduate Center, New York, New York, USA
²Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, USA
³Department of Physical Sciences, CUNY Kingsborough College, Brooklyn, New York, USA
⁴Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC, USA
⁵Department of Earth and Environmental Sciences, Columbia University, New York, New York, USA
Published by arrangement with John Wiley & Sons

Measurements of bulk H, N, and C abundances and isotopic compositions were conducted on (metal-free) aliquots of 12 powdered enstatite chondrite (EC) samples, from both EH and EL chemical groups, and four aubrites. The ECs covered a range of petrologic types, including both falls and finds. To understand the internal H distributions, the H concentrations of individual silicate minerals were analyzed in situ by NanoSIMS in polished thick sections of six of the ECs. Using these data, combined with published data on H carriers and their modal abundances in ECs, we estimate here that the major silicate minerals, matrix, and mesostasis in unequilibrated ECs account for less than 20% of the total H budget. For the metamorphosed E4–6 chondrites, which exhibit a recrystallized matrix and mesostasis, over 99% of the bulk H contents remain unexplained. We attribute the discrepancies between our analyzed bulk H elemental compositions and the bulk H values reconstituted from in situ measurements are attributed to terrestrial contamination, as water adheres to grain boundaries, surfaces, and fractures. Water also reacts with reduced phases, regardless of whether the meteorite is a fall or find. Similar H isotopic compositions for falls and heavily weathered finds are consistent with, but do not require, that the majority of EC H is terrestrial. Attempts to remove organic terrestrial contamination by solvent extractions only served to moderately shift the H, N, and C isotopic compositions. The δD, δ15N, and δ13C values of EC powders are lighter than BSE, although δD and δ13C values partially overlap with atmospheric values. Reconstruction of the H budget of an EL-like parent body with an onion-shell structure suggests that such bodies could account for at most a fourth of the bulk silicate Earth’s (BSE’s) water budget.

¹Toni Schulz,¹Sophia Wernitznig,¹Christian Koeberl,²Bérengère Mougel,³Alessandro Montanari,⁴Frédéric Moynier
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70174]
¹Department of Lithospheric Research, University of Vienna, Vienna, Austria
²Instituto de Geociencias, UNAM, Queretaro, Mexico
³Osservatorio Geologico di Coldigioco, Frontale di Apiro, MC, Italy
⁴Universite Paris Cite, Institut de Physique du Globe de Paris, CNRS, 75005, Paris, France
Published by arrangement with John Wiley & Sons

Within the Danian Scaglia Rossa Formation appears a regionally correlatable horizon cutting across multiple sections and outcrops within the Umbria–Marche Basin of NE Italy, where it is intercalated with uniform pelagic carbonate successions. This horizon is called “ALE layer” and has tentatively been interpreted as a fine-grained volcanic ash. A key motivation for this study is the striking agreement between the ages of the ALE bed (65.440 ± 0.005 Ma) and the Boltysh impact event (65.39 ± 0.14/0.16 Ma), raising the possibility that the ALE layer preserves a distal Boltysh ejecta component transported over ~1600 km, while its bulk may reflect a longer duration volcanosedimentary depositional interval. To test this hypothesis, we combine impact-scaling considerations with highly siderophile element (HSE) and Cr-Os isotope data for Boltysh impactites and geochemical and Os isotopic analyses of the ALE horizon. Chromium isotope compositions of the Boltysh impactites (as low as ε54Cr = −0.31) may indicate an extraterrestrial contribution; however, their interpretation remains ambiguous. If interpreted as such, implausibly high IIIAB iron meteoritic admixtures would be required. By contrast, HSE abundances and 187Os/188Os systematics indicate clearly resolvable meteoritic components of up to 1 wt% CI-equivalent, forming coherent crust–chondrite mixing arrays. The ALE bed, though dominated by volcanosedimentary material, consistently shows Os–Ir–Pt–Pd enrichments far above the pelagic background, requiring up to ~0.8 wt% CI meteoritic input if interpreted in terms of an impact event horizon. Unradiogenic 187Os/188Os excursions occur primarily within the ALE layer, but in some cases extend into adjacent pelagic carbonate layers stratigraphically above and below the ALE layer. These unradiogenic 187Os/188Os excursions define chondritic-trending trajectories that mirror those in the Boltysh samples and are interpreted as diffusion-modified expressions of an originally ALE-centered meteoritic Os input. Taken together, the temporal coincidence between the Boltysh impact event and the ALE layer, impact-scaling relationships, and HSE- and Os-isotopic signatures favors the interpretation that the ALE layer preserves a distal equivalent of the Boltysh impact ejecta diluted within a volcanosedimentary depositional system that was subsequently modified by diagenetic processes.

¹K. Righter et al. (>10)
Meteoritics & Planetary Science (in Press) Open Access Link to Articlel [https://doi.org/10.1111/maps.70182]
¹Department of Earth and Environmental Sciences, University of Rochester, Rochester, New York, USA
Published by arrangement with John Wiley & Sons

Examination of 10 Bennu aggregate particles has revealed the presence of many phases which taken together can provide constraints on the oxygen fugacity (fO2) of Bennu samples. Phyllosilicates (saponite and serpentine), carbonates, oxides (magnetite, chromite), sulfides (pyrrhotite, pentlandite), phosphate (hydroxyapatite, Na-Mg-phosphate), and phosphides (schreibersite, andreyivanovite) all occur in most Bennu particles. The Bennu samples have experienced a high degree of aqueous alteration leaving only <1% of the original mineralogy unaltered. However, both the precursor anhydrous and alteration phases can present different constraints on fO2. Precursor phases include olivine, pyroxene, spinel, hibonite, chromite, phosphide, very rare Fe-Ni metal, apatite, and possibly MgS and MnS, all of which are typically <25 μm in size. Alteration phases include phyllosilicates, carbonates, magnetite, sulfides, sulfates, phosphates, chlorides, and fluorides. Detailed calculations of fO2 rely on having quantitative electron microprobe analyses of the phases involved in equilibria amongst both the precursor and alteration phases. In general, the absence of Fe-Ni metal, coupled with the stability of the Fe3O4 component in chromite, places a lower limit on the fO2. Concomitantly, the absence of Fe sulfates places an upper limit on fO2. Altogether, the textures, mineral compositions, and calculations suggest that some components in the Bennu samples (chondrules, inclusions) may have originally equilibrated at fO2 well below the iron-wüstite buffer but then experienced higher fO2 near or higher than the fayalite-magnetite-quartz (FMQ) buffer during aqueous alteration that produced coarser grained oxidized assemblages.

¹A. C. Singleton,¹G. R. Osinski
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70184]
¹Department of Earth Sciences, University of Western Ontario, London, Ontario, Canada
Published by arrangement with John Wiley & Sons

The ~28 km Kamestastin (Mistastin) Lake impact structure is a relatively well-preserved and well-exposed complex impact structure. The central uplift of this structure is accessible as two islands in the middle of Kamestastin Lake. We present an updated, detailed geological map and description of Horseshoe and Bullseye islands that provides increased accuracy and detail of the target rock outcrop and contact locations. In addition, we document six occurrences of impact melt-poor breccia dikes and one occurrence of impact melt rock on Horseshoe Island for the first time. The impact melt rock outcrop is proposed to be a remnant of a veneer of impact melt on the original central peak, and the impact melt-bearing breccia dikes to have had a dynamic emplacement mechanism. We also carried out the first detailed, systematic shock study of the central uplift. Planar deformation features in quartz and diaplectic feldspar glass suggest local peak shock pressure of up to 45 GPa. These shock pressures are higher than the peak pressures recorded in the central uplifts of similarly sized impact structures. We suggest that this difference is due to the minimal erosion of the central uplift at the Kamestastin Lake impact structure.

¹Glenn J. MacPherson, ²Kazuhide Nagashima, ²Alexander N. Krot, ³Noriko T. Kita, ^3,4Takayuki Ushikubo, ²Elena Dobrică
Geochimica et Cosmochimica Acta (in Press) Link to Article [10.1016/j.gca.2026.06.023]
¹Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington DC 20560, the United States of America
²University of Hawai‘i at Mānoa, Honolulu, HI 96822, the United States of America
³WiscSIMS, Department of Geoscience, University of Wisconsin-Madison, Madison, WI 53706, the United States of America
⁴Kochi Institute for Core Sample Research, JAMSTEC, Nankoku, Kochi 783-8502 Japan
Copyright Elsevier

Using secondary ion mass-spectrometry, we analyzed the Al/Mg isotopic compositions of cleanly resolved Wark-Lovering (WL) rim layers on six calcium-aluminum-rich inclusions (CAIs) of different petrologic types from the Vigarano CV3 chondrite. In five cases, the inferred initial ²⁶Al/²⁷Al ratios [(²⁶Al/²⁷Al)₀] are within analytical error of the ratios of the host inclusions and of each other, and in the sixth case the value for the rim sequence is suspect and not deemed reliable. The results for the five reliable CAIs mean that the maximum age difference between the rim sequences and their host inclusions is at most 10⁵ years and possibly less. Petrologic observations show that the effects of the rim-forming process were not limited to the rims themselves but extended well into the inclusion interiors. The fact that the (²⁶Al/²⁷Al)₀ of WL rims are within analytical error of each other raises the possibility that all WL rim sequences formed during a single nebula-wide event, but the fact that the inclusions are diverse petrologically makes this unlikely. We propose instead that the diverse rims formed during multiple nebular reheating events after the initial formation of the inclusions, leading to surface melting, volatilization, and recondensation. Our isotopic data for some rim phases, especially forsterite and diopside, tend to be isotopically lighter (lower δ²⁵Mg) than their host inclusion interiors, suggesting that they formed predominantly by recondensation.

^1,2Longye Du, ^1,3Xiaoxiao Yu, ⁴Yiliang Li, ¹Xiao Wu, ¹Lin Gong, ¹Gangjian Wei, ¹Qiang Wang, ^1,5Mang Lin
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [10.1016/j.gca.2026.06.019]
¹State Key Laboratory of Deep Earth Processes and Resources, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
²University of Chinese Academy of Sciences, Beijing 100049, China
³College of Earth Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China
⁴Department of Earth and Planetary Sciences, the University of Hong Kong, Hong Kong Special Administrative Region of China
⁵Center for Advanced Planetary Science (CAPS), Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
Copyright Elsevier

A primary objective of Mars sample return missions is the detection and characterization of potential biosignatures. Sulfates, among the most abundant hydrated minerals on Mars, represent promising targets for such investigation. Terrestrial studies have shown that gypsum can preserve life-associated organic matter and that its δ34S signatures provide key evidence for microbial sulfate reduction as early as ∼ 3.5 billion years ago. This study analyzes quadruple sulfur (δ34S, Δ33S, Δ36S) and triple oxygen (δ18O, Δ́17O) isotopes in gypsum from three strong evaporation basins on the Qinghai-Tibet Plateau, where sulfate deposition is extensive but surface environments are only marginally habitable due to severe limitations in water, soil development, and nutrient availability. We focus on the Qaidam Basin as a Mars analog environment and place it in context through comparison with a higher-elevation region (Shuanghu) and a magmatic rock-dominated region (Yushu). Together with isotopic mixing models, an open-system steady-state sulfur cycle model, and triple-oxygen isotope oxidation pathway calculations, our quadruple sulfur and triple oxygen isotope measurements reveal that the studied gypsum deposits preserve distinct isotopic biosignatures. In particular, the isotopic compositions of the samples reflect microbial sulfur disproportionation and cryptic sulfur cycling, both of which extend beyond widespread microbial sulfate reduction, demonstrating how sulfur can be internally recycled and energetically utilized to sustain life in Mars-analog environments. This integrated isotopic approach significantly advances our capability to decipher sulfur cycling in extreme terrestrial environments, including Mars analog systems, and provides critical methodology for interpreting potential biosignatures in returned Martian samples.

^1,2Yankun Di, ¹Magdalena H. Huyskens, ²Qing-Zhu Yin, ^1,3Yuri Amelin
Geochimica et Cosmoschimica Acta (in Press) Open Access Link to Article [10.1016/j.gca.2026.06.017]
¹Research School of Earth Sciences, Australian National University, Acton, ACT 2601, Australia
²Department of Earth and Planetary Sciences, University of California Davis, Davis, CA 95616, USA
³State Key Laboratory of Deep Earth Processes and Resources, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
Copyright Elsevier

Compared to the Earth and inner Solar System planets, calcium–aluminium-rich inclusions (CAIs) possess nucleosynthetic Sr isotope anomalies manifested as elevated ⁸⁴Sr/⁸⁶Sr after internal normalisation using ⁸⁸Sr/⁸⁶Sr. These anomalies can be generated by heterogeneous incorporation of s-, r-, or p-process nucleosynthesis components. Accurately distinguishing between the enrichment or depletion in those components is critical for correctly understanding the timing of planetary volatile depletion, as they predict very different anomalies in ⁸⁷Sr/⁸⁶Sr and lead to disparate interpretations of ⁸⁷Rb–⁸⁷Sr chronology. Here, we constrain the origin of Sr isotope anomalies in the original Mason and Taylor (1982) set of Allende CAIs by examining their nucleosynthetic Sr and Nd isotope systems. Most CAIs analysed exhibit positive μ⁸⁴Sr and negative μ^145,148,150Nd anomalies (μ-values are defined as part-per-million deviations of isotopic ratios relative to terrestrial standards) in agreement with previous studies, but we also detected significant isotope heterogeneities among them, including discovery of CAIs with Sr and Nd isotope anomalies in directions opposite to the majority. The Nd isotope heterogeneity among CAIs is predominantly consistent with variations in the abundance of the s-process component, with a minor but clearly resolved p-process deficit on μ¹⁴²Nd_corr (μ¹⁴²Nd_corr is μ¹⁴²Nd corrected for ¹⁴⁶Sm decay). The less steep μ¹⁴²Nd_corr vs. μ¹⁴⁸Nd slope defined by the CAIs compared to that predicted by stellar models supports the recent suggestion that the accessible Earth has a small radiogenic excess in μ¹⁴²Nd relative to chondrites. Correlated Sr and Nd isotope anomalies in the CAIs suggest that (1) they formed from at least two isotopically distinct reservoirs, one with and the other without p-process Sr excesses relative to Earth, (2) the majority of CAIs formed in the p-process-Sr-enriched reservoir with additional s-process excesses, and (3) variations in r-process Sr and Nd are not observed among the CAIs. The s-process-induced ⁸⁷Sr/⁸⁶Sr anomalies in CAIs (relative to the inner Solar System) predicted based on Nd isotopes are below the typical measurement precision, negating the need for nucleosynthetic correction on CAIs’ ⁸⁷Sr/⁸⁶Sr in chronological interpretations

^1,2Yankun Di, ²Magdalena H. Huyskens, ²Qing-Zhu Yin, ^1,3Yuri Amelin
Geochimcia et Cosmochimica Acta (in Press) Open Access Link to Article [10.1016/j.gca.2026.06.017]
¹Research School of Earth Sciences, Australian National University, Acton, ACT 2601, Australia
²Department of Earth and Planetary Sciences, University of California Davis, Davis, CA 95616, USA
³State Key Laboratory of Deep Earth Processes and Resources, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
Copyright Elsevier

Compared to the Earth and inner Solar System planets, calcium–aluminium-rich inclusions (CAIs) possess nucleosynthetic Sr isotope anomalies manifested as elevated ⁸⁴Sr/⁸⁶Sr after internal normalisation using ⁸⁸Sr/⁸⁶Sr. These anomalies can be generated by heterogeneous incorporation of s-, r-, or p-process nucleosynthesis components. Accurately distinguishing between the enrichment or depletion in those components is critical for correctly understanding the timing of planetary volatile depletion, as they predict very different anomalies in ⁸⁷Sr/⁸⁶Sr and lead to disparate interpretations of ⁸⁷Rb–⁸⁷Sr chronology. Here, we constrain the origin of Sr isotope anomalies in the original Mason and Taylor (1982) set of Allende CAIs by examining their nucleosynthetic Sr and Nd isotope systems. Most CAIs analysed exhibit positive μ⁸⁴Sr and negative μ^145,148,150Nd anomalies (μ-values are defined as part-per-million deviations of isotopic ratios relative to terrestrial standards) in agreement with previous studies, but we also detected significant isotope heterogeneities among them, including discovery of CAIs with Sr and Nd isotope anomalies in directions opposite to the majority. The Nd isotope heterogeneity among CAIs is predominantly consistent with variations in the abundance of the s-process component, with a minor but clearly resolved p-process deficit on μ¹⁴²Nd_corr (μ¹⁴²Nd_corr is μ¹⁴²Nd corrected for ¹⁴⁶Sm decay). The less steep μ¹⁴²Nd_corr vs. μ¹⁴⁸Nd slope defined by the CAIs compared to that predicted by stellar models supports the recent suggestion that the accessible Earth has a small radiogenic excess in μ¹⁴²Nd relative to chondrites. Correlated Sr and Nd isotope anomalies in the CAIs suggest that (1) they formed from at least two isotopically distinct reservoirs, one with and the other without p-process Sr excesses relative to Earth, (2) the majority of CAIs formed in the p-process-Sr-enriched reservoir with additional s-process excesses, and (3) variations in r-process Sr and Nd are not observed among the CAIs. The s-process-induced ⁸⁷Sr/⁸⁶Sr anomalies in CAIs (relative to the inner Solar System) predicted based on Nd isotopes are below the typical measurement precision, negating the need for nucleosynthetic correction on CAIs’ ⁸⁷Sr/⁸⁶Sr in chronological interpretations