^1,2Kyusei Tsuno, ³Hideharu Kuwahara, ¹Varun Manilal, ²Axel Wittmann, ^2,4Kurt Leinenweber, ³Tetsuo Irifune, ¹Damanveer S Grewal
Earth and Planetary Science Letters (in Press) Link to Article [DOI: 10.1016/j.epsl.2026.120246]
¹Department of Earth and Planetary Sciences, Yale University, New Haven, CT, 06511, United States
²Eyring Materials Center, Arizona State University, Tempe, AZ, 85287, United States
³Geodynamic Research Center, Ehime University, Matsuyama, 790-8577, Japan
⁴School of Molecular Sciences, Arizona State University, Tempe, AZ, 85287, United State
Copyright Elsevier

Geochemical constraints imply that a solid silicate layer existed between the base of the Martian magma ocean (∼14 GPa) and the core-mantle boundary (∼18–20 GPa) during early differentiation. Both S-poor metallic melts segregated during core formation and S-rich sulfide melts exsolved upon subsequent magma ocean cooling must have percolated through this layer to the core, but the efficiency of this process is poorly constrained. At ∼18 GPa, this layer comprises roughly equal proportions of ringwoodite and majorite garnet, yet no dihedral angles in majorite garnet have been reported. We conducted experiments at 18 GPa and 1723–2200 K to determine dihedral angles between Fe(-Ni)-S-O alloy melts (25–46 mol% S+O) and both ringwoodite and majorite garnet. Dihedral angles decrease with increasing temperature, S+O content, and oxygen fugacity, while Ni has no effect. Dihedral angles in majorite garnet are systematically ∼10° lower than in ringwoodite under comparable conditions. Despite this, all dihedral angles (89°-126°) remain above the 60° threshold for melt interconnection, so the entire mineral assemblage acts as a percolation barrier. Because our experimental S+O contents exceed those of the S-poor core-forming alloy (∼15 mol% S), the measured angles represent a lower bound; the barrier for core-forming metal was even more severe. Theoretical models predict that for such angles, a few (> ∼1–2) vol.% of melt remains trapped as isolated pockets upon network disconnection. Such melts constitute a hidden deep mantle reservoir of highly siderophile elements (HSEs) and siderophile volatiles (C, N), explaining their abundances in bulk silicate Mars without requiring a late veneer.

¹Fabrice Gaillard, ²Yves Marrocchi, ¹Gregory Rogerie, ³Mohamed A. Bouhif, ¹Camille Bernard, ⁴Mathieu Roskosz
Earth and Planetary Science Letters, 692, 120245 Link to Article [DOI: 10.1016/j.epsl.2026.120245]

¹Institut Des Sciences de la Terre d’Orléans, CNRS/Université d’Orléans/BRGM, 1a Rue de la Férollerie 2, Orléans, 45071 CEDEX, France
²Université de Lorraine, CNRS, CRPG, Nancy, F-54000, France
³Laboratoire Magmas et Volcans, Université Clermont Auvergne, CNRS, IRD, OPGC, Clermont-Ferrand, F-63000, France
⁴IMPMC, MNHN, CNRS, UMR 7590, Muséum National d’Histoire Naturelle, Sorbonne Universités, CP 52, 57 rue Cuvier, Paris, F-75231, France
Copyright Elsevier

The Mercury-Venus-Earth-Mars-Vesta planetary suite exhibits large variations in oxidation state as defined by the Fe to FeO ratio (i.e. core to silicate ratio), with increasingly oxygen-depleted bodies toward the centre of the solar system. As undifferentiated materials (i.e., chondrites) likely display a similar heliocentric FeO-gradient, planetary and chondritic oxidation states should be related in this respect. We develop an approach wherein, the equilibrium oxygen redistribution during gas – silicate melt – molten metal alloy during differentiation is resolved for bodies of various compositions and sizes. As a case study, three chondritic end-members were considered: enstatite, ordinary, and carbonaceous. A broad range of planetary oxidation states are obtained that encompass the above-mentioned planetary suite. The oxidation state during the growth of small bodies (<2000 km in radius) of constant bulk composition is affected by metal-vapour carbon redistribution, whereas on larger bodies, the incorporation of hydrogen, oxygen and silicon in the core prevails, causing the convergence toward a putative universal magma ocean FeO content. A dual regime is observed for the water content in the silicate magma ocean, which increases up to a planetary radius of ∼3000 km, whereas in larger bodies, hydrogen incorporation into the core brings about dehydration of the complementary silicate mantles. The accretion of ordinary chondrites perfectly matches the oxidation state of Mars and produces a core with C-H-S-N contents matching the Martian core density as suggested by the Insight missions. Finally, Vesta’s oxidation state seemingly requires an H2O-rich oxidizing component during the formation of planetesimals.

^1,2,6Ranjan Sarkar, ³Ed Cloutis, ³Daniel Applin, ³Nathalie Turenne, ⁴Daniel Mège, ⁵Andreas Beinlich, ⁵Stanley A. Mertzman
Icarus (in Press) Link to Article [DOI: 10.1016/j.icarus.2026.117282]
¹Max Planck Institute for Solar System Research, Göttingen, Germany
²Indian Institute of Technology, Kharagpur, India
³Department of Geography, University of Winnipeg, Winnipeg, MB, Canada R3B 2E9
⁴Centrum Badań Kosmicznych Polskiej Akademii Nauk (CBK PAN), ul. Bartycka 18a, 00-716, Warszawa, Poland
⁵Institut für Geologische Wissenschaften, Freie Universität Berlin, Kaiserswerther Str. 16-18, 14195 Berlin, Germany.
⁶Department of Earth and Environment, Franklin and Marshall College, Lancaster, PA 17604, USA.
Copyright Elsevier

Listvenites are extensively carbonated ultramafic rocks such as peridotites and serpentinites that commonly containing carbonates (magnesite, dolomite), quartz, and often the accessory mineral fuchsite—a green, chromium-bearing variety of muscovite. Listvenites form distinctive yellow-orange ridges in areal views due to their mechanically-resistant carbonate-silica mineralogy and iron oxidation. They form when an ultramafic protolith comes into contact with CO₂-rich fluids and undergoes a progressive replacement of the Fe/Mg-bearing olivines and pyroxenes or serpentinites into increasingly carbonate-rich assemblages, and ultimately to carbonate-quartz rocks. We analyzed listvenite samples from the Atlin area, British Columbia, Canada using a variety of analytical techniques, including X-ray diffraction (XRD), X-ray fluorescence (XRF), wet chemistry (WC), visible-near infrared (VNIR) reflectance spectroscopy (0.35-2.5 μm), and Raman spectroscopy. VNIR and Raman spectroscopies were able to successfully identify all major mineral phases through their diagnostic absorption (VNIR) or emission (Raman) features. We found that listvenite composition is readily derivable from VNIR reflectance and Raman spectra, with fuchsite providing a diagnostic signature in VNIR spectra due to its unique Cr³⁺ absorption bands that remain detectable even at low concentrations. These findings establish a spectroscopic framework for identifying listvenites in remote sensing applications, relevant for exploration of Solar System bodies, particularly Mars, where such carbonated ultramafic rocks can produce H₂ and CH₄, and may preserve biosignatures and might indicate past habitable conditions associated with their low-temperature formation.

^1,2Oleg I. Siidra, ³Artem S. Borisov, ⁴Victoria A. Ginga, ¹Veronika R. Abdulina, ⁵Dmitri O. Charkin, ⁶Anatoly V. Kasatkin, ³Astrid Holzheid, ⁴Annette Setzer, ⁷Vladimir N. Bocharov
Icarus (in Press) Link to Article [DOI: 10.1016/j.icarus.2026.117275]
¹Department of Crystallography, St. Petersburg State University, University Emb. 7/9, 199034 St. Petersburg, Russia
²Kola Science Center, Russian Academy of Sciences, Apatity 184200, Murmansk Region, Russia
³Institut für Geowissenschaften der Universität Kiel, Olshausenstr. 40, D-24098 Kiel, Germany
⁴Felix Bloch Institute for Solid-State Physics, Leipzig University, Linnestrasse 5, D-04103 Leipzig, Germany
⁵Chemistry Department, Moscow State University, Vorobievy Gory 1-3, Moscow 119991 Russia
⁶Fersman Mineralogical Museum of the Russian Academy of Sciences, Leninsky Prospekt 18-2, 119071 Moscow, Russia
⁷Geomodel Resource Center, St. Petersburg State University, University Emb. 7/9, 199034 St. Petersburg, Russia
Copyright Elsevier

Copiapite-group minerals are among the most common hydrated iron sulfate minerals in a variety of geological environments on Earth. They are also believed to be widespread on the Martian surface. The transformation and stability of the copiapite-group minerals are examined in this study using a diverse array of methods, including low- (LT) and high-temperature (HT) single-crystal X-ray diffraction (SCXRD), LT- and HT-powder X-ray diffraction (PXRD), vacuum powder X-ray diffraction, HT-Raman spectroscopy, magnetization and heat capacity measurements. The research is conducted over a broad temperature range (−175–740 °C) and under vacuum (~ 600 Pa) conditions that are partially similar to those found on the Martian surface (from −153 °C to over 20 °C and ~ 600 Pa). The obtained results indicate that aluminocopiapite, (Al0.54Fe3+0.13)Σ0.67Fe3+4(SO4)6(OH)2(H2O)20, is unstable under low vacuum conditions and undergoes a structural transition to a post-aluminocopiapite phase, (Al0.63Fe3+0.04)Σ0.67Fe3+4(SO4)6(OH)2(H2O)12.44 with a significantly lower water and iron content and a higher aluminum content. Schwertmannite, Fe3+16O16(OH)9.6(SO4)3.2·10H2O is formed as a film/shell on the crystal surface of post-aluminocopiapite via a single crystal-to-single crystal (SC-SC) topotactic transformation and exsolution. After 14 days of exposure to air, the post-aluminocopiapite crystal with schwertmannite shell undergoes a reversible process, reverting to its initial aluminocopiapite state. A closely analogous transformation, involving partial dehydration, was observed for copiapite, Fe2+Fe3+4(SO4)6(OH)2(H2O)20, demonstrating that this behavior is a general feature of the copiapite group.
It is therefore unlikely that copiapite-group minerals would exist on the surface of Mars and in comparable extraterrestrial environments in their initial form. Instead, under Mars surface conditions with low vacuum, post-copiapites and schwertmannite may be among the most common minerals in hydrated iron sulfate mineral associations. This is relevant for decoding past geo- and climatic environments on Mars and for selecting the conditions for the return of intact samples collected by rovers to Earth.

¹Jillian Kirk, ¹Myriam Telus, ¹Pranvera Hyseni, ¹Fatima Jorge-Chavez, ²Vanessa Mendoza, ³Steven J. Desch, ⁴Dale Burns, ⁵Steven Simon
Icarus (in Press) Open Access Link to Article [DOI: 10.1016/j.icarus.2026.117263]
¹University of California Santa Cruz, Department of Earth and Planetary Sciences, 1156 High Street, Santa Cruz, 95064, CA, USA
²Western Washington University, Geology Department, 516 High St, Bellingham, 98225, WA, USA
³Arizona State University, School of Earth and Space Exploration, 781 Terrace Mall, Tempe, 85287, AZ, USA
⁴Stanford University, Department of Geological Sciences, 450 Jane Stanford Way, Stanford, 94305, CA, USA
⁵University of New Mexico, Institute of Meteoritics, 221 Yale Blvd NE MSC03 2050, Albuquerque, 87131, NM, USA
Copyright Elsevier

Chondrules are small igneous particles that formed in the protoplanetary disk and make up the bulk of chondrites. Chondrule rims offer insights into the composition of dust in the solar nebula and the conditions and heating mechanisms associated with chondrule formation. High-resolution elemental mapping of pristine CO3 chondrite thin sections revealed igneous chondrule rims enriched in manganese, a moderately volatile element (MVE), which is sensitive to thermal processing. These chondrule rims have not previously been characterized, in part due to their small thicknesses (
30
m). Characterization of Mn-rich rims in CO3 chondrites reveals that this enrichment exists in a variety of textures, some of which are associated with non-igneous fine-grained rims, while many clearly formed from a melt. Mn-rich pyroxenes in CO3 chondrule rims are also enriched in Na, K, and Cr, as compared to pyroxene in host chondrules (i.e., chondrules hosting the Mn-rich rims) and no-rim chondrules (chondrules without Mn-rich rims). These enrichments seem to be the result of nebular processing of chondrules as opposed to parent-body processing, as enrichments do not correlate with petrologic subtypes. Pyroxene with similar enrichments in these elements occur within igneous chondrule rims seen in CR chondrites, indicating that these rims may have formed across different locations and times in the nebula. Previous studies have suggested that MVE enrichment of chondrule rims occurred during interaction with MVE-enriched nebular gas. Our results could support an alternative scenario involving accretion of MVE-enriched dust onto solidified chondrules, which subsequently experienced varying degrees of thermal processing, possibly facilitated by a planetesimal or planetary embryo bow shock, resulting in MVE-enriched chondrule rims. Future work is needed to validate this idea. This study highlights the potential role of outgassing planetesimals and/or planetary embryos as a source of MVE-rich dust in the solar nebula.

¹R. J. Windmill, ¹I. A. Franchi, ¹X. Zhao, ¹R. C. Greenwood, ¹M. Anand
Meteoritics & Planetary Science (in Press) Open Source Link to Article [DOI: 10.1111/maps.70210]
¹Planetary and Space Sciences, School of Physical Sciences, The Open University, Milton Keynes, UK
Published by arrangement with John Wiley & Sons

The light element distribution in planetary cores and the processes driving core evolution in rocky planets are poorly understood. Magmatic iron meteorites are samples from the cores of ancient embryonic planetesimals and therefore provide a window into the processes governing core evolution. We performed high precision oxygen isotope analyses on chromite from IIIAB iron meteorites to investigate the oxygen isotopic evolution across a protoplanetary core using laser-assisted fluorination. We identify three unexpected and hitherto unreported discrete isotopic subgroups within the IIIAB chemical group and discuss possible causes for their existence. The most likely explanation is that they may be sampling multiple parent bodies, either completely unrelated or mixed during an impact. This would have significant implications for the use of the chemical classification scheme for iron meteorites as well as models for IIIAB core evolution. Second, that they may be evidence that oxygen mobility across the core was controlled by diffusion. If this is the case, they may represent homogenized melt pools in a wider core context, recording oxygen diffusion into a planetary core, which could help explain the density deficit observed in Earth’s core. Third, we discuss whether core rain out through a heterogeneous IIIAB mantle and inefficient mixing in the core could explain the isotopic results. Finally, we compare these IIIAB oxygen isotopic signatures to published data for main group pallasite minerals and conclude that the meteorite groups cannot be from a common parent body, answering a long-standing question in meteoritical science.

I

¹Yasuaki Tsuruoka, ^1,5Hideto Yoshida, ^2,6Yuki Inoue, ²Daiki Yamamoto, ³Hiroyuki Kagi, ⁴Akira Miyake, ¹Shogo Tachibana
Meteoritics & Planetary Science (in Press) Open Source Link to Article [DOI: 10.1111/maps.70213]

¹Department of Earth and Planetary Science, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
²Department of Earth and Planetary Sciences, Kyushu University, Nishi-ku, Fukuoka, Japan
³Geochemical Research Center, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
⁴Department of Geology and Mineralogy, Kyoto University, Sakyo-ku, Kyoto, Japan
⁵The Kiso Observatory, Institute of Astronomy, The University of Tokyo, Kiso-machi, Nagano, Japan
⁶Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa-shi, Chiba, Japan
Published by arrangement with John Wiley & Sons

Dmisteinbergite is a metastable polymorph of CaAl₂Si₂O₈, which has been found in calcium−aluminum-rich inclusions (CAIs) in chondrites, although anorthite is the predominant CaAl₂Si₂O₈ phase in natural type B CAIs. The occurrence/absence of igneous dmisteinbergite would put tighter constraints on the thermal history of CAIs. However, little attention has been paid for crystallization of dmisteinbergite in CAI melts even though its kinetically controlled crystallization (i.e., crystallization from a supercooled melt) has been proposed. In this study, we conducted dynamic crystallization experiments on CAI analogs in the presence of low-pressure hydrogen gas (1–10 Pa) to simulate the formation of igneous CAIs and to understand crystallization behavior of CaAl₂Si₂O₈ phases. Dmisteinbergite was found in samples cooled at rates of 1–20 °C h⁻¹, while anorthite was found in samples cooled at 5 °C h⁻¹, suggesting that the slow cooling (likely slower than on the order of 1 °C h⁻¹) might promote the formation of anorthite. Because the slow cooling rates during the final stage of crystallization of CAIs likely reflect conditions approaching the background temperature of CAI-forming regions, CaAl₂Si₂O₈ phases in type B CAIs could constrain the thermal history and formation environment of those regions.

Dmisteinbergite is a metastable polymorph of CaAl₂Si₂O₈, which has been found in calcium−aluminum-rich inclusions (CAIs) in chondrites, although anorthite is the predominant CaAl₂Si₂O₈ phase in natural type B CAIs. The occurrence/absence of igneous dmisteinbergite would put tighter constraints on the thermal history of CAIs. However, little attention has been paid for crystallization of dmisteinbergite in CAI melts even though its kinetically controlled crystallization (i.e., crystallization from a supercooled melt) has been proposed. In this study, we conducted dynamic crystallization experiments on CAI analogs in the presence of low-pressure hydrogen gas (1–10 Pa) to simulate the formation of igneous CAIs and to understand crystallization behavior of CaAl₂Si₂O₈ phases. Dmisteinbergite was found in samples cooled at rates of 1–20 °C h⁻¹, while anorthite was found in samples cooled at 5 °C h⁻¹, suggesting that the slow cooling (likely slower than on the order of 1 °C h⁻¹) might promote the formation of anorthite. Because the slow cooling rates during the final stage of crystallization of CAIs likely reflect conditions approaching the background temperature of CAI-forming regions, CaAl₂Si₂O₈ phases in type B CAIs could constrain the thermal history and formation environment of those regions.

¹Giovanna Agrosì, ²Paola Manzari, ¹Daniela Mele, ^3,4Johan Villeneuve, ⁵Tiziano Catelani, ⁶Mattew J. Genge, ⁷Luca Bindi
Meteoritics & Planetary Science (in Press) Open Source Link to Article [DOI: 10.1111/maps.70215]

¹Dipartimento di Scienze della Terra e Geoambientali, Università di Bari, Bari, Italy ²Agenzia Spaziale Italiana, Centro Spaziale Giuseppe Colombo, Matera, Italy
³Centre de Recherches Pétrographiques et Géochimiques, CNRS, Nancy, France
⁴Universite Paris-Cite, Institut de Physique du Globe de Paris, CNRS, Paris, France ⁵Centro di Servizi di Microscopia Elettronica e Microanalisi, Università di Firenze, Florence, Italy
⁶Department of Earth Science and Engineering, Imperial College London, London, UK ⁷Dipartimento di Scienze della Terra, Università di Firenze, Florence, Italy
Published by arrangement with John Wiley & Sons

We report the discovery of the second (Al,Cu)-alloy–bearing micrometeorite, FB-A2, recovered from Mount Gariglione (southern Italy), representing the sixth such occurrence worldwide. Although chondritic in nature, FB-A2 differs markedly from previously described microspherules. It is a scoriaceous micrometeorite dominated by silicates and contains a relict clast composed of Mg-rich olivine and pyroxene phenocrysts set in a Fe-rich silicate matrix. The particle rim hosts fine aggregates of phosphates, magnetite, Ni-bearing magnetite, and sulfides, whereas the interior contains nepheline crystals. A 120 μm (Al,Cu)-alloy grain occurs at one corner of the particle. The porphyritic texture of the clast indicates a chondrule fragment—the first identified in an (Al,Cu)-bearing micrometeorite—while polyhedral sub-grain boundaries and metal–sulfide veins record shock metamorphism. Iron-rich alteration of relict silicates is consistent with high-temperature (<560 °C) metasomatism typical of CV3 chondrites and is supported by oxygen isotope compositions close to the Carbonaceous Chondrite Anhydrous Mineral Line. Brecciation of chondrule olivine suggests impact-induced fluid pressure excursions during early Solar System metasomatism, whereas impact melt enveloping elongate olivines indicates a later impact that introduced the (Al,Cu)-alloys. Overall, the texture, mineralogy, and isotopic composition of FB-A2 provide the most detailed constraints yet on the origin of (Al,Cu)-bearing micrometeorites and confirm a genetic link to the Khatyrka meteorite.

¹Jin-Young Lee, ²Jeongmin Kim, ¹Sei-Sun Hong
Meteoritics & Planetary Science (in Press) Open Source Link to Article [DOI: 10.1111/maps.70216]

¹Quaternary Geological Research Center, Korea Institute of Geoscience and Mineral Resources, Daejeon, Korea
²Research Center of Earth and Environmental Sciences, Korea Basic Science Institute, Cheongju, Korea
Published by arrangement with John Wiley & Sons

We present the first micrometer-scale, phase-resolved compositional characterization of impact melt glass from the Hapcheon crater (~1.4 km apparent diameter), the first confirmed impact structure on the Korean Peninsula, integrating EPMA-WDS (5 μm spot), confocal Raman spectroscopy (<1 μm spot), XRD, and 40Ar/39Ar step-heating geochronology. EPMA of 37 points resolves three compositionally distinct groups separated by a clear compositional gap: silica-glass cores (CORE; n = 23; 98.4 wt% SiO2, K2O 0.023 wt%), feldspathic–mafic mantling glass (MANTLE; n = 6; ~55 wt% SiO2, K2O 2.24 wt%), and feldspathic glass clasts (UNCERTAIN; n = 8; ~61 wt% SiO2, K2O 3.10 wt%), demonstrating phase-segregated melting of the quartz and feldspathic–mafic fractions of the Cretaceous Dongmyeong target rock rather than whole-rock homogenization. Confocal Raman spectroscopy confirms coesite in 74% of 34 spectra and identifies diaplectic quartz glass, documenting micrometer-scale shock heterogeneity; a 30-point colocation data set confirms coesite within the ultralow-K2O glass phase. The ultralow K2O causes systematic 40Ar/39Ar age overestimation through inherited 40Ar; all seven plateau ages (1.8–5.6 Ma) exceed the independent 10Be burial age of 1.33 Ma. Step-heating Ca/K systematics confirm multiphase assemblages, and inverse-isochron 40Ar/36Ar intercepts independently corroborate inherited 40Ar. The youngest compositionally anchored age brackets the impact at 1.33–3.07 Ma (Plio-Pleistocene).

^1,3Qi-ao Chen, ¹Wen Yu, ^2,4Hao Yan, ¹Tian Zhang, ¹Hong Tang, ¹Xiongyao Li
Earth and Planetary Science Letters, 692, 120236 (2026) Link to Article [DOI: 10.1016/j.epsl.2026.120236]

¹Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081, China
²International Center for Isotope Effects Research, State Key Laboratory of Critical Earth Material Cycling and Mineral Deposits, Nanjing University, Nanjing, 210023, China
³College of Resources and Environment, University of Chinese Academy of Sciences, Beijing, 100049, China
⁴Frontiers Science Center for Critical Earth Material Cycling, School of Earth Sciences and Engineering, Nanjing University, Nanjing, 210023, China
Copyright Elsevier

Solar wind implantation is widely recognized as a primary source of hydroxyl (OH) and water on the lunar surface, yet the kinetics and controlling mechanisms of this process remain poorly constrained. Here we present proton implantation experiments on San Carlos olivine conducted at 20, 90, and 130°C to quantify the kinetics and saturation behavior of OH formation. The OH abundance increases with H⁺ fluence following an exponential function and approaches a temperature-dependent saturation level. The fitted saturation concentration decreases with increasing temperature, whereas the apparent rate constant increases, indicating a decoupling between reaction kinetics and OH yield. Post-implantation heating experiments demonstrate negligible OH loss, ruling out thermal instability as the cause of reduced OH abundance at elevated temperatures. Instead, we propose a temperature-dependent branching mechanism in which implanted hydrogen partitions between OH formation and H₂ recombination. Higher temperatures enhance hydrogen mobility, promoting H-H recombination and suppressing OH formation efficiency. The conversion ratio of H⁺ to OH decreases progressively with fluence, providing a unified explanation for the large discrepancies reported in previous studies. These results provide a quantitative framework for solar wind-induced water formation and a mechanistic explanation for the latitude-dependent distribution of OH/H₂O on the Moon.