¹N. Meunier-Mili, ¹M.-A. Kaczmarek, ²M. Bystricky
Geochimica et Cosmochimica Acta (in Press), Open Source Link to Article [DOI: 10.1016/j.gca.2026.08.025]
¹Géosciences Environnement Toulouse (GET), CNRS – CNES – IRD – Université de Toulouse, Observatoire Midi Pyrénées, 14 avenue E. Belin, 31400 Toulouse, France
²Institut de Recherche en Astrophysique et Planétologie (IRAP), CNRS – CNES – Université de Toulouse, Observatoire Midi Pyrénées, 14 avenue E. Belin, 31400 Toulouse, France
Copyright Elsevier

Chassignite meteorites are martian achondrites that display a magmatic cumulate texture and are mainly composed of olivine with a small amount of poikilitic pyroxene. This study presents a detailed petrological and microstructural analysis using electron backscatter diffraction of all Chassignite meteorites documented up to now, Chassigny, NWA 2737 and NWA 8694, in order to decipher early magmatic, deformation and shock processes. The new results reveal that olivine crystals in Chassignite meteorites initially formed through synneusis, a magmatic process where individual crystals accumulate and aggregate together in specific orientations in the earlier stages of consolidation. Many olivine crystals stick together along (100) crystalline faces as evidenced by the significant concentration of misorientation [100] axes at grain boundaries for all three samples. Synneusis was probably interrupted and progressively replaced by crystal settling until complete crystallisation was achieved. Olivine crystallographic preferred orientations indicate slip on 100 and olivine subgrain boundaries reveal high densities of geometrically necessary dislocations of the 100 type. The 100 slip system is active at high temperatures and low stresses in the Earth’s upper mantle and is often observed in plastically deformed peridotites, though it is not necessarily dominant in terrestrial olivine cumulative rocks. Furthermore, pyroxene crystallographic preferred orientations are consistent with those of olivine ([100] olivine axes parallel to pyroxene [001] axes), supporting the hypothesis of minor plastic deformation of olivine and pyroxene at high temperatures and low stresses. These observations are consistent with possible crystallization and emplacement of the Chassignite magma in the shallow Martian crust. Finally the strong shock events recorded by these meteorites is supported by significant internal deformation of olivine grains, concentration of misorientation axes along their [100] axes, and the activation of the 001 slip system leading to formation of olivine subgrain boundaries. Altogether these results are good indicators to decipher primary planetary processes.

¹Kang Liu, ¹Li Zhang, ¹Hesan Wu, ¹Wan-Cai Li, ^1,2Huaiwei Ni
Geochimica et Cosmochimica Acta (in Press), Link to Article [DOI: 10.1016/j.gca.2026.08.028]
¹State Key Laboratory of Lithospheric and Environmental Coevolution, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China
²Deep Space Exploration Laboratory, Hefei 230088, China
Copyright Elsevier

Lunar volcanic glass beads preserve records of sulfur evolution in primitive lunar magmas and provide important constraints on the sulfur inventory of the lunar interior. Reconstruction of their pre-eruptive sulfur contents requires sulfur diffusivity data for lunar melts, which have remained largely unavailable. Here we experimentally determined sulfur diffusivities in three synthetic lunar basaltic melts, spanning compositions from Apollo green (low TiO₂, 0.52 wt%) and orange (intermediate TiO₂, 8.58 wt%) to red (high TiO₂, 13.93 wt%), with SiO₂ decreasing from 45.35 to 35.92 wt% and MgO from 16.00 to 11.00 wt%, using diffusion-couple experiments at 0.5 GPa and 1674–1876 K in a piston cylinder apparatus. Sulfur diffusivity increases systematically from green to orange to red glass compositions, with NBO/T rising from 1.76 to 2.49 to 2.82, respectively. At 1673 K, sulfur diffusivity in lunar melts is 6–13 times higher than that in terrestrial basaltic melts (NBO/T = 0.61–0.79), primarily owing to the more depolymerized structure of lunar melts. Combining these results with published experimental data, we develop a general parameterization for sulfur diffusivity in anhydrous lunar and terrestrial silicate melts under reduced conditions as a function of temperature (T) and melt composition (X_Si+Al, expressed by the combined mole fraction of Si + Al), which reproduces nearly all available experimental data within a factor of 2. Applying our new sulfur diffusivity data to Apollo green and orange glass beads yields revised pre-eruptive sulfur concentrations of 282–311 and 331 μg/g, corresponding to mantle source sulfur abundances of 9–28 and 27–63 μg/g, respectively. These estimates differ substantially from values previously inferred for Apollo and Chang’e mare basalts, indicating significant sulfur heterogeneity within the lunar interior, likely inherited from lunar magma ocean differentiation and subsequent mantle overturn.

Cosmochemistry Papers will have a short Summer Break from 28.08.2026 to 14.09.2026.

¹Ziqing Li, ²Mengfan Zhang, ¹Bo Zhang, ³Yuqi Qian, ⁴Tao Long, ⁴Xiaochao Che, ¹Ao Su, ⁵James W. Head
Journal of Geophysical Research: Planets, 131, e2026JE009898 Open Source Link to Article [DOI: 10.1029/2026JE009898]
¹Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing, China
²School of Earth and Space Sciences and Institute of Energy, Peking University, Beijing, China
³Department of Earth and Planetary Sciences, NWU-HKU Joint Center of Earth and Planetary Sciences, The University of Hong Kong, Hong Kong, China
⁴Beijing SHRIMP Center, Institute of Geology, Chinese Academy of Geological Sciences, Beijing, China
⁵Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, RI, USA
Published by arrangement with John Wiley & Sons

The cause of the observed mare basalt asymmetry between the lunar nearside and farside remains a long-lasting conundrum. In this study, we characterized the petrology and geochemistry of the Chang’e-6 low-Ti basalts from the lunar farside, performed petrological modeling of major elements and conducted Monte Carlo simulation of trace elements, for Chang’e-6 and Chang’e-5 basalts. The results from multiple approaches indicate that the young Chang’e-6 (2.8 Ga) and Chang’e-5 (2.0 Ga) basalts both originated from shallow, depleted ilmenite-bearing cumulate (IBC). Based on remote sensing and thermodynamic constraints, we estimated the mantle source ilmenite abundance for young shallow-source basalts (<3.0 Ga) globally. The modeling results indicate that the mantle sources of these basalts on the nearside generally contains ∼16–32 wt% ilmenite, especially beneath the PKT, whereas the mantle sources of these basalts beneath the farside SPA basin only has ∼13–24 wt% ilmenite. The phase equilibrium calculations show that the nearside mantle sources with higher ilmenite abundance leads to a significant decrease in melting point and tends to produce more melt compared to farside mantle sources. Therefore, asymmetric IBCs may play a key role in accounting for asymmetric nearside/farside volcanism.

¹F. Alberquilla (>10)
Journal of Geophysical Research: Planets, 131, e2026JE009742 Open Source Link to Article [DOI: 10.1029/2026JE009742]
¹University of the Basque Country (EHU), Leioa, Spain
Published by arrangement with John Wiley & Sons

Volcanic tubes provide stable environments where unique mineralogical assemblages can form and be preserved, making them valuable terrestrial analogs for Martian studies. This work investigates tree-like structures within two lava tubes on La Palma Island (Canary Islands, Spain) through a comprehensive geochemical and mineralogical characterization. Samples were analyzed using X-ray diffraction (XRD), micro Energy Dispersive X-Ray fluorescence (µ-EDXRF), Raman microscopy, Scanning Electron Microscopy Energy-Dispersive X-ray Spectroscopy (SEM-EDX), Short-Wave infrared (SWIR) hyperspectral imaging, and multivariate analysis Principal Component Analysis and Multivariate Curve Resolution-Alternating Least Squares (PCA and MCR-ALS) to identify primary mineral phases and assess potential organic matter preservation. The results reveal that these structures are predominantly composed of hydrated silica (opal-A), with secondary phyllosilicates, carbonates, sulfates, and iron oxides. Organic signatures were identified as spectral features consistent with microbial pigments such as β-carotene within the opal matrix, suggesting the potential encapsulation and preservation during silica precipitation. Hyperspectral analyses revealed spectral features consistent with the presence of opal-A, calcite, and nontronite, highlighting complex mineral associations. The comparison with CRISM observations from Jezero Crater revealed similarities in mineral assemblages and suggests that comparable alteration pathways may have affected basaltic substrates, with hydrated silica formation followed by carbonate precipitation under evolving fluid conditions. These findings underscore the relevance of terrestrial lava tubes as analogs for Martian volcanic environments and emphasize the potential of hydrated silica deposits to preserve biosignatures in extraterrestrial contexts.

¹Alessandro Pisello (>10)
Journal of Geophysical Research: Planets 131, e2025JE009371 Open Source Link to Article [DOI: 10.1029/2025JE009371]
¹Department of Physics and Geology, University of Perugia, Perugia, Italy
Published by arrangement with John Wiley & Sons

Understanding how the glass/crystal ratio influences the spectral response of volcanic rocks is crucial for interpreting planetary remote sensing data. Here, four mafic rocks simulating a possible Martian composition were synthesized with identical bulk chemistry but different mineralogical assemblages, from fully amorphous to ∼70 wt.% crystal content, to investigate how crystal content affects Visible and Near-Infrared (VNIR) reflectance spectra. Bi-directional VNIR reflectance was collected at room temperature across a range of incidence (0°, 30°, 60°) and emergence (−70° to +70°) angles. The diagnostic absorptions of the two most abundant phases, pyroxene and glass, are not distinguishable in the spectra and can even reproduce the spectral fingerprint of olivine, absent from the samples; only minor iron oxides (magnetite and hematite, ∼1–7 wt.%) produce clearly identifiable absorptions. Instead, spectral slope emerges as the primary proxy for the glass/crystal ratio: NIR/VNIR slope decreases systematically with increasing crystal content, driven jointly by the incorporation of iron oxides and the loss of the positive-slope contribution of residual glass. Principal Component Analysis and k-means clustering independently confirm this control, identifying three clusters that map onto the glass/crystal ratio. This decoupling indicates that the crystal content of a mafic terrain cannot be inferred from pyroxene- or glass-related absorptions alone, but rather from spectral slope and iron-oxide features. These results experimentally support previous hypotheses linking the spectral diversity of Martian mafic terrains to their degree of crystal content and oxidation state and highlight variable glass abundance as an under-considered contributor to the spectral interpretation of the Martian surface.

^1,2,3Scott M. Perl, ^2,4Aaron J. Celestian, ⁴Frank A. Corsetti
Journal of Geophysical Research: Planets 131, e2026JE009730 Link to Article [DOI: 10.1029/2026JE009730]
¹Earth, Planetary, and Space Sciences, University of California Los Angeles, Los Angeles, CA, USA
²Mineral Sciences, Los Angeles Natural History Museum, Los Angeles, CA, USA
³Blue Marble Space Institute of Science, Seattle, WA, USA
⁴Department of Earth Sciences, University of Southern California, Los Angeles, CA, USA
Published by arrangement with John Wiley & Sons

Evaporite minerals can capture and entomb organic matter within their intercrystalline and intracrystalline structure because they precipitate relatively quickly (nomenclature adopted from Schopf et al. (2012), https://doi.org/10.1089/ast.2012.0827). Thus, evaporite minerals constitute a target for biosignature investigation on Earth and Mars, where evaporitic deposits are known to exist. However, little is known about the process of organic preservation and detection in evaporites, or the stability of such molecules when exposed to significant UV radiation as would be present on the surface of Mars. Here, we investigate the incorporation of β-carotene into halite (NaCl) by growing halite in the lab in the presence of know concentrations of β-carotene and examining the resultant precipitated crystals and fluid inclusions via Raman spectroscopy. Following brine evaporation, the experimental β-carotene-containing halite was exposed to UV-C to simulate conditions on the Martian surface. Results reveal that β-carotene has a strong Raman signature that remains intact even when entombed in halite. In particular, fluid inclusions within the halite displayed particularly strong β-carotene Raman signatures after UV-C exposure. Little change was observed even after several days of UV-C delivery. Our results reveal that complex organic molecules like β-carotene should be preserved well in halite (especially in fluid inclusions) and that halite does provide protection from organic matter degradation from UV-C radiation. Thus, evaporites constitute a good target for the search for biomarkers on Mars. These findings will allow for proper criteria for the discovery of any potential physical biosignature and chemical biomarker that would be on active ocean worlds (Europa, Enceladus) and for future Mars subsurface drilling missions.

¹S. Desikamani, ²L.D. Peterson, ¹M.E. Newcombe, ³C.M.O’D. Alexander, ³J. Wang, ¹R.D. Ash, ⁴S.G. Nielsen, ¹P.M. Piccoli, ³E.S. Bullock
Geochimica et Cosmochimica Acta, (in Press) Link to Article [DOI: 10.1016/j.gca.2026.08.024]
¹University of Maryland, College Park, MD 20742, USA
²Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
³Carnegie Institution for Science, Washington DC 20015, USA
⁴Centre de Recherches Pétrographiques et Géochimiques (CRPG – CNRS), Nancy 54501, France
Copyright Elsevier

Nucleosynthetic isotope signatures indicate that the Earth is predominantly made from inner solar system non-carbonaceous (NC) materials. However, a major uncertainty in models of water addition to the proto-Earth is the extent to which H (calculated in this study as µg/g H₂O, but present as H-bearing species) in nominally anhydrous minerals (NAMs) from NC materials could contribute to the bulk Earth water budget. The preserved water concentration of NC meteorite NAMs may also shape our understanding of processes occurring in the solar protoplanetary disk (e.g., implantation of H on the surfaces of NAM grains) and in planetesimals (e.g., metamorphism in chondrite parent bodies). Reported water contents for NAMs from the ordinary chondrites (OCs), the dominant NC material falling to Earth today, range between 10⁰-10⁴ µg/g H₂O. In order to better constrain the potential contribution of ordinary chondrites to the Earth’s water budget we have measured water concentrations in NAMs from eight equilibrated OCs, six of which have not previously been investigated for water, and two of which (Chelyabinsk and Bensour) were previously measured in other laboratories. We find that olivine and low-Ca pyroxene from equilibrated OCs contain less than ∼ 10 µg/g H₂O. Based on these measurements, the water content of the NAM fraction of equilibrated OCs is < 10 µg/g H₂O (a factor of ∼ 60–120 lower than prior estimates). Combining these constraints of equilibrated OC NAM water contents with published measurements of NAMs and glassy mesostases from unequilibrated OCs, we estimate that NAMs and glass in OC parent bodies could have delivered no more than ∼ 0.2 ocean masses of water to Earth (∼1% of an assumed total water budget of 18 ocean masses). Additional water could have been delivered from phyllosilicates and organics in the most primitive OC material that is not considered in our modeling. The difference in NAM water concentrations obtained here relative to some prior studies may be rooted in analytical artifacts associated with their nanoscale secondary ion mass spectrometric measurements.

¹Fabrizio Di Fiore, ²Michele Cassetta
Journal of Geophysical Research: Planets, 131, e2026JE009904 Open Source Link to Article [DOI: 10.1029/2026JE009904]
¹Istituto Nazionale di Geofisica e Vulcanologia (INGV), Rome, Italy
²Department of Engineering for Innovation Medicine, University of Verona, Verona, Italy
Published by arrangement with John Wiley & Sons

Silicate melt viscosity plays a pivotal role in the evolution of rocky bodies within the Solar System, exerting first-order control on mantle differentiation and stratification, while dictating the metal-silicate separation and the subsequent volcanic activity. Thus, predicting the viscosity of planetary compositions is essential to model and better understand their thermomechanical evolution. Notably, the chemical signatures of primordial planetary magmas, marked by extreme Fe, Mg, and Ca enrichment, drive a highly depolymerized and fragile rheological regimes that frequently fall beyond the calibration data sets used to model the viscosity. In this study, we characterize the effect on viscosity by doping a basalt with iron, magnesium, and calcium to resemble an exotic planetary composition. By integrating high- and low-temperature viscometry with Raman spectroscopy and ultrasonic data, we show that this chemical enrichment significantly impacts the rheology, elasticity and the structural organization of the doped melt. In particular, viscosity decreases ∼2 times at high temperatures compared to the original basalt. This behavior is driven by the extreme depolymerization of the melt, and it is reflected in a shift toward Q² and Q¹ structural units. Vibrational analysis via the Boson Peak confirms a highly fragile state characterized by noticeably small correlation lengths. We tested several widely used semi-empirical models and found that while traditional empirical formulations struggle to accurately predict the viscosity of these exotic compositions, spectroscopy-based frameworks provide significantly better accuracy. This performance highlights the fundamental link between atomic-scale vibrational properties and melt-scale dynamics.

¹S. R. Baker, ^1,2,3,4B. L. Ehlmann
Journal of Geophysical Research: Planets, 131, e2025JE009605 Open Source Link to Article [DOI: 10.1029/2025JE009605]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
²Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, USA
³Department of Geological Sciences, University of Colorado, Boulder, CO, USA
⁴Department of Astrophysical & Planetary Sciences, University of Colorado, Boulder, CO, USA
Published by arrangement with John Wiley & Sons

Aluminum phyllosilicates occur in 1–10s of km² exposures of Noachian (∼3.7 Ga) rock across Mars and typically appear stratigraphically above Fe/Mg-phyllosilicates. These units have been proposed to represent pedogenic basalt weathering sequences. We examine Al-phyllosilicates in the Nili Fossae region, combining mineral maps generated from imaging spectroscopy with digital elevation models and high-resolution imagery to determine mineral assemblages, their geologic relationships, and their history of formation. We find that the Al-phyllosilicate is dominantly kaolinite and lacks associated Fe oxide. The Al-phyllosilicates typically have a distinct texture relative to Fe/Mg-phyllosilicate units, indicating an unconformity, and two different protoliths rather than formation as a pedogenic weathering sequence. Layers in some kaolinite deposits and their preferential association with sedimentary basins suggest reworked sedimentary material. The most plausible source is an Al/Si-enriched (non-basaltic) airfall volcanic deposit. We detect sparse jarosite closely associated with kaolinite but not Fe/Mg-phyllosilicate. We interpret that the jarosite, which is metastable under present surface conditions, formed from reaction between Fe-enriched fluids and S that is found sufficiently only within the kaolinite-bearing protolith. Collectively, these observations suggest less intense near-surface oxidative weathering than the basalt pedogenesis hypothesis, namely, an upper bound of several million cumulative years of aqueous activity in Nili Fossae that largely ended after the formation of jarosite. Detection of Al-phyllosilicate-bearing float rocks in nearby Jezero Crater by the Perseverance Rover shows that sample return has potential to conclusively determine processes and environmental conditions forming Nili Fossae’s distinctive Al-phyllosilicates.