¹Jasmijsn Van der Graaf, ²John F. Mustard, ¹Annemiek C. Waajen, ³Frank J.A. Van Ruitenbeek, ^4,5Christopher S. Romanek, ^1,4Mónica Sánchez-Román
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2026.117262]
¹Geobiology Lab, Earth Sciences Department, Vrije Universiteit Amsterdam, De Boelelaan 1100, 1081HV Amsterdam, the Netherlands
²Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI, USA
³Department of Applied Earth Sciences, Faculty of Geo-Information Science and Earth Observation, University of Twente, Drienerlolaan 5, 7500 AE Enschede, the Netherlands
⁴NASA Astrobiology Institute, USA
⁵Department of Earth and Environmental Sciences, Furman University, Greenville, SC, USA
Copyright Elsevier

Microbial activity plays a crucial role in the precipitation of carbonate minerals, mediated by bacterial cells and their secreted extracellular polymeric substances (EPS). Traditional detection of such biosignatures often requires invasive chemical treatments. This study explores the potential of Fourier Transform Infrared (FTIR) spectroscopy as a non-destructive tool to identify compositional features and microbial imprints in mixed-cation carbonates, providing a new pathway for remote sensing applications and in situ mineralogical studies. Carbonate samples from natural settings and laboratory experiments, under both biotic and abiotic conditions were analyzed to reveal their distinct spectral characteristics. The minerals studied include dolomite, siderite, ankerite, (hydro)magnesite, and various carbonate hydroxides, with varying amounts of the cations Ca2+, Mg2+ and Fe2+.
Distinct FTIR spectral characteristics were observed: dolomites, in particular, exhibited consistent clustering in overtone band positions around 2300 nm and 2500 nm. While this clustering was less apparent in other carbonate types, Fe2+ content could be reliably traced through a unique near-infrared absorption feature, whose intensity correlated with Fe2+ abundance following a square root function.
Despite the overlap of biosignature and mineral spectral features, specific markers emerged in biogenic samples. These included weak absorptions near 3310 nm (indicative of alkene bonds) and enhanced OH− bands around 1400 nm and 2760 nm, possibly related to phenols, alcohols, or structural water-components often associated with microbial EPS. FTIR spectroscopy is sensitive to trace amounts of water and organic compounds, making it a promising tool for evaluating precipitation conditions and the diagenetic history of mixed-cation carbonates.

¹Sophie Benaroya, ¹Christopher D.K. Herd
Earth and Planetary Science Letters 691, 120176 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2026.120176]
¹Department of Earth and Atmospheric Sciences, 1-26 Earth Sciences Building, University of Alberta, Edmonton, AB T6G 2E3, Canada
Copyright Elsevier

Constraining the oxygen fugacity (fO2) of the mantle of Mars is critical for understanding planetary differentiation processes and magmatic evolution. The degree to which the shergottite martian meteorites faithfully record the redox states of their mantle sources remains obscured by several factors. One of these factors is the various methods used to estimate fO2: Fe-based oxybarometers require multiple minerals to be found in chemical equilibrium, which can be challenging to obtain, while previous V-based values rely on estimated parental melt compositions. Here, we present new, mineral-specific V/Sc oxybarometers calibrated for olivine and pyroxene in shergottites using experimentally determined partition coefficients. This method obviates the need for parental melt V concentrations and allows for fO2 determination from single mineral phases, bypassing the equilibrium constraints that limit Fe-oxybarometry. We applied these calibrations to a petrologically diverse suite of geochemically depleted, intermediate, and enriched shergottites. Our results reveal that: (1) basaltic shergottites, previously estimated at fO2 ∼FMQ-1, record a significantly lower initial/magmatic fO2 of ∼FMQ-1.7; (2) the magmatic fO2 of shergottites is correlated with their geochemical enrichment; and (3) all shergottites show oxidation of a magnitude of >0.5 log units with progressive crystallization. The V/Sc oxybarometers provide a robust tool for estimating the magmatic fO2 of shergottites and tracking their redox changes throughout their petrogenetic histories.

¹Farshid Nozarian,²Suzette Timmerman,¹Ingo Leya
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70201]
¹Physics Institute, Space Science and Planetology, University of Bern, Bern, Switzerland
²Institute of Geological Sciences, University of Bern, Bern, Switzerland
Published by arrangement with John Wiley & Sons

The 40K-K cosmic-ray exposure (CRE) dating system offers a promising method for determining exposure ages of iron meteorites by combining the radioactive cosmogenic 40K with the stable cosmogenic isotopes 39K and 41K. However, earlier applications relied on semi-empirical production models and inconsistent analytical data sets, limiting their reliability. This study presents a comprehensive reassessment of the 40K-K and 4He/21Ne system using state-of-the-art model calculations. Production rates of 39K, 40K, and 41K were simulated with the GEANT4–INCL++6 framework, incorporating updated excitation functions and fully considering depth-dependent shielding effects. The resulting model yields physically robust relationships between K isotopes and noble gas shielding proxies, such as 4He/21Ne. In addition to revisiting the classical approach used by Voshage and co-workers, we introduce two new alternative strategies for calculating CRE ages: a two-component mixing model and a native-K correction approach that mitigates contamination effects. Overall, these developments establish a more accurate and physically consistent framework for future applications of the 40K–K system in cosmochemistry and studies of galactic cosmic rays.

¹C.L. Kirkland, ²M. Brown, ³P. Sutton, ¹T.E. Johnson
Earth and Planetary Science Letters 691, 120201 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2026.120201]
¹Timescales of Mineral Systems Group, School of Earth and Planetary Sciences, Curtin University, Perth, WA, 6845, Australia
²Laboratory for Crustal Petrology, Department of Geological, Environmental, and Planetary Sciences, University of Maryland, College Park, MD, 20742-4211, USA
³School of Engineering and Physical Sciences, University of Lincoln, Lincoln, LN6 7TS, UK
Copyright Elsevier

The pock-marked surface of the Moon provides a stark reminder of the impact flux endured by the early Earth. Notwithstanding, the role of exogenic (impact-driven) processes in the generation and evolution of Earth’s continental crust has attracted relatively little attention compared to endogenic processes driven by loss of heat from the planet’s interior. Here we explore various isotope time series inferred to track crust production within the context of changing local mass density for the Solar System over the duration of its orbit through the Milky Way galaxy. Using a global dataset of zircon Hf isotopes during the Archean, we find an enhanced probability of a step change in composition during entry into the galactic spiral arms, on a periodicity of ∼190 Myr. Fluctuations in zircon oxygen isotopes between normal and non-normal distributions also reveal periods of less normality corresponding to spiral arm entry, implying the production of a greater volume of buoyant lithosphere due to an enhanced flux of energetic impacts. Additionally, the age distributions of post-Archean terrestrial hypervelocity impact craters and lunar impact-melt clasts show elevated probabilities during the predicted phases of spiral-arm crossing. For a Sun–spiral-arm recurrence interval of ∼190 Myr, the local Galactic rotation model predicts a radial epicyclic period of approximately ∼150 Myr, which is also resolved in the zircon Hf change-point record for the ancient Earth. Both frequencies have been related to periodic disturbance of the Oort cloud and modifications to the impact flux in the inner Solar System. Together, these correlations suggest that some episodes of production and reworking of continental crust during the Archean were triggered by large impacts, some of which were probably comets. That there seems to be a fundamental connection between events on Earth and the galactic tide supports a role for periods of catastrophism through Earth’s history.

¹Xi Deng, ¹Jinting Kang, ²Pei-Yi Li, ²Yun Jiang, ¹Haolan Tang, ³Yang Xiao, ^1,4Fang Huang
Geochimica et Cosmochimica Acta (in Press) Link to Article [10.1016/j.gca.2026.07.022]
¹State Key Laboratory of Lithospheric and Environmental Coevolution, University of Science and Technology of China, Hefei 230026, China
²Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210023, China
³Sichuan Chuangyuan Weipu Analytical Technology Co., Ltd, Chengdu 610300, China
⁴Deep Space Exploration Laboratory, Hefei 230026, China
Copyright Elsevier

Rubidium (Rb) is a moderately volatile element (MVE), and its isotopic system has been widely applied to constrain evaporation and condensation processes during solar nebular evolution and planetary accretion. Tektites, natural glasses formed by the rapid melting and quenching of terrestrial crustal materials during hypervelocity impacts of extraterrestrial bodies, serve as critical geological archives for quantifying impact-driven volatile loss, particularly for MVE. Here, we report high-precision Rb isotopic data for tektites from the Australasian, North American, Central European, and Ivory Coast strewn fields, obtained via both micro-drilling (in-situ) and bulk dissolution analyses. In-situ edge–center–edge profile analyses of three australasites reveal negligible Rb concentration variations (<10%) and remarkable isotopic homogeneity, with δ87Rb ranging from –0.16 ± 0.01‰ to –0.09 ± 0.03‰ (2SD). The absence of resolvable elemental or isotopic zoning across these profiles rules out diffusion-limited evaporation as the dominant control on Rb behavior during tektite formation. Bulk δ87Rb for all analyzed tektites range from –0.22 ± 0.05‰ to –0.12 ± 0.03‰, yielding a weighted mean of –0.16 ± 0.06‰ (2SD, n = 14). This uniformity indicates no resolvable Rb isotopic fractionation and is consistent with the composition of the upper continental crust (δ87Rb = –0.14 ± 0.01‰). To further evaluate the volatility behavior of MVE under Earth-surface conditions, we perform thermodynamic modeling at ambient atmospheric pressure and oxidizing conditions. The model predicts a volatility sequence of Zn ≫ Rb ≥ K, consistent with the well-documented large Zn isotopic fractionations in tektites and the absence of measurable isotopic shifts in Rb and K. Collectively, these results may imply that Rb isotope fractionation is effectively suppressed during impact-induced evaporation under the oxidized, near-surface conditions of Earth.

¹Dafilgo Fernandes,^1,2N. G. Rudraswami,^1,2V. P. Singh
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70206]
¹National Institute of Oceanography (Council of Scientific and Industrial Research), Dona Paula, India
²Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, India
Published by arrangement with John Wiley & Sons

We report 14 Antarctic and 15 deep-sea partially melted micrometeorites containing ~71 to 458 μm rounded, porous, and intact igneous objects. These objects likely represent non-porphyritic igneous chondrules. Analyzing these objects allows us to better relate them to the constituents of their parent bodies, thereby improving our understanding of the chondrule properties inherent to micrometeorite precursors. Seven identified Antarctic spherules and all deep-sea spherules primarily exhibit radial pyroxene (Rp) textures; one Antarctic composite spherule contains an Rp object embedded within an olivine matrix. Additionally, four Antarctic spherules show barred olivine (Bo) textures, two of which are surrounded by igneous rims, while two other Antarctic spherules show cryptocrystalline (Cc) textures. The bulk major and minor element oxides for the Rp objects vary significantly: MgO ~25.4 to 39.0 wt%, Al₂O₃ ~ 0.03 to 3.23 wt%, SiO₂ ~ 44.7 to 55.1 wt%, CaO ~0.02 to 2.72 wt%, Cr₂O₃ ~ 0.18 to 1.44 wt%, MnO ~0.18 to 1.51 wt%, and FeO ~11.4 to 22.1 wt%. The chemical compositions of the pyroxene within the Rp spherules suggest they originate primarily from unequilibrated–equilibrated ordinary chondrites (UOC–EOC) rather than carbonaceous chondrites. Conversely, the glass chemical compositions of the Cc spherules (MgO ~32.9 to 42.4 wt% and FeO ~0.73 to 10.5 wt%; En98-83) largely support an origin from chondritic carbonaceous materials. Atmospheric entry heating has progressively altered the chemical composition of the Bo spherules beyond recognition from their original chondrule states. Ultimately, their collective chemical compositions suggest that these spherules may consist of chondrules similar to non-porphyritic chondrules in carbonaceous and ordinary chondrites. Based on their textures and mineralogy, these spherules indicate that the parent sources of these micrometeorites are chondrule-bearing asteroid bodies.

^1,2Elizabeth J. Catlos,¹Andrew F. Parisi,¹Michael E. Brookfield,³Timmons Erickson,^1,2Sean P.S. Gulick,^4,5Axel K. Schmitt,^1,2Daniel F. Stockli,⁶Daniel P. Miggins,⁷Ben Ruchte,¹Mark Cloos
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70191]
¹Department of Earth & Planetary Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, Texas,USA
²Center for Planetary Systems Habitability, The University of Texas at Austin, Austin, Texas, USA
³Amentum – JETS II, Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, Houston,Texas, USA
⁴Institute of Earth Sciences, Heidelberg University, Heidelberg, Germany
⁵John de Laeter Centre, Curtin University, Bentley, Western Australia, Australia
⁶College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, Oregon, USA
⁷IXRF, Inc., Austin, Texas, USA
Published by arrangement with John Wiley & Sons

The Ames impact structure (Oklahoma) is thought to have formed during the Ordovician Meteor Event, based on conodont biostratigraphy of its crater fill. Here, U–Pb zircon dates from its impact-melt portion, conducted using secondary ion mass spectrometry and laser ablation–inductively coupled plasma–mass spectrometry (n = 37 spots), yield a Mesoproterozoic emplacement age for the impacted granodiorite (1401.2 ± 8.1 Ma, ±2σ, upper Concordia intercept). However, the youngest zircon dates define a weighted mean age of 369.7 ± 5.9 Ma (n = 10/11), with MSWD = 0.71 and p(χ²) = 0.7. Cathodoluminescence and electron backscattered diffraction images reveal that most zircons, including the youngest Devonian-age grains, show primary oscillatory zoning and lack deformation. However, two have impact-related textures, including regions of low-angle grain boundaries within microcracks and discrete arrays of granular zircon crosscutting oscillatory growth zoning. Plagioclase (n = 6 samples, ⁴⁰Ar/³⁹Ar) yields Late Carboniferous (~310.5 Ma) and Permian (~250.5 Ma) approximate total fusion dates that overlap the timing of heating and hydrocarbon maturation in the crater, suggesting the argon system records postimpact thermal overprinting. Based on the youngest zircon dates, the Ames impact structure may record activity near the Frasnian–Famennian boundary, contemporaneous with other North American impacts.

¹Z. Vaci,²Z. Tian,²P. Koefoed,³M. Habermann,⁴M. Humayun,³K. Ziegler,⁵H. Busemann,⁵D. Krietsch,⁶J. M. D. Day,²K. Wang
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70199]
¹Institute of Petrology and Structural Geology, Charles University, Prague, Czech Republic
²Department of Earth, Environmental, and Planetary Sciences, Washington University in St. Louis, St. Louis, Missouri, USA
³Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, USA
⁴National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida, USA
⁵Institute of Geochemistry and Petrology, ETH Z€urich, Z€urich, Switzerland
⁶Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, USA
Published by arrangement with John Wiley and Sons

Some of the oldest igneous rocks in the Solar System include evolved and silica-rich achondrites that originate from parent bodies less than 1000 km in diameter, referred to as planetesimals. While Earth was initially in a molten state and required continental crust formation and plate tectonics to generate andesite bulk compositions, evolved and silica-rich achondrites likely formed from smaller degrees of melting and differentiation on initially chondritic parent bodies. Petrographic descriptions, bulk and in situ chemical analyses, oxygen and potassium isotope measurements, and noble gas analyses are presented to constrain the petrogenesis and possible associations of a suite of evolved and silica-rich achondrites including a trachyandesitic clast from the Almahata Sitta fall (ALM-A), Northwest Africa (NWA) 6698, NWA 11119, its launch pair NWA 11558, NWA 11575, and Graves Nunataks 06128 and 06129. In addition, leaching experiments were conducted that included terrestrial samples to examine the effects potential weathering-induced alteration might have on potassium isotope compositions. The measured potassium isotopic compositions do not covary with volatile depletion, as found when comparing samples from Earth, the Moon, Mars, and the asteroid Vesta, indicating that the planetary depletion trend observed in larger bodies does not apply in the absence of complete planetary differentiation. Modeled noble gas retention ages confirm the ancient formation times of several of these achondrites, while cosmic ray exposure ages suggest separation from their parent bodies in the past ~25 million years.

^1,2Robert W. Nicklas,²Dylan M. Seal,²Melody Z. Chen,²Kyra L. Schroeder,³James M. D. Day,⁴Ben G. Rider-Stokes,⁵Anthony B. Love,⁴James Malley
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70202]
¹Lunar and Planetary Institute, USRA, Houston, Texas, USA
²Department of Earth and Environmental Sciences, Boston College, Chestnut Hill, Massachusetts, USA
³Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, USA
⁴School of Physical Sciences, The Open University, Milton Keynes, UK
⁵Department of Geological and Environmental Sciences, Appalachian State University, Boone, North Carolina, USA
Published by arrangement with John Wiley & Sons

As the most common samples available from Mars, shergottites offer important constraints on the igneous history of the planet into the Amazonian epoch. The newly recognized shergottite Northwest Africa (NWA) 13440 is here classified as a gabbroic shergottite and is likely launched-paired with NWA 6963, exhibiting many of the unusual textural features of that sample. The Sm-Nd isotope systematics of NWA 13440 yielded an errorchron age of 206 ± 34, with an εNdi = −7.1. This age and εNdi, coupled with a bulk rock (La/Yb)N of 1.02, allow for its classification as an enriched shergottite. The presence of unusual augite inclusions in pigeonite laths testifies to the importance of undercooling and nonequilibrium crystallization early in the history of the parental magma of the meteorite. Additionally, Si-rich mesostasis consisting of fine-grained irregular quartz-alkaline feldspar intergrowths suggests extreme fractional crystallization of the final few percent of melt. Shock textures indicate a moderate shock stage of approximately M-S4. The discovery of NWA 13440 supports the model that many of the enriched shergottites are the martian equivalent of a continental flood basalt province.

¹Yasuhiro Oba et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [10.1016/j.gca.2026.06.040]
¹Institute of Low Temperature Science (ILTS), Hokkaido University, N19W8, Kita-ku, Sapporo, Hokkaido 060-0819, Japan
Copyright Elsevier

Carbonaceous meteorites preserve organic records of early Solar System chemistry, yet nucleobase inventories remain difficult to interpret owing to potential terrestrial contamination and parent–body processing effects. Here we report high–resolution liquid chromatography/Orbitrap mass spectrometry analyses of purine and pyrimidine bases in six Antarctic carbonaceous meteorites (CM: Y–791198, A–12236, Y–793321, B–7904; CR: A–881828, Y–002540) using rigorously controlled extractions (hot water and 20% HCl treatments) performed in ISO–class clean environments, together with Antarctic ice as an environmental blank. All five canonical nucleobases were identified in Y–791198, A–12236, and A–881828; subsets were found in Y–793321 and Y–002540; and none were detected in B–7904 or in the ice meltwater/hydrolysate. These patterns, coupled with the thermal metamorphic history of B–7904, indicate no detectable incorporation of nucleobases from Antarctic ice during ∼ 105–year residence. Total pyrimidines correlate positively with NH3 across Antarctic meteorites and previously reported extraterrestrial samples, whereas purines do not, implicating NH3-facilitated pyrimidine formation and the involvement of additional precursors (e.g., cyanides) in purine synthesis. Cytosine is systematically depleted relative to other canonical bases, likely reflecting its low–temperature hydrolysis to uracil; leaching losses appear negligible as highly water-soluble species (e.g., hydroxypyrimidines and NH3) are retained within the meteorites. Our results establish Antarctic meteorites as some of the least contaminated materials for constraining nucleobase distributions and underscore the need for direct cyanide measurements to resolve purine formation pathways.