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.

¹Yuki Masuda, ²Yoshiaki Shiraishi, ²Tetsuya Yokoyama, ³Tsuyoshi Iizuka, ¹Martin Schiller, ¹Martin Bizzarro
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [10.1016/j.gca.2026.07.004]
¹Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, Øster Voldgade 5-7, 1350 Copenhagen, Denmark
²Department of Earth and Planetary Sciences, Institute of Science Tokyo, Meguro, Tokyo 152-8551, Japan
³Department of Earth and Planetary Science, University of Tokyo, Hongo 7-3-1, Bunkyo, Tokyo 113-0033, Japan
Copyright Elsevier

Chondrules are high-temperature products formed in the protoplanetary disk and are ubiquitous components of undifferentiated extraterrestrial materials. Nucleosynthetic isotope anomalies preserved in chondrules provide a valuable record of isotopic evolution of solids from presolar dust to the accretion of planets. Among various types of chondrules, Al-rich chondrules (ARCs) possess intermediate isotopic and chemical compositions between calcium-aluminum-rich inclusions (CAIs) and ferromagnesian chondrules (FMCs), providing insights into mixing processes of various materials formed in different regions and/or at different times in the protoplanetary disk. This study performed analyses of the abundances of 54 elements and multi-elemental isotopic compositions of Ca-Ti-Cr-Sr on fourteen ARCs extracted from four Vigarano-type chondrites (CVs). Their element abundance patterns demonstrate enrichments reaching up to 10 times of Ivuna-type carbonaceous chondrites (CIs) in refractory elements and depletions down to < 0.05 × CI in volatile elements. Eight ARCs show highly fractionated rare-earth-elements (REEs) signatures, while six ARCs display flat REE patterns. These features suggest that CV ARCs have recycled refractory inclusions, including fine-grained CAIs (FG-CAIs) and other REE-unfractionated types, in addition to less-refractory components with chondritic or matrix-like compositions similar to those contributing to FMCs. The Ca, Ti, and Sr isotopic compositions of the ARCs exhibit variations ranging from those of non-carbonaceous chondrite (NC) components to coarse-grained CAIs (CG-CAIs) and FG-CAIs. The observed isotopic compositions are not consistent with a simple mixture of NC with a single type of refractory inclusion, suggesting that they contain various types of refractory materials. The Cr isotopic compositions of CV ARCs are intermediate between those of NCs and CIs. The observed isotopic variation indicates that components of NC, CI, and refractory inclusions coexisted in the CV chondrule-forming region. This is in contrast to NC chondrule-forming regions, which do not exhibit isotopic anomalies characteristic of refractory inclusions. The significant difference in the degree of CAI signatures between OC ARCs and CV ARCs suggests that CAIs were trapped between the accretion regions of NC and CC parent bodies, leading to an isotopic dichotomy based on the presence or absence of isotopically anomalous CAIs. Meanwhile, fine dust grains with NC or CI isotopic compositions, which are smaller in size than CAIs, were distributed extensively in NC and CC accretion regions, resulting in continuous variations in chondrule isotopic composition.

^1,2C. Deligny,¹M. J. Whitehouse,³R. E. Merle,¹H. Jeon,^4,5A. A. Nemchin,⁶B. L. Jolliff
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70204]
¹Department of Geosciences, Swedish Museum of Natural History, Stockholm, Sweden
²School of Physical Sciences, The Open University, Milton Keynes, UK
³Department of Earth Sciences, Uppsala University, Uppsala, Sweden
⁴School of Earth and Planetary Sciences, Curtin University, Perth, Australia
⁵School of Earth Sciences and Engineering, Nanjing University, Nanjing, China
⁶Department of Earth, Environmental, and Planetary Sciences and the McDonnell Center for the Space Sciences, WashingtonUniversity in St. Louis, St. Louis, Missouri, USA
Published by arrangement with John Wiley & Sons

Basaltic sample 12032,366-18 from the Apollo 12 landing site is distinct among basalts collected at this site, other Apollo landing sites, and lunar meteorites in terms of its age, bulk rock composition, and isotopic composition. We present new Pb isotopic data obtained by in situ Secondary Ion Mass Spectrometry on multiple mineral phases in 12032,366–18. These data yield a crystallization age of 3400 ± 16 Ma, older than other Apollo 12 basalts, which crystallized between ~3.1 and 3.3 Ga. The initial Pb isotopic composition plots slightly below the mixing line between KREEP (an incompatible-element-rich lunar reservoir enriched in K, rare Earth elements, and P) and a depleted lunar mantle reservoir with low-μ (μ = ²³⁸U/²⁰⁴Pb) value. The bulk composition is characterized by elevated incompatible trace element abundances, including high thorium (~7 ppm), relatively high FeO, and intermediate Ti contents, distinguishing it from other Apollo 12 and lunar basalts. Although it shares some affinities with Apollo KREEP basalts, its higher bulk rock Al₂O₃ content and the presence of olivine are more consistent with high-Al basalts. Together, 12032,366–18 is not indigenous to the Apollo 12 landing site but instead represents material transported from a distant source region, most plausibly within western Oceanus Procellarum, potentially linked to the Kepler impact crater region.