^1,2R.H. Hewins et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2025.05.037]
¹IMPMC, Sorbonne Université, MNHN, UMR CNRS7590, 75005 Paris, France
²EPS, Rutgers Univ., Piscataway, NJ 08854, USA
Copyright Elsevier

An understanding of the differences between ungrouped, or anomalous, and normal carbonaceous chondrites could provide information on the population of parent bodies required to explain a chondrite group and on first solid accretion and evolution in the outer protoplanetary disk. The CR chondrites are key in this respect, as they display a unique formation history that distinguishes them from other groups. They are known to have formed between 4.1 and 4.6 Myr after CAI, with two generations of chondrules. Northwest Africa (NWA) 14674 is a CR2 anomalous (CR2-an) chondrite with very similar oxygen isotope composition, dark inclusion (DI) content, and serpentine-magnetite matrix to Al Rais (CR2-an). Both are petrologic subtype 2.3 with fresh magnesian olivine, and partly altered ferroan olivine, pyroxene, and metal. Additionally, NWA 14674 contains residual GEMS-like material at the nanoscale within preserved moderately altered areas. DI and matrix in NWA 14674 are mineralogically similar but they have different fabrics, and matrix is more porous than both DI and fine-grained rims (FGR). Matrix has aligned framboidal magnetite aggregates swathing the chondrules, suggesting slight compaction of the chondrite. Some DI have inner chondrule fragments and concentric layers richer and poorer in magnetite, indicating formation as accretionary pellets and lapilli: they are pebbles rather than clasts. The framboidal magnetite abundance is consistent with an alkaline alteration fluid potentially due to NH3 ice mixed with the more common water ice, which implies late distal accretion. Comparison with the CR chondrites Bells (regolith-like) and NWA 801 (with high-pressure clasts) indicates that a complex history involving inward drift, disruption of the grandparent body, and reaccretion of debris along with chondrules, DI pebbles, and dust is required to explain CR chondrite formation. The diverse facies observed in CR chondrites may be explained by the formation of relatively large parent bodies, comprising distinct layers (core to regolith). Some material has been inherited from a chondritic protoplanet that formed during the oligarchic growth phase of planetary formation. Subsequently, this initial body underwent disruption and partial reaccretion into the CR parent body.

¹Wei Dai,¹Frédéric Moynier,¹Zheng-Yu,^1,2Linru Fang,³James M. D. Day,⁴Marine Paquet,¹Julien Siebert
Proceedings of the National Academy of Science of the USA (PNAS) 22, e2422726122 Link to Article [https://doi.org/10.1073/pnas.242272612]
¹Université Paris Cité, Institut de Physique du Globe de Paris, CNRS, Paris 75005, France
²Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, Copenhagen K DK-1350, Denmark
³Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0244
⁴Université de Lorraine, CNRS, Centre de Recherches Pétrographiques et Géochimiques, Nancy F-54000, France

The extent of moderately volatile elements (MVE) depletion and its effects on the Moon’s evolutionary history remain contentious, partly due to unintentionally biased sampling by the Apollo missions from the Procellarum KREEP Terrane. In this study, we analyzed the Zn and K isotope compositions of a series of lunar basaltic meteorites, which vary in Th content and are likely to represent a broader sampling range than previous studies, including samples from the far side of the Moon. Our findings indicate remarkably consistent Zn and K isotope compositions across all lunar basalt types, despite significant variations in Th content. This consistency suggests a relatively homogeneous isotopic composition of volatile elements within the Moon, unaffected by subsequent impact events that formed major basins. Our results suggest that the estimates of MVE abundance and isotopic compositions from the Apollo returned samples are likely representative of the bulk Moon, supporting a globally volatile-depleted lunar interior.