A. N. KROT¹, K. NAGASHIMA¹ , S. EBERT², M. I. PETAEV³, C. MA⁴, J. HAN⁵, and T. L. DUNN⁶
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70044]
¹Hawai’i Institute of Geophysics & Planetology, School of Ocean and Earth Science and Technology, University of Hawai‘i at
Manoa, Honolulu, Hawaii, USA
²Institut für Planetologie, University of Münster, Münster, Germany
³Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
⁴Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
⁵Amentum, NASA Johnson Space Center, Houston, Texas, USA
¹6Department of Geology, Colby College, Waterville, Maine, USA
Published by arrangement with John Wiley & Sons

We report on the mineralogy, petrography, and oxygen and aluminum-magnesium isotopic systematics of the corundum-bearing Ca,Al-rich inclusions (CAIs) from the CK3 (Karoonda-type) carbonaceous chondrites NWA (Northwest Africa) 4964-#1 and -Homer, NWA 5343-#1, and LAR (Larkman Nunatak) 12002-#1. These CAIs experienced extensive metasomatic alteration: melilite and possibly anorthite and AlTi-diopside are nearly completely replaced by secondary corundum, grossular, CaNa-plagioclase, FeAl-diopside, and FeO-rich spinel; perovskite is largely replaced by ilmenite. Two types of corundum grains occur in the NWA 4964 CAIs: (1) compact, FeO-poor grains zoned in cathodoluminescent (CL) images and (2) FeO-bearing (up to 1.5 wt% FeO), porous grains showing no detectable CL; the porous corundum grains overgrow the compact ones. Corundum grains in CAIs from LAR 12002 and NWA 5343 belong to the first and second types, respectively. Hibonite, primary spinel, and rare perovskite inclusions in spinel retained the original, ¹⁶O-rich compositions (Δ¹⁷O ~ −24 ± 2‰), whereas melilite, most perovskite grains, and secondary corundum and spinel are ¹⁶O-depleted (Δ¹⁷O ~ −5 ± 2‰). Hibonite and melilite have excesses of radiogenic ²⁶Mg (²⁶Mg*) corresponding to approximately the canonical initial ²⁶Al/²⁷Al ratio [(²⁶Al/²⁷Al)₀] of ~5 × 10⁻⁵ suggesting that corundum-bearing CAIs studied belong to a population of the canonical inclusions, dominant in most chondrite groups. Corundum grains in LAR 12002-#1, NWA 4964-#1, NWA 4964-Homer, and NWA 5343-#1 show resolvable ²⁶Mg* correlated with ²⁷Al/²⁴Mg ratio which corresponds to much lower than the canonical (²⁶Al/²⁷Al)₀: (3.10 ± 0.48) × 10⁻⁶, (3.03 ± 0.23) × 10⁻⁶, (2.72 ± 0.19) × 10⁻⁶, and (3.5 ± 1.2) × 10⁻⁷, respectively. Porous Fe-bearing corundum grains in NWA 4964 CAIs Homer and #1 have low ²⁶Mg* not correlated with ²⁷Al/²⁴Mg ratio. We conclude that compact corundum grains in the CK3 CAIs studied are secondary parent body products that resulted from metasomatic alteration of the host inclusions by hydrothermal fluid ~3−5 Ma after their crystallization. Porous corundum grains may have formed by dehydration of diaspore [AlO(OH)] during subsequent thermal metamorphism.

Le ZHANG¹ et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70048]
¹State Key Laboratory of Deep Earth Processes and Resources, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China
Published by arrangement with John Wiley & Sons

This study presents a comprehensive analysis of the mineralogical, geochemical properties, and in situ Sr-Nd-Pb isotopic systematics of a newly discovered unbrecciated lunar basaltic meteorite NWA 14526 (NWA refers to northwest Africa). Bulk composition derived through both mineral modes and impact melt vein classifies NWA 14526 as a low-Ti, low-Al, and low-K mare basalt. In situ Pb isotopic analyses define a Pb–Pb isochron yielding an age of 3009 ± 43 Ma, representing the meteorite’s crystallization age. In situ Rb-Sr isotopic analyses of plagioclase and maskelynite provide an initial ⁸⁷Sr/⁸⁶Sr ratio of 0.69969 ± 0.00024 (2σ), while phosphate and mesostasis in situ Sm-Nd analyses yield an initial εNd value of +10.7 ± 2.1 (2σ). Although NWA 14526 shares comparable mineralogical, bulk-rock composition, and Sr isotopic characteristics with contemporaneous lunar basaltic meteorites (NWA 4734, LAP 02205, NWA 14137, and NWA 10597), its significantly elevated εNd values preclude genetic pairing with these specimens. Isotopic modeling indicates minimal KREEP component contribution (<0.5%) in its mantle source. Our compilation of lunar Sr-Nd isotopic data reveals two distinct evolutionary trends corresponding to depleted lunar mantle and urKREEP reservoirs, respectively. Notably, no temporal correlation between basalt source KREEP enrichment and eruption age is observed, suggesting that the KREEP component did not necessarily play a decisive role in driving late-stage lunar magmatism and volcanism.

George D. Cody^a, et al. (>10)

Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2025.09.009]
^aEarth and Planets Laboratory, Carnegie Science, Washington, DC, United States
Copyright Elsevier

We present the first investigation into the molecular structure of organic solids (insoluble organic matter, IOM) in samples of the carbonaceous asteroid (101955) Bennu returned by the OSIRIS-REx mission. We used ¹H and ¹³C solid-sate nuclear magnetic resonance (ssNMR) to analyze three subsamples of aggregate Bennu material. However, the IOM isolated from two of the three subsamples exhibited substantial magnetic inhomogeneity, due to contaminant magnetic grains. The resulting magnetic interference degraded NMR signals for both ¹H and ¹³C and likely introduced spectral distortions. The third subsample was pretreated with 6 N HCl prior to IOM isolation and exhibited minimal (i.e., typical) magnetic interference. In this subsample’s IOM, we find a very low fraction of aromatic carbon, and a high fraction of aliphatic hydrogen, relative to IOM from Bennu’s closest meteoritic analogs, the petrologic type 1 and 2 carbonaceous chondrites. Elemental analysis–isotope ratio mass spectrometry (EA-IRMS) further reveals a high H/C × 100 atomic values, relative to type 1 and 2 chondritic IOM. These data indicate that Bennu’s organic solids, at least in this aggregate sample, suffered minimal to no molecular evolution from thermal perturbation throughout this material’s long history—starting with accretion of a planetesimal, followed by disruption and gravitational reassembly to form a rubble-pile asteroid, and ultimately migration from the Main Belt to a near-Earth orbit. The state of molecular evolution recorded in IOM places a strong constraint on the magnitude of temperature and pressure derived from impact events that yielded the rubble-pile asteroid Bennu.