^1,2Y. Li,^1,2P. J. A. McCausland,^1,2R. L. Flemming,^1,2G. R. Osinski
Meteoritics & Planetary Society (in Press) Link to Article [https://doi.org/10.1111/maps.14301]
¹Department of Earth Sciences, Western University, London, Ontario, Canada
²Institute for Earth and Space Exploration, Western University, London, Ontario, Canada
Published by arrangement with John Wiley & Sons

Lunar impact breccia meteorites contain clasts from unknown lunar regions, including areas not studied by past missions. These meteorites offer a unique opportunity to expand our knowledge of the Moon’s crustal and mantle composition and processes. The recently classified lunar meteorite Northwest Africa (NWA) 11515 is a moderately shocked feldspathic breccia with anorthite plagioclase and mafic minerals. In this work, we report the shock history of lithic clasts using 2-D micro-X-ray diffraction, detailed mineralogy from micro-X-ray fluorescence, and electron probe microanalysis. NWA 11515 shows moderately shocked anorthite and highly shocked olivine and pyroxene. The plagioclase composition is invariant (An96.4 ± 0.7, n = 52), with variable mafic clasts overlapping Mg- and FAN-suite lithologies (Mg# 84.5 to 45.6 for olivine; Mg# 85.6 to 32.2 for pyroxene), similar to KREEP-depleted troctolites in Allan Hills A81005. Spinel-group oxides vary from aluminous spinel to chromite and ulvöspinel. We also observed slow-cooled augite Ca-poor pyroxene exsolution clasts and fast-quenched fine-grained anorthite–olivine co-crystallized clasts (<5 μm), indicating different cooling histories. Combining petrological observations with published geochemical data, we show NWA 11515 has the mixed lithology of ferroan anorthosites with KREEP-poor magnesian rock fragments. With shock analysis, the materials are likely from a crater with minimum size of 7 km. Finally, we examined the published geochemical data for other lunar meteorites and hypothesize that other typical feldspathic breccias could contain magnesian clasts, suggesting the subdivision of typical feldspathic breccia into magnesian clast-hosting breccia and ferroan feldspathic breccia. This implies that non-KREEP magnesian magmatism might be more widespread in the post-LMO era on lunar highlands.

¹P. Ghaznavi,²C. Burkhardt,³F. L. H. Tissot,¹I. Leya
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14300]
¹Space Science and Planetology, Physics Institute, University of Bern, Bern, Switzerland
²Max-Planck Institut für Sonnensystemforschung, Göttingen, Germany
³Division of Geological and Planetary Sciences, The Isotoparium, Caltech, Pasadena, California, USA
Published by arrangement with John Wiley & Sons

Calcium-aluminum-rich inclusions (CAIs) are the first objects that formed in the solar accretion disk and therefore provide valuable insights into the evolution of the early solar system. A long-standing question regarding this earliest formative period relates to the storage of CAIs in the 1–4 Myr time period between their formation and later accretion into chondrite parent bodies. Were the CAIs stored in a pre-existing parent body, or in distant parts of the solar accretion disk? In the latter scenario, CAIs might have been exposed to cosmic rays, either from the galaxy or from the Sun and such pre-accretion irradiation effects might be detectable. We searched for such pre-accretional irradiation effects in 7 fine- and 11 coarse-grained CAIs from the CV 3.6 carbonaceous chondrite Allende. The extracted samples were analyzed for their major chemical composition and all samples were analyzed using μCT techniques. Using physical model calculations, ²¹Ne_cos and (²²Ne/²¹Ne)_cos production rate ratios were calculated for each CAI by fully considering their individual chemical composition. Measured He, Ne, Ar, and Kr isotope compositions of the CAIs show cosmogenic signals; clear signals for He and Ne isotopes; and detectable signals for some of the Ar and Kr isotopes. In addition, most samples show clear indications for radiogenic ⁴He and some samples show evidence for radiogenic ⁴⁰Ar. Higher ³⁶Ar/³⁸Ar, ²²Ne/²¹Ne, ⁸⁰Kr/⁸⁴Kr, and ⁸²Kr/⁸⁴Kr ratios together with lower cosmogenic ³⁸Ar_cos concentrations in fine-grained CAIs compared to coarse-grained CAIs are consistent with more alteration of the former compared to the latter. The CRE ages for the CAIs range between 4.12 ± 0.41 Myr and 6.40 ± 0.63 Myr. Statistical tests indicate that the data are normally distributed with no outliers, indicating that all CAIs share a common irradiation history, likely the irradiation in the Allende meteoroid. The average CRE age of 4.87 ± 0.19 Myr agrees with the nominally accepted CRE age of Allende of ~5.2 Myr. There is no correlation between ²¹Ne_cos concentrations and indicators of aqueous alteration like Na and/or U concentrations. The lack of correlation together with the finding of normally distributed modeled CRE ages indicates that either none of the studied CAIs experienced a pre-accretion irradiation before parent body compaction and/or that any pre-accretion irradiation effects have been completely erased during aqueous alteration events. Taking alteration aside, the findings are not in favor of X-wind type models but are more consistent with the idea of CAI outward transport in an expanding disk.