¹Mehmet Yesiltas,²Yoko Kebukawa,³Timothy D. Glotch,⁴Michael Zolensky,⁴Marc Fries,⁵Namik Aysal,⁵Fatma S. Tukel
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13893]
¹Faculty of Aeronautics and Space Sciences, Kirklareli University, Kirklareli, 39100 Turkey
²Faculty of Engineering, Yokohama National University, 240-8501 Yokohama, Japan
³Department of Geosciences, Stony Brook University, Stony Brook, New York, 11790 USA
⁴Astromaterials Research and Exploration Science, Johnson Space Center, NASA, Houston, Texas, 77058 USA
⁵Department of Geological Engineering, Istanbul University-Cerrahpasa, Istanbul, 34320 Turkey
Published by arrangement with John Wiley & Sons

Ungrouped carbonaceous chondrites are not easily classified into one of the well-established groups due to compositional/petrological differences and geochemical anomalies. Type 2 ungrouped carbonaceous chondrites represent a very small fraction of all carbonaceous chondrites. They can potentially represent different aspects of asteroids and their regolith material. By conducting a multitechnique investigation, we show that Queen Alexandra Range (QUE) 99038 and Elephant Moraine (EET) 83226 do not resemble type 2 carbonaceous chondrites. QUE 99038 exhibits coarse-grained matrix, Fe-rich rims on olivines, and an apparent lack of tochilinite, suggesting that QUE 99038 has been metamorphosed. Its polyaromatic organic matter structures closely resemble oxidized CV3 chondrites. EET 83226 exhibits a clastic texture with high porosity and shows similarities to CO3 chondrites. It consists of numerous large chondrules with fine-grained rims that are often fragmented and discontinuous and set within matrix, suggesting a formation mechanism for the rims in a regolith environment. The kind of processes that can result in such chemical compositions as in QUE 99038 and EET 83226 is currently not fully known and clearly presents a conundrum. Tarda is a highly friable carbonaceous chondrite with close resemblance to Tagish Lake (ungrouped C2 chondrite). It comprises different types of chondrules (some with Fe-rich rims), framboid magnetite, sulfides, carbonates, and phyllosilicate- and carbon-rich matrix, and is consistent with being an ungrouped C2 chondrite.

¹Steven D. Dibb,¹James F. Bell III,^1,2Laurence A. J. Garvie
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13891]
¹School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, 85287 USA
²Buseck Center for Meteorite Studies, Arizona State University, Tempe, Arizona, 85287 USA
Published by arrangement with John Wiley & Sons

The 350–2500 nm reflectance spectra of five enstatite achondrites (aubrites), five metal-rich chondrites (CBa, CBb, CH/CBb, and ungrouped), and seven sulfide mineral samples (three troilites, pyrrhotite, pentlandite, a mixture of pentlandite and chalcopyrite, and oldhamite) have been measured to search for spectral parameters that may offer insight into the surface composition of so-called “spectrally featureless” asteroids. Spectral data were acquired from powders, slabs, and hand samples. Aubrites exhibit high reflectance, generally positive slopes at visible wavelengths, and low-to-negative infrared slopes, consistent with E-/Xe-type asteroids. The metal-rich chondrites exhibit low reflectance, moderate visible slopes, and low near-infrared slopes, somewhat consistent with M−/X-complex asteroids. The metal-rich chondrites exhibit absorption features at ~900 nm arising from Fe2+-bearing silicates. Sulfides exhibit low to moderate reflectance and high visible and near-infrared slope, intermediate to the T- and L-type asteroids. The D-type asteroids, which have high visible and near-infrared slopes, are not well-matched by sulfides. Spectral data of the largest M−/X-type asteroid, (16) Psyche, are consistent with both powder from the Isheyevo CH/CBb chondrite and powder of meteoritic troilite. The data presented here will support interpretation of data returned from future spacecraft missions to “spectrally featureless” asteroids, like the Psyche, Lucy, and DART/Hera missions.

¹Keqing Zong et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.06.037]
¹State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China
Copyright Elsevier

Lunar soil is a fine mixture of local rocks and exotic components. The bulk-rock chemical composition of the newly returned Chang’E-5 (CE-5) lunar soil was studied to understand its chemical homogeneity, exotic additions, and origin of landing site basalts. Concentrations of 48 major and trace elements, including many low-concentration volatile and siderophile elements, of two batches of the scooped CE-5 soil samples were simultaneously obtained by inductively coupled plasma mass spectrometry (ICP-MS) with minimal sample consumption. Their major and trace elemental compositions (except for Ni) are uniform at milligram levels (2–4 mg), matching measured compositions of basaltic glasses and estimates based on mineral modal abundances of basaltic fragments. This result indicates that the exotic highland and KREEP (K, rare earth elements, and P-rich) materials are very low (<5%) and the bulk chemical composition (except for Ni) of the CE-5 soil can be used to represent the underlying mare basalt. The elevated Ni concentrations reflect the addition of about 1 wt% meteoritic materials, which would not influence the other bulk composition except for some highly siderophile trace elements such as Ir. The CE-5 soil, which is overall the same as the underlying basalt in composition, displays low Mg# (34), high FeO (22.7 wt%), intermediate TiO2 (5.12 wt%), and high Th (5.14 µg/g) concentrations. The composition is distinct from basalts and soils returned by the Apollo and Luna missions, however, the depletion of volatile or siderophile elements such as K, Rb, Mo, and W in their mantle sources is comparable. The incompatible lithophile trace element concentrations (e.g., Ba, Rb, Th, U, Nb, Ta, Zr, Hf, and REE) of the CE-5 basalts are moderately high and their pattern mimics high-K KREEP. The pattern of these trace elements with K, Th, U, Nb, and Ta anomalies of the CE-5 basalts cannot be explained by the partial melting and crystallization of olivine, pyroxene, and plagioclase. Thus, the mantle source of the CE-5 landing site mare basalt could have contained KREEP components, likely as trapped interstitial melts. To reconcile these observations with the initial unradiogenic Sr and radiogenic Nd isotopic compositions of the CE-5 basalts, clinopyroxene characterized by low Rb/Sr and high Sm/Nd ratios could be one of the main minerals in the KREEP-bearing mantle source. Consequently, we propose that the CE-5 landing site mare basalts very likely originated from partial melting of a shallow and clinopyroxene-rich (relative to olivine and orthopyroxene) upper mantle cumulate with a small fraction (about 1–1.5 %) of KREEP-like materials.

^1,2Piers Koefoed,^1,3Olga Pravdivtseva,^1,3Ryan Ogliore,⁴Yun Jiang,^1,2Katharina Lodders,^1,2Mason Neuman,^1,2Kun Wang王昆
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.06.021]
¹McDonnell Center for the Space Sciences, Washington University in St. Louis, St. Louis, MO 63130, USA
²Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO 63130, USA
³Department of Physics, Washington University in St. Louis, St. Louis, MO 63130, USA
⁴CAS Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, China
Copyright Elsevier

The many unique characteristics of CB chondrites have resulted in the impact hypothesis becoming the favoured model for their formation. Here, we further investigate the formation mechanisms of CB chondrites by analysing the elemental and K isotope compositions of chondrules and bulk fractions from the CBa chondrite Gujba. Similar to previous work, the refractory element ratios in the Gujba chondrules show evidence of a differentiated precursor, with the Nb/Ta, Zr/Hf, Sc/Th and Zr/Th ratios showing fractionation relative to other chondrites. In addition, the bulk fractions, and to a lesser extent the chondrules with attached matrix and metals, display significantly more refractory element fractionation and a large enrichment in light REEs. Based on EDS elemental mapping and comparisons with previous studies, the most likely source of this highly fractionated material appears to be the small amount of heterogeneously distributed interstitial fine-grained material within Gujba. These large refractory element fractionations (i.e., Nb/Ta, Zr/Hf, Sc/Th Zr/Th, and LREE/HREE) are best explained by a significant partial melting process such as crustal formation. Nevertheless, the mechanism of patrial melting cannot be conclusively determined with the data available here. The K isotopic compositions of the Gujba chondrules analyzed here range from −2.24‰ to −0.41‰ in δ41K, whereas the bulk analyses show δ41K values of −0.81‰ to −0.72‰. This range of chondrule K isotope compositions is significantly larger, and extends to much lighter compositions, compared to all other chondrites measured so far by bulk ICP-MS. In addition, the Gujba chondrules display a clear negative correlation of K isotopic composition with K concentration, with the chondrules showing the lightest K isotope compositions having the highest K concentrations. This distinctive correlation indicates that evaporation was likely the dominant process affecting the K isotopic variation observed in the Gujba chondrules. Nevertheless, the extremely light δ41K values seen in the most K-rich chondrules (which are lighter than any other early solar system material so far measured) indicate that incomplete condensation likely took place before evaporation. As such, we propose a two-stage model to explain the formation of chondrules in Gujba, with Stage 1 characterized by incomplete condensation of vaporized material with an average isotopic fractionation factor (α) of 0.9984 (when using the most K enriched chondrule to constrain the model), and Stage 2 representing partial evaporation in a vapor plume with an average α range of 0.9976 to 0.9990. Using these α values we calculate an approximate vapor saturation index value of 0.935 for condensation and between 0.903 and 0.960 for evaporation. This formation process requiring both condensation and evaporation for CB chondrules is consistent with an impact generated vapor plume and further expands our understanding of CB chondrite formation.