¹Kun Wang(王昆),²Weiqiang Li,²Shilei Li,¹Zhen Tian,¹Piers Koefoed,³Xin-Yuan Zheng
Chemie der Erde [Geochemistry] (in Press) Link to Article [https://doi.org/10.1016/j.chemer.2021.125786]
¹Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St. Louis, MO 63130, USA
²School of Earth Sciences and Engineering, Nanjing University, Nanjing, Jiangsu 210023, China
³Department of Earth and Environmental Sciences, University of Minnesota – Twin Cities, Minneapolis, MN 55455, USA

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¹Jan L.Hellmann,^1,2Timo Hopp,¹Christoph Burkhardt,³Harry Becker,^1,4Mario Fischer-Gödde,¹Thorsten Kleine
Geochimica et Cosmochimcia Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.06.038]
¹Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany
²Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA
³Institut für Geologische Wissenschaften, Freie Universität Berlin, Malteserstraße 74-100, 12249 Berlin, Germany
⁴Institut für Geologie und Mineralogie, Universität zu Köln, Zülpicher Straße 49b, 50674 Köln, Germany
Copyright Elsevier

Tellurium stable isotope compositions and abundances (δ^128/126Te relative to SRM 3156) are reported for 43 ordinary, enstatite, and Rumuruti chondrites, which together with results from a companion study on carbonaceous chondrites are used to assess the origin of volatile element fractionations in chondrites. Whereas Te isotope variations among carbonaceous chondrites predominantly reflect mixing between isotopically light chondrules/chondrule precursors and CI-like matrix, Te isotope variations among non-carbonaceous chondrites mainly result from Te redistribution during parent body thermal metamorphism. The enstatite chondrites in particular display increasingly heavy Te isotopic compositions and decreasing Te concentrations with increasing degree of metamorphism, indicating migration of isotopically light Te from the strongly metamorphosed inner parts towards the cooler outer regions of the parent bodies. By contrast, ordinary and Rumuruti chondrites display less systematic Te isotope variations, implying more localized redistribution of Te during parent body thermal metamorphism.

We also report Te stable isotope data for 19 terrestrial mantle-derived rocks. Peridotites with Al₂O₃ contents close to those inferred for the bulk silicate Earth (BSE) exhibit uniform δ^128/126Te values, which we interpret to represent the Te isotopic composition of the BSE. This composition overlaps with the Te isotope composition of some volatile-rich carbonaceous chondrites (most notably CM chondrites), but also with that of enstatite chondrites. Comparison of the Te results to Se isotopes and Se/Te ratios shows that due to uncertainties in the composition of the BSE and the isotopic composition of bulk chondrite parent bodies, neither Te isotopes alone nor the combined Se-Te elemental and isotopic systematics can distinguish between a carbonaceous and enstatite chondrite-like late veneer, which is the presumed source of Se and Te in the BSE. Together, the results of this study illustrate that the relative abundances and mass-dependent isotope compositions of volatile elements like Se and Te are modified by physical and chemical processes occurring after planetary accretion, which severely complicates their use as genetic tracers. A corollary of this is that contrary to prior proposals the Se-Te systematics are not contradicting an inner solar system origin of the late veneer, as it has been inferred using nucleosynthetic isotope anomalies of other elements.

^1,2Roger Hewins et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.06.035]
¹IMPMC, Sorbonne Univ, MNHN, UPMC Paris 06, UMR CNRS 7590, 75005 Paris, France
²EPS, Rutgers Univ, Piscataway, NJ 08854, USA
Copyright Elsevier

Many asteroids in the main belt have spectra like those of Mighei-type CM chondrites, but some Near Earth Objects (NEO) resemble less well known types of C2 chondrite. Northwest Africa (NWA) 12563, a new find with affinities to C2 chondrites, could help us understand the differences between observations of CM2 chondrites and bodies that are currently being studied by the Hayabusa 2 and Osiris-Rex space missions. NWA 12563 contains 14% chondrules supported by 86% fine grained matrix consistent with CM2 chondrites, but differs from them in other respects. In both matrix and chondrules, olivine is unaltered and pyroxene shows incipient alteration. Metal in chondrules is pseudomorphed by serpentine, and mesostasis is replaced by serpentine- saponite and chlorite. Many Type I chondrules have highly irregular shapes resulting from fracturing and selective metal replacement. Type II porphyritic chondrules are clusters of phenocrysts set in matrix-like material. Type II chondrules may be kinked and partially disbarred. The matrix of NWA 12563 differs from CM2 chondrites in the absence of tochilinite-cronstedtite intergrowths. It contains hydrated and oxidized amorphous silicate (Fe3+/∑Fe ∼75%) richer in magnesium than in other chondrites (with embedded sulfides). Serpentine-saponite is also present, as well as abundant framboidal magnetite.

NWA 12563 has similarities to a number of ungrouped magnetite-rich and 18O-rich chondrites (Bells, Essebi, Niger I, WIS 91600, Tagish Lake, and MET 00432) that we call C2-ung1, as opposed to C2-ung2 chondrites (poorer in 18O and magnetite). The oxygen isotopic composition coupled with a magnetic susceptibility of log χ = 4.67 places NWA 12563 with these ungrouped chondrites in a cluster distinct from CM2 chondrites. NWA 12563 is closest to WIS 91600 among the C2-ung1 chondrites in alteration style and light element compositions. WIS 91600, however, has suffered light thermal metamorphism, suggesting that NWA 12563 might represent its altered but unheated precursor material within the same parent body if it were zoned. The average Vis-NIR spectrum of NWA 12563 matches the asteroid taxonomic class K and resembles that of CO3 Frontier Mountain (FRO) 95002, but its spectra range from very “red” in dark matrix areas and very “blue” in magnetite-rich areas. The average MIR spectrum shows features indicating phyllosilicates, aliphatic CH compounds, hydrated silicates, and olivine. It is significantly different from those of other chondrites including FRO 95002, and closest to Bells (from which it differs in carbon isotopic composition) and WIS91600. The variety of mineralogical, chemical and isotopic properties among C2-ung1 chondrites requires several different parent bodies. However, the high abundance of magnetite common to this cluster of ungrouped chondrites, and to a lesser extent CI chondrites, indicates that they should be considered as possible material from Bennu, which has an 18 µm magnetite signal in its spectrum not seen in the CM2 chondrites (Hamilton et al., 2019).

¹C.M.Lisse et al. (>10)
The Astrophysical Journal 894, 116 Link to Article [DOI https://doi.org/10.3847/1538-4357/ab7b80]
¹ JHU-APL, 11100 Johns Hopkins Road, Laurel, MD 20723, USA; carey.lisse@jhuapl.edu, ron.vervack@jhuapl.edu

We report here time-domain infrared spectroscopy and optical photometry of the HD 145263 silica-rich circumstellar-disk system taken from 2003 through 2014. We find an F4V host star surrounded by a stable, massive 1022–1023 kg (MMoon to MMars) dust disk. No disk gas was detected, and the primary star was seen rotating with a rapid ~1.75 day period. After resolving a problem with previously reported observations, we find the silica, Mg-olivine, and Fe-pyroxene mineralogy of the dust disk to be stable throughout and very unusual compared to the ferromagnesian silicates typically found in primordial and debris disks. By comparison with mid-infrared spectral features of primitive solar system dust, we explore the possibility that HD 145263’s circumstellar dust mineralogy occurred with preferential destruction of Fe-bearing olivines, metal sulfides, and water ice in an initially comet-like mineral mix and their replacement by Fe-bearing pyroxenes, amorphous pyroxene, and silica. We reject models based on vaporizing optical stellar megaflares, aqueous alteration, or giant hypervelocity impacts as unable to produce the observed mineralogy. Scenarios involving unusually high Si abundances are at odds with the normal stellar absorption near-infrared feature strengths for Mg, Fe, and Si. Models involving intense space weathering of a thin surface patina via moderate (T < 1300 K) heating and energetic ion sputtering due to a stellar super-flare from the F4V primary are consistent with the observations. The space-weathered patina should be reddened, contain copious amounts of nanophase Fe, and should be transient on timescales of decades unless replenished.

¹Alexey Potapov,¹Cornelia Jäger,²Thomas Henning
The Astrophysical Journal 894, 110 Link to Article [DOI https://doi.org/10.3847/1538-4357/ab86b5]
¹Laboratory Astrophysics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University Jena, Institute of Solid State Physics, Helmholtzweg 3, D-07743 Jena, Germany; alexey.potapov@uni-jena.de
²Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany

The catalytic role of dust grain surfaces in the thermal reaction CO2 + 2NH3 → NH4+NH2COO− was recently demonstrated by our group. The rate coefficients for the reaction at 80 K on the surface of nanometer-sized carbon and silicate grains were measured to be up to three times higher compared to the reaction rate coefficients measured on KBr. In this study, the reaction was performed on carbon grains and on KBr in the extended temperature range of 50–80 K and with the addition of water ice. The reaction activation energy was found to be about three times lower on grains compared to the corresponding ice layer on KBr. Thus, the catalytic role of the dust grain surface in the studied reaction can be related to a reduction of the reaction barrier. Addition of water to NH3:CO2 ice on grains slowed the reaction down. At the H2O:CO2 ratio of 5:1, the reaction was not detected on the experimental timescale. This result calls into question the thermal formation of ammonium carbamate in dense molecular clouds and outer regions of protostellar and protoplanetary environments with dominating water ice mantle chemistry. However, it can still happen in inner regions of protostellar and protoplanetary environments in crystalline ices.

¹Florian Kirchschlager,¹M. J. Barlow,¹Franziska D. Schmidt
The Astrophysical Journal 893, 70 Link to Article [DOI https://doi.org/10.3847/1538-4357/ab7db8]
¹Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK; f.kirchschlager@ucl.ac.uk

Core-collapse supernovae can condense large masses of dust post-explosion. However, sputtering and grain–grain collisions during the subsequent passage of the dust through the reverse shock can potentially destroy a significant fraction of the newly formed dust before it can reach the interstellar medium. Here we show that in oxygen-rich supernova remnants like Cassiopeia A, the penetration and trapping within silicate grains of the same impinging ions of oxygen, silicon, and magnesium that are responsible for grain surface sputtering can significantly reduce the net loss of grain material. We model conditions representative of dusty clumps (density contrast of χ = 100) passing through the reverse shock in the oxygen-rich Cassiopeia A remnant and find that, compared to cases where the effect is neglected as well as facilitating the formation of grains larger than those that had originally condensed, ion trapping increases the surviving masses of silicate dust by factors of up to two to four, depending on initial grain radii. For higher density contrasts (χ gsim 180), we find that the effect of gas accretion on the surface of dust grains surpasses ion trapping, and the survival rate increases to ~55% of the initial dust mass for χ = 256.

^1,2Bidong Zhang,³Yangting Lin,¹Desmond E.Moser,²Paul H.Warren,³Jialong Hao,¹Ivan R.Barker,¹Sean R.Shieh,¹Audrey Bouvierd
Earth and Planetary Science Letters 569, 117046 Link to Article [https://doi.org/10.1016/j.epsl.2021.117046]
¹The University of Western Ontario, Department of Earth Sciences, London, Ontario N6A 3K7, Canada
²Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095, USA
³Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
⁴Universität Bayreuth, Bayerisches Geoinstitut, Bayreuth 95447, Germany
Copyright Elsevier

The lunar Mg-suite magmatic rocks are commonly thought to represent mafic intrusions into the anorthositic flotation crust of the lunar magma ocean (LMO). Their geochronology is, therefore, important for constraining evolution models of the LMO. Petrogenetic models of the Mg-suite hold that their parent magmas were derived from primary LMO sources (Mg-cumulates, An-rich plagioclase, and melts enriched in KREEP—potassium, rare earth elements, and phosphorus). Previous radiogenic isotopic age interpretations of Mg-suite and putatively older, related ferroan anorthosites (FANs) overlap over a 200-million-year interval. The Apollo 78238 norite is an exemplary Mg-suite rock, with a relict coarse igneous texture modified by shock metamorphism. In-situ secondary ion mass spectrometry U-Pb analyses of zircon and baddeleyite in 78238 yield discordant arrays, attributed to recent impact metamorphism, with upper intercepts that constrain its crystallization age. The four oldest baddeleyite analyses give a weighted mean 207Pb/206Pb age of 4332 ± 18 Ma (2σ, MSWD = 0.06, P = 0.98), which is interpreted as the crystallization age of the norite. The overlap of the baddeleyite age with previously reported Sm-Nd and Pb-Pb mineral isochron ages for 78238 (Edmunson et al., 2009) supports a moderately fast cooling of the norite. Moreover, it is distinguishably younger than the most precisely dated sample of FAN (Apollo 60025), measured at 4360 ± 3 Ma by Sm-Nd and Pb-Pb mineral isochrons (Borg et al., 2011). Together with the baddeleyite 207Pb/206Pb age of Apollo Mg-suite troctolite 76535 at 4328 ± 8 Ma (White et al., 2020), the chronological record of the 78238 norite indicates a significant Mg-suite magmatic event at 4.33 Ga and a lower age limit on LMO differentiation.

¹Thomas Kenkmann
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13657]
¹Institute of Earth and Environmental Sciences, Geology, Albert-Ludwigs-Universität Freiburg, Albertstraße 23b, Freiburg im Breisgau, 79104 Germany
Published by arrangement with John Wiley & Sons

The number of newly discovered and confirmed impact structures on earth is growing continuously. In this review paper, the main attributes of 198 confirmed impact structures and 10 further structures, for which final confirmation based on the identification of shock features is not yet entirely satisfying, are presented. The impact craters are compared statistically, with regard to their morphology, structure, and status of erosion or burial. The size– and age–frequency distributions of terrestrial impact structures are presented. Additional aspects concern target petrography and shock effects found in the craters. Based on the discovery statistics of presently known crater structures, an estimate can be made of the number of craters that await discovery. The paper is complementary to the recently published atlas of terrestrial impact structures by Gottwald et al. (2020).

¹J.Gattacceca et al. (>10)
Earth & Plantetary Science Letters 569, 117049 Link to Article [https://doi.org/10.1016/j.epsl.2021.117049]
¹CNRS, Aix Marseille Univ, IRD, INRAE, CEREGE, 13545 Aix-en-Provence, France
Copyright Elsevier

Glassy ejecta are associated to a limited number of impact craters, and yet hold key information about hypervelocity impact processes. Here we report on the discovery of a ∼650 km2 impact glass strewnfield in the Central Depression of the Atacama Desert. These cm-sized splash-form objects, that we refer to as atacamaites, are essentially composed of a dacitic glass formed by high-temperature melting of local magmatic rocks, with the addition of a variable iron meteorite contamination, 5 wt.% on average. The most likely nature for the impactor is the IIAB iron group. The fission-track plateau method, on two samples, yielded a mean formation age of Ma. No associated impact crater has been discovered so far, suggesting it may be a relatively small, km-sized crater. The glassy nature, aerodynamic shapes, elevated formation temperature, and low water content are reminiscent of tektites. However, their small size, heterogeneity, oxidation state, significant contamination by the impactor, and likely more proximal provenance distinguish them from tektites. Atacamaites have no equivalent among the few known terrestrial ejected impact glasses, and increase the intriguing diversity of such products that we propose to name “tektoids”.

^1,2Guillaume Florin,¹Béatrice Luais,^2,3Olivier Alard,²Tracy Rushmer
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13698]
¹CNRS, CRPG, Université de Lorraine, Nancy, F-5400 France
²Department of Earth and Planetary Sciences, Macquarie University, Sydney, New South Wales, 2109 Australia
³Géosciences Montpellier, UMR 5243, CNRS & Université Montpellier, Montpellier, 34095 France
Published by arrangement with John Wiley & Sons

We analyzed the highly siderophile element (HSE) contents and bulk Ge isotopic compositions of large metal grains in the CB chondrites Bencubbin (CBa), Gujba (CBa), and HaH 237 (CBb). Our results suggest that the large grains were formed by the aggregation of smaller condensed grains, and the two Benccubinite groups are distinguishable based on their bulk metal δ74/70Ge mass-dependent isotopic values of 0.99 ± 0.30‰ (CBa) and −0.65 ± 0.10‰ (CBb). Based on our observations of these three samples, the isotopic compositions of metal in CBa chondrites are best explained by condensation at slow cooling rates in the center of an impact plume, whereas the metal in CBb chondrites formed under fast cooling rates along the plume edges. We also analyzed the Ge contents and isotopic compositions of the core, intermediate, and rim fractions of two Gujba metal grains, which were separated by sequential digestion. These results show a gradual decrease in δ74/70Ge and [Ge] from core to rim. We suggest that these δ74Ge zonations result from near-equilibrium condensation and evaporation processes in a heterogeneous plume. We propose a model for their formation in which (1) small grains (to become grain cores) condensed at equilibrium; (2) these grains were transported to a warmer region of the plume where they reached temperatures lower than that of Fe-Ni condensation, but high enough for the rapid evaporation of Ge; (3) Ge evaporation followed by slow cooling enriched the grains in heavy Ge isotopes and the surrounding gas in light Ge isotopes; and (4) equilibrium recondensation of metal from the gas and around the small grains formed the light Ge isotopic zonations observed in grain rims.