¹Cyrena Anne Goodrich,^1,2David A. Kring,³Richard C. Greenwood
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13738]
¹Lunar and Planetary Institute, USRA, 3600 Bay Area Blvd, Houston, Texas, 77058 USA
²NASA Solar System Exploration Research Virtual Institute
³Planetary and Space Sciences, The Open University, Milton Keynes, MK76AA UK
Published by arrangement with John Wiley & Sons

Foreign clasts (xenoliths) in meteoritic breccias are a serendipitous source of information about the impact environment in which their hosts formed, including impactor flux and cosmochemical types. These parameters may be related to timing and/or heliocentric distance of xenolith origin and implantation, and thus can be used to test or inform models of early solar system dynamics. We use xenoliths in ordinary chondrites (OCs) and ureilites to do this. We first conducted a petrologic and oxygen isotope study of a new, cm-sized igneous-textured clast in L3.7 Northwest Africa (NWA) 092, which highlighted some of the difficulties of identifying xenoliths in meteorites. Results indicate that this clast is not a xenolith but an impact melt of non-local OC material. We add this result to a literature survey of more than 3000 OCs and find that the fraction of OCs that contain xenoliths is <<1%, and, even in these, the abundance and the diversity of xenoliths are very low. This contrasts markedly with the ureilites, ˜5% of which contain ˜1–10 vol% xenoliths from every major meteorite class, including multiple groups and petrologic types. To investigate reasons for this difference, we compare the histories of OC and ureilite parent bodies. The OC and ureilitic parent bodies accreted in the inner solar system within ˜1 AU of one another. The OC bodies accreted ˜2–3 Myr after calcium-aluminum-rich inclusion (CAI) formation and were heated slowly, experiencing thermal metamorphism over ˜50–60 Myr. The ureilite parent body (UPB) accreted <1 Myr after CAIs and was heated rapidly, experiencing partial melting over ˜4 Myr. Both OC parent bodies and the UPB were catastrophically disrupted and reassembled into rubble piles. For ureilites, this occurred ˜5.0–5.4 Ma after CAIs, while for OCs, it did not occur until 50–60 Myr after CAIs. Xenoliths in OC and ureilitic breccias were acquired as fragments of impactors on the rubble piles. The presence in polymict ureilites of xenoliths of all OC groups (H, L, LL) and petrologic types (3–6), and the intimate scale on which these and myriad other xenolith types are mixed, indicate that most xenoliths were acquired within a short time period around ˜50–60 Myr after CAIs when OC (likely also Rumuruti chondrite and enstatite chondrite) parent bodies were disrupted. This timing is consistent with the early instability dynamical model for a period of excitation in the asteroid belt. Outer solar system (CC) xenoliths were also acquired during this period, but were derived indirectly from C-type bodies that had already been emplaced in orbits in the asteroid belt. The large discrepancy in xenolith abundance between ureilites and OC may be due to different physical properties of their regoliths at 50–60 Myr after CAIs. CC-like xenoliths in OC may represent a different, more recently acquired, population than those in polymict ureilites.

¹Evelyn Füri,¹Laurent Zimmermann,²Harald Hiesinger
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13749]
¹Institut für Planetologie, Westfälische Wilhelms-Universität, Münster, D-48149 GermanyCNRS, CRPG, Université de Lorraine, Nancy, F-54000 France
²Institut für Planetologie, Westfälische Wilhelms-Universität, Münster, D-48149 Germany
Published by arrangement with John Wiley & Sons

Cosmic ray exposure (CRE) ages of rocks that were ejected by the impacts that created Cone and North Ray craters provide two crucial calibration points at <100 Ma for the lunar cratering chronology function, which relates the crater density of geological units on the Moon to their absolute age. To reassess the formation ages of these two craters, we determine here the accumulated abundances of “cosmogenic” noble gas nuclides (3Hecosm, 21Necosm, 38Arcosm), as well as the corresponding CRE ages, in six Apollo 14 rocks (i.e., one breccia and five basalts) and two Apollo 16 anorthosites that were collected near the rims of Cone and North Ray craters, respectively. Although noble gas concentrations allow CRE ages to be derived, the calculated 21Ne and 38Ar exposure ages of a given sample cover a significant range of values because published empirical or theoretical production rates of cosmogenic nuclides are highly variable. Nonetheless, it is evident that mare basalts 14053 and 14072 as well as breccia 14068, which were collected near the rim of Cone crater, were exposed at the lunar surface more recently than the three KREEP basalts (14073, 14077, 14078) collected farther away. The 38Ar exposure ages of anorthosites 67075 and 67955 from North Ray crater slightly exceed those of samples 14053, 14068, and 14072. These results confirm that Cone crater is younger than North Ray crater. However, the formation ages of Cone and North Ray craters have larger uncertainties than previously acknowledged. This implies that the uncertainties of noble gas exposure ages should be taken into account when remotely dating young surfaces on the Moon and on other planetary bodies in the solar system.

¹Yanhao Lin,^1,2Wim van Westrenen,¹Ho-Kwang Mao
Proceedings of the National Academy of the United States of America (PNAS) 118, e2110427118 Link to Article [https://doi.org/10.1073/pnas.2110427118]
¹Center for High Pressure Science and Technology Advanced Research, Beijing 100094, People’s Republic of China;
²Department of Earth Sciences, Faculty of Science, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, The Netherlands

Refractory oxygen bound to cations is a key component of the interior of rocky exoplanets. Its abundance controls planetary properties including metallic core fraction, core composition, and mantle and crust mineralogy. Interior oxygen abundance, quantified with the oxygen fugacity (fO2), also determines the speciation of volatile species during planetary outgassing, affecting the composition of the atmosphere. Although melting drives planetary differentiation into core, mantle, crust, and atmosphere, the effect of fO2 on rock melting has not been studied directly to date, with prior efforts focusing on fO2-induced changes in the valence ratio of transition metals (particularly iron) in minerals and magma. Here, melting experiments were performed using a synthetic iron-free basalt at oxygen levels representing reducing (log fO2 = −11.5 and −7) and oxidizing (log fO2 = −0.7) interior conditions observed in our solar system. Results show that the liquidus of iron-free basalt at a pressure of 1 atm is lowered by 105 ± 10 °C over an 11 log fO2 units increase in oxygen abundance. This effect is comparable in size to the well-known enhanced melting of rocks by the addition of H2O or CO2. This implies that refractory oxygen abundance can directly control exoplanetary differentiation dynamics by affecting the conditions under which magmatism occurs, even in the absence of iron or volatiles. Exoplanets with a high refractory oxygen abundance exhibit more extensive and longer duration magmatic activity, leading to more efficient and more massive volcanic outgassing of more oxidized gas species than comparable exoplanets with a lower rock fO2.

¹Aleksandr A. Zubov,¹Tatyana G. Shumilova,¹Andrey V. Zhuravlev,¹Sergey I. Isaenko
American Mineralogist 106, 1860-1870 Link to Article [http://www.minsocam.org/msa/ammin/toc/2021/Abstracts/AM106P1860.pdf]
¹Institute of Geology of Komi Science Center of the Ural Branch of the Russian Academy of Sciences, Pervomayskaya st. 54, Syktyvkar, 167982, Russia
Copyright: The Mineralogical Society of America

X‑ray computed microtomography (CT) of impact rock varieties from the Kara astrobleme is used to test the method’s ability to identify the morphology and distribution of the rock components. Three types of suevitic breccias, clast‑poor melt rock, and a melt clast from a suevite were studied with a spatial resolution of 24 μm to assess CT data values of 3D structure and components of the impactites.
The purpose is first to reconstruct pore space, morphology, and distribution of all distinguishable
crystallized melt, clastic components, and carbon products of impact metamorphism, including the impact glasses, after‑coal diamonds, and other carbon phases. Second, the data are applied to analyze
the morphology and distribution of aluminosilicate and sulfide components in the melt and suevitic
breccias. The technical limitations of the CT measurements applied to the Kara impactites are discussed. Because of the similar chemical composition of the aluminosilicate matrix, glasses, and some lithic and crystal clasts, these components are hard to distinguish in tomograms. The carbonaceous matter has absorption characteristics close to air, so the pores and carbonaceous inclusions appear similar.
However, X‑ray microtomography could be used to prove the differences between the studied types
of suevites from the Kara astrobleme using structural‑textural features of the whole rock, porosity,
and the distributions of carbonates and sulfides.

^1,2Laurence A.J. Garvie,³Chi Ma,²Soumya Ray,⁴Kenneth Domanik,⁵Axel Wittmann,²Meenakshi Wadhwa
American Mineralogist 106, 1828-1834 Link to Article [http://www.minsocam.org/msa/ammin/toc/2021/Abstracts/AM106P1828.pdf]
¹Center for Meteorite Studies, Arizona State University, 781 East Terrace Road, Tempe, Arizona 85287-6004, U.S.A.
²School of Earth and Space Exploration, Arizona State University, 781 East Terrace Road, Tempe, Arizona 85287-6004, U.S.A.
³Division of Geological and Planetary Sciences, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125, U.S.A.
⁴Lunar and Planetary Laboratory, University of Arizona, 1415 N 6th Avenue, Tucson, Arizona 85705, U.S.A.5Eyring Materials Center, Arizona State University, Tempe, Arizona 85287, U.S.A.
Copyright: The Mineralogical Society of America

Carletonmooreite (IMA 2018-68), Ni3Si, is a new nickel silicide mineral that occurs in metal nodules from the Norton County aubrite meteorite. These nodules are dominated by low-Ni iron (kamacite), with accessory schreibersite, nickelphosphide, perryite, and minor daubréelite, tetratae-nite, taenite, and graphite. The chemical composition of the holotype carletonmooreite determined by wavelength-dispersive electron-microprobe analysis is (wt%) Ni 82.8 ± 0.4, Fe 4.92 ± 0.09, and Si 13.08 ± 0.08 (n = 6, total = 100.81) giving an empirical formula of (Ni2.87Fe0.18)Σ3.05Si0.95, with an end-member formula of Ni3Si. Further grains discovered in the specimen after the new mineral submission extend the composition, i.e., (wt%) Ni 81.44 ± 0.82, Fe 5.92 ± 0.93, Cu 0.13 ± 0.02, and Si 13.01 ± 0.1 (n = 11, total = 100.51 ± 0.41), giving an empirical formula (Ni2.83Fe0.22Cu0.004)Σ3.05Si0.95. The backscat-
tered electron-diffraction patterns were indexed by the Pm3m auricupride (AuCu3)-type structure and
give a best fit to synthetic Ni3Si, with a = 3.51(1) Å, V = 43.2(4) Å3, Z = 1, and calculated density of
7.89 g/cm3. Carletonmooreite is silver colored with an orange tinge, isotropic, with a metallic luster and occurs as euhedral to subhedral crystals 1 × 5 μm to 5 × 14 μm growing on tetrataenite into kamacite. The dominant silicide in the Norton County aubrite metal nodules is perryite (Ni,Fe)8(Si,P)3, with
carletonmooreite restricted to localized growth on rare plessite fields. The isolated nature of small euhedral carletonmooreite single crystals suggests low-temperature growth via solid-state diffusion
from the surrounding kamacite and epitaxial growth on the tetrataenite. This new mineral is named in honor of Carleton B. Moore, chemist and geologist, and founding director of the Center for Meteorite Studies at Arizona State University, for his many contributions to cosmochemistry and meteoritics.

¹Emily A Worsham ,¹Thorsten Kleine
Science Advances 7, 44 Link to Article [DOI: 10.1126/sciadv.abh2837]
¹Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, Münster 48149, Germany

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

^1,2,3,4Ye Li,^4,5Alan E. Rubin,^1,2Weibiao Hsu
American Mineralogist 106, 1751–1767 Link to Article [https://doi.org/10.2138/am-2021-7689]
¹CAS Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210034, China 2
²CAS Center for Excellence in Comparative Planetology, Hefei 230026, China 3
³The State Key Laboratory of Planetary Science, Macau University of Science and Technology, Macau 4
⁴Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, California 90095-1567, U.S.A. 5
⁵Maine Mineral and Gem Museum, 99 Main Street, P.O. Box 500, Bethel, Maine 04217, U.S.A.
Copyright: The Mineralogical Society of America

Studies of the new growth and re-distribution of Cu-rich phases in chondrites of different petrologic subtypes can potentially provide insights into post-accretionary parent-body processes. We present a systematic study of the distribution of Cu-rich phases and metallic Cu in Ornans-like carbonaceous chondrites (CO3) that underwent little aqueous alteration or shock (most with shock stages of S1) but exhibit a range of thermal metamorphism (subtype 3.0–3.7). A comparison to ordinary chondrites (OCs), which have undergone a larger range of shock levels, allows us to constrain the relative roles of radiogenic and shock heating in the origin of Cu distribution in chondrites. We found that the Cu content of Ni-rich metal and calculated bulk Cu content of CO3 chondrites (based on mass-balance calculations) show an increase from CO3.0 to CO3.2 chondrites. We speculate that some unidentified phases in the matrix account for a significant portion (nearly ~100 ppm) of the Cu budget in bulk samples of CO3.0 chondrites, while Ni-rich metal is the main Cu-carrier for CO3.2–3.7 chondrites. Within CO3.2–3.7 chondrites, Cu and Ni contents of Ni-rich metal are positively correlated, showing a systematic decrease from lower to higher subtype (~0.41 wt% Cu and ~45.0 wt% Ni in CO3.2 Kainsaz; ~0.28 wt% Cu and ~38.8 wt% Ni in CO3.7 Isna). Metallic Cu grains were found in every sample of CO3.2–3.7 chondrites, but not in any CO3.0–3.1 chondrites. Metallic Cu is: (1) present at metallic-Fe-Ni-pyrrhotite interfaces; (2) associated with fine irregular pyrrhotite grains in Ni-rich-metal-pyrrhotite nodules; (3) associated with fizzed pyrrhotite (fine-grained mixtures of irregularly shaped metal grains surrounded by pyrrhotite); (4) present at the edges of metallic Fe-Ni grains; and (5) present as isolated grains. In some metallic-Cu-bearing mineral assemblages, pyrrhotite has higher Cu concentrations than adjacent Ni-rich metal and shows a drop in Cu concentration at the interface between metallic Cu and Cu-rich pyrrhotite. This implies that the precipitation of metallic Cu grains could be related to the local Cu enrichment of pyrrhotite. We consider that radiogenic heating is mainly responsible for the formation of opaque phases in CO chondrites based on the relatively slow metallographic cooling rate (~0.1–5 °C/Ma), the increasing uniformity of Ni contents in Ni-rich metal with increasing CO subtype (44.3 ± 17.3 wt% in CO3.00 to 38.8 ± 3.4 wt% in CO3.7 chondrite), and the relatively narrow range of pyrrhotite metal/sulfur ratios (~0.976–0.999). Metal/sulfur ratios of pyrrhotite grains in most CO3.2–3.7 chondrites (mean = ~0.986–0.997; except Lancé) are slightly higher than those in CO3.0–3.1 chondrites (mean = ~0.981–0.987; except Y-81020), possibly indicative of a release and re-mobilization of sulfur during progressive heating as previously reported for type-3 chondrites. In this regard, we suggest most metallic Cu grains in CO3 chondrites may have precipitated from Cu-rich pyrrhotite due to sulfidation of Fe-Ni metal during parent-body thermal metamorphism. Locally, a few metallic Cu grains associated with fizzed pyrrhotite could have formed during transient shock-heating. Both thermal and shock metamorphism could be responsible for the formation of metallic Cu.

Although the systematic decrease in the Ni contents of Ni-rich metal from subtype-3.2 to subtype-3.8 also occurs in OCs, the average Cu contents of Ni-rich metal grains are indistinguishable among type-3 OCs of different subtypes. The paucity of metallic Cu in weakly shocked type-3 OCs could be related to: (1) the relatively low-bulk Cu contents of OCs, and/or (2) the relatively rapid metallographic cooling rates at <500–600 °C (~1–10 °C/Ma for LL chondrites), possibly resulting from early disturbance of OC parent bodies. The intergrowth of metallic Cu and irregular pyrrhotite more commonly occurs in shocked type-4 to type-6 OCs than in CO3 chondrites. This could be due to S in type-4 to type-6 OCs being more mobilized due to shock heating than in unshocked CO3 chondrites. We predict that some other groups of carbonaceous chondrites (e.g., CI and CM) are less likely to produce metallic Cu due to the: (1) relatively low amount of metallic Fe-Ni; (2) relatively low parent-body temperatures of ~100–300 °C; (3) high mobility of Cu in solution for aqueously altered samples; and (4) the short heating duration for metamorphosed samples.

¹John J. Donovan,²Julien M. Allaz,³Anette von der Handt,⁴Gareth G.E. Seward,⁵Owen Neill,⁶Karsten Goemann,¹Julie Chouinard,⁷Paul K. Carpenter
American Mineralogist 106, 1717–1735 Link to Article [http://www.minsocam.org/msa/ammin/toc/2021/Abstracts/AM106P1717.pdf]
¹CAMCOR, University of Oregon, Eugene, Oregon, 97403, U.S.A. 2
²Institute of Geochemistry and Petrology, ETH Zürich, 8092 Zürich, Switzerland 3
³Department of Earth Sciences, University of Minnesota, Minneapolis, Minnesota 55455, U.S.A. 4
⁴Department of Earth Science, University of California Santa Barbara, Santa Barbara, California 93101, U.S.A.
⁵Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, Michigan 48013, U.S.A. 6
⁶Central Science Laboratory, University of Tasmania, Hobart, Tasmania 7001, Australia 7
⁷Department of Earth and Planetary Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, Missouri 63130, U.S.A.
Copyright: The Mineralogical Society of America

While much progress has been made in electron-probe microanalysis (EPMA) to improve the accuracy of point analysis, the same level of attention has not always been applied to the quantification
of wavelength-dispersive spectrometry (WDS) X-ray intensity maps at the individual pixel level. We
demonstrate that the same level of rigor applied in traditional point analysis can also be applied to the
quantification of pixels in X-ray intensity maps, along with additional acquisition and quantitative
processing procedures to further improve accuracy, precision, and mapping throughput. Accordingly,
X-ray map quantification should include pixel-level corrections for WDS detector deadtime, corrections
for changes in beam current (beam drift), changes in standard intensities (standard drift), high-accuracy
removal of background intensities, quantitative matrix corrections, quantitative correction of spectral
interferences, and, if required, time-dependent corrections (for beam and/or contamination sensitive
materials). The purpose of quantification at the pixel level is to eliminate misinterpretation of intensity
artifacts, inherent in raw X-ray intensity signals, that distort the apparent abundance of an element.
Major and minor element X-ray signals can contain significant artifacts due to absorption and fluorescence effects. Trace element X-ray signals can contain significant artifacts where phases with different
average atomic numbers produce different X-ray continuum (bremsstrahlung) intensities, or where a
spectral interference, even an apparently minor one, can produce a false-positive intensity signal. The
methods we propose for rigorous pixel quantification require calibration of X-ray intensities on the
instrument using standard reference materials, as we already do for point analysis that is then used to
quantify multiple X-ray maps, and thus the relative time overhead associated with such pixel-by-pixel
quantification is small. Moreover, the absolute time overhead associated with this method is usually less
than that required for quantification using manual calibration curve methods while resulting in significantly better accuracy. Applications to geological, synthetic, or engineering materials are numerous as
quantitative maps not only show compositional 2D variation of fine-grained or finely zoned structures
but also provide very accurate quantitative analysis, with precision approaching that of a single point
analysis, when multiple-pixel averaging in compositionally homogeneous domains is utilized.

^1,2,3Achen Duan,^1,4Yunzhao Wu,⁵Edward A. Cloutis,^1,2Jinfei Yu,¹Shaolin Li,^1,2Yun Jiang
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13750]
¹Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, 210023 China
²School of Astronomy & Space Sciences, University of Science and Technology of China, Hefei, 230026 China
³Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application, Nanjing, 210023 China
⁴CAS Center for Excellence in Comparative Planetology, China
⁵Department of Geography, University of Winnipeg, 515 Portage Avenue, Winnipeg, R3B 2E9 Manitoba, Canada
⁶State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau, PR China
⁷CAS Center for Excellence in Comparative Planetology, China
Published by arrangement with John Wiley & Sons

Carbonaceous chondrites (CCs) are important materials for understanding the early evolution of the solar system and delivery of organic material to the early Earth. Spectral analysis of CCs can establish the relationship between them and their possible parent asteroids, which helps to determine the surface composition of the asteroid. In this paper, the 0.3–26 μm reflectance spectra of a series of coals ranging from lignite to anthracite (Earth analogs of organic matter contained in CCs), a coal heated to various durations and temperatures, and reflectance spectra of CM2 meteorites were analyzed in conjunction with compositional information to derive spectral–compositional relationships. All types of coals have strong aromatic absorptions (3.28 and 5–6.5 μm) and aliphatic “triplet” absorptions (3.38, 3.41, and 3.48 μm). In contrast, CM2 meteorites have obvious aliphatic absorptions and lack aromatic absorptions. The reason is the weak absorption coefficients of aromatic materials and the overlap with strong OH/H₂O absorption. Absorptions in the coal spectra are strongly related to elemental H/C ratio. When the H/C ratio is >0.55, the absorption intensity of an aliphatic increases linearly with the increase of H/C. For heated coal, increasing heating time above 1 h at 450 °C causes the disappearance of the aliphatic “triplet” absorptions. Similarly, heating Murchison meteorite to 400 °C for 1 week causes all the organic absorptions to disappear. This implies that in remote sensing detections, only asteroids (e.g., with CM and CI carbonaceous chondrites compositions) that experienced low thermal metamorphism (<400 °C) are suitable as potential targets for detecting organic compounds using features in the 3–4 µm region.

¹Edward D. Young
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13752]
¹Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California, 90095 USA
Published by arrangement with John Wiley & Sons

The trapped melt fractional crystallization model for the IIIAB iron meteorites put forward by J. T. Wasson two decades prior is revisited. The basic precepts upon which the model was based remain true, and the model can be implemented using Ir and Au solid/liquid distribution coefficients that are broadly consistent with experimental data. For this reason, the difference between the Wasson model and some more recent trapped melt models lies mainly with inferences about the S concentrations of the core of the IIIAB iron meteorite parent body. For the Wasson model, S bulk concentrations of about 2 wt% are implied. For the more recent model, much greater concentrations of between about 12–15 wt% are indicated. The two different trapped melt models profoundly influence the interpretation of high δ⁵⁷Fe values relative to chondrites in the IIIAB irons. The Wasson model suggests that there should be more variations in δ⁵⁷Fe than are observed among these meteorites, while the more recent trapped melt model relies on the crystallization of FeS from the trapped melt to raise the δ⁵⁷Fe of the latter, thus minimizing the variability. The interpretation of Fe isotope ratios in the IIIAB meteorites therefore depends critically on the S concentration of the parent body core.