¹Thomas Smith,^1,2,3Huaiyu He,⁴Shijie Li,¹P. M. Ranjith,^1,2Fei Su,⁵Jérôme Gattacceca,⁵Régis Braucher,⁵ASTER-Team
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13760]
¹State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
²Institutions of Earth Science, Chinese Academy of Sciences, Beijing, 100029 China
³College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, 100049 China
⁴Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081 China
⁵Centre Européen de Recherche et d’Enseignement de Géosciences de l’Environnement (CEREGE), CNRS, Aix-Marseille University, IRD, INRAE, Aix-en-Provence, France
Published by arrangement with John Wiley

We measured noble gas concentrations and isotopic ratios (He, Ne, and Ar isotopes) in six recent ordinary chondrite falls: Mangui (L6), Viñales (L6), Ozerki (L6), Tamdakht (H5), Kheneg Ljouâd (LL5/6), and Katol (L6). Among them, the three L6 chondrites Mangui, Viñales, and Ozerki fell in only a few months interval; their apparent similar petrographic and mineralogic characteristics might indicate source crater pairing. To test this hypothesis, we have investigated those meteorites for their cosmic ray exposure (CRE) histories, using the cosmogenic noble gases 3He, 21Ne, and 38Ar. We systematically (re)calculated the CRE ages as well as the gas retention ages of these meteorites. The CRE age of the Mangui is, based on noble gases, <1 Ma, which is unusually short for an L chondrite. Indeed, the range of exposure ages for L chondrites is generally distributed between ˜1 and ˜60 Ma, with major peaks occurring around ˜5, ˜30, and ˜40 Ma. In addition, the cosmogenic 3Hecos data of two Mangui duplicates are consistent with a remarkably high loss of helium by diffusion due to heating by solar radiation. Such a short parent body-Earth transfer time (<1 Ma) can be explained by a delivery from an Earth-crossing object. Regarding the other L6 chondrites, Viñales has a nominal CRE age of ˜9.4 Ma, whereas the Ozerki meteorite has a nominal CRE age of ˜1.2 Ma, which is consistent with Korochantseva et al. (2019). Based on their CRE ages as well as on their gas retention ages, it appears that none of these three recent L6 chondrite falls are source crater paired, and therefore, all three originate from different meteoroids. The nominal exposure ages of Tamdakht, Kheneg Ljouâd, and Katol are ˜3.2, ˜11, and ˜30 Ma, respectively, and are consistent with identified age peaks on the exposure age histogram of H, LL, and L chondrites, respectively. The nominal CRE age of Tamdakht is consistent with previous observations for H chondrites and implies that they are dominated by small impact events occurring in several parent bodies.

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.