¹Alex M.Ruzicka, ²Richard C.Greenwood, ^1,3Katherine Armstrong, ¹Kristy L.Schepker,²Ian A.Franchi
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.01.017]
¹Portland State University, Department of Geology and Cascadia Meteorite Laboratory, 17 Cramer Hall, 1721 SW Broadway, Portland, OR, USA
²Planetary Sciences Research Institute, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
³Universität Bayreuth, Bayrisches Geoinstitut, D-95440, Bayreuth, DE
Copyright Elsevier

Large (>3.5 mm and up to 4 cm across) igneous inclusions poor in metal and sulfide are a minor but not uncommon component in ordinary chondrites, and have implications for the nature of physiochemical and melting processes in the early solar system. We obtained petrographic-chemical data for forty-two large igneous inclusions in ordinary chondrites of various groups (H, L, LL) and petrographic types (3-6) and oxygen isotope data for a subset of twelve of these inclusions and their host chondrites. Different inclusions formed both before and after the thermal metamorphism experienced by their host chondrites. The bulk chemical compositions of the inclusions vary broadly around whole-rock chondrite composition, comprise four main chemical types and some other variants, and show little evidence of having formed as igneous differentiates. Oxygen isotope compositions overlap ordinary chondrite compositions and are related to inclusion chemical type. Most prevalent in type 3 and 4 chondrites are inclusions, often droplets, of the vapor-fractionated (Vfr) chemical type, either enriched in refractory lithophile elements, or depleted in volatile lithophile elements, or both. These inclusions have low Δ¹⁷O (∼0.1-0.6‰) and high δ¹⁸O (∼4-8‰) values and formed in reservoirs with Δ¹⁷O lower than their hosts, primarily as evaporative melts and mixtures that probably experienced kinetic isotopic fractionation. Another chemical type (Unfr+K) has unfractionated abundances of lithophile elements except for being strongly enriched in K, a signature also found in some impact melts from melt rocks and melt breccias. These inclusions formed by impact melting of chondritic material and accompanying K enrichment. Inclusions with unfractionated (Unfr) lithophile element abundances are present in type 3-6 chondrites and are prevalent in type 5 and 6. Some are spatially associated with coarse metal-sulfide nodules in the chondrites and likely formed by in situ impact melting. Others were melted prior to thermal metamorphism and were chemically but not isotopically homogenized during metamorphism; they are xenoliths that formed in oxygen reservoirs different than the hosts in which they were metamorphosed. The latter inclusions provide evidence for nebular or collisional mixing of primitive materials prior to thermal metamorphism of asteroid bodies, including transport of H-like source materials to the L body, LL-like source materials to the L body, and low-Δ¹⁷O materials to the LL body. Feldspar-rich (FldR) inclusions have compositions similar to melt pockets and could have formed by disequilibrium melting and concentration of feldspar during an impact event to form large droplets or large masses. Overall, the results of this study point to important and varied roles for both “planetary” impact melting and “nebular” evaporative melting processes to form different large igneous inclusions in ordinary chondrites. Chondrules may have formed by processes similar to those inferred for large inclusions, but there are important differences in the populations of these objects.

¹Sara Mazrouei, ^1,2Rebecca R. Ghent, ³William F. Bottke, ³Alex H. Parker, ⁴Thomas M. Gernon
Science 363, 253-257 Link to Article [DOI: 10.1126/science.aar4058]
¹Department of Earth Sciences, University of Toronto, Toronto, ON, Canada.
²Planetary Science Institute, Tucson, AZ, USA.
³Southwest Research Institute, Boulder, CO, USA.
⁴School of Ocean and Earth Science, University of Southampton, Southampton, UK.
Reprinted with permission from AAAS

The terrestrial impact crater record is commonly assumed to be biased, with erosion thought to eliminate older craters, even on stable terrains. Given that the same projectile population strikes Earth and the Moon, terrestrial selection effects can be quantified by using a method to date lunar craters with diameters greater than 10 kilometers and younger than 1 billion years. We found that the impact rate increased by a factor of 2.6 about 290 million years ago. The terrestrial crater record shows similar results, suggesting that the deficit of large terrestrial craters between 300 million and 650 million years ago relative to more recent times stems from a lower impact flux, not preservation bias. The almost complete absence of terrestrial craters older than 650 million years may indicate a massive global-scale erosion event near that time.

¹Masayuki Uesugi,²Motoo Ito,³Hikaru Yabuta,⁴Hiroshi Naraoka,⁴Fumio Kitajima,⁵Yoshinori Takano,⁶Hajime Mita,⁷Yoko Kebukawa,⁸Aiko Nakato,⁹Yuzuru Karouji
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13236]
¹Japan Synchrotron Radiation Research Institute (JASRI), Sayo, Hyogo, 679‐5198 Japan
²Institute for Core Sample Research, Japan Agency for Marine‐Earth Science Technology (JAMSTEC), Nankoku, Kochi, 783‐8502 Japan
³Department of Earth and Planetary Systems Science, Hiroshima University, Hiroshima, 739‐8526 Japan
⁴Department of Earth and Planetary Science, Faculty of Science, Kyushu University, Hakozaki, Fukuoka, 812‐8581 Japan
⁵Department of Biogeochemistry, Japan Agency for Marine‐Earth Science and Technology (JAMSTEC), Yokosuka, 237‐0061 Japan
⁶Life, Environment and Materials Science, Fukuoka Institute of Technology, Fukuoka, 811‐0295 Japan
⁷Faculty of Engineering, Yokohama National University, Yokohama, 240‐8501 Japan
⁸Division of Earth and Planetary Sciences, Kyoto University,Sakyo, Kyoto, 606‐8502 Japan
⁹Space Exploration Innovation Hub Center, Japan Aerospace Exploration Agency (JAXA), , Sagamihara, Kanagawa, 252‐5210 Japan
Published by arrangement with John Wiley & Sons

Carbonaceous materials in the sample catcher of the Hayabusa spacecraft were assigned as category 3 particles. We investigated the category 3 particles with a suite of in situ microanalytical methods. Possible contaminants collected from the cleanrooms of the spacecraft assembly and extraterrestrial sample curation center (ESCuC) were also analyzed in the same manner as category 3 particles for comparison. Our data were integrated with those of the preliminary examination team for category 3 particles. Possible origins for the category 3 particles include contamination before and after the operation of the Hayabusa spacecraft.

¹Morgan A. Cox,¹Aaron J. Cavosie,²Ludovic Ferrière,¹Nicholas E. Timms,¹Phil A. Bland,¹Katarina Miljković,^1,3Timmons M. Erickson,³Brian Hess
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13238]
¹Space Science and Technology Centre, School of Earth and Planetary Sciences, Curtin University, , Perth, WA, 6102 Australia
²Natural History Museum, , A‐1010 Vienna, Austria
³Jacobs‐JETS, Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, , Houston, Texas, 77058 USA
⁴NASA Astrobiology Institute, Department of Geoscience, University of Wisconsin–Madison, , Madison, Wisconsin, 53706 USA
Published by arrangement with John Wiley & Sons

Yallalie is a ~12 km diameter circular structure located ~200 km north of Perth, Australia. Previous studies have proposed that the buried structure is a complex impact crater based on geophysical data. Allochthonous breccia exposed near the structure has previously been interpreted as proximal impact ejecta; however, no diagnostic indicators of shock metamorphism have been found. Here we report multiple (27) shocked quartz grains containing planar fractures (PFs) and planar deformation features (PDFs) in the breccia. The PFs occur in up to five sets per grain, while the PDFs occur in up to four sets per grain. Universal stage measurements of all 27 shocked quartz grains confirms that the planar microstructures occur in known crystallographic orientations in quartz corresponding to shock compression from 5 to 20 GPa. Proximity to the buried structure (~4 km) and occurrence of shocked quartz indicates that the breccia represents either primary or reworked ejecta. Ejecta distribution simulated using iSALE hydrocode predicts the same distribution of shock levels at the site as those found in the breccia, which supports a primary ejecta interpretation, although local reworking cannot be excluded. The Yallalie impact event is stratigraphically constrained to have occurred in the interval from 89.8 to 83.6 Ma based on the occurrence of Coniacian clasts in the breccia and undisturbed overlying Santonian to Campanian sedimentary rocks. Yallalie is thus the first confirmed Upper Cretaceous impact structure in Australia.

¹Michael Willig,¹Andreas Stracke
Earth and Planetary Science Letters 509, 55-65 Link to Article [https://doi.org/10.1016/j.epsl.2018.12.004]
¹Westfälische Wilhelms-Universität Münster, Corrensstr. 24, 48149 Münster, Germany
Copyright Elsevier

Combined Ce and Nd isotope ratios provide a time-integrated record of the light rare earth element (LREE) abundances of their source materials. Here, we present new high precision Ce isotope data for chondrites and basalts from ocean islands (OIB) and mid ocean ridges (MORB). The new Ce isotope ratios in chondritic meteorites define a precise new CHUR reference value. In Ce–Nd isotopic space, the MORB and OIB form a well-defined array that intersects with the Ce–Nd chondritic reference value. The simplest first-order explanation is that the bulk silicate Earth (BSE) has chondritic LREE and Ce–Nd isotope ratios. We show, however, that the intercept and slope of the Ce–Nd isotope mantle array depend on several factors. Perhaps most important are whether the BSE is chondritic and how closely the mantle average reflected in the MORB and OIB data corresponds to the Ce–Nd isotope ratio of the BSE. A significant difference between the accessible mantle’s average Ce–Nd isotope ratio and that of BSE could result from the permanent storage of a considerable proportion of Earth’s total LREE budget in the continental crust or potential isolated reservoirs. We show that the formation of isolated reservoirs either has a minor effect on the average Ce–Nd composition of the average mantle, or is geochemically and geodynamically implausible. If, due to formation of the continental crust, a significant shift in the average mantle’s Ce–Nd isotope composition relative to BSE occurs, this shift is parallel to the Ce–Nd mantle array, and does not affect its chondritic intercept. The chondritic intercept of the Ce–Nd isotope mantle array therefore is strong evidence that BSE’s relative LREE and Ce–Nd isotope composition is chondritic. However, an apparent difference between the accessible mantle’s average Ce–Nd isotope ratio and that of BSE could also result if MORB and OIB do not sample the accessible mantle in a representative manner. Although we cannot entirely exclude the latter, it would require a fortuitous combination of factors to cause the observed chondritic intercept of the Ce–Nd isotope mantle array. We therefore conclude that the bulk silicate Earth has chondritic LREE and Ce–Nd isotope ratios.

¹Camille Lepaulard,¹Jérôme Gattacceca,²Nicholas Swanson‐Hysell, ¹Yoann Quesnel, ¹François Demory, ^3,4Gordon R. Osinski
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13239]
¹Aix Marseille Univ, CNRS, IRD, Coll France, INRA, CEREGE, , Aix‐en‐Provence, France
²Department of Earth and Planetary Science, University of California, , Berkeley, California, 94720–4767 USA
³Department of Earth Sciences, Centre for Planetary Science and Exploration, University of Western Ontario, , London, Ontario, N6A 5B7 Canada
⁴Department of Physics & Astronomy, University of Western Ontario, , London, Ontario, N6A 5B7 Canada
Published by arrangement with John Wiley & Sons

We report paleomagnetic directions from the target rocks of the Tunnunik impact structure, as well as from lithic impact breccia dikes that formed during the impact event. The target sedimentary rocks have been remagnetized after impact‐related tilting during a reverse polarity interval. Their magnetization is unblocked up to 350 °C. The diabase dikes intruding into these sediments retained their original magnetization which unblocks above 400 °C. The impact breccia records a paleomagnetic direction similar to that of the overprints in the target sedimentary rocks. The comparison of the resulting virtual geomagnetic pole for the Tunnunik impact structure with the apparent polar wander path for Laurentia combined with biostratigraphic constraints from the target sedimentary rocks is most consistent with an impact age in the Late Ordovician or Silurian, around 430–450 Ma, soon after the deposition of the youngest impacted sedimentary rocks. Our results from the overprinted sedimentary rocks and diabase dikes imply that the postimpact temperature of the studied rocks was about 350 °C.

¹M. Mercer, ¹Kip V. Hodges, ²Bradley L. Jolliff, ¹Matthijs C. Van Soest, ^1,3Jo‐Anne Wartho, ^1,4John R. Weirich
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13240]
¹School of Earth and Space Exploration, Arizona State University, , Tempe, Arizona, 85287 USA
²Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University, , St. Louis, Missouri, 63130 USA
³ Helmholtz Centre for Ocean Research Kiel, , D‐24148 Kiel, Germany
⁴ Science Institute, , Tucson, Arizona, 85719 USA
Published by arrangement with John Wiley & Sons

⁴⁰Ar/³⁹Ar incremental heating experiments on whole‐rock lunar samples commonly provide evidence of varying degrees of radiogenic ⁴⁰Ar (⁴⁰Ar*) loss. However, these experiments provide limited information about whether or not ⁴⁰Ar* is preferentially lost from specific glasses, minerals, or polyphase domains. Ultraviolet laser ablation microprobe (UVLAMP) ⁴⁰Ar/³⁹Ar dating and electron probe microanalysis of mineral clasts and polyphase melt assemblages in Apollo 17 poikilitic impact melt rock 77135 show evidence of geochemical controls on ⁴⁰Ar/³⁹Ar dates. Potassium‐rich glass and K‐feldspar in the mesostasis are the dominant sources for Ar released during low‐temperature steps of published ⁴⁰Ar/³⁹Ar release spectra for this rock, while pyroxene oikocrysts with enclosed plagioclase chadacrysts contribute Ar predominantly to intermediate‐ to high‐temperature steps. Additionally, UVLAMP analysis of a mm‐scale plagioclase clast demonstrates the potential to use stranded ⁴⁰Ar* diffusive loss profiles to constrain the thermal evolution of lunar impact melt deposits and indicates that the melt component of 77135 cooled quickly. While some submillimeter clasts of plagioclase are distinctly older than the melt, other small clasts yield dates younger than the oldest melt components in 77135, plausibly due to subgrain fast diffusion pathways and/or ⁴⁰Ar* loss during brief episodes of reheating at high temperatures. Our data suggest that integrated petrologic and microanalytical geochronologic studies are necessary complements to bulk sample geochronologic studies in order to fully evaluate competing models for the impactor flux during the first billion years of the Moon’s evolution.

¹L.Riu,¹ F.Poulet,¹J.-P.Bibring,¹B.Gondet
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.01.002]
¹IAS, Institut d’Astrophysique Spatiale, bâtiment 121Université Paris-Saclay, Orsay 91405, France
Copyright Elsevier

This paper is the first paper of a series that will present the derivation of the modal mineralogy of Mars (M3 project) at a global scale from the near-infrared dataset acquired by the imaging spectrometer OMEGA (Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité) on board ESA/Mars Express. The objective is to create and provide a global 3-D image-cube of Mars at 32 px/° covering most of Mars surface. This product has several advantages. First, it can be used to instantaneously extract atmospheric- and aerosol-corrected near-infrared (NIR) spectra from any location on Mars. Second, several new data maps can be built as discussed here. That includes new global mineral distributions, quantitative mineral abundance distributions and maps of Martian surface chemistry (wt% oxide) detailed in a companion paper (Riu et al, 2018). Here we present the method to derive the global hyperspectral cube from several hundred millions of spectra. Global maps of some mafic minerals are then shown, and compared to previous works.

¹Peng Ni(倪鹏), ¹Youxue Zhang(张有学), ¹Sha Chen(陈沙),²Joel Gagnon
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.12.034]
¹Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI 48109-1005, USA
²Department of Earth and Environmental Sciences, University of Windsor, Windsor, Ontario N9B 3P4, Canada
Copyright Elsevier

Earth’s Moon was thought to be highly depleted in volatiles due to its formation by a giant impact. Over the last decade, however, evidence has been found in apatites, lunar volcanic glass beads, nominally anhydrous minerals and olivine-hosted melt inclusions, to support a relatively “wet” Moon. In particular, based on H₂O/Ce, F/Nd, and S/Dy ratios, recent melt inclusion (MI) work estimated volatile (H₂O, F, and S) abundances in lunar rocks to be similar to or slightly lower than the terrestrial depleted mantle. Uncertainties still occur, however, in whether the limited numbers of lunar samples studied are representative of the primitive lunar mantle, and whether the high H₂O/Ce ratio for 74220 is due to local heterogeneity. In this paper, we report major element, trace element, volatile, and transition metal data in MIs for 5 mare basalt samples (10020, 12040, 15016, 15647 and 74235) and a pyroclastic deposit (74220).

With our new lunar MI data, H₂O/Ce ratios are still found to vary significantly among different lunar samples, from ∼ 50 for 74220, to ∼ 9 for 10020, ∼ 3 for 74235, 1.7 to 0.9 for 12008, 15016, and 15647, and 0.5 for 12040. H₂O/Ce ratios for these samples show positive correlation with their cooling rates, indicating a possible effect of post-eruptive loss of H on their H₂O/Ce variations. It is evident that most other lab and lunar processes, including loss of H₂O during homogenization, mantle partial melting, magma evolution, and ingassing during or post eruption are unlikely the causes of high H₂O/Ce variations among different lunar samples. By comparing ratios of F/Nd, S/Dy, Zn/Fe, Pb/Ce, Cs/Rb, Rb/Ba, Cl/K, Na/Sr, Ga/Lu, K/Ba, and Li/Yb between 74220 and other lunar samples, the possibility of 74220 originating from a volatile-enriched heterogeneity in the lunar mantle can also be excluded. With all the above considerations, we think that the H₂O/Ce ratio for 74220 best represents the pre-degassing lunar basaltic melt and primitive lunar mantle, either because it was formed by a rapid eruption process, or it was sourced from a deeper part of the lunar mantle that experienced less degassing H₂O loss during lunar magma ocean crystallization. With an H₂O/Ce ratio of ∼50, the primitive lunar mantle is estimated to contain ∼84 ppm H₂O.

Comparing volatile abundances in melt inclusions, glassy embayments, and glass beads in 74220 yields the following volatility trend for volcanic eruptions on the lunar surface:

H₂O >> Cl >> Zn ≈ Cu ≈ F > S ≈ Ga ≈ Cs > Rb ≈ Pb > Na > K ≈ Li.

Using the melt inclusion data obtained thus far, the volatile depletion trend for the Moon from a MI perspective is estimated. Our results show that most of the volatile elements in the lunar mantle are depleted relative to the bulk silicate Earth by a factor of 2 to 20, however, a good correlation between half condensation temperature and the volatile depletion trend is not observed. The relatively flat pattern for the lunar volatile depletion trend requires a lunar formation model that can reconcile the abundances of these volatiles in the lunar mantle.

¹D. R. Schmidt,¹ N. J. Woolf, ²T. J. Zega, ^2,3,4L. M. Ziurys
Nature 564, 378-381 Link to Article [https://doi.org/10.1038/s41586-018-0763-1]
¹Department of Astronomy, Steward Observatory, University of Arizona, Tucson, AZ, USA
²Department of Planetary Science, Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
³Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ, USA
⁴Arizona Radio Observatory, Steward Observatory, University of Arizona, Tucson, AZ, USA

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