¹D.L.Schrader,²T.J.Zega
Geochimica et Cosmochimcia Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.08.015]
¹Center for Meteorite Studies, School of Earth and Space Exploration, Arizona State University, 781 East Terrace Road, Tempe, AZ 85287, USA
²Lunar and Planetary Laboratory, 1629 E. University Blvd., University of Arizona, Tucson, AZ 85721, USA
Copyright Elsevier

Sulfide minerals occur in many types of extraterrestrial samples and are sensitive indicators of the conditions under which they formed or were subsequently altered. Here we report that chemical and petrographic analyses of Fe,Ni sulfides can be used to determine the metamorphic type of the host LL chondrite, and constrain their alteration conditions. Our data show that the major- and minor-element compositions of the pyrrhotite-group sulfides (dominantly troilite) and pentlandite vary with degree of thermal metamorphism experienced by their host chondrite. We find that Fe,Ni sulfides in LL3 chondrites formed during chondrule cooling prior to accretion, whereas those in LL4 to LL6 chondrites formed during cooling after thermal metamorphism in the parent body, in agreement with previous work. High degrees of shock (i.e., ≥S5) caused distinct textural, structural, and compositional changes that can be used to identify highly shocked samples. Distinct pyrrhotite-pentlandite textures and minerals present in Appley Bridge (LL6) suggest that they cooled more slowly and therefore occurred at greater depth(s) in the host parent body than those of the other metamorphosed LL chondrites studied here. Sulfides in all LL chondrites studied formed under similar sulfur fugacities, and the metamorphosed LL chondrites formed under similar oxygen fugacities. The data reported here can be applied to the study of other LL chondrites and to sulfides in samples of asteroid Itokawa returned by the Hayabusa mission in order to learn more about the formation and alteration history of the LL chondrite parent body.

¹Zhen Tian,¹Heng Chen,¹Bruce Fegley Jr,¹Katharina Lodders,²Jean-Alix Barrat,³James M.D.Day,¹KunWang (王昆)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.08.012]
¹Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130, USA
²Univ Brest, CNRS, UMR 6538 (Laboratoire Géosciences Océan), Institut Universitaire Européen de la Mer (IUEM), Place Nicolas Copernic, 29280 Plouzané, France
³Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, 92093 USA
Copyright Elsevier

We report new high-precision stable K isotope data for thirty achondrites, including three martian meteorites, one lunar meteorite, one ordinary chondrite, four terrestrial igneous United States Geological Survey (USGS) reference materials, and twenty howardite–eucrite–diogenite [HED] meteorites. The four martian samples define a relatively narrow δ⁴¹K range with an average of −0.36 ± 0.12‰ (2 SD) that is slightly heavier than the Bulk Silicate Earth (BSE) K isotopic composition (−0.48 ± 0.03‰). Except for the four Northwest Africa samples which were terrestrially contaminated, all HED meteorites reveal substantial ⁴¹K enrichment compared to BSE, lunar samples, martian meteorites, and chondrites. We propose that the average δ⁴¹K (+0.36 ± 0.16‰) obtained from HED meteorites is representative of Bulk Silicate 4-Vesta. The coupled volatile depletion and heavy K isotope enrichment in 4-Vesta could be attributed to both nebula-scale processes and parent-body events. The asteroid 4-Vesta is likely to have accreted from planetary feedstocks that have been significantly volatile-depleted prior to the major phases of planetary accretion in the early Solar System, with secondary effects of K loss during accretionary growth and magma ocean degassing.

^1,2Litasov, K.D.,³Badyukov, D.D.
Geochemistry International 57, 912-922 Link to Article [DOI: 10.1134/S001670291908007X]
¹Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, prosp. Akademika Koptyuga 3, Novosibirsk, 630090, Russian Federation
²Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russian Federation
³Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, ul. Kosygina 19, Moscow, 119991, Russian Federation

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^1,2Manfred Vogt,¹Jens Hopp,³Hans-Peter Gail,^4,5Ulrich Otta,¹Mario Trieloff
Geochimica et Cosmochimcia Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.08.016]
¹Institut für Geowissenschaften, Klaus-Tschira-Labor für Kosmochemie, Universität Heidelberg, INF 236, 69120 Heidelberg, Germany
²Institut für Nukleare Entsorgung (INE), Karlsruher Institut of Technologie (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
³Institut für Theoretische Astrophysik, Zentrum für Astronomie, Universität Heidelberg, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany
⁴MTA Atomki, Bem tér 18/c, 4026 Debrecen, Hungary
⁵Max-Planck-Institut für Chemie, Hahn-Meitner-Weg 1, 55128 Mainz, Germany
Copyright Elsevier

Earth’s mantle contains Ne resembling the solar wind implanted Ne-B component in meteorites (²⁰Ne/²²Ne_Ne-B: ∼12.7). The atmosphere, instead, displays a “planetary” signature (²⁰Ne/²²Ne_Atm: 9.80). We explore the parameter space of a model that explains these isotopic variations by the contribution of late accreting volatile-rich material (e.g., carbonaceous chondrite-like) to Earth́s atmosphere, while Earth́s mantle incorporated solar wind type Ne that was previously implanted into part of the accreting material.

Analyses of the present-day terrestrial influx mass distributions show two major peaks at large bodies >1km and small ∼200 µm dust particles. The latter dominate the influx of the surface implanted Ne-B component. Ne measurements of small particles define a maximum surface flux (neon reaching the terrestrial surface) peaking at 9 µm, while larger micrometeorites experience ablation losses and isotopic fractionation upon atmospheric entry. Using these data, we reconstruct the unfractionated Ne-B upper atmosphere flux which peaks at ∼75 µm. As the extraterrestrial influx mass distribution between larger bodies and debris dust is governed by equilibrium due to collisions and fragmentation, it is an approximation of the early solar system (after nebula dissipation), where the mass distribution was similar but total fluxes were higher.

Contributions of Ne-B by small dust and planetary Ne-A from larger bodies strongly depend on formation region. Originating around the 1 AU region, early accretionary fluxes were dominated by Ne-B as large bodies likely contained only negligible amounts of Ne-A. Ne-B will be ultimately delivered to the earliest protoatmosphere by impact or thermal degassing and a significant fraction of Ne-B can enter the Earth́s interior via dissolution into a magma ocean before the Moon-forming impact. After the Moon-forming impact, Ne-B reenters the atmosphere by mantle degassing and a later meteoritic contribution modified the atmospheric composition. This meteoritic component was likely dominated by Ne-A, as the only remaining planetesimals at that time were in the asteroid belt or beyond, leading to preferential contributions of carbonaceous chondrite-type material.

In our model we take into account possible variations of several parameters, e.g. the isotopic composition of the late accretion (i.e., ²⁰Ne/²²Ne: 5.2–9.2). For example, a ²⁰Ne/²²Ne ratio of 8.2 (Ne-A composition) would imply ∼2% mass increase of Earth from CC-type material after the Moon-forming impact, and would require that todaýs atmosphere (²⁰Ne/²²Ne=9.8) formed by roughly equal mixing of late accreted Ne-A and mantle Ne-B. The amount of Ne-B added from the mantle implies a certain degree of mantle degassing (in this case 82–96%, depending on todaýs mantle neon inventory) and constrains two further parameters: the fraction of solar wind irradiated material delivered to Earth before the Moon-forming impact and the magma ocean depth. The latter determines the fraction of Ne-B dissolved from a protoatmosphere. For example, magma ocean depths between 500 and 2900 km allow 4–15% dissolution of the protoatmospheric Ne-B inventory, and would require only less than 10% of irradiated accreting material. Only unreasonable magma ocean depths lower than 200 km require several ten percent of irradiated material.

¹Yakovlev, O.I., ¹Shornikov, S.I.
Geochemistry International 57, 851-864 Link to Article [DOI: 10.1134/S0016702919080123]
¹Vernadsky Institute of Geochemistry and Analytical Chemistry (GEOKhI), Russian Academy of Sciences, Moscow, 119991, Russian Federation

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¹El Abassi, D.,¹Faiz, B.,^2,3Ibhi, A.,¹Aboudaoud, I.
Journal of Environmental and Engineering Geophysics 24, 277-285 Link to Article [DOI: 10.2113/JEEG24.2.277]
¹Laboratory of Metrology and Information Processing, Faculty of Sciences, Ibn Zohr University, Agadir, Morocco
²Laboratory of Petrology, Metallogeny and Meteorites, Department of Geology, Ibn Zohr University, Agadir, Morocco
³University Museum of Meteorites, Ibn Zohr University Complex, Agadir, Morocco

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¹Shornikov, S.I.
Geochemistry International 57, 865-872 Link to Article [DOI: 10.1134/S001670291908010X]
¹Vernadsky Institute of Geochemistry and Analytical Chemistry (GEOKhI), Russian Academy of Sciences, Moscow, 119991, Russian Federation

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¹A.J.King,^1,2H.C.Bates,³D.Krietsch,³H.Busemann,⁴P.L.Clay,¹P.F.Schofield,¹S.S.Russell
Geochemistry (Chemie der Erde) (In Press) Link to Article [https://doi.org/10.1016/j.chemer.2019.08.003]
¹Planetary Materials Group, Department of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD, UK
²Atmospheric, Oceanic and Planetary Physics Department, Clarendon Laboratory, University of Oxford, Sherrington Road, Oxford, OX1 3P, UK
³Institute of Geochemistry and Petrology, ETH Zürich, Clausiusstrasse 25, 8092 Zürich, Switzerland
⁴School of Earth and Environmental Sciences, University of Manchester, Manchester, M13 9PL, UK
Copyright Elsevier

We report new mineralogical, petrographic and noble gas analyses of the carbonaceous chondrite meteorites Y-82162 (C1/2_ung), Y-980115 (CI1), Y-86029 (CI1), Y-86720 (C2_ung), Y-86789 (C2_ung), and B-7904 (C2_ung). Combining our results with literature data we show that these meteorites experienced varying degrees of aqueous alteration followed by short-lived thermal metamorphism at temperatures of >500 °C. These meteorites have similar mineralogy, textures and chemical characteristics suggesting that they are genetically related, and we strongly support the conclusion of Ikeda (1992) that they form a distinct group, the CYs (“Yamato-type”). The CY chondrites have the heaviest oxygen isotopic compositions (δ¹⁷O ˜12 ‰, δ¹⁸O ˜22 ‰) of any meteorite group, high abundances of Fe-sulphides (˜10 ‒ 30 vol%) and phosphates, and contain large grains of periclase and unusual objects of secondary minerals not reported in other carbonaceous chondrites. These features cannot be attributed to parent body processes alone, and indicate that the CYs had a different starting mineralogy and/or alteration history to other chondrite groups, perhaps because they formed in a different region of the protoplanetary disk. The short cosmic-ray exposure ages (≤1.3 Ma) of the CY chondrites suggest that they are derived from a near-Earth source, with recent observations by the Hayabusa2 spacecraft highlighting a possible link to the rubble-pile asteroid Ryugu.

^1,2R.Jaumann et al. (>10)
Science 365, 817-820 Link to Article [DOI: 10.1126/science.aaw8627]
¹German Aerospace Center (DLR), Institute of Planetary Research, Berlin, Germany.
²Free University of Berlin, Institute of Geosciences, Berlin, Germany.
Reprinted with permission from AAAS

The near-Earth asteroid (162173) Ryugu is a 900-m-diameter dark object expected to contain primordial material from the solar nebula. The Mobile Asteroid Surface Scout (MASCOT) landed on Ryugu’s surface on 3 October 2018. We present images from the MASCOT camera (MASCam) taken during the descent and while on the surface. The surface is covered by decimeter- to meter-sized rocks, with no deposits of fine-grained material. Rocks appear either bright, with smooth faces and sharp edges, or dark, with a cauliflower-like, crumbly surface. Close-up images of a rock of the latter type reveal a dark matrix with small, bright, spectrally different inclusions, implying that it did not experience extensive aqueous alteration. The inclusions appear similar to those in carbonaceous chondrite meteorites.

^1,2De Carvalho, W.P.,^1,2Rios, D.C.,³Zucolotto, M.E.,^1,2,4Conceição, H.,⁵Tosi, A.A.,²Gomes, M.M.
Pesquisas em Geosciencias 45, e0666 Link to Article [DOI: 10.22456/1807-9806.88647]
¹Universidade Federal da Bahia, Rua Barão de Jeremoabo, 147, Salvador, BA CEP 40.170-115, Brazil
²Grupo de Pesquisa Laboratório de Petrologia Aplicada à Pesquisa Mineral, Rua Barão de Jeremoabo, 147, Salvador, BA CEP 40.170-115, Brazil
³Museu Naciona, Universidade Federal do Rio de Janeiro, Quinta da Boa Vista. São Cristóvão, Rio de Janeiro, RJ CEP 20940-040, Brazil
⁴Universidade Federal de Sergipe, Av. Marechal Rondon, Jardim Rosa Elze, São Cristóvão, SE CEP 49.100-000, Brazil
⁵Labsonda, Instituto de Geociências, Universidade Federal do Rio de Janeiro, Av. Athos da Silveira Ramos, 274, Cidade Universitária, Ilha do Fundão, Rio de Janeiro, RJ CEP 21044-020, Brazil

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