CV chondrites: More than one parent body

Earth and Planetary Science 547, 116467 Link to Article []
1CNRS, Aix Marseille Univ, IRD, INRAE, CEREGE, Aix-en-Provence, France
2Institut de Planétologie et d’Astrophysique de Grenoble, Université Grenoble Alpes, CNRS CNES, 38000 Grenoble, France
Copyright Elsevier

CV chondrites are one of the most studied group of carbonaceous chondrites. Based on a number of mineralogical features, they have been divided into three sub-groups: CVOxA, CVOxB, and CVRed. These sub-groups are classically interpreted as coming from a single parent body, with a common protolith affected by significant parent body fluid-assisted metasomatism occurring at different temperatures and/or redox conditions. In this work, we studied a set of 53 CV chondrites. We classified them into the three sub-groups, measured their apparent chondrule sizes and their matrix modal abundance. We measured the triple oxygen isotopic composition for 17 of them. The distributions of chondrule size and matrix abundances in CVOxA and CVOxB cannot be statistically distinguished. Conversely, CVRed and CVOx have distinct distributions. These two robust and simple petrographic indicators combined with the previous knowledge of the peak metamorphic temperatures experienced by these meteorites show that CVOx and CVRed originate from two distinct parent bodies. On the other hand, CVOxA and CVOxB likely originate from the same parent body, with CVOxA representing deeper, more metamorphosed levels. For clarification of the chondrite classification scheme, in which one group should ultimately represent a single parent body, we propose to divide the CV group into two proper groups (and not subgroups as in the current scheme), keeping the names CVRed and CVOx. These two groups can be readily separated by estimating the average nickel content of their sulfides.

Constraining the Evolutionary History of the Moon and the Inner Solar System: A Case for New Returned Lunar Samples

1Romain Tartèse,2,3Mahesh Anand,4Jérôme Gattacceca,1Katherine H. Joy,2James I. Mortimer,1John F. Pernet-Fisher,3Sara Russell,5Joshua F. Snape,6Benjamin P. Weiss
Space Science Reviews 215, 54 Link to Article [DOI]
1Department of Earth and Environmental Sciences, The University of Manchester, Manchester, M13 9PL, UK
2Planetary and Space Sciences, School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
3Department of Earth Sciences, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK
4CNRS, Aix-Marseille Univ, IRD, Coll France, INRA, CEREGE, Aix-en-Provence, France
5Faculty of Sciences, Department of Earth Sciences, Vrije Universiteit, Amsterdam, The Netherlands
6Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA

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Organic Matter in the Solar System—Implications for Future on-Site and Sample Return Missions

1Zita Martins,2Queenie Hoi Shan Chan,3Lydie Bonal,4Ashley King,5Hikaru Yabuta
Space Science Reviews 216, 54 Link to Article [DOI]
1Centro de Química Estrutural, Departamento de Engenharia Química, Instituto Superior Técnico, Universidade de Lisboa, Avenida Rovisco Pais 1, 1049-001, Lisboa, Portugal
2Planetary and Space Sciences, School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
3Institut de Planétologie et d’Astrophysique de Grenoble, Univ. Grenoble Alpes, CNRS, CNES, 38000, Grenoble, France
4The Natural History Museum, Cromwell Road, London, SW7 5BD, UK
5Department of Earth and Planetary Systems Science, Hiroshima University, 1-3-1 Kagamiyama, Hiroshima, 739-8526, Japan

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Back‐transformation mechanisms of ringwoodite and majorite in an ordinary chondrite

1Kanta Fukimoto,1Masaaki Miyahara,2Takeshi Sakai,2Hiroaki Ohfuji,3Naotaka Tomioka,4Yu Kodama,5Eiji Ohtani,6,7Akira Yamaguchi
Meteoritics & Planetary Science (in Press) Link to Article []
1Graduate School of Advanced Science and Engineering, Hiroshima University, Higashi‐Hiroshima, 739‐8526 Japan
2Geodynamics Research Center, Ehime University, Matsuyama, 790‐8577 Japan
3Kochi Institute for Core Sample Research, Japan Agency for Marine‐Earth Science and Technology (JAMSTEC), Nankoku, Kochi, 783‐8502 Japan
4Marine Works Japan, Nankoku, Kochi, 783‐8502 Japan
5Department of Earth Sciences, Graduate School of Science, Tohoku University, Sendai, 980‐8578 Japan
6National Institute of Polar Research, Tokyo, 190‐8518 Japan
7Department of Polar Science, School of Multidisciplinary Science, SOKENDAI (The Graduate University for Advanced Studies), Tokyo, 190‐8518 Japan
Published by arrangement with John Wiley & Son

We investigated the back‐transformation mechanisms of ringwoodite and majorite occurring in a shock‐melt vein (SMV) of the Yamato 75267 H6 ordinary chondrite during atmospheric entry heating. Ringwoodite and majorite in the shock melt near the fusion crust have back‐transformed into olivine and enstatite, respectively. Ringwoodite (Fa~18) occurs in the SMV as a fine‐grained polycrystalline assemblage. Approaching the fusion crust, fine‐grained polycrystalline olivine becomes dominant instead of ringwoodite. The back‐transformation from ringwoodite to olivine proceeds by incoherent nucleation and by an interface‐controlled growth mechanism: nucleation occurs on the grain boundaries of ringwoodite, and subsequently olivine grains grow. Majorite (Fs16–17En82–83Wo1) occurs in the SMV as a fine‐grained polycrystalline assemblage. Approaching the fusion crust, the majorite grains become vitrified. Approaching the fusion crust even more, clino/orthoenstatite grains occur in the vitrified majorite. The back‐transformation from majorite to enstatite is initiated by the vitrification, and growth continues by the subsequent nucleation in the vitrified majorite.

Potassium isotope systematics of the LL4 chondrite Hamlet: Implications for chondrule formation and alteration

1,2Piers Koefoed,1,3Olga Pravdivtseva,1,2Heng Chen,4Carina Gerritzen,5Maxwell M. Thiemens,1,2Kun Wang
Meteoritics & Planetary Science (in Press) Link to Article []
1McDonnell Center for the Space Sciences, Washington University in St. Louis, St. Louis, Missouri, 63130 USA
2Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, Missouri, 63130 USA
3Department of Physics, Washington University in St. Louis, St. Louis, Missouri, 63130 USA
4Institut für Mineralogie und Geologie, Universität zu Köln, Köln, Germany
5Laboratoire G‐Time, CP 160/02, Université Libre de Bruxelles, Av. F. Roosevelt 50, Bruxelles, Belgium

Published by arrangement with John Wiley & Sons

Here, we apply recently developed high‐precision K isotope analyses to individual components of the LL4 chondrite Hamlet in order to investigate key processes which occurred during chondrite formation. The K isotopic compositions of all Hamlet chondrules range from −1.36‰ to −0.24‰ δ41K while the matrix and bulk samples show ranges of −0.89‰ to −0.80‰ and −0.86‰ to −1.08‰ δ41K, respectively. This range of δ41K values is significantly less than what was seen by in situ K isotopic analysis of Semarkona and Bishunpur chondrules, a likely effect of the different chondrite petrologic types, analytical artifacts in the SIMS analyses, and chondrule rim effects. Strong evidence for secondary parent‐body alteration effects within Hamlet suggests its K fractionation and distribution are dominantly controlled by these processes. Interestingly, the strong correlation between δ41K and chondrule mass suggests that chondrule size played a significant role in the K isotopic distribution within Hamlet. This trend is likely a result of either inherited initial differences in the chondrule K isotopic ratios which were not completely overprinted or mechanisms involved in the metamorphism processes creating variations. This K isotope correlation with chondrule mass could also be suggestive of chondrule‐forming nebular processes; nevertheless, it is currently unable to definitively favor any specific model. The K isotopic similarities between Hamlet and bulk ordinary chondrites suggest that all LL chondrites, if not all ordinary chondrites, may have formed via the same processes. Nevertheless, analysis of more pristine chondrules from chondrites of lower metamorphic grade is required to further assess any nebular processes of chondrule formation.

Partial core vaporization during Giant Impacts inferred from the entropy and the critical point of iron

1Zhi Li,1,2Razvan Caracas,1François Soubiran
Earth and Planetary Science Letters 547, 116463 Link to Article []
1CNRS, Ecole Normale Supérieure de Lyon, Laboratoire de Géologie de Lyon UMR 5276, Centre Blaise Pascal, 46 allée d’Italie, 69364 Lyon, France
2The Center for Earth Evolution and Dynamics (CEED), University of Oslo, Oslo, Norway
Copyright Elsevier

Giant impacts are disruptive events occurring in the early stages of planetary evolution. They may result in the formation of a protolunar disk or of a synestia. A central planet and one or several moons condense upon cooling bearing the chemical signature of the silicate mantles of the initial bodies; the iron cores may partly vaporize, fragment and/or merge. Here we determine from ab initio simulations the critical point of iron in the temperature range of 9000-9350 K, and the density range of 1.85-2.40 g/cm3, corresponding to a pressure range of 4-7 kbars. This implies that the iron core of the proto-Earth may become supercritical after giant impacts and during the condensation and cooling of the protolunar disk. We show that the iron core of Theia partially vaporized during the Giant Impact. Part of this vapor may have remained in the disk, to eventually participate in the Moon’s small core. Similarly, during the late veneer a large fraction of the planetesimals have their cores undergoing partial vaporization. This would help mixing the highly siderophile elements into magma ponds or oceans.

Hydrothermal alteration associated with the Chicxulub impact crater upper peak-ring breccias

Earth and Planetary Science Letters 547,116425 Link to Article []
1Department of Earth Sciences, Institute for Earth and Space Exploration, The University of Western Ontario, ON, N6A 3K7, Canada
2Lunar and Planetary Institute, Universities Space Research Association, Houston, TX, 77058 United States of America
Copyright Elsevier

The 66 Ma, ∼180 km Chicxulub impact structure in the northern Yucatán peninsula and southern Gulf of Mexico is the best-preserved large impact crater on Earth with a well-developed peak ring. The most recent drilling campaign took place offshore during the joint International Ocean Discovery Program – International Continental Scientific Drilling Program (IODP–ICDP) Expedition 364 at site M0077A (21.45°N, 89.95°W) and recovered ∼830 m of continuous core. Initial examination revealed that the peak-ring comprises four main lithological units (from the base upwards): crystalline basement granitoid rocks (Unit 4); a thin layer of impact melt rocks (Units 3A and B); melt-bearing breccias (Units 2A–C); and post-impact sedimentary rocks (Unit 1). Preliminary analysis of the drill core indicated that hydrothermal alteration has affected all lithologies and is especially pervasive in the melt-bearing breccias of Unit 2 (721.6 to 617.33 meters below sea floor, mbsf). Here we present the first detailed investigation of hydrothermal alteration within the melt-bearing breccias. Alteration phases are predominantly Fe-Mg clay minerals, zeolites, alkali feldspars, calcite and minor sulfides, sulfates, opal and Fe-Ti oxides. Alteration is especially intense proximal to lithologic contacts, particularly at the base of subunit 2B where there is an abrupt increase in host rock porosity ∼30 m above the impact melt rocks. The pervasiveness of clay minerals and zeolites is attributed to the high amounts of devitrified silicate glass throughout Unit 2. The phases preserved here are consistent with the findings of previous hydrothermal studies in other areas of the Chicxulub structure, and suggest an evolving water-rock system that was alkaline-saline, comparable to seawater-volcanic glass alteration.

Fumarolic-like activity on carbonaceous chondrite parent body

1Clément Ganino,2,3Guy Libourel
Science Advances 6, eabb1166 Link to Articles [DOI: 10.1126/sciadv.abb1166]
1Université Côte d’Azur, OCA, CNRS, IRD, Géoazur, 250 rue Albert Einstein, Sophia-Antipolis, 06560 Valbonne, France.
2Université Côte d’Azur, OCA, CNRS, Lagrange, Boulevard de l’Observatoire, CS 34229, 06304 Nice Cedex 4, France.
3Hawai’i Institute of Geophysics and Planetology, School of Ocean, Earth Science and Technology, University of Hawai’i at Mānoa, Honolulu, HI i 96821, USA.

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Exploring the Bimodal Solar System via Sample Return from the Main Asteroid Belt: The Case for Revisiting Ceres

1Burbine, T.H.,2Greenwood, R.C.
Space Science Reviews 216, 59 Link to Article [DOI: 10.1007/s11214-020-00671-0]
1Department of Astronomy, Mount Holyoke College, South Hadley, MA 01075, United States
2Planetary and Space Sciences, School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, United Kingdom

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The Non-carbonaceous–Carbonaceous Meteorite Dichotomy

1Kleine, T.,1Budde, G.,1Burkhardt, C.,2Kruijer, T.S.,1Worsham, E.A.,3Morbidelli, A.,
4Nimmo, F.
Space Science Reviews 216, 55 Link to Article [DOI: 10.1007/s11214-020-00675-w]
1Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, Münster, 48149, Germany
2Lawrence Livermore National Laboratory, Nuclear and Chemical Sciences Division, 7000 East Avenue, Livermore, CA 94550, United States
3Observatoire de la Cote d’Azur, CS 34229, Nice Cedex 4, 06304, France
4Department of Earth and Planetary Sciences, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, United States

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