Rapid effects of terrestrial alteration on highly siderophile elements in the Sutter’s Mill meteorite

1Richard J. Walker, 2Qing‐Zhu Yin, 3,4Philipp R. Heck
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13102]
1Department of Geology, University of Maryland, , Maryland, USA
2Department of Earth and Planetary Sciences, University of California at Davis, Davis, California, USA
3Robert A. Pritzker Center for Meteoritics and Polar Studies, Field Museum of Natural History, Chicago, Illinois, USA
4Department of the Geophysical Sciences, Chicago Center for Cosmochemistry, University of Chicago, Chicago, Illinois, USA
Published by arrangement with John Wiley & Sons

The 187Re‐187Os isotopic systematics of many bulk chondrites plot well beyond analytical uncertainties of a primordial isochron. Limited variations in 187Os/188Os, coupled with large variations in Re/Os ratios among chondrites, suggest that this apparently open‐system behavior is a result of the comparatively recent gain or loss of Re and/or Os. In order to assess whether or not rapid alteration in the terrestrial environment could be responsible for open‐system behavior in chondrites, four pieces of the Sutter’s Mill meteorite were examined for Os isotopic systematics and abundances of highly siderophile elements. Pieces SM1 and SM2 were collected prior to a rain event, within 2 days of the fall. Pieces SM51 and SM53 were collected after a rain event. There are significant but minor relative and absolute variations in the abundances of the highly siderophile elements, as well as 187Os/188Os among the four pieces. Rhenium‐Os isotopic data for SM1 and SM2 plot within analytical uncertainties of a primordial isochron, while powders made from SM51 and SM53 do not. These results suggest that interactions with rain caused some redistribution of Re, and to a lesser extent Os, within small pieces of the meteorite. Thus, Re‐Os isotopic systematics of <dm‐size pieces of chondrites must be considered susceptible to modification after only a short time on the surface, where exposed to rain.

Depositional processes of impactites from the YAX‐1 drill core in the Chicxulub impact structure inferred from vertical profiles of PDF orientations and grain size distributions of shocked quartz

1Yu Chang, 2Kazuhisa Goto, 1Yasuhito Sekine, 1Eiichi Tajika
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13082]
1Department of Earth and Planetary Science, The University of Tokyo, , Tokyo, Japan
2International Research Institute of Disaster Science, Tohoku University, , Sendai, Japan
Published by arrangement with John Wiley & Sons

Core samples from the Chicxulub impact structure provide insights into the formation processes of a shallow‐marine‐target, complex crater. Although previous studies investigated the impactites (generally suevitic and polymict breccias) of the Yaxcopoil‐1 (YAX‐1) drill core in the Chicxulub impact structure, the interpretation of its deposition remains controversial. Here, we analyze planar deformation features (PDFs), grain size, and abundance of shocked quartz throughout the YAX‐1 impactite sequence (794–895 m in depth). PDF orientations of most quartz grains in YAX‐1 impactites show a distribution of both low angles ({10urn:x-wiley:10869379:media:maps13082:maps13082-math-00034}, {10urn:x-wiley:10869379:media:maps13082:maps13082-math-00043}, {10urn:x-wiley:10869379:media:maps13082:maps13082-math-00052}) and high angles (orientations higher than 55° to c‐axis), while the lower part of the impactite sequence contains quartz showing only PDF orientations of low angles. High‐abundance, coarse‐grained shocked quartz is found from the lower to middle parts of the impactites, whereas it abruptly changes to low‐abundance, fine‐grained shocked quartz within the upper part. In the uppermost part of the impactites, repeated oscillations in contents of these two components are observed. PDF orientation pattern suggests most of the shocked quartz grains experienced a range of shock pressure, except two samples in the lower part of impactites, which experienced only a high level of shock. We suggest that the base and lower part of the impactite sequence were formed by ejecta curtain and melt surge deposits, respectively. Our results are also consistent with the interpretation that the middle part of the impactite sequence is fallback ejecta from the impact plume. Additionally, we support the contention that massive seawater resurges into the crater occurred during the deposition of the upper and uppermost part of the impactites.

A new type of oxidized and pre-irradiated micrometeorite

1Carole Cordier, 2,3Bastian Baecker, 2,3,4Ulrich Ott, 5Luigi Folco, 2Mario Trieloff
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.04.010]
1Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, IRD, IFSTTAR, ISTerre, 38000 Grenoble, France
2Institut für Geowissenschaften, Klaus-Tschira-Labor für Kosmochemie, Universität Heidelberg, Im Neuenheimer Feld 234-236, 69120 Heidelberg, Germany
3Max-Planck-Institut für Chemie, Hahn-Meitner-Weg 1, 55128 Mainz, Germany
4Magyar Tudományos Akadémia Atommagkutató Intézet, Bem tér 18/c, 4026 Debrecen, Hungary
4Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, 65126 Pisa, Italy
Copyright Elsevier

This paper investigates the mineralogy and noble gas composition of a unique micrometeorite from the Transantarctic Mountains, #45c.29. The magnetite rim and the particle interior with olivine, pyroxene and magnetite relict grains (30 to 250 µm in size) set in a vesicular mesostasis are typical features of coarse-grained, partially melted micrometeorites. Particle #45c.29 stands out from other micrometeorites of this type by the texture of the mesostasis made of abundant plagioclase and augite laths, the remarkably high Ni contents in magnetite and olivine relict grains, and by the similarly high abundance of cosmogenic noble gases (21Necos up to 1.62 x 10-7 cm3 STP/g and 38Ar up to 7.2 x 10-8 cm3 STP/g). The high Ni content of Fa26 olivine relict grains (NiO ∼ 0.65 wt%), the high Ni (NiO ∼ 0.8 wt%) and Ti (TiO2 ∼ 0.3 wt%) contents of magnetite relicts, and the oxygen isotope composition of a sample of the particle (δ18O ∼ 2.3 ‰, δ17O ∼ -1.5 ‰), suggest a parentage with rare equilibrated CK chondrites. Pyroxene and plagioclase are not expected to crystallize during atmospheric entry of micrometeoroids. Their occurrence in #45c.29 may be explained by the Ca-, Al- and Na- rich composition of its precursor – in agreement with the high abundance of plagioclase reported in the matrix of CK chondrites – if combined with a relatively low cooling rate and, therefore, unusual atmospheric entry parameters (velocity/angle) of the micrometeoroid. Given these specific entry parameters, the particle has recorded unique information on mineralogical and textural transformations of micrometeoroids during atmospheric entry, with solid-state oxidation of the olivine relict grains in the igneous rim, and partial melting of relict mineral phases and relict/melt reactions in the particle interior. The cosmogenic 21Ne/22Ne ratio of 0.94 ± 0.02 is incompatible with major production by cosmogenic ray irradiation of a small particle in space. We propose that micrometeorite #45c.29 mostly records an earlier irradiation stage, in a meteoroid or more likely near the surface (< 20 cm in depth) of an asteroid. In contrast, most of the other unmelted and scoriaceous micrometeorites analyzed for noble gases – if coming from asteroidal sources of the Main Belt – seem to have sampled deeper parts of their parent body, where they were shielded from cosmic rays and from where they were excavated during high-energy disruptive processes.

Aggregation in particle rich environments: a textural study of examples from volcanic eruptions, meteorite impacts, and fluidized bed processing

1Sebastian B. Mueller, 1Ulrich Kueppers, 2,3Matthew S. Huber, 1Kai-Uwe Hess, 4Gisela Poesges, 5Bernhard Ruthensteiner, 1Donald B. Dingwell
Bulletin of Volcanology 80, 32 Link to Article [DOI
1Ludwig-Maximilians-Universität München LMU, Munich, Germany
2University of the Free State Bloemfontein, South Africa
3Vrije Universiteit Brussel, Brussels, Belgium
4Ries Krater Museum Nördlingen, Nördlingen, Germany
5Zoologische Staatssammlung München, Munich, Germany

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Surface Composition of (99942) Apophis

1,8Vishnu Reddy, 2,8Juan A. Sanchez, 3Roberto Furfaro, 4,8Richard P. Binzel, 5,8Thomas H. Burbine, 2,8Lucille Le Corre, 2,8Paul S. Hardersen, 6William F. Bottke, 7Marina Brozovic
The Astronomical Journal 155, 140 Link to Article [https://doi.org/10.3847/1538-3881/aaaa1c]
1Lunar and Planetary Laboratory, University of Arizona, 1629 E University Boulevard, Tucson, AZ 85721-0092, USA
2Planetary Science Institute, 1700 East Fort Lowell Road, Tucson, AZ 85719, USA
3Systems and Industrial Engineering, University of Arizona, 1127 E. James E. Rogers Way, Tucson, AZ 85721-0020, USA
4Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
5Department of Astronomy, Mount Holyoke College, South Hadley, MA 01075, USA
6Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, CO 80302, USA
7Jet Propulsion Laboratory, 4800 Oak Grove Drive, Mail Stop 301-120, Pasadena, CA 91109-8099, USA
8Visiting Astronomer at the Infrared Telescope Facility, which is operated by the University of Hawaii under contract NNH14CK55B with the National Aeronautics and Space Administration.

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Evidence for a sulfur-undersaturated lunar interior from the solubility of sulfur in lunar melts and sulfide-silicate partitioning of siderophile elements

1,2E.S. Steenstra, 1A.X. Seegers, 1J. Eising, 1B.G.J. Tomassen, 1F.P.F. Webers, 3J. Berndt, 3S. Klemme, 4S. Matveev, 1W. van Westrenen
Geochmica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.04.008]
1Faculty of Science, Vrije Universiteit, Amsterdam, The Netherlands
2The Geophysical Laboratory, Carnegie Institution of Science, Washington D. C., United States
3Institute of Mineralogy, University of Münster, Germany
4Faculty of Geosciences, Utrecht University, The Netherlands
Copyright Elsevier

Sulfur concentrations at sulfide saturation (SCSS) were determined for a range of low- to high-Ti lunar melt compositions (synthetic equivalents of Apollo 14 black and yellow glass, Apollo 15 green glass, Apollo 17 orange glass and a late-stage lunar magma ocean melt, containing between 0.2 and 25 wt.% TiO2) as a function of pressure (1 – 2.5 GPa) and temperature (1683 – 1883 K). For the same experiments, sulfide-silicate partition coefficients were derived for elements V, Cr, Mn, Co, Cu, Zn, Ga, Ge, As, Se, Mo, Sn, Sb, Te, W and Pb. The SCSS is a strong function of silicate melt composition, most notably FeO content. An increase in temperature increases the SCSS and an increase in pressure decreases the SCSS, both in agreement with previous work on terrestrial, lunar and martian compositions. Previously reported SCSS values for high-FeO melts were combined with the experimental data reported here to obtain a new predictive equation to calculate the SCSS for high-FeO lunar melt compositions. Calculated SCSS values, combined with previously estimated S contents of lunar low-Ti basalts and primitive pyroclastic glasses, suggest their source regions were not sulfide saturated. Even when correcting for the currently inferred maximum extent of S degassing during or after eruption, sample S abundances are still >700 ppm lower than the calculated SCSS values for these compositions. To achieve sulfide saturation in the source regions of low-Ti basalts and lunar pyroclastic glasses, the extent of degassing of S in lunar magma would have to be orders of magnitude higher than currently thought, inconsistent with S isotopic and core-to-rim S diffusion profile data. The only lunar samples that could have experienced sulfide saturation are some of the more evolved A17 high-Ti basalts, if sulfides are Ni- and/or Cu rich.

Sulfide saturation in the source regions of lunar melts is also inconsistent with the sulfide-silicate partitioning systematics of Ni, Co and Cu. Segregation of significant quantities of (non)-stoichiometric sulfides during fractional crystallization would result in far larger depletions of Ni, Co and Cu than observed, whereas trends in their abundances are more likely explained by olivine fractionation. The sulfide exhaustion of the lunar magma source regions agrees with previously proposed low S abundances in the lunar core and mantle, and by extension with relatively minor degassing of S during the Moon-forming event. Our results support the hypothesis that refractory chalcophile and highly siderophile element systematics of low-Ti basalts and pyroclastic glasses reflect the geochemical characteristics of their source regions, instead of indicating the presence of residual sulfides in the lunar interior.

New clues from Earth’s most elusive impact crater: Evidence of reidite in Australasian tektites from Thailand

1Aaron J. Cavosie, 1Nicholas E. Timms, 2Timmons M. Erickson, 3,4Christian Koeberl
Geology 46, 203-206 Link to Article [DOI: https://doi.org/10.1130/G39711.1]
1The Institute for Geoscience Research (TIGeR), Department of Applied Geology, Curtin University, Perth, WA 6102, Australia
2Lunar and Planetary Institute, Universities Space Research Association, Houston, Texas 77058, USA
3Natural History Museum, 1010 Vienna, Austria
4Department of Lithospheric Research, University of Vienna, 1090 Vienna, Austria

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