¹Andrea Patzer, ²Dominik C. Hezel, ²Verena Bendel, ²Andreas Pack
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13084]
¹Geowissenschaftliches Zentrum, Universität Göttingen, , Göttingen, Germany
²Institut für Geologie und Mineralogie, Universität zu Köln, , Köln, Germany
Published by arrangement with John Wiley & Sons

We performed a LA‐ICP‐MS study of refractory lithophile trace elements in 32 individual objects selected from a single section of the reduced CV3 chondrite Leoville. Ingredients sampled include ferromagnesian type I and II chondrules, Al‐rich chondrules (ARCs), calcium‐aluminum‐rich inclusions (CAIs), a single amoeboid olivine aggregate (AOA), and matrix. The majority of rare earth element (REE) signatures identified are either of the category “group II” or they are relatively flat, i.e., more or less unfractionated. Data derived for bulk Leoville exhibit characteristics of the group II pattern. The bulk REE inventory is essentially governed by those of CAIs (group II), ARCs (flat or group II), type I chondrules (about 90% flat, 10% group II), and matrix (group II). Leoville matrix also shows a superimposed positive Eu anomaly. The excess in Eu is possibly due to terrestrial weathering. The group II pattern, however, testifies to volatility‐controlled fractional condensation from a residual gas of solar composition at still relatively high temperature. In principle, this signature (group II) is omnipresent in all types of constituents, suggesting that the original REE carrier of all components was CAI‐like dust. In addition, single‐element anomalies occasionally superimposing the group II signature reveal specific changes in redox conditions. We also determined the bulk chemical composition of all objects studied. For Mg/Si, Mg/Fe, and Al/Ca, Leoville’s main ingredients—type I chondrules and matrix—display a complementary relationship. Both components probably formed successively in the same source region.

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.

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.

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.