¹Knut Metzler
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13091]
¹Institut für Planetologie, Westfälische Wilhelms‐Universität Münster, , Münster, Germany
Published by arrangement with John Wiley & Sons

In order to characterize the relation between apparent chondrule sizes (2D) and true chondrule sizes (3D), three ordinary chondrites of the H, L, and LL group have been analyzed. The diameters of a large number of chondrule cut faces in thin sections (2D; n = 2037) and of separated chondrules from the same meteorites (3D: n = 2061) have been measured. The obtained 2D/3D mean chondrule sizes (μm) for the H, L, and LL chondrite are 450/490, 500/610, and 690/830; the corresponding median values (μm) are 370/420, 450/530, and 580/730. The data show that there is a cutoff for small chondrule sizes in each sample. Possibly characteristic minimum sizes exist for the various groups, increasing in the (3D) sequence H (~90 μm) <L (~180 μm) <LL (~240 μm). No systematics were found for the maximum chondrule sizes. The investigated samples show very similar chondrule volume (mass) distributions relative to the mode (peak) of their size‐frequency distributions. About 2.6–2.9% and 97.1–97.4% of the total chondrule volume (mass) is present in chondrule sizes smaller and larger than the mode, respectively. It was found that 2D sectioning consistently results in a shift of the true 3D size‐frequency distributions toward smaller sizes. This effect leads to the underestimation of the values for (1) the true mean chondrule size by 8–18%, (2) the true chondrule median value by 12–21%, and (3) the true mode value of the size‐frequency distributions by 12–17% (50 μm binning). This is the opposite of what popular 2D/3D correction models predict (e.g., Eisenhour 1996).

¹Alexander Hubbard, ¹Mordecai‐Mark Mac Low, ²Denton S. Ebel
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13101]
¹Department of Astrophysics, American Museum of Natural History, New York, New York, USA
²Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, USA
Published by arrangement with John Wiley & Sons

Meteoritical and astrophysical models of planet formation make contradictory predictions for dust concentration factors in chondrule‐forming regions of the solar nebula. Meteoritical and cosmochemical models strongly suggest that chondrules, a key component of the meteoritical record, formed in regions with solids‐to‐gas mass ratios orders above the solar nebula average. However, models of dust grain dynamics in protoplanetary disks struggle to surpass concentration factors of a few except during very short‐lived stages in a dust grain’s life. Worse, those models do not predict significant concentration factors for dust grains the size of chondrule precursors. We briefly develop the difficulty in concentrating dust particles in the context of nebular chondrule formation and show that the disagreement is sufficiently stark that cosmochemists should explore ideas that might revise the concentration factor requirements downward.

¹Rebecca Winkler, ²Robert Luther, ¹Michael H. Poelchau, ²Kai Wünnemann, ¹Thomas Kenkmann
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13080]
¹Institute of Earth and Environmental Sciences—Geology, Albert‐Ludwigs‐Universität Freiburg (ALU), , Freiburg, Germany
²Museum für Naturkunde Berlin, Leibniz Institute for Evolution and Biodiversity Science, , Berlin, Germany
Published by arrangement with John Wiley and Sons

Two impact cratering experiments on nonporous rock targets were carried out to determine the influence of target composition on the structural mechanisms of subsurface deformation. Projectiles of 2.5 mm diameter were accelerated to ~5 km s⁻¹and impacted onto blocks of marble or quartzite. Subsurface deformation was mapped and analyzed on the microscale using thin sections of the bisected craters. Additionally, both experiments were modeled and the calculated strain zones underneath the craters were compared to experimental deformation features. Microanalysis shows that the formation of radial, tensile, and intragranular cracks is a common response of both nonporous materials to impact cratering. In the quartzite target, the subsurface damage is additionally characterized by highly localized deformation along shear bands with intense grain comminution, surrounded by damage zones. In contrast, the marble target shows closely spaced calcite twinning and cleavage activation. Crater diameter and depth as well as the damage lens underneath the crater are unexpectedly smaller in the marble target compared to the quartzite target, which is in contradiction to the marble’s much weaker compressive and tensile strengths. However, numerical models result in craters that are similar in size as well as in strain accumulation at the end of transient crater formation, indicating that current models should still be viewed cautiously when compared to experimental details.

¹J. F. Rapp,²D. S. Draper
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13086]
¹Jacobs JETS, NASA Johnson Space Center, Houston, Texas, USA
²Astromaterials Research Office, EISD, NASA Johnson Space Center, Houston, Texas, USA
Published by arrangement with John Wiley & Sons

We report results of systematic experimental simulation of fractional crystallization of a lunar magma ocean (LMO) with the Lunar Primitive Upper Mantle bulk composition. These results complement prior work that simulated equilibrium crystallization. In contrast to previous numerical models for investigating magma ocean solidification processes and implications, our combined program simulates these processes directly using petrologic experimentation. Our experiments mimic LMO crystallization that is fractional throughout the process, rather than switching from initially equilibrium to fractional crystallization partway through. To do this, we adopted an iterative approach in which the starting material for each run is synthesized using the composition of the melt phase from the prior run. We compare our results to those from long‐standing numerical models of LMO crystallization and show that although some features of those models are broadly reproduced, there are key differences in liquid lines of descent and the cumulate lithologies generated. Our results can be used to estimate the possible thickness of a primordial lunar crust formed from flotation of plagioclase during magma ocean solidification. Our estimate is greater than that from the recent Gravity Recovery and Interior Laboratory (GRAIL) mission, but consistent with the criteria on which the starting bulk composition was originally calculated. It assumes perfectly efficient separation of all plagioclase formed from the crystallizing magma ocean, which is likely not the case. We also demonstrate that a non‐chondritic bulk composition, with respect to trace elements, is not required in order to generate a KREEP (potassium, rare earth elements, and phosphorus) signature from magma ocean crystallization.

^1,2Masahiro Kayama,^3,4Toshimori Sekine,⁵Naotaka Tomioka,⁶Hirotsugu Nishido,³Yukako Kato,⁶Kiyotaka Ninagawa,⁷Takamichi Kobayashi,^8,9Akira Yamaguchi
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13092]
¹Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University, Sendai, Japan
²Creative Interdisciplinary Research Division, Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai, Japan
³Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, Higashi‐Hiroshima, Japan
⁴Center for High Pressure Science and Technology Advanced Research, , Shanghai, China
⁵Kochi Institute for Core Sample Research, Japan Agency for Marine‐Earth Science and Technology, , Nankoku City, Kochi, Japan
⁶Department of Biosphere‐Geosphere Science, Okayama University of Science, , Okayama, Japan
⁷National Institute for Materials Science, , Tsukuba, Ibaraki, Japan
⁸National Institute of Polar Research, Tachikawa, Tokyo, Japan
⁹Department of Polar Science, School of Multidisciplinary Science, SOKENDAI (The Graduate University for Advanced Studies), Hayama, Tokyo, Japan
Published by arrangement with John Wiley & Sons

Cathodoluminescence (CL) analyses were carried out on maskelynite and lingunite in L6 chondrites of Tenham and Yamato‐790729. Under CL microscopy, bright blue emission was observed in Na‐lingunite in the shock veins. Dull blue‐emitting maskelynite is adjacent to the shock veins, and aqua blue luminescent plagioclase lies farther away. CL spectroscopy of the Na‐lingunite showed emission bands centered at ~330, 360–380, and ~590 nm. CL spectra of maskelynite consisted of emission bands at ~330 and ~380 nm. Only an emission band at 420 nm was recognized in crystalline plagioclase. Deconvolution of CL spectra from maskelynite successfully separated the UV–blue emission bands into Gaussian components at 3.88, 3.26, and 2.95 eV. For comparison, we prepared K‐lingunite and experimentally shock‐recovered feldspars at the known shock pressures of 11.1–41.2 GPa to measure CL spectra. Synthetic K‐lingunite has similar UV–blue and characteristic yellow bands at ~550, ~660, ~720, ~750, and ~770 nm. The UV–blue emissions of shock‐recovered feldspars and the diaplectic feldspar glasses show a good correlation between intensity and shock pressure after deconvolution. They may be assigned to pressure‐induced defects in Si and Al octahedra and tetrahedra. The components at 3.88 and 3.26 eV were detectable in the lingunite, both of which may be caused by the defects in Si and Al octahedra, the same as maskelynite. CL of maskelynite and lingunite may be applicable to estimate shock pressure for feldspar‐bearing meteorites, impactites, and samples returned by spacecraft mission, although we need to develop more as a reliable shock barometer.

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.

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
https://doi.org/10.1007/s00445-018-1207-3]
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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