^1,2M. Ebert, ^2,3L. Hecht, ^2,3C. Hamann, ²R. Luther
Meteoritics & Planetary Sciences (in Press) Link to Article [DOI: 10.1111/maps.12809]
¹Institut für Geo- und Umweltnaturwissenschaften, Albert-Ludwigs-Universität Freiburg (ALU), Freiburg, Germany
²Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Museum für Naturkunde (MfN), Berlin, Germany
³Institut für Geologische Wissenschaften, Freie Universität Berlin, Berlin, Germany
Published by arrangement with John Wiley & Sons

This study introduces an experimental approach using direct laser irradiation to simulate the virtually instantaneous melting of target rocks during meteorite impacts. We aim at investigating the melting and mixing processes of projectile (iron meteorite; steel) and target material (sandstone) under idealized conditions. The laser experiments (LE) were able to produce features very similar to those of impactites from meteorite craters and cratering experiments, i.e., formation of lechatelierite, partial to complete melting of sandstone, and injection of projectile droplets into target melts. The target and projectile melts have experienced significant chemical modifications during interaction of these coexisting melts. Emulsion textures, observed within projectile-contaminated target melts, indicate phase separation of silicate melts with different chemical compositions during quenching. Reaction times of 0.6 to 1.4 s could be derived for element partitioning and phase-separation processes by measuring time-depended temperature profiles with a bolometric detector. Our LE allow (i) separate melting at high temperatures to constrain primary melt heterogeneities before mixing of projectile and target, (ii) quantification of element partitioning processes between coexisting projectile and target melts, (iii) determination of cooling rates, and (iv) estimation of reaction times. Moreover, we used a thermodynamic approach to calculate the entropy gain during laser melting. The entropy changes for laser-melting of sandstone and iron meteorite correspond to shock pressures and particle velocities produced during the impact of an iron projectile striking a quartz target at a minimum impact velocity of ~6 km s−1, inducing peak shock pressures of ~100 GPa in the target.

^1,2A. Yamaguchi, ³N. Shirai, ³C. Okamoto, ³M. Ebihara
Meteoritics & Planetary Science (in Press) link to Article [DOI: 10.1111/maps.12821]
¹National Institute of Polar Research, Tachikawa, Tokyo, Japan
²Department of Polar Science, School of Multidisciplinary Science, SOKENDAI (The Graduate University for Advanced Studies), Tokyo, Japan
¹Department of Chemistry, Tokyo Metropolitan University, Hachioji, Tokyo, Japan
Published by arrangement with John Wiley & Sons

We report petrology and geochemistry of an achondrite EET 92023 and compare it with normal and anomalous eucrites. EET 92023 is an unbrecciated achondrite and shows a granular texture mainly composed of low-Ca pyroxene and plagioclase, petrologically similar to normal cumulate eucrites such as Moore County. However, this rock contains a significant amount of kamacite and taenite not common in unbrecciated, crystalline eucrites. EET 92023 contains a significant amount of platinum group elements (PGEs) (ca. 10% of CI), several orders of magnitude higher than those of monomict eucrites. We suggest that the metallic phases carrying PGEs were incorporated by a projectile during or before igneous crystallization and thermal metamorphism. The projectile was likely to be an iron meteorite rather than chondritic materials, as indicated by the lack of olivine and the presence of free silica. Therefore, the oxygen isotopic signature is indigenous, rather than due to contamination of the projectile material with different oxygen isotopic compositions. A significant thermal event involving partial melting and metamorphism after the impact event indicates that EET 92023 records early impact events which took place shortly after the crust formation on a differentiated protoplanet when the crust was still hot.

¹Jian Chen, ²Tiekuang Dong, ^1,3Zhongzhou Ren
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12817]
¹Department of Physics and Key Laboratory of Modern Acoustics, Institute of Acoustics, Nanjing University, Nanjing, China
²Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, CAS, Nanjing, China
³Center of Theoretical Nuclear Physics, National Laboratory of Heavy-Ion Accelerator, Lanzhou, China
Published by arrangement with John Wiley & Sons

A physical model based on the open-source toolkit Geant4 for production rates of cosmogenic nuclei on the lunar surface is proposed and calibrated. The fluxes of proton and neutron beneath the lunar surface are obtained by simulating the physical processes between the cosmic-ray particles and the lunar surface material. By combining the experimental proton cross sections and the a posteriori neutron cross sections, we calculate the production rate depth profiles of long-lived nuclei (10Be, 14C, 26Al, 36Cl, and 53Mn). Through comparing experimental and theoretical data for these nuclei, we find that for all the selected nuclei, experimental and theoretical production rate depth profiles agree well with each other by introducing a single normalization factor. It means that the physical model based on Geant4 can also reproduce the depth profiles of cosmogenic nuclei, and that this model can be used by everyone worldwide. In addition, we predict the production rates of three stable nuclei (21Ne, 22Ne, and 38Ar).

¹I. S. Sanders, ²E. R. D. Scott, ³J. S. Delaney
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12820]
¹Department of Geology, Trinity College, Dublin 2, Ireland
²Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Mānoa, Honolulu, Hawaii, USA
³Department of Geological Sciences, Rutgers University, Piscataway, New Jersey, USA
Published by arrangement with John Wiley & Sons

Ureilite meteorites are abundant, carbon-rich, primitive achondrites made of coarse-grained, equilibrated olivine and pyroxene (usually pigeonite). They probably sample the baked, heterogeneous, melt-depleted mantle of a large, once-chondritic parent body that was broken up catastrophically while still young and hot. Heterogeneity in the parent body is inferred from a considerable “slope-1” variation from one meteorite to another in oxygen isotopes (−2.5‰ < Δ17O < −0.2‰), which correlates with both molar FeO/MgO (range 0.03–0.35) and molar FeO/MnO (range 3–57), i.e., Δ17O correlates with the redox state. No consensus has yet emerged on the cause of these correlated trends. One view favors their inheritance via silicates from hot nebular (preaccretion) processes. Another invokes smelting (reduction of FeO by C in the hot parent body). Here, guided mainly by similar trends among equilibrated ordinary and R chondrites, studies of their unequilibrated counterparts, and work on other primitive achondrites, we propose a new model for ureilites in which the parent body accreted nebular ice with high-∆17O, Mg-rich silicates with low ∆17O, and varying amounts of metallic iron. Water from the thawing ice then oxidized the metal yielding secondary FeO-bearing minerals with high ∆17O that, with metamorphism, became incorporated into the ureilite silicates. FeO/MgO, FeO/MnO, and ∆17O correlate because they rose in unison by amounts that varied spatially, depending on the local amount of metal that was oxidized. We suggest that the parent body was so large (radius ≫ 100 km) that smelting was inhibited and that carbon played a passive role in ureilite evolution. Although ureilites are regarded as complicated meteorites, we believe our analysis explains their mass-independent oxygen isotope trend and related FeO variation through well-understood processes and enlightens our understanding of the evolution of early planetesimals from cold, wet bodies to hot, dry ones.

¹Krzysztof Szopa, ¹Tomasz Brachaniec, ¹Łukasz Karwowski, ¹Tomasz Krzykawski
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12815]
¹Department of Geochemistry, Mineralogy and Petrography, Faculty of Earth Science, University of Silesia, Sosnowiec, Poland
Published by arrangement with John Wiley & Sons

Fossil iron meteorites are extremely rare in the geological sedimentary record. The paleometeorite described here is the first such finding at the Cretaceous-Paleogene (K-Pg) boundary. In the boundary clay from the outcrop at the Lechówka quarry (Poland), fragments of the paleometeorite were found in the bottom part of the host layer. The fragments of meteorite (2–6 mm in size) and meteoritic dust are metallic-gray in color and have a total weight of 1.8181 g. Geochemical and petrographic analyses of the meteorite from Lechówka reveal the presence of Ni-rich minerals with a total Ni amount of 2–3 wt%. The identified minerals are taenite, kamacite, schreibersite, Ni-rich magnetite, and Ni-rich goethite. No relicts of silicates or chromites were found. The investigated paleometeorite apparently represents an independent fall and does not seem to be derived from the K-Pg impactor. The high degree of weathering did not permit the chemical classification of the meteorite fragments. However, the recognized mineral inventory, lack of silicates, and their pseudomorphs and texture may indicate that the meteorite remains were an iron meteorite.

^1,2François Faure, ^1,2Laurent Tissandier, ^1,2Léa Florentin, ^3,4Karine Devineau
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2017.01.034]
¹Université de Lorraine, CRPG, UMR 7358, 15 rue Notre Dame des Pauvres F-54501 Vandoeuvre-lès-Nancy France
²CNRS, CRPG, UMR 7358, 15 rue Notre Dame des Pauvres F-54501 Vandoeuvre-lès-Nancy France
³Université de Lorraine, GeoRessources, UMR 7359, Faculté des Sciences et Technologies rue Jacques Callot BP 70239, F-54506 Vandoeuvre-lès-Nancy Cedex, France
⁴CNRS, GeoRessources, UMR 7359, Faculté des Sciences et Technologies rue Jacques Callot BP 70239, F-54506 Vandoeuvre-lès-Nancy Cedex, France
Copyright Elsevier

Rare silica-rich glass inclusions (69 < SiO2 < 82 wt.%) are described within magnesian olivines of porphyritic Type IA chondrules. These glass inclusion compositions are clearly out of equilibrium with their host Mg-olivines and their presence within the olivines is generally attributed to an unclear secondary process such as a late interaction with nebular gases. We performed dynamic crystallisation experiments that demonstrate that these Si-rich glass inclusions are actually magmatic in origin and were trapped inside olivines that crystallized slowly from a magma with a CI, i.e. solar, composition. Their silica-rich compositions are the consequence of the small volumes of inclusions, which inhibit the nucleation of secondary crystalline phase (Ca-poor pyroxene) but allow olivine to continue to crystallize metastably on the walls of the inclusions. We suggest that Si-rich glass inclusions could be the only reliable relicts of what were the first magmas of the solar system, exhibiting a CI, i.e. non-fractionated, composition.

¹Mario Fischer-Gödde, ¹Thorsten Kleine
Nature 541, 525-527 Link to Article [doi:10.1038/nature21045]
¹Institut für Planetologie, University of Münster, Wilhelm-Klemm-Strasse 10, 48149 Münster, Germany

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¹Nicolas Dauphas
Nature 541, 521-524 Link to Article [doi:10.1038/nature20830]
¹Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago, Illinois 60637, USA

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^1,2Philipp R. Heck, ^1,3Birger Schmitz, ⁴William F. Bottke, ^1,2Surya S. Rout, ⁵Noriko T. Kita, ³Anders Cronholm, ³Céline Defouilloy, ^6,7Andrei Dronov, ³Fredrik Terfelt
Nature Astronomy 1, 35 Link to Article [doi:10.1038/s41550-016-0035]
¹Robert A. Pritzker Center for Meteoritics and Polar Studies, The Field Museum of Natural History, 1400 South Lake Shore Drive, Chicago, Illinois 60605, USA
²Chicago Center for Cosmochemistry and Department of the Geophysical Sciences, The University of Chicago, 5734 South Ellis Avenue, Chicago, Illinois 60637, USA
³Astrogeobiology Laboratory, Department of Physics, Lund University, PO Box 118, SE-22100 Lund, Sweden
⁴Department of Space Studies, Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, Colorado 80302, USA
⁵WiscSIMS, Department of Geoscience, University of Wisconsin-Madison, 1215 W. Dayton Street, Madison, Wisconsin 53706-1692, USA
⁶Geological Institute, Russian Academy of Sciences, Pyzhevsky Pereulok 7, 119017 Moscow, Russia
⁷Kazan (Volga Region) Federal University, Kremlevskaya ulitsa 18, 420008 Kazan, Russia

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¹S. Antonellini, ¹J. Bremer, ¹I. Kamp, ²P. Riviere-Marichalar, ^1,3F. Lahuis, ⁴W.-F. Thi, ⁵P. Woitke, ⁶R. Meijerink, ^1,7G. Aresu,¹M. Spaans
Astronomy & Astrophysics 597, A72 Link to Article [http://dx.doi.org/10.1051/0004-6361/201527820]
¹Kapteyn Astronomical Institute, Postbus 800, 9700 AV Groningen, The Netherlands
²Centro de Astrobiología (INTA-CSIC) – Depto. Astrofísica, POB 78, ESAC Campus, 28691 Villanueva de la Cañada, Spain
³SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV Groningen, The Netherlands
⁴Max-Planck-Institut für extraterrestrische Physisk, Giessenbachstrasse 1, 85748 Garching, Germany
⁵St. Andrews University, School of Physics and Astronomy, St. Andrews KY16 9SS, UK
⁶Leiden Observatory, Leiden University, PO Box, 2300 RA Leiden, The Netherlands
⁷INAF–Osservatorio Astronomico di Cagliari, via della Scienza 5, 09047 Selargius, Italy

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