¹Pedro Corona-Chávez, ²María del Sol Hernández-Bernal, ³Pietro Vignola, ⁴Rufino Lozano-Santacruz, ⁵Juan Julio Morales-Contreras, ⁴Margarita Reyes-Salas, ⁵ Jesús Solé-Viñas, ⁶José F.Molina
Chemie der Erde (in Press) Link to Article [https://doi.org/10.1016/j.chemer.2017.12.003]
¹Universidad Michoacana de San Nicolás de Hidalgo, Instituto de Investigaciones en Ciencias de la Tierra, Edificio U, Ciudad Universitaria, Morelia, 58020, Mexico
²Universidad Nacional Autónoma de México, Escuela Nacional de Estudios Superiores, Unidad Morelia, 58190, Mexico
³Consiglio Nazionale delle Ricerche (CNR) – Istituto per la dinamica dei processi ambientali, via Botticelli 23, 20133 Milan, Italy
⁴Universidad Nacional Autónoma de México, Instituto de Geología, Circuito interior Ciudad Universitaria, 04510, Mexico
⁵Universidad Nacional Autónoma de México, Instituto de Geofísica, Unidad Morelia, 58190, Mexico
⁶Departamento de Mineralogía y Petrología, Universidad de Granada, Spain
Copyright Elsevier

We present the results of physical properties, petrography, bulk chemistry, mineral compositions, phase relations modelling and Noble gases study of the meteorite El Pozo. The petrography and mineral compositions indicate that the meteorite is an L5 chondrite with a low shock stage of S2-S3. Heterogenous weathering was preferentially along shock structures. Thermobarometric calculations indicate thermal equilibrium conditions between 768 °C and 925 °C at ∼4 to 6 kb, which are substantially consistent with the petrological metamorphism type 5. A pseudosection phase diagram is relatively consistent with the mineral assemblage observed and PT conditions calculated. Temperature vs. fO2 diagram shows that plagioclase compositional stability is very sensitive to Tschermack substitution in orthopyroxene, clinopyroxene and XAn plagioclase during the high temperature metamorphic process. Based on noble gases He, Ne, Ar and K contents a cosmogenic exposure age CRE of 1.9 Myr was calculated. The 21Ne would be totally cosmogenic, with no primordial Ne. The 21Ne/22Ne value (0.97) is higher than solar value. According to the cosmogenic Ne content, we argue that El Pozo chondrite originally had a pre-atmospheric mass of 9–10 kg, which would have been produced by a later collision after the recognized collision of the L-chondrite parent body ∼470 Ma ago.

^1,2Julien Siebert, ¹Paolo A. Sossi, ¹Ingrid Blanchard, ¹Brandon Mahan, ^1,3James Badro, ^1,2Frédéric Moynier
Earth and Planetary Science Letters 485, 130-139 Link to Article [https://doi.org/10.1016/j.epsl.2017.12.042]
¹Institut de Physique du Globe de Paris, Université Sorbonne Paris Cité, 75005, Paris, France
²Institut Universitaire de France, France
³Earth and Planetary Science Laboratory, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
Copyright Elsevier

The depletion pattern of volatile elements on Earth and other differentiated terrestrial bodies provides a unique insight as to the nature and origin of planetary building blocks. The processes responsible for the depletion of volatile elements range from the early incomplete condensation in the solar nebula to the late de-volatilization induced by heating and impacting during planetary accretion after the dispersion of the H2-rich nebular gas. Furthermore, as many volatile elements are also siderophile (metal-loving), it is often difficult to deconvolve the effect of volatility from core formation. With the notable exception of the Earth, all the differentiated terrestrial bodies for which we have samples have non-chondritic Mn/Na ratios, taken as a signature of post-nebular volatilization. The bulk silicate Earth (BSE) is unique in that its Mn/Na ratio is chondritic, which points to a nebular origin for the depletion; unless the Mn/Na in the BSE is not that of the bulk Earth (BE), and has been affected by core formation through the partitioning of Mn in Earth’s core. Here we quantify the metal–silicate partitioning behavior of Mn at deep magma ocean pressure and temperature conditions directly applicable to core formation. The experiments show that Mn becomes more siderophile with increasing pressure and temperature. Modeling the partitioning of Mn during core formation by combining our results with previous data at lower P–T conditions, we show that the core likely contains a significant fraction (20 to 35%) of Earth’s Mn budget. However, we show that the derived Mn/Na value of the bulk Earth still lies on the volatile-depleted end of a trend defined by chondritic meteorites in a Mn/Na vs Mn/Mg plot, which tend to higher Mn/Na with increasing volatile depletion. This suggests that the material that formed the Earth recorded similar chemical fractionation processes for moderately volatile elements as chondrites in the solar nebula, and experienced limited post nebular volatilization.

^1,2Daisuke Nakashima,^3,4Keisuke Nagao,⁵Anthony J. Irving
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13039]
¹Department of Earth and Planetary Material Sciences, Faculty of Science, Tohoku University, Sendai, Miyagi, Japan
²Geochemical Research Center, Graduate School of Science, University of Tokyo, Bunkyo, Tokyo, Japan
³Geochemical Research Center, Graduate School of Science, University of Tokyo, Bunkyo, Tokyo, Japan
⁴Division of Polar Earth-System Sciences, Korea Polar Research Institute, Incheon, Korea
⁵Department of Earth & Space Sciences, University of Washington, Seattle, Washington, USA
Published by arrangement with John Wiley & Sons

Noble gases in the five angrites Northwest Africa (NWA) 1296, 2999, 4590, 4801, and 4931 were analyzed with total melting and stepwise heating methods. The noble gases consist of in situ components: spallogenic, radiogenic, nucleogenic, and fission. Cosmic-ray exposure ages of the angrites (including literature data) spread uniformly from <0.2 to 56 Ma, and coarse-grained angrites have longer exposure ages than fine-grained angrites. It is implied that the parent bodies from which the two subgroups of angrites were ejected are different and have distinct orbital elements. The ²⁴⁴Pu-¹³⁶Xe relative ages of the angrites obtained by using ²⁴⁴Pu/¹⁵⁰Nd ratios are as old as that of Angra dos Reis, reflecting their early formation. On the other hand, another method to obtain ²⁴⁴Pu-¹³⁶Xe relative ages, using fission ¹³⁶Xe, spallogenic ¹²⁶Xe, and Ba/REE ratios, yields systematically older ²⁴⁴Pu-¹³⁶Xe ages than those obtained by using ²⁴⁴Pu/¹⁵⁰Nd ratios, which is explained by apparently high Ba/REE ratios caused by Ba contamination during terrestrial weathering. The ²⁴⁴Pu/²³⁸U ratio at 4.56 Ga of angrites is estimated as 0.0061 ± 0.0028, which is consistent with those for chondrules, chondrites, achondrites, and a terrestrial zircon. It is suggested that initial ²⁴⁴Pu/²³⁸U ratio has been spatially homogeneous at least in the inner part of the early solar system.

^1,2,3Surya S. Rout,^1,2,4Philipp R. Heck,^1,5Birger Schmitz
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13041]
¹Robert A. Pritzker Center for Meteoritics and Polar Studies, The Field Museum of Natural History, Chicago, Illinois, USA
²Chicago Center for Cosmochemistry, Chicago, Illinois, USA
³Physikalisches Institut, Space Research and Planetary Sciences, Universität Bern, Bern, Switzerland
⁴Department of the Geophysical Sciences, The University of Chicago, Chicago, Illinois, USA
⁵Astrogeobiology Laboratory, Department of Physics, Lund University, Lund, Sweden
Published by arrangement with John Wiley & Sons

Chrome-spinel grains from the fossil ungrouped achondrite Österplana 065 (Öst 065) recovered from Middle Ordovician limestone in Sweden were studied using Raman spectroscopy and TEM. All the studied chrome-spinel grains have a high density of planar fractures and planar features, not seen in chromites from the other L chondritic Ordovician fossil meteorites. Raman spectra of the host chrome-spinel grain and its planar features are similar and no signatures of high-pressure phases of chromite were found. The planar features occur along planar fractures, are enriched in ZnO, and are most probably produced due to enhanced leaching during terrestrial weathering in the marine sediment. Dislocation densities within two FIB sections prepared from two chrome-spinel grains from Öst 065 are similar to the dislocation densities found within chromite grains from the matrix of Tenham L6 chondrite. Using this observation and taking into account the presence of significant fracturing in all the grains, we conclude that the Öst 065 chrome-spinel grains were subjected to moderate to very strong shock corresponding to shock stages of S4–S6. This makes Öst 065 fossil achondrite the highest shocked fossil meteorite studied so far. This is consistent with the hypothesis that Öst 065 is a piece of the impactor that led to the L chondrite parent body breakup.

¹Shan-Shan Li et al. (>10)
Gondwana Research 54, 81-101 Link to Article [https://doi.org/10.1016/j.gr.2017.10.006]
¹School of Earth Science and Resources, China University of Geosciences, Beijing 100083,

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^1,2Marianna Mészáros,^2,3Beda A. Hofmann,¹Ingo Leya
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13037]
¹Space Research and Planetary Sciences, University of Bern, Bern, Switzerland
²Natural History Museum Bern, Bern, Switzerland
³Institute of Geological Sciences, University of Bern, Bern, Switzerland
Published by arrangement with John wiley & Sons

We collected the published noble gas data of altogether 35 lunar meteorites. This compilation includes the stable isotopes of He, Ne, Ar, Kr, and Xe. We also give a summary of cosmogenic, trapped, and radiogenic noble gas components of lunar meteorites for which data are available in the literature.

¹Leticia Gómez-Nubla, ¹Julene Aramendia, ¹Silvia Fdez-Ortiz de Vallejuelo, ¹Juan Manuel Madariaga
Microchemical Journal 137, 392-401 Link to Article [https://doi.org/10.1016/j.microc.2017.11.019]
¹Department of Analytical Chemistry, Faculty of Science and Technology, University of the Basque Country UPV/EHU, P.O. Box 644, E-48080 Bilbao, Basque Country, Spain

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¹Evan E. Groopman, ¹Kenneth S. Grabowski, ²Albert J. Fahey, ³Levke Kööp
Journal of Analytical Atomic Spectrometry 32, 2153-2163 Link to Article [DOI: 10.1039/C7JA00294G]
¹Materials Science and Technology Division, U.S. Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, USA
²Microscopy & Surface Analysis, Corning, Inc., Corning, USA
³Department of the Geophysical Sciences, University of Chicago, 5734 S. Ellis Ave., Chicago, USA

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^1,2Noël Chaumard,³Munir Humayun,¹Brigitte Zanda,^1,4Roger H. Hewins
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13040]
¹Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Sorbonne Universités, Muséum national d’histoire naturelle, UPMC Université Paris 06, UMR CNRS 7590, IRD, UMR 206, Paris Cedex 05, France
²Department of Geoscience, WiscSIMS, University of Wisconsin-Madison, Madison, Wisconsin, USA
³Department of Earth, Ocean & Atmospheric Science, and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida, USA
⁴Department of Earth & Planetary Sciences, Rutgers University, Piscataway, New Jersey, USA
Published by arrangement with John Wiley & Sons

Cooling rates are one of the few fundamental constraints on models of chondrule formation. In this study, we used Cu and Ga diffusion profiles in metal grains to determine the cooling rates of type I chondrules in the Renazzo CR2 chondrite. To improve previous estimations of cooling rates obtained using this method, we used CT scanning and serial polishing of our sections to analyze equatorial sections of large metal grains. Through the cores of these metal grains situated at the surface of chondrules, the cooling rates calculated range from 21 to 86 K h−1 for a peak temperature Tp ~ 1623–1673 K. A metal grain embedded in the core of a chondrule exhibits a cooling rate of 1.2 K h−1 at a Tp ~ 1573 K. We also measured Cu-Ga diffusion profiles from nonequatorial sections of metal grains and calculated a lower range of cooling rates of 15–69 K h−1 for Tp ~ 1473–1603 K compared to our results from equatorial sections. The high cooling rates inferred from the lightning model (several thousand K h−1) are clearly at odds with the values obtained in this work. The X-wind model predicts cooling rates (~6–10 K h−1) lower than most of our results. The cooling rates calculated here are in close agreement with those inferred from shock wave models, in particular for temperatures at which olivine crystallizes (from ~10 to several hundreds K h−1 between 1900 and 1500 K). However, the chemical compositions of metal grains in Renazzo are consistent with the splashing model, in which a spray of metal droplets originated from a partially molten planetesimal. Volatile siderophile element depletion is explained by evaporation before metal was engulfed within silicate droplets. Liquid metal isolated from the liquid silicate crystallized during cooling, reacted with the ambient gas, and then re-accreted within partially molten chondrules.

¹R. J. Charles,¹Pierre-Yves F. Robin,¹Donald W. Davis,^1,2,3Phil J. A. McCausland
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13038]
¹Department of Earth Sciences, University of Toronto, Toronto, Ontario, Canada
²Centre for Planetary Science and Exploration, Western University, London, Ontario, Canada
³Western Paleomagnetic and Petrophysical Laboratory, Western University, London, Ontario, Canada
Published by arrangement with John Wiley & Sons

The approximately spherical shapes of chondrules has long been attributed to surface tension acting on ~1 mm melt droplets that formed and cooled in the microgravity field of the solar nebula. However, chondrule shapes commonly depart significantly from spherical. In this study, 109 chondrules in a sample of CR2 chondrite NWA 801 were imaged by X-ray computed tomography and best-fitted to ellipsoids. The analysis confirms that many chondrules are indeed not spherical, and also that the chondrules’ collective shape fabric records a definite 13% compaction in the host meteorite. Dehydration of phyllosilicates within chondrules may account for that strain. However, retro-deforming all chondrules shows that a large majority were already far from spherical prior to accretion. Possible models for these initial shapes include prior deformation of individual chondrules in earlier hosts, and, as suggested by previous authors, rotation of chondrules as they were solidifying, and/or “streaming” of molten chondrules by their differential velocities with their gaseous hosts after melting. More in situ 3-D work such as this study on a variety of unequilibrated chondrites, combined with detailed structural petrography, should help further constrain these models and refine our understanding of chondrite formation.