Analytical methodology to elemental quantification of weathered terrestrial analogues to meteorites using a portable Laser-Induced Breakdown Spectroscopy (LIBS) instrument and Partial Least Squares (PLS) as multivariate calibration technique

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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Rapid, molecule-free, in situ rare earth element abundances by SIMS-SSAMS

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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Cooling rates of type I chondrules from Renazzo: Implications for chondrule formation

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.

Shapes of chondrules determined from the petrofabric of the CR2 chondrite NWA 801

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.

The Varre-Sai chondrite, a Brazilian fall: petrology and geochemistry

1Caio Vinícius Gabrig Turbay Rangel, 2Marcos Tadeu D’Azeredo Orlando, 3Cláudio De Morisson Valeriano, 4Alexandre de Oliveira Chaves
International Geology Review 59, 1966-1973 Link to Article [https://doi.org/10.1080/00206814.2017.1308842]
1Geology Department, Universidade Federal do Espirito Santo, Alegre, Brasil
2Department of Physics, Universidade Federal do Espirito Santo, Alegre, Brasil
3TECTO, Universidade do Estado Rio de Janiero, Rio de Janiero, Brazil
4ICG, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil

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Utilization of nondestructive techniques for analysis of the Martian meteorite NWA 6963 and its implications for astrobiology

1Bruno L. do Nascimento-Dias,1,2Davi F. de Oliveira,2Alessandra S. Machado,2Olga M.O. Araújo,2Ricardo T. Lopes,2Marcelino J. dos Anjos
X-Ray Spectrometry 47, 86-91 Link to Article [DOI: 10.1002/xrs.2815]
1Physics Institute Armando Dias Tavares, University of State of Rio de Janeiro, Rio de Janeiro, Brazil
2Nuclear Instrumentation Laboratory, PEN, COPPE, UFRJ, Rio de Janeiro, Brazil

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