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American Mineralogist

Journal of Earth and Planetary Materials

Ed. by Putirka, Keith / Swainson, Ian

12 Issues per year


IMPACT FACTOR 2016: 2.021

CiteScore 2016: 1.88

SCImago Journal Rank (SJR) 2016: 0.952
Source Normalized Impact per Paper (SNIP) 2016: 0.955

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1945-3027
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Volume 100, Issue 11-12 (Nov 2015)

Issues

Shock-induced mobilization of metal and sulfide in planetesimals: Evidence from the Buck Mountains 005 (L6 S4) dike-bearing chondrite

Alex Ruzicka
  • Corresponding author
  • Cascadia Meteorite Laboratory, Portland State University, 1721 SW Broadway, Portland, Oregon 97207, U.S.A.
  • Department of Geology, Portland State University, 17 Cramer Hall, 1721 SW Broadway, Portland, Oregon 97207, U.S.A.
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/ Ryan Brown
  • Cascadia Meteorite Laboratory, Portland State University, 1721 SW Broadway, Portland, Oregon 97207, U.S.A.
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/ Jon Friedrich
  • Department of Chemistry, Fordham University, Bronx, New York 10458, U.S.A.
  • Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York 10024, U.S.A.
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/ Melinda Hutson
  • Cascadia Meteorite Laboratory, Portland State University, 1721 SW Broadway, Portland, Oregon 97207, U.S.A.
  • Department of Geology, Portland State University, 17 Cramer Hall, 1721 SW Broadway, Portland, Oregon 97207, U.S.A.
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/ Richard Hugo
  • Department of Geology, Portland State University, 17 Cramer Hall, 1721 SW Broadway, Portland, Oregon 97207, U.S.A.
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/ Mark Rivers
  • Consortium for Advanced Radiation Sources, University of Chicago, Argonne, Illinois 60439, U.S.A.
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Published Online: 2015-11-24 | DOI: https://doi.org/10.2138/am-2015-5225

Abstract

The conditions under which metal cores formed in silicate-metal planetary bodies in the early Solar System are poorly known. We studied the Buck Mountains 005 (L6) chondrite with serial sectioning, X‑ray computed microtomography, and optical and electron microscopy to better understand how metal and troilite were redistributed as a result of a moderately strong (shock stage S4) shock event, as an example of how collisional processes could have contributed to differentiation. The chondrite was recovered on Earth in multiple small pieces, some of which have a prominent, 1.5-3 mm wide holocrystalline shock melt dike that forms a jointed, sheet-like structure, as well as an associated shock vein network. The data suggest that metal and troilite within the dike were melted, sheared, and transported as small parcels of melt, with metal moving out of the dike and along branching veins to become deposited as coarser nodules and veins within largely unmelted host. Troilite also mobilized but partly separated from metal to become embedded as finer-grained particles, vein networks, and emulsions intimately intergrown with silicates. Rock textures and metal compositions imply that shock melts cooled rapidly against relatively cool parent body materials, but that low-temperature annealing occurred by deep burial within the parent body. Our results demonstrate the ability of shock processes to create larger metal accumulations in substantially unmelted meteorite parent bodies, and they have implications for the formation of iron meteorites and for core formation within colliding planetesimals.

Keywords: Lunar and planetary studies; shock metamorphism; L6 chondrite; petrography; chondrite; olivine; kamacite; taenite; troilite; electron microscopy; FeNi metal

About the article

Received: 2014-10-19

Accepted: 2015-04-14

Published Online: 2015-11-24

Published in Print: 2015-11-01


Citation Information: American Mineralogist, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am-2015-5225.

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© 2015 by Walter de Gruyter Berlin/Boston.

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