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A single asteroidal source for extraterrestrial Ordovician chromite grains from Sweden and China: High-precision oxygen three-isotope SIMS analysis

Heck, Philipp R.; Ushikubo, Takayuki; Schmitz, Birger LU ; Kita, Noriko T.; Spicuzza, Michael J. and Valley, John W. (2010) In Geochimica et Cosmochimica Acta 74(2). p.497-509
Abstract
We examined oxygen three-isotope ratios of 48 extraterrestrial chromite (EC) grains extracted from mid-Ordovician sediments from two different locations in Sweden, and one location in south-central China. The ages of the sediments (similar to 470 Ma) coincide with the breakup event of the L chondrite parent asteroid. Elemental compositions of the chromite grains are generally consistent with their origin from L or LL chondrite parent bodies. The average Delta O-17 (parts per thousand-deviation from the terrestrial mass-fractionation line, measured in situ from 15 mu m spots by secondary ion mass spectrometry; SIMS) of EC grains extracted from fossil meteorites from Thorsberg and Brunflo are 1.17 +/- 0.09 parts per thousand (2 sigma) and... (More)
We examined oxygen three-isotope ratios of 48 extraterrestrial chromite (EC) grains extracted from mid-Ordovician sediments from two different locations in Sweden, and one location in south-central China. The ages of the sediments (similar to 470 Ma) coincide with the breakup event of the L chondrite parent asteroid. Elemental compositions of the chromite grains are generally consistent with their origin from L or LL chondrite parent bodies. The average Delta O-17 (parts per thousand-deviation from the terrestrial mass-fractionation line, measured in situ from 15 mu m spots by secondary ion mass spectrometry; SIMS) of EC grains extracted from fossil meteorites from Thorsberg and Brunflo are 1.17 +/- 0.09 parts per thousand (2 sigma) and 1.25 +/- 0.16 parts per thousand, respectively, and those of fossil micrometeorites from Thorsberg and Puxi River are 1.10 +/- 0.09 parts per thousand, and 1.11 +/- 0.12 parts per thousand, respectively. Within uncertainty these values are all the same and consistent with the L chondrite group average Delta O-17 = 1.07 +/- 0.18 parts per thousand, but also with the LL chondrite group average Delta O-17 = 1.26 +/- 0.24 parts per thousand. (Clayton et al., 1991). We conclude that the studied EC grains from correlated sediments from Sweden and China are related, and most likely originated in the same event, the L chondrite parent body breakup. We also analyzed chromites of modern H, L and LL chondrites and show that their Delta O-17 values coincide with averages of Delta O-17 of bulk analyses of H, L and LL chondrites. This study demonstrates that in situ oxygen isotope data measured by SIMS are accurate and precise if carefully standardized, and can be used to classify individual extraterrestrial chromite grains found in sediments. (c) 2009 Elsevier Ltd. All rights reserved. (Less)
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type
Contribution to journal
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published
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in
Geochimica et Cosmochimica Acta
volume
74
issue
2
pages
497 - 509
publisher
Elsevier
external identifiers
  • wos:000273325500005
  • scopus:70649108812
ISSN
0016-7037
DOI
10.1016/j.gca.2009.10.027
language
English
LU publication?
yes
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6fa9cc02-1480-45b9-8f72-e7b6bc39b5ec (old id 1547860)
date added to LUP
2010-02-23 08:40:35
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2018-05-29 11:57:30
@article{6fa9cc02-1480-45b9-8f72-e7b6bc39b5ec,
  abstract     = {We examined oxygen three-isotope ratios of 48 extraterrestrial chromite (EC) grains extracted from mid-Ordovician sediments from two different locations in Sweden, and one location in south-central China. The ages of the sediments (similar to 470 Ma) coincide with the breakup event of the L chondrite parent asteroid. Elemental compositions of the chromite grains are generally consistent with their origin from L or LL chondrite parent bodies. The average Delta O-17 (parts per thousand-deviation from the terrestrial mass-fractionation line, measured in situ from 15 mu m spots by secondary ion mass spectrometry; SIMS) of EC grains extracted from fossil meteorites from Thorsberg and Brunflo are 1.17 +/- 0.09 parts per thousand (2 sigma) and 1.25 +/- 0.16 parts per thousand, respectively, and those of fossil micrometeorites from Thorsberg and Puxi River are 1.10 +/- 0.09 parts per thousand, and 1.11 +/- 0.12 parts per thousand, respectively. Within uncertainty these values are all the same and consistent with the L chondrite group average Delta O-17 = 1.07 +/- 0.18 parts per thousand, but also with the LL chondrite group average Delta O-17 = 1.26 +/- 0.24 parts per thousand. (Clayton et al., 1991). We conclude that the studied EC grains from correlated sediments from Sweden and China are related, and most likely originated in the same event, the L chondrite parent body breakup. We also analyzed chromites of modern H, L and LL chondrites and show that their Delta O-17 values coincide with averages of Delta O-17 of bulk analyses of H, L and LL chondrites. This study demonstrates that in situ oxygen isotope data measured by SIMS are accurate and precise if carefully standardized, and can be used to classify individual extraterrestrial chromite grains found in sediments. (c) 2009 Elsevier Ltd. All rights reserved.},
  author       = {Heck, Philipp R. and Ushikubo, Takayuki and Schmitz, Birger and Kita, Noriko T. and Spicuzza, Michael J. and Valley, John W.},
  issn         = {0016-7037},
  language     = {eng},
  number       = {2},
  pages        = {497--509},
  publisher    = {Elsevier},
  series       = {Geochimica et Cosmochimica Acta},
  title        = {A single asteroidal source for extraterrestrial Ordovician chromite grains from Sweden and China: High-precision oxygen three-isotope SIMS analysis},
  url          = {http://dx.doi.org/10.1016/j.gca.2009.10.027},
  volume       = {74},
  year         = {2010},
}