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Noble gases in individual L chondritic micrometeorites preserved in an Ordovician limestone

Meier, M. M. M.; Schmitz, Birger LU ; Baur, H. and Wieler, R. (2010) In Earth and Planetary Science Letters 290(1-2). p.54-63
Abstract
We have measured the He and Ne concentrations and isotopic ratios of individual sediment-dispersed extraterrestrial chromite grains (63-180 mu m in diameter) from an Ordovician limestone in southern Sweden. In the same sediment, many fossil meteorites were found and have been attributed to the L chondrite parent body breakup event similar to 470 Ma ago. In this analysis of 37 individual extraterrestrial chromite grains of L chondritic major element composition, at least 35 (similar to 95%) contain surface-implanted helium and neon of fractionated solar wind composition, implying that these grains are (relict parts of) fossil micrometeorites of asteroidal origin. Similar to what has been observed in recent micrometeorites collected in the... (More)
We have measured the He and Ne concentrations and isotopic ratios of individual sediment-dispersed extraterrestrial chromite grains (63-180 mu m in diameter) from an Ordovician limestone in southern Sweden. In the same sediment, many fossil meteorites were found and have been attributed to the L chondrite parent body breakup event similar to 470 Ma ago. In this analysis of 37 individual extraterrestrial chromite grains of L chondritic major element composition, at least 35 (similar to 95%) contain surface-implanted helium and neon of fractionated solar wind composition, implying that these grains are (relict parts of) fossil micrometeorites of asteroidal origin. Similar to what has been observed in recent micrometeorites collected in the polar regions. significant amounts of cosmogenic Ne-21 were found in several grains, resulting in cosmic ray exposure (CRE) ages of up to similar to 77 Myr. These ages exceed both dynamical lifetimes for asteroidal micrometeorites of this size as well as CRE ages observed in chromites from fossil meteorites from the same sediment beds. Significant contributions from terrestrial sources, like nucleogenic and cosmic-ray muon induced Ne-21 can be excluded in the extraterrestrial chromites, since 11 terrestrial chrome spinel grains from the same sediment beds did not contain any measurable Ne-21 excesses. Having found micrometeorites of undisputed asteroidal origin with cosmic ray exposure ages of several 10(7) years implies that high cosmic ray exposure ages alone are not a good indicator of cometary origin, in opposition to what has been suggested for recent micrometeorites and IDPs. We propose instead that these grains collected their cosmogenic Ne-21 while residing in the regolith layer of their parent body. (C) 2009 Elsevier B.V. All rights reserved. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
IDPs, micrometeorites, noble gases, fossil meteorites, regolith
in
Earth and Planetary Science Letters
volume
290
issue
1-2
pages
54 - 63
publisher
Elsevier
external identifiers
  • wos:000274844700007
  • scopus:74249084918
ISSN
1385-013X
DOI
10.1016/j.epsl.2009.11.056
language
English
LU publication?
yes
id
98e16208-66ce-45ac-a33e-0edcbcf4a9da (old id 1568260)
date added to LUP
2010-03-23 14:20:50
date last changed
2018-05-29 12:02:04
@article{98e16208-66ce-45ac-a33e-0edcbcf4a9da,
  abstract     = {We have measured the He and Ne concentrations and isotopic ratios of individual sediment-dispersed extraterrestrial chromite grains (63-180 mu m in diameter) from an Ordovician limestone in southern Sweden. In the same sediment, many fossil meteorites were found and have been attributed to the L chondrite parent body breakup event similar to 470 Ma ago. In this analysis of 37 individual extraterrestrial chromite grains of L chondritic major element composition, at least 35 (similar to 95%) contain surface-implanted helium and neon of fractionated solar wind composition, implying that these grains are (relict parts of) fossil micrometeorites of asteroidal origin. Similar to what has been observed in recent micrometeorites collected in the polar regions. significant amounts of cosmogenic Ne-21 were found in several grains, resulting in cosmic ray exposure (CRE) ages of up to similar to 77 Myr. These ages exceed both dynamical lifetimes for asteroidal micrometeorites of this size as well as CRE ages observed in chromites from fossil meteorites from the same sediment beds. Significant contributions from terrestrial sources, like nucleogenic and cosmic-ray muon induced Ne-21 can be excluded in the extraterrestrial chromites, since 11 terrestrial chrome spinel grains from the same sediment beds did not contain any measurable Ne-21 excesses. Having found micrometeorites of undisputed asteroidal origin with cosmic ray exposure ages of several 10(7) years implies that high cosmic ray exposure ages alone are not a good indicator of cometary origin, in opposition to what has been suggested for recent micrometeorites and IDPs. We propose instead that these grains collected their cosmogenic Ne-21 while residing in the regolith layer of their parent body. (C) 2009 Elsevier B.V. All rights reserved.},
  author       = {Meier, M. M. M. and Schmitz, Birger and Baur, H. and Wieler, R.},
  issn         = {1385-013X},
  keyword      = {IDPs,micrometeorites,noble gases,fossil meteorites,regolith},
  language     = {eng},
  number       = {1-2},
  pages        = {54--63},
  publisher    = {Elsevier},
  series       = {Earth and Planetary Science Letters},
  title        = {Noble gases in individual L chondritic micrometeorites preserved in an Ordovician limestone},
  url          = {http://dx.doi.org/10.1016/j.epsl.2009.11.056},
  volume       = {290},
  year         = {2010},
}