Advanced

He and Ne in individual chromite grains from the regolith breccia Ghubara (L5): Exploring the history of the L chondrite parent body regolith

Meier, Matthias LU ; Schmitz, Birger LU ; Alwmark, Carl LU ; Trappitsch, Reto; Maden, Colin and Wieler, Rainer (2014) In Meteoritics and Planetary Science 49(4). p.576-594
Abstract
Abstract We analyzed He and Ne in chromite grains from the regolith breccia Ghubara (L5), to compare it with He and Ne in sediment-dispersed extraterrestrial chromite (SEC) grains from mid-Ordovician sediments. These SEC grains arrived on Earth as micrometeorites in the aftermath of the L chondrite parent body (LCPB) breakup event, 470 Ma ago. A significant fraction of them show prolonged exposure to galactic cosmic rays for up to several 10 Ma. The majority of the cosmogenic noble gases in these grains were probably acquired in the regolith of the LCPB (Meier et al. ). Ghubara, an L chondritic regolith breccia with an Ar-Ar shock age of 470 Ma, is a sample of that regolith. We find cosmic-ray exposure ages of up to several 10 Ma in some... (More)
Abstract We analyzed He and Ne in chromite grains from the regolith breccia Ghubara (L5), to compare it with He and Ne in sediment-dispersed extraterrestrial chromite (SEC) grains from mid-Ordovician sediments. These SEC grains arrived on Earth as micrometeorites in the aftermath of the L chondrite parent body (LCPB) breakup event, 470 Ma ago. A significant fraction of them show prolonged exposure to galactic cosmic rays for up to several 10 Ma. The majority of the cosmogenic noble gases in these grains were probably acquired in the regolith of the LCPB (Meier et al. ). Ghubara, an L chondritic regolith breccia with an Ar-Ar shock age of 470 Ma, is a sample of that regolith. We find cosmic-ray exposure ages of up to several 10 Ma in some Ghubara chromite grains, confirming for the first time that individual chromite grains with such high exposure ages indeed existed in the LCPB regolith, and that the > 10 Ma cosmic-ray exposure ages found in recent micrometeorites are thus not necessarily indicative of an origin in the Kuiper Belt. Some Ghubara chromite grains show much lower concentrations of cosmogenic He and Ne, indicating that the 4 pi (last-stage) exposure age of the Ghubara meteoroid lasted only 4-6 Ma. This exposure age is considerably shorter than the 15-20 Ma suggested before from bulk analyses, indicating that bulk samples have seen regolith pre-exposure as well. The shorter last-stage exposure age probably links Ghubara to a small peak of Ar-40-poor L5 chondrites of the same exposure age. Furthermore, and quite unexpectedly, we find a Ne component similar to presolar Ne-HL in the chromite grains, perhaps indicating that some presolar Ne can be preserved even in meteorites of petrologic type 5. (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Meteoritics and Planetary Science
volume
49
issue
4
pages
576 - 594
publisher
Wiley-Blackwell
external identifiers
  • wos:000334680200005
  • scopus:84899122854
ISSN
1086-9379
DOI
10.1111/maps.12275
language
English
LU publication?
yes
id
f0e72773-4ca2-4a5c-aefb-fe672531f604 (old id 4488950)
date added to LUP
2014-06-23 13:20:35
date last changed
2017-08-13 04:02:39
@article{f0e72773-4ca2-4a5c-aefb-fe672531f604,
  abstract     = {Abstract We analyzed He and Ne in chromite grains from the regolith breccia Ghubara (L5), to compare it with He and Ne in sediment-dispersed extraterrestrial chromite (SEC) grains from mid-Ordovician sediments. These SEC grains arrived on Earth as micrometeorites in the aftermath of the L chondrite parent body (LCPB) breakup event, 470 Ma ago. A significant fraction of them show prolonged exposure to galactic cosmic rays for up to several 10 Ma. The majority of the cosmogenic noble gases in these grains were probably acquired in the regolith of the LCPB (Meier et al. ). Ghubara, an L chondritic regolith breccia with an Ar-Ar shock age of 470 Ma, is a sample of that regolith. We find cosmic-ray exposure ages of up to several 10 Ma in some Ghubara chromite grains, confirming for the first time that individual chromite grains with such high exposure ages indeed existed in the LCPB regolith, and that the > 10 Ma cosmic-ray exposure ages found in recent micrometeorites are thus not necessarily indicative of an origin in the Kuiper Belt. Some Ghubara chromite grains show much lower concentrations of cosmogenic He and Ne, indicating that the 4 pi (last-stage) exposure age of the Ghubara meteoroid lasted only 4-6 Ma. This exposure age is considerably shorter than the 15-20 Ma suggested before from bulk analyses, indicating that bulk samples have seen regolith pre-exposure as well. The shorter last-stage exposure age probably links Ghubara to a small peak of Ar-40-poor L5 chondrites of the same exposure age. Furthermore, and quite unexpectedly, we find a Ne component similar to presolar Ne-HL in the chromite grains, perhaps indicating that some presolar Ne can be preserved even in meteorites of petrologic type 5.},
  author       = {Meier, Matthias and Schmitz, Birger and Alwmark, Carl and Trappitsch, Reto and Maden, Colin and Wieler, Rainer},
  issn         = {1086-9379},
  language     = {eng},
  number       = {4},
  pages        = {576--594},
  publisher    = {Wiley-Blackwell},
  series       = {Meteoritics and Planetary Science},
  title        = {He and Ne in individual chromite grains from the regolith breccia Ghubara (L5): Exploring the history of the L chondrite parent body regolith},
  url          = {http://dx.doi.org/10.1111/maps.12275},
  volume       = {49},
  year         = {2014},
}