Advanced

Determining the impactor of the Ordovician Lockne crater: Oxygen and neon isotopes in chromite versus sedimentary PGE signatures

Schmitz, Birger LU ; Heck, Philipp R.; Alwmark, Carl LU ; Kita, Noriko T.; Meier, Matthias LU ; Peucker-Ehrenbrink, Bernhard; Ushikubo, Takayuki and Valley, John W. (2011) In Earth and Planetary Science Letters 306(3-4). p.149-155
Abstract
Abundant chromite grains with L-chondritic composition in the resurge deposits of the Lockne impact crater (458 Myr old: dia. similar to 10 km) in Sweden have been inferred to represent relict fragments of an impactor from the break-up of the L-chondrite parent body at 470 Ma. This view has been challenged based on It/Cr and platinum group element (PGE) patterns of the same resurge deposits, and a reinterpretation of the origin of the chromite grains. An impactor of the non-magmatic iron meteorite type was proposed instead. Here we show that single-grain oxygen and noble-gas isotope analyses of the chromite grains from the resurge deposits further support an origin from an L-chondritic asteroid. We also present PGE analyses and Ir/Cr... (More)
Abundant chromite grains with L-chondritic composition in the resurge deposits of the Lockne impact crater (458 Myr old: dia. similar to 10 km) in Sweden have been inferred to represent relict fragments of an impactor from the break-up of the L-chondrite parent body at 470 Ma. This view has been challenged based on It/Cr and platinum group element (PGE) patterns of the same resurge deposits, and a reinterpretation of the origin of the chromite grains. An impactor of the non-magmatic iron meteorite type was proposed instead. Here we show that single-grain oxygen and noble-gas isotope analyses of the chromite grains from the resurge deposits further support an origin from an L-chondritic asteroid. We also present PGE analyses and Ir/Cr ratios for fossil L-chondritic meteorites found in mid-Ordovician marine limestone in Sweden. The L-chondritic origin has been confirmed by several independent methods, including major element and oxygen isotopic analyses of chromite. Although the meteorites show the same order-of-magnitude PGE and Cr concentrations as recent L chondrites, the elements have been redistributed to the extent that it is problematic to establish the original meteorite type from these proxies. Different PGE data processing approaches can lead to highly variable results, as also shown here for the Lockne resurge deposits. We conclude that the Lockne crater was formed by an L-chondritic impactor, and that considerable care must be taken when inferring projectile type from PGEs in sedimentary ejecta deposits. (C) 2011 Elsevier B.V. All rights reserved. (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
extraterrestrial chromite, impact projectile, asteroid impact, oxygen, isotopes, platinum group elements, impact crater
in
Earth and Planetary Science Letters
volume
306
issue
3-4
pages
149 - 155
publisher
Elsevier
external identifiers
  • wos:000291907200002
  • scopus:79956297803
ISSN
1385-013X
DOI
10.1016/j.epsl.2011.04.028
language
English
LU publication?
yes
id
645c957c-23ee-4756-bc41-68747e78f1c7 (old id 2049172)
date added to LUP
2011-07-26 13:42:37
date last changed
2017-03-05 03:16:10
@article{645c957c-23ee-4756-bc41-68747e78f1c7,
  abstract     = {Abundant chromite grains with L-chondritic composition in the resurge deposits of the Lockne impact crater (458 Myr old: dia. similar to 10 km) in Sweden have been inferred to represent relict fragments of an impactor from the break-up of the L-chondrite parent body at 470 Ma. This view has been challenged based on It/Cr and platinum group element (PGE) patterns of the same resurge deposits, and a reinterpretation of the origin of the chromite grains. An impactor of the non-magmatic iron meteorite type was proposed instead. Here we show that single-grain oxygen and noble-gas isotope analyses of the chromite grains from the resurge deposits further support an origin from an L-chondritic asteroid. We also present PGE analyses and Ir/Cr ratios for fossil L-chondritic meteorites found in mid-Ordovician marine limestone in Sweden. The L-chondritic origin has been confirmed by several independent methods, including major element and oxygen isotopic analyses of chromite. Although the meteorites show the same order-of-magnitude PGE and Cr concentrations as recent L chondrites, the elements have been redistributed to the extent that it is problematic to establish the original meteorite type from these proxies. Different PGE data processing approaches can lead to highly variable results, as also shown here for the Lockne resurge deposits. We conclude that the Lockne crater was formed by an L-chondritic impactor, and that considerable care must be taken when inferring projectile type from PGEs in sedimentary ejecta deposits. (C) 2011 Elsevier B.V. All rights reserved.},
  author       = {Schmitz, Birger and Heck, Philipp R. and Alwmark, Carl and Kita, Noriko T. and Meier, Matthias and Peucker-Ehrenbrink, Bernhard and Ushikubo, Takayuki and Valley, John W.},
  issn         = {1385-013X},
  keyword      = {extraterrestrial chromite,impact projectile,asteroid impact,oxygen,isotopes,platinum group elements,impact crater},
  language     = {eng},
  number       = {3-4},
  pages        = {149--155},
  publisher    = {Elsevier},
  series       = {Earth and Planetary Science Letters},
  title        = {Determining the impactor of the Ordovician Lockne crater: Oxygen and neon isotopes in chromite versus sedimentary PGE signatures},
  url          = {http://dx.doi.org/10.1016/j.epsl.2011.04.028},
  volume       = {306},
  year         = {2011},
}