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An Early Ordovician 40Ar-39Ar age for the ∼50 km Carswell impact structure, Canada

Alwmark, Carl LU ; Bleeker, Wouter; LeCheminant, Anthony; Page, Laurence LU and Scherstén, Anders LU (2017) In Geological Society of America Bulletin 129(11/12). p.1442-1449
Abstract
The formation age of the large (∼50 km) Carswell impact structure, Canada, has been a matter of debate ever since its discovery five decades ago, with proposed ages ranging from Mesoproterozoic to Early Cretaceous. Here, we present new 40Ar-39Ar data for aliquots of euhedral adularia, separated from vesicles in an impact melt rock from the central uplift of the structure. The analyses of the adularia yielded a statistically robust Early Ordovician crystallization age of 481.5 ± 0.8 Ma (2σ, mean square of weighted deviates = 1.06, P = 0.30). The most plausible explanation for the formation of vesicle-filling adularia is through low-temperature mineral precipitation during residual hydrothermal circulation that followed the impact, as no... (More)
The formation age of the large (∼50 km) Carswell impact structure, Canada, has been a matter of debate ever since its discovery five decades ago, with proposed ages ranging from Mesoproterozoic to Early Cretaceous. Here, we present new 40Ar-39Ar data for aliquots of euhedral adularia, separated from vesicles in an impact melt rock from the central uplift of the structure. The analyses of the adularia yielded a statistically robust Early Ordovician crystallization age of 481.5 ± 0.8 Ma (2σ, mean square of weighted deviates = 1.06, P = 0.30). The most plausible explanation for the formation of vesicle-filling adularia is through low-temperature mineral precipitation during residual hydrothermal circulation that followed the impact, as no other known major intrusive, extrusive, or thermal events have occurred in the Carswell region in the Phanerozoic. The new age of the Carswell impact structure overlaps within uncertainty with the most precise Ar-Ar ages proposed for the L-chondrite parent body breakup event, but not with the age of the stratigraphic sequence from which the meteorites and micrometeorites from this event were recovered. Thus, either the Carswell impact represents a separate, unrelated impact event, or the dynamic evolution of the L-chondrite parent body breakup is more complicated than presently understood, and Carswell represents one of the earliest and largest known impacts of this event on Earth. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Impact, Ordovician, Carswell
in
Geological Society of America Bulletin
volume
129
issue
11/12
pages
1442 - 1449
publisher
Geological Society of America
ISSN
0016-7606
DOI
10.1130/B31666.1
language
English
LU publication?
yes
id
cf5ac508-6ed9-40be-a7de-da9f7779b6c5
date added to LUP
2019-05-15 10:15:45
date last changed
2019-05-16 14:50:30
@article{cf5ac508-6ed9-40be-a7de-da9f7779b6c5,
  abstract     = {The formation age of the large (∼50 km) Carswell impact structure, Canada, has been a matter of debate ever since its discovery five decades ago, with proposed ages ranging from Mesoproterozoic to Early Cretaceous. Here, we present new 40Ar-39Ar data for aliquots of euhedral adularia, separated from vesicles in an impact melt rock from the central uplift of the structure. The analyses of the adularia yielded a statistically robust Early Ordovician crystallization age of 481.5 ± 0.8 Ma (2σ, mean square of weighted deviates = 1.06, P = 0.30). The most plausible explanation for the formation of vesicle-filling adularia is through low-temperature mineral precipitation during residual hydrothermal circulation that followed the impact, as no other known major intrusive, extrusive, or thermal events have occurred in the Carswell region in the Phanerozoic. The new age of the Carswell impact structure overlaps within uncertainty with the most precise Ar-Ar ages proposed for the L-chondrite parent body breakup event, but not with the age of the stratigraphic sequence from which the meteorites and micrometeorites from this event were recovered. Thus, either the Carswell impact represents a separate, unrelated impact event, or the dynamic evolution of the L-chondrite parent body breakup is more complicated than presently understood, and Carswell represents one of the earliest and largest known impacts of this event on Earth.},
  author       = {Alwmark, Carl and Bleeker, Wouter and LeCheminant, Anthony and Page, Laurence and Scherstén, Anders},
  issn         = {0016-7606},
  keyword      = {Impact, Ordovician, Carswell},
  language     = {eng},
  month        = {06},
  number       = {11/12},
  pages        = {1442--1449},
  publisher    = {Geological Society of America},
  series       = {Geological Society of America Bulletin},
  title        = {An Early Ordovician 40Ar-39Ar age for the ∼50 km Carswell impact structure, Canada},
  url          = {http://dx.doi.org/10.1130/B31666.1},
  volume       = {129},
  year         = {2017},
}