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A Cryogenian impact structure lurking in the shadows of northern Sweden

Alwmark, C. LU ; Kenny, G. G. ; Alwmark, S. LU ; Minde, P. ; Plado, J. ; Hietala, S. and Whitehouse, M. J. (2024) In Meteoritics and Planetary Science 59(12). p.3305-3321
Abstract

Here we report on findings for four rock samples with melt texture found in a gravel pit within a glaciofluvial deposit near the small town of Kitkiöjärvi in northernmost Sweden. The samples are comprised of granitic clasts embedded in a brown fine-grained melt matrix. The samples all contain quartz grains and/or clasts exhibiting multiple sets of planar deformation features oriented parallel to crystallographic planes characteristic of shock metamorphism. The samples also contain Former Reidite In Granular Neoblastic (FRIGN) zircon. We therefore conclude that the investigated samples represent impact melt rock. We interpret a U-Pb concordia age of 658.9 ± 6.9 Ma (Cryogenian) derived using secondary-ion mass spectrometry analysis of... (More)

Here we report on findings for four rock samples with melt texture found in a gravel pit within a glaciofluvial deposit near the small town of Kitkiöjärvi in northernmost Sweden. The samples are comprised of granitic clasts embedded in a brown fine-grained melt matrix. The samples all contain quartz grains and/or clasts exhibiting multiple sets of planar deformation features oriented parallel to crystallographic planes characteristic of shock metamorphism. The samples also contain Former Reidite In Granular Neoblastic (FRIGN) zircon. We therefore conclude that the investigated samples represent impact melt rock. We interpret a U-Pb concordia age of 658.9 ± 6.9 Ma (Cryogenian) derived using secondary-ion mass spectrometry analysis of shocked zircon, as the best estimate for the age of the impact event that formed the melt rocks. Zircon grains from two of the samples yield younger lower intercept ages, raising the possibility that the samples came from multiple impact events of different ages. Although we cannot exclude this possibility, we interpret the younger ages from the clast-rich melt rocks to reflect non-impact-related Pb loss events and suggest that all samples likely came from the same structure. Analysis of the glaciofluvial history of the region, along with the relatively high frequency of finds (five in total, as one similar melt rock was found in the pit in 2018), points to a short-distance glacial transportation of the samples from the southwest. Since there are no known impact structures in Sweden within that area and/or of similar age, we conclude that an old (the oldest known yet) impact structure in Sweden potentially is yet to be discovered somewhere in the vicinity of the gravel pit.

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author
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organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Meteoritics and Planetary Science
volume
59
issue
12
pages
17 pages
publisher
Wiley-Blackwell
external identifiers
  • scopus:85208433395
ISSN
1086-9379
DOI
10.1111/maps.14280
language
English
LU publication?
yes
additional info
Publisher Copyright: © 2024 The Author(s). Meteoritics & Planetary Science published by Wiley Periodicals LLC on behalf of The Meteoritical Society.
id
b89c8e79-80eb-46b4-ab25-a3637cb4bab3
date added to LUP
2025-02-18 10:00:17
date last changed
2025-04-04 14:47:25
@article{b89c8e79-80eb-46b4-ab25-a3637cb4bab3,
  abstract     = {{<p>Here we report on findings for four rock samples with melt texture found in a gravel pit within a glaciofluvial deposit near the small town of Kitkiöjärvi in northernmost Sweden. The samples are comprised of granitic clasts embedded in a brown fine-grained melt matrix. The samples all contain quartz grains and/or clasts exhibiting multiple sets of planar deformation features oriented parallel to crystallographic planes characteristic of shock metamorphism. The samples also contain Former Reidite In Granular Neoblastic (FRIGN) zircon. We therefore conclude that the investigated samples represent impact melt rock. We interpret a U-Pb concordia age of 658.9 ± 6.9 Ma (Cryogenian) derived using secondary-ion mass spectrometry analysis of shocked zircon, as the best estimate for the age of the impact event that formed the melt rocks. Zircon grains from two of the samples yield younger lower intercept ages, raising the possibility that the samples came from multiple impact events of different ages. Although we cannot exclude this possibility, we interpret the younger ages from the clast-rich melt rocks to reflect non-impact-related Pb loss events and suggest that all samples likely came from the same structure. Analysis of the glaciofluvial history of the region, along with the relatively high frequency of finds (five in total, as one similar melt rock was found in the pit in 2018), points to a short-distance glacial transportation of the samples from the southwest. Since there are no known impact structures in Sweden within that area and/or of similar age, we conclude that an old (the oldest known yet) impact structure in Sweden potentially is yet to be discovered somewhere in the vicinity of the gravel pit.</p>}},
  author       = {{Alwmark, C. and Kenny, G. G. and Alwmark, S. and Minde, P. and Plado, J. and Hietala, S. and Whitehouse, M. J.}},
  issn         = {{1086-9379}},
  language     = {{eng}},
  number       = {{12}},
  pages        = {{3305--3321}},
  publisher    = {{Wiley-Blackwell}},
  series       = {{Meteoritics and Planetary Science}},
  title        = {{A Cryogenian impact structure lurking in the shadows of northern Sweden}},
  url          = {{http://dx.doi.org/10.1111/maps.14280}},
  doi          = {{10.1111/maps.14280}},
  volume       = {{59}},
  year         = {{2024}},
}