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Vertical profiling of shock attenuation at the Rochechouart impact structure, France

Struzynska, P. LU orcid ; Alwmark, S. LU ; Alwmark, C. LU ; Poelchau, M. H. and Lambert, P. (2025) In Meteoritics and Planetary Science
Abstract

Rochechouart, south-west France, is a complex impact structure. Here, we present the first report of shock barometry of quartz from what are likely parautochthonous basement units at depth, based on samples from the 2017 C.I.R.I.R drilling campaign. The crystallographic orientations of 725 sets of PDFs in 512 quartz grains in samples from four drill cores were measured. We find basal PDFs (Brazil twins) as shear indicators and rhombohedral PDFs recording moderate shock pressures of 10–15 GPa, with numbers of sets per grain ranging from 1.0 to 2.1. A staggering 59.5% of the measured parautochthonous PDF sets are basal PDFs. We find a decrease of shock-metamorphic overprint from 10–15 to 5–10 GPa at site SC16 (Montoume), ~4.5 km south of... (More)

Rochechouart, south-west France, is a complex impact structure. Here, we present the first report of shock barometry of quartz from what are likely parautochthonous basement units at depth, based on samples from the 2017 C.I.R.I.R drilling campaign. The crystallographic orientations of 725 sets of PDFs in 512 quartz grains in samples from four drill cores were measured. We find basal PDFs (Brazil twins) as shear indicators and rhombohedral PDFs recording moderate shock pressures of 10–15 GPa, with numbers of sets per grain ranging from 1.0 to 2.1. A staggering 59.5% of the measured parautochthonous PDF sets are basal PDFs. We find a decrease of shock-metamorphic overprint from 10–15 to 5–10 GPa at site SC16 (Montoume), ~4.5 km south of what is currently held as the apparent crater center. Based on the abundance of low-to-moderate shock pressures and a lack of more highly shocked parautochthonous units, we discuss two well-defined scenarios for this occurrence. Scenario 1 attributes Rochechouart parautochthonous basement target material to have been subjected to at most 15 GPa as per our results. In scenario 2, the drilling only sampled the flanks of the central uplift but not its more strongly shocked center. Our favored hypothesis is the latter, and thus we relate our lack of highly shocked parautochthonous units to a lack of samples from the immediate center of the structure. Finally, based on the extent of PDFs from our shock barometry study of quartz, we estimate the minimum extent for the diameter of the structure to be 24 km.

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Meteoritics and Planetary Science
publisher
Wiley-Blackwell
external identifiers
  • scopus:105023855220
ISSN
1086-9379
DOI
10.1111/maps.70078
language
English
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yes
id
e1b8c55b-fb26-4343-bf21-7fc5414dfba1
date added to LUP
2026-01-12 09:12:30
date last changed
2026-01-12 09:21:52
@article{e1b8c55b-fb26-4343-bf21-7fc5414dfba1,
  abstract     = {{<p>Rochechouart, south-west France, is a complex impact structure. Here, we present the first report of shock barometry of quartz from what are likely parautochthonous basement units at depth, based on samples from the 2017 C.I.R.I.R drilling campaign. The crystallographic orientations of 725 sets of PDFs in 512 quartz grains in samples from four drill cores were measured. We find basal PDFs (Brazil twins) as shear indicators and rhombohedral PDFs recording moderate shock pressures of 10–15 GPa, with numbers of sets per grain ranging from 1.0 to 2.1. A staggering 59.5% of the measured parautochthonous PDF sets are basal PDFs. We find a decrease of shock-metamorphic overprint from 10–15 to 5–10 GPa at site SC16 (Montoume), ~4.5 km south of what is currently held as the apparent crater center. Based on the abundance of low-to-moderate shock pressures and a lack of more highly shocked parautochthonous units, we discuss two well-defined scenarios for this occurrence. Scenario 1 attributes Rochechouart parautochthonous basement target material to have been subjected to at most 15 GPa as per our results. In scenario 2, the drilling only sampled the flanks of the central uplift but not its more strongly shocked center. Our favored hypothesis is the latter, and thus we relate our lack of highly shocked parautochthonous units to a lack of samples from the immediate center of the structure. Finally, based on the extent of PDFs from our shock barometry study of quartz, we estimate the minimum extent for the diameter of the structure to be 24 km.</p>}},
  author       = {{Struzynska, P. and Alwmark, S. and Alwmark, C. and Poelchau, M. H. and Lambert, P.}},
  issn         = {{1086-9379}},
  language     = {{eng}},
  publisher    = {{Wiley-Blackwell}},
  series       = {{Meteoritics and Planetary Science}},
  title        = {{Vertical profiling of shock attenuation at the Rochechouart impact structure, France}},
  url          = {{http://dx.doi.org/10.1111/maps.70078}},
  doi          = {{10.1111/maps.70078}},
  year         = {{2025}},
}