Carswell - Hypervelocity Impact Crater

Alternate Names Carswell Lake
Local Language
Coordinates 58° 25' 19" N; 109° 31' 34" W
Notes
  1. Northern Saskatchewan, 140 km SSW of Uranium City.
Country Canada
Region Saskatchewan
Date Confirmed 1964
Notes
  1. Confirmed by fragments of gneiss having shatter cones in the area of the central uplift (Innes, 1964).
Buried? No
Notes
  1. Much of the central core is covered in glacial drift (Beals and Halliday, 1967).
Drilled? Yes
Notes
  1. (Tona et al., 1985) include drill hole locations on plan map and show profiles of regional geology using these data.
Target Type Mixed
Notes
  1. Basement complex composed of Aphebian or Archean gneisses and granitoids, surrounded by Athabasca sandstones, Helikian in age, which in turn are encompassed by the Carswell Formation dolomites (Fahrig, 1961).
Sub-Type Dolomite, Gneiss, Granitoid, Sandstone
Apparent Crater Diameter (km) 39 km
Age (Ma) 481.5 ± 0.8
Notes :
  1. 481.5 ± 0.8 Ma determined by 40Ar/39Ar of adularia in impact melt rock (Alwmark et al., 2017) Previous age constraints: 115 ± 10 Ma determined by 40Ar/39Ar of impact melt rocks (Bottomley et al., 1990)

Method :
  1. 40Ar/39Ar
Impactor Type Not determined
Notes
  1. Melt rocks are chemically similar to the average basement rock chemistry; no meteorite type has been determined (Pagel et al., 1985).

Advanced Data Fields

Notes

Erosion
7
  1. An estimated 200 m or more of erosion has occurred, removing the crater-fill products and exposing the substructure (Dence, 1964). The structure has been eroded below the crater-fill impactites (Reimold et al., 2005).
Final Rim Diameter
Unknown
Apparent Rim Diameter
39 km
  1. (Currie, 1969) ((Ogilvie et al., 1984) (Pagel et al., 1985)
Rim Reliability Index
2
  1. Comprises an outer ring of cliffs (39 km in diameter), an inner ring (29 km in diameter), both surrounding a marginal depression, an inner slope, and a central, raised core. Minimum uplift is 800-1200 m (Baudemont et al., 1996).
Crater Morphology
Complex
Central Uplift Diameter
18km
Central Uplift Height
90 m
Uplift Reliability Index
2
Structural Uplift
1.2 km
Thickness of Seds
Target Age
Precambrian
Marine
No
Impactor Type
Not determined
  1. Melt rocks are chemically similar to the average basement rock chemistry; no meteorite type has been determined (Pagel et al., 1985).
Other Shock Metamorphism
Shocked/recrystallized Apatite grains
  1. (Kenny et al., 2019) notes that Carswell Structure has apatite with "apparent recrystallization along grain margins.
Shatter Cones
Yes
  1. Poorly-developed shatter cones occur in gneiss from the near centre of the structure (Innes, 1964). Shatter cones are usually one to several centimeters in length, poorly-developed, and typically have a random orientation (Pagel et al., 1985). They occur in aluminous gneisses and two were also noted within quartzite pebbles in the conglomerates immediately adjacent to the basement contact (Pagel et al., 1985). Outcrops where (Innes, 1964) identified "shatter cones" were revisited by (Currie, 1969). However, this author do not confirm that the observed features are shatter cones because: they "do not show radiating striae" and they also "do not show conical surfaces". Shatter cones present in the basement rock (Harper, 1982).
Planar Fractures
Yes
  1. PFs seen on grains that do not have PDFs (Currie, 1969).
Planar Deformation Features
Yes
  1. PDF in quartz (Currie, 1969) (Harper, 1983) (Pagel, 1975). Quartz grains from the basement rock may show deformation lamellae (Fig. 15) and a few were seen on perthite and microcline grains (Currie, 1969). PDFs in quartz and feldspar of the basement rock (Harper, 1982).
Diaplectic Glass
Yes
  1. Diaplectic glass in the central uplift (Duhamel-Achin et al., 2005)
Coesite
No
Stisovite
No
Crater Fill
  1. Psuedotachylite veins (Harper, 1983). "Injected dikes of tagamite (or another impact melt rock), mylolisthenite and polymict lithic breccia comprising wandering clasts are widespread" (Koeberl et al., 2005). The structure has been eroded below the crater floor and only dykes of breccia (LB or MB?) and melt rock remain in the exposed basement rocks" (Reimold et al., 2005). Currie (1969) used the term ‘Cluff Breccias’, to include autochthonous monomict breccias, and dykes of allochthonous polymict lithic breccias, melt-bearing breccias, and clast-rich impact melt rocks
Proximal Ejecta
Distal Ejecta
Dykes
M, MB, LB, P
Volume of Melt
Depth of Melting

References

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J Donaldson, P L Money, D M Ward (1972) Precambrian geology of the Lake Athabaska area, Saskatchewan, and Baker Lake area, Northwest Territories, Guidebook - International Geological Congress 24, Part A(A32a-A32b), p. 45, url

C T Harper (1982) Geology of the Carswell Structure, central part; (parts of NTS areas 74K-5,-6,-11,-12), Annual Report - Department of Mineral Resources (Regina) 214, p. 6, Saskatchewan Mineral Resources, Regina, SK, url

C T Harper (1983) The geology and uranium deposits of the central part of the Carswell Structure, northern Saskatchewan, Canada, The geology and uranium deposits of the central part of the Carswell Structure, northern Saskatchewan, Canada, p. 587, url

E Ruhlmann (1985) Mineralogy and metallogeny of uraniferous occurrences in the Carswell structure, The Carswell Ore Uranium Deposits, Saskatchewan 29, R Laine, D Alonso, M Swab (ed.), p. 105-120, Toronto: Canadian Geological Association Special Paper

M Pilkington (1994) Magnetic anomalies over impact craters; some Canadian examples, Eos, Transactions, American Geophysical Union 75(16, Suppl.), p. 122, American Geophysical Union, Washington, DC, url

C T Harper (1996) The Cluff breccias, Carswell impact structure, Saskatchewan, Abstract Volume (Geological Association of Canada) 21, p. 1, Geological Association of Canada, Waterloo, ON, url

R A F Grieve (2005) Economic natural resource deposits at terrestrial impact structures, Geological Society Special Publications 248, I McDonald, A J Boyce, I B Butler, R J Herrington, D A Polya (ed.), p. 1-29, Geological Society of London, London, url

Isabelle Duhamel, Serge Genest, F Robert, A Tremblay (2005) Carswell impact structure, Saskatchewan, Canada: Geological, petrographical and geophysical results, and implications for the age of the astrobleme, Meteoritics & Planetary Science 40(9), p. A41-A41

W U Reimold, C Koeberl, Roger L Gibson, Burkhard O Dressler (2005) Economic mineral deposits in impact structures; a review, European Science Foundation workshop on Impact tectonics, Christian Koeberl, Herbert Henkel, Christian Koeberl (ed.), p. 479-552, Springer Verlag, Berlin, url, doi:10.1007/3-540-27548-7_20

Isabelle Duhamel (2006) La structure de Carswell (Saskatchewan, Canada); caracterisation petrographique du metamorphisme de choc, geophysique et dimensions de la structure d'impact, La structure de Carswell (Saskatchewan, Canada); caracterisation petrographique du metamorphisme de choc, geophysique et dimensions de la structure d'impact, p. 188, url

Carl Alwmark, W Bleeker, A LeCheminant, L Page, A Scherstén (2017) An Early Ordovician 40Ar-39Ar age for the ∼50 km Carswell impact structure, Canada, GSA Bulletin, doi:10.1130/B31666.1

G G Kenny, A Karlsson, M Schmieder, M J Whitehouse, A A Nemchin, Jeremy J Bellucci (2020) Recrystallization and chemical changes in apatite in response to hypervelocity impact, Geology 48(1), p. 19-23, Geological Society of America, doi:10.1130/G46575.1