Nicholson - Hypervelocity Impact Crater

Alternate Names Nicholson Lake (McGregor et al., 2017).
Coordinates 62° 39' 44" N; 102° 39' 57" W
Notes
  1. 480 km NE of Uranium City and 320 km E of Fort Reliance.
Country Canada
Region Northwest Territories
Date Confirmed 1968
Notes
  1. Confirmed based on the presence of shatter cones and PDFs in quartz and feldspar (Dence et al., 1968).
Buried? No
Notes
  1. Palaeozoic sediments covered the structure until glaciation deeply eroded and exposed it (Ogilvie et al., 1984).
Drilled? No
Target Type Mixed
Notes
  1. Gneissic rocks of granitic and granodioritic composition with amphibolite bands; Churchill Province (Dence et al., 1968). Late Middle Ordovician limestone (cover rocks) apparently unshocked (Ogilvie et al., 1984).
Sub-Type Gneiss, Limestone
Apparent Crater Diameter (km) 12.5 km
Age (Ma) 387 ± 5
Notes :
  1. 387 ± 5 Ma determined by U-Pb dating of apatite from impact melt rock (McGregor et al., 2018). Additional age constraints: 400 Ma determined by 40Ar/39Ar dating of melt rocks provides a maximum age (Bottomley et al., 1990). Palaeozoic sediments covered the structure until glaciation deeply eroded and exposed it (Ogilvie et al., 1984).

Method :
  1. U-Pb
Impactor Type Achondrite
Notes
  1. From analyses on samples of the breccia, (Wolf et al., 1980) identified a Ni and Cr enrichment; meteorite determined as olivine-rich achondrite.

Advanced Data Fields

Notes

Local Language
N/A
Erosion
6
  1. Crater floor partly exposed; clastic breccias overlain by inclusion-rich melt crop out on a number of small islands and on a large promontory on the western side of the lake (Dence et al., 1968).
Final Rim Diameter
Unknown
Apparent Rim Diameter
12.5 km
  1. Structure occupies by an oval lake and is estimated at ~12.5 km in diameter (Grieve et al., 1988).
Rim Reliability Index
3
  1. There is virtually no morphological indication of a circular outline. The crater comprises a central uplift island of basement gneises surrounded by an annular depression containing preserved Palaeozoic limestone (Dence et al., 1968).
Crater Morphology
Complex
Central Uplift Diameter
Unknown
Central Uplift Height
50 m
Uplift Reliability Index
4
Structural Uplift
Unknown
Thickness of Seds
Unknown
Target Age
Palaeozoic
Marine
No
Impactor Type
Achondrite
  1. From analyses on samples of the breccia, (Wolf et al., 1980) identified a Ni and Cr enrichment; meteorite determined as olivine-rich achondrite.
Other Shock Metamorphism
No
Shatter Cones
Yes
  1. Shatter cones in gneisses of central uplift, up to 10 cm in length (Dence et al., 1968) (Ogilvie et al., 1984). Near the lake's centre, the basement (granodioritic) gneisses display shatter cones (Dence et al., 1968). The best developed cones are the ones from the western promontory. Shatter cones occur in a "pale green, equigranular, medium-grained, weakly foliated, leucocratic biotite-granodiorite gneiss slightly altered to chlorite and epidote". Quartz and feldspar grains within shatter cone samples are irregularly fractures (no PFs and PDFs seen) (Dence et al., 1968). An ~10 cm in length shatter cone is presented in (Dence et al., 1968).
Planar Fractures
No
Planar Deformation Features
Yes
  1. PDF in quartz and feldspar grains (Dence et al., 1968). "In the centre, the gneisses contain quartz and microcline with PDFs however not strongly developed with the occurance of only basal ω{1013} features (Grieve, 2006). Near the lake's centre, development of planar features of Types A and B in quartz and sharply defined planar features in microcline (Dence et al., 1968). Well-developed planar features in both microcline and plagioclase present in breccias (Dence et al., 1968). Fig. 15 (Robertson et al., 1968) shows quartz with non-decorated Type D planar features. Measurements and orientations of 134 planar features from 53 quartz grains taken from breccia fragments and clastic matrix showed Types A, B, and D (Dence et al., 1968). Gneisses from the centre of the lake show distinct evidence of weak shock action, with the development of planar features in quartz, microcline, and some fine kink bands in mica (Dence et al., 1968). Non-decorated planar features in quartz (Robertson et al., 1968). Well developed planar features seen in feldspars of all compositions (Dence et al., 1968).
Diaplectic Glass
No
Coesite
No
Stisovite
No
Crater Fill
LB, MB, M
  1. Monomict and polymict breccias, (including suevite) and melt rocks are present (McGregor et al., 2018). Polymict breccias overlie strongly fractured and altered granodiorite gneiss and have a maximum thickness of ~300 m. Two breccia lithologies are identified. First breccia contains <30% glassy material and is weak and crumble/break readily when struck. The second lithology is a welded breccia which is hard, fracture subconchoidally, and distinctly jointed. Welded breccias are typically grey-green and purple in colour in outcrops whereas weaker breccias have pale green hues mottled with red and black (Dence et al., 1968).
Proximal Ejecta
Unknown
Distal Ejecta
Unknown
Dykes
Unknown
Volume of Melt
Unknown
Depth of Melting
Unknown

References

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Robert S Dietz (1971) Shatter cones (shock fractures) in astroblemes, Meteorics and Planetary Science 6(4), p. 258-259, Miami, FL, url, doi:https://doi-org/10.1111/j.1945-5100.1971.tb00117.x

R Wolf, A B Woodrow, R A F Grieve (1980) Meteoritic material at four Canadian impact craters, Geochimica et Cosmochimica Acta 44(7), p. 1015-1022, Pergamon, Oxford, url, doi:10.1016/0016-7037(80)90289-6

B Y Ogilvie, B Robertson, R A F Grieve (1984) Meteorite impact features in Canada: an inventory and an evaluation, p. 180

M McGregor, C R M McFarlane, John G Spray (2017) The Nicholson lake impact structure, Canada: Shock features and age of formation, 48th Lunar and Planetary Science Conference, p. 2151-2151, Houston: Lunar and Planetary Science Conference, pdf

M McGregor, C R M McFarlane, J G Spray (2018) In situ LA-ICP-MS apatite and zircon U–Pb geochronology of the Nicholson lake impact structure, Canada: Shock and related thermal effects, Earth and Planetary Science Letters 504, p. 185-197, url, doi:10.1016/j.epsl.2018.10.006