IMPACT CRATER EXPLORATIONS
by: Charles O'Dale
CLEARWATER EAST IMPACT CRATER
An article by Beals et al in the 1964 Journal of the RASC article (below) proposed that the Clearwater Lakes double structure may be the result of a cosmic impact. This report was published before any geological studies were performed at the site in order to find impact features.
West* craters are a classic example of the impact of a contact binary asteroid creating this twin crater phenomenon, very rarely recognized on Earth (Grieve 2006).
*The larger Clearwater Lake West Crater (in the NASA/LPI image) shows a prominent ring of islands that has a diameter of about 10 kilometres (6 miles). The islands constitute a central uplifted area and are covered with units of breccias and impact melt.
During an expedition to the structures in the winters of 1962-63 and 1963-64, drilling and gravity surveys were performed. The results were interpreted in favour of the structures being of impact origin (Dence, 1964; Dence et al, 1965).
Clearwater East is defined as a highly eroded roughly circular depression, filled with water that submerges the central peak of this complex meteorite crater.
Melt rock samples from Clearwater East are strongly enriched in Os, Ir, Ru, Rh and Pd relative to crustal concentrations. This work confirms earlier findings and demonstrates similarly high enrichments of Ru and Rh. The average Os/Ir, Ru/Ir, Rh/Ir ratios of the melt samples from Clearwater east is CI-chondritic. Recent analyses of platinum group elemental abundances in the melt rocks suggest either a C1 or L-chondrite (Evans et al., 1993).
We approached these twin craters from the northeast under a 1500’ cloud layer, the weather patterns over each crater were completely different. Clearwater East had a couple of rain systems covering the south shore of the crater while Clearwater West was almost completely clear. Fuel constrains prevented a longer stay over the area to wait out the weather. After exploring as long as fuel would allow we departed to the west.
Just to the west of the crater’s common rim we started our exploration of Clearwater West.
|1. Sudbury Impact Structure happened almost two billion years before the nearby Wanapitei Impact Crater impact (right in the image), whereas the Clearwater impacts were simultaneous. (Aerial Radar Courtesy of the Planetary and Space Science Centre at the (Aerial Radar Courtesy of the Planetary and Space Science Centre at the Image courtesy of Earth Impact Database, UNB, 2003.))|
The left image, taken just to the east of the Richmond Gulf, is typical of the geology of the area.
The right image is facing east through Le Goulet gap connecting Hudson Bay and the Richmond Gulf, in the background.
I just wanted to share this with you.
Possible Multiple Impact
Beals, C. S., Ferguson, G. M., & Landau, A., [Scientists Report II.] A Search for Analogies Between Lunar and Terrestrial Topography on Photographs of the Canadian Shield, Part II, Journal of the Royal Astronomical Society of Canada, Vol. 50, p.257-258
Dence, M. R., A comparative structural and petrographic study of probable Canadian meteorite craters. Meteoritics, v. 2, pp. 249-270. 1964.
Dence, M. R., Innes, M.J.S. and Beals,C.S., On the probable meteorite origin of the Clearwater Lakes, Quebec. Journal of the Royal Astronomical Society of Canada, v. 59, pp. 13-22. 1965.
Evans, N. J., Gregoire, D.C., Grieve, R.A.F., Goodfellow, W.D. and Veizer,J., Use of platinum-group elements for impactor identification: Terrestrial impact craters and Cretaceous-Tertiary boundary. Geochemica et Cosmochimica Acta, v. 57, pp. 3737-3748. 1993.
Grieve, R.A.F., Impact Structures in Canada. Geological Association of Canada, 2006.
Melosh, H.J., Stansberry, J. Doublet craters and the tial disruption of binary asteroids [abstract]: Meteoritics, v 26, p. 371-372, 1991.
McDonald, I. Clearwater East impact structure: A re-interpretation of the projectile type using new platinum-group element data from meteorites. Meteoritics & Planetary Science, March 2002
Reimold, W. U., Grieve, R.A.F. and Palme,H., Rb-Sr dating of the impact melt from East Clearwater, Quebec. Contributions to Mineralogy and Petrology, v. 76, pp. 73-76. 1981.
Schmidt, Gerhard; Clues to the nature of the impacting bodies from platinum-group elements (rhenium and gold) in borehole samples from the Clearwater East crater..... Meteoritics and Planetary Science, 1997.
TAGLE, R. and HECHT, L., Geochemical identification of projectiles in impact rocks. Meteoritics & Planetary Science Volume 41, 26 JAN 2010.
Wanless, R. K., Stevens, R.D., Lachance, G.R. and Rimsaite,J.Y.H., Age determinations and geologic studies, Part I. Isotopic ages, Report 5. Geological Survey of Canada Paper 64-17, 126 p. 1964.