Odale-Articles-LacLaMoinerie

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IMPACT CRATER EXPLORATIONS

by: Charles O'Dale

LAC LA MOINERIE IMPACT CRATER

Lac La Moinerie, Quebec.
Lac La Moinerie (left of centre).
  • Age (ma): 400 ± 50
  • Diameter: 8 km
  • Location: Quebec, Canada. N 57° 26' W 66° 37'
  • Shock Metamorphism: PDF in quartz clasts (Gold et al., 1978).
  • Dating Method: 40Ar-39Ar Isotopic studies of three melt samples (Bottomley et al., 1990).
General Area: Subdued topography in the Canadian Shield. The area is only lightly wooded, being close to the tree-line, and has been glaciated. The target rocks are crystalline.
Specific Features: The structure is a roughly circular lake 8 km in diameter, which contrasts with other linear and irregular lakes in the area. The crater cuts regional structure that takes the form of a large southeasterly plunging fold. Erosion has removed all signs of the rim and the lake is taken as the original diameter. The geology at the structure has been examined only at the reconnaissance level.

Lac La Moinerie, a highly eroded complex meteorite crater, is visible just to the left of center in the above landsat image (Courtesy NASA/LPI). The structure was visited by D.P. Gold (Pennsylvania State University), who discovered impact breccia float on the northern shoreline (Grieve 2006). The central islands in the lake are thought to be the remains of the crater’s central peak. There is a gravity low coincident with the basin area of the crater but is distorted considerably by the presence of a strong regional gradient. The amplitude of this gravity low, estimated to be about 5 mgal, is a value consistent with other impact sites of similar size. Granophyre breccia has been recovered from the crater area (Gold et al., 1978).


Possible link to the Late Devonian Extinction
Lac La Moinerie.
The red dot represents the approximate area of the Lac La Moinerie impact 400 million years ago in the Devonian Period.
The target rocks around the crater are Archean quartz-feldspathic and granitic gneisses of the Nain Province, folded in a large southeast plunging antiform. Extensive glaciation has removed much of the original structure, including the crater-fill products and most of the central uplift. The preservation of such a relatively small structure of Middle Paleozoic age suggests that the crater may have been partially protected from erosion by a post-crater sedimentary cover. Silurian fossiliferous limestone has been found in the crater. At the time of the Lac La Moinerie impact the earliest land plants as well as the first sharks were just beginning to evolve.

Aerial Exploration

Lac La Moinerie - south.
Lac La Moinerie - east.
We approached Lac La Moinerie from the south after our exploration of the Mistastin Crater. Fuel constraints would only allow us a relatively short time for observation. The sequence of this series of images was taken counter-clockwise from the south, from the east and from the north east of the crater respectively. Eons of erosion has taken its toll on this crater as all that appears to remain of the original structure is a circular water filled hole in the bedrock. It would be very difficult to recognize the structure as an impact site without pre-knowledge of the studies done here.
Lac La Moinerie - north.

Side Note

Small crater north of Lac La Moinerie?
Small crater north of Lac La Moinerie?
The water in the small lakes is so clear that we were able to see the bottoms of the lakes from our altitude of over 1500’ above the ground. We departed the area to the north heading for Kuujjuaq. I wanted to document a small circular lake that I noticed. The lake is visible in the foreground with Lac La Moinerie Meteorite Crater in the background. These images were taken about 30 seconds apart as we passed the northern area of La Moinerie Crater. To my knowledge there has not been any investigation to determine the cause of this structure. I hypothesize that this small lake may be an impact site associated with the Lac La Moinerie Meteorite Crater, a double crater structure similar to the Clear Lakes Meteorite Craters. Note the esker visible on the right (west) part of the circular lake. This “might” indicate a shallow part of the lake caused by a rim structure.

References

Bottomley, R. J., York, D. and Grieve,R.A.F., 40Argon-39Argon dating of impact craters. Proceedings Lunar and Planetary Science Conference 20th, pp. 421-431. 1990.

Gold, D. P., Tanner, J.G. and Halliday,D.W., The Lac La Moinerie crater: A probable impact site in New Quebec (abstract). Geological Society of America, v. 10, p. 44. 1978.

Grieve, R.A.F., Impact Structures in Canada. Geological Association of Canada, 2006.

Earth Impact Database





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