HIGH ROCK LAKE STRUCTURE
by: Charles O’Dale
- Type: Complex
- Age Ma: 435 ±10 (Geological dating)a – SILURIAN
- Diameter: ~5 km
- Location: N 51° 27.5’ W 097° 41.2’
a The age granite from the southwestern rim was annealed. An alternate impact age estimate: Raw fission track ages for the High Rock Lake impact are 389 ± 26 and 396 ± 33 Ma (Kohn et al 1995).
ABSTRACT: The High Rock Lake structure, on the northeastern flank of the Williston Basin in Manitoba, is a circular crater commonly thought to be an astrobleme. Apatite fission-track (FT) ages from basement rocks in the structure is markedly younger than those previously derived in the region. Constraints from regional geohistory combined with forward modelling of apatite FT data indicate that at High Rock Lake, apatites in a weakly foliated granite and a brecciated and metasomatised granite from the uplifted southwestern crater rim, were totally, or nearly totally, annealed in the range of ~435 ± 10 Ma. This range is interpreted as dating the time of cratering and is in excellent agreement with stratigraphic evidence which constrains the event as Late Ordovician to Mid-Silurian. The resetting of apatite FT clocks within the basement rocks by two discrete Phanerozoic cratering events (High Rock Lake and St. Martin structures) provides a unique opportunity to study the post cratering thermal history of the region. At High Rock Lake and Lake St. Martin samples achieved maximum paleotemperatures (~60-70° C) during the Eocene. This temperature range is in good agreement with data independently attained from organic maturity indicators elsewhere in the northeastern Williston Basin area (Bezys 2000).
Two Precambrian granite inliers near High Rock Lake, south of Lake St. Martin, suggest a circular feature of very complex origin (McCabe, 1981; 1982). The two Precambrian granite inliers are approximately 180 m above their expected position in the regional structure. As well, disturbed Paleozoic outcrops exist north and west of the granite outcrops. The structurally disturbed area is shown to be coincident with a well defined aeromagnetic low (McCabe, 1981).
R.K. Bezys STRATIGRAPHIC INVESTIGATIONS AND COREHOLE DRILLING PROGRAM, 2000 in Report of Activities 2000, Manitoba Industry, Trade and Mines, Manitoba Geological Survey, p. 196-201.
Barry P. Kohn, Kirk G. Osadetz, Ruth K. Bezys – Apatite Fission-Track Dating of Two Crater Structures in the Canadian Williston Basin Bulletin of Canadian Petroleum Geology Vol. 43 (1995), No. 1. (March), Pages 54-64
Brent Dalrymple, Radiometric Dating Does Work! Reports of the National Center for Science Education
McCabe, H.R. High Rock Lake structure. Manitoba Mineral Resources Division, Report of Field Activities, p. 78-82 1981.
McCabe, H.R. High Rock Lake Crater structure. Manitoba Mineral Resources Division, Report of Field Activities, p. 69-74 1982.