ABSTRACT

Regional seismic data in the Colville Hills and Anderson Plains record up to 15 km of strata comprising five seismic-stratigraphic packages considered equivalents of 1) seismic basement; 2) Hornby Bay Group; 3) Dismal Lakes Group and Coppermine basalts; 4) Rae Group and Mackenzie Mountains supergroup; and 5) Phanerozoic strata. Equivalents of Rae Group and Mackenzie Mountains supergroup underlie parts of Anderson Plains but are virtually missing from the Colville Hills area. Under Colville Hills, basement and Hornby Bay (1663 Ma) were compressively deformed into large, northtrending basement block uplifts with structural relief of up to 6 km. These uplifts were peneplained, resulting in a major unconformity at the base of the Dismal Lakes Group (pre-1267 Ma) and could represent intra-continental adjustments related to the Racklan Orogeny (pre-1268 Ma) in the northern Cordillera. Northward in Anderson Plains, younger, southeast-verging thrusts postdate the Dismal Lakes Group and predate the Rae Group, and may be related to pre-Rae Group deformation on Coppermine Homocline. Long-wavelength folding (70-90 km) affected Coppermine basalt and older strata in the Colville Hills area. Large Proterozoic extension faults, younger than Coppermine basalt, occur in the Colville Hills area, and are possibly related to the 778 Ma Hayhook rifting event documented in the northern Cordillera. Laramide, Colville Hills anticlinal ridges have been localized, at least partly, by reactivation along weaknesses inherent in both the north-trending and northeast-trending sets of older structures.

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