ABSTRACT

Subsurface Proterozoic strata in the Colville Hills region, Northwest Territories, occur in two major successions separated by a regional unconformity (C). The deeper succession, I, comprising three sub-units, is tentatively correlated with units mapped on Coppermine Homocline to the east. Succession II is correlated with the Mackenzie Mountains supergroup to the west, and the Rae Group to the east. Some sub-horizontal discordant reflections are considered to be intrusive sheets. Phanerozoic formations, unconformably overlying the Proterozoic, have not been examined.

Four compressional deformational phases are inferred. First, large structures offsetting the deeper succession I include rotated blocks, both eastward and westward verging, (vertical offsets of 5-6 km), and an anticline 20 km wide and 4 km high. The fault blocks are interpreted as being underlain by steep, curved, reverse faults that detach at a minimum depth of 14 km. They are truncated by unconformity C, but have a vertical post-unconformity reactivation of 1 to 2 km. Second, east-verging thrusts (maximum 6 km displacement) also offset unit I. They are flatter and shallower than the larger structures, and are considered to represent a separate phase of deformation. These may be related to a regional orogeny interpreted by F.A. Cook (1988), although cumulative displacements are modest compared to the 50 to 90 km of shortening interpreted by him. Third, small thrust faults cut succesion II. These features may be reactivated phase 2 structures although phase 1 structures were also reactivated at this time. A final deformational event affecting Phanerozoic and older strata resulted in the development of the structures that form the present-day Colville Hills.

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