On a regional grid of seismic lines from the Colville Hills in the northern Interior Plains of Canada, subsurface strata can be subdivided into four seismic-stratigraphic packages, each of which has been affected by one or more of four compressional and one extensional phases of deformation. The tentative Proterozoic stratigraphy (Hornby Bay Group, Dismal Lakes Group, and Coppermine basalts) can be mapped regionally but can be tied neither to outcrop nor good well control. It is the result of comparison of unconformities, structures and deformation phases mapped in outcrop to the east and a chemical comparison of basalts cored in the area with the Coppermine basalts. The Proterozoic compressional events involved faults that soled deep within basement and produced minor shortening. The extensional phase reversed the throw on some of the older faults. The location of structures produced during the last compressional phase (Laramide) has been influenced by pre-existing Proterozoic features. These interpretations are at odds with the published literature, which invokes up to 200 km of shortening on shallow detachments and backthrust faults. They are, however, consistent across the regional grid and link to a similar study to the north.

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