The northern Franklin Mountains and the Colville Hills, District of Mackenzie, are a series of ridges of divergent trends, separated by broad, mostly drift-covered valleys. Some ridges are supported by thrust plates, others by asymmetric anticlines. These structures, which represent shortening of the sedimentary cover, record tangential compression. Despite a variety of structural trends, there is no evidence for more than one phase of compression.

The structural province is characterized by enigmatic “reversals” in the sense that a southwest-dipping thrust plate, traced along strike, can be replaced abruptly by a northeast-dipping plate. In most cases the opposing blocks are separated by a transverse fault which indicates longitudinal shortening of the range in addition to the more obvious shortening perpendicular to it.

Anticlines are asymmetric but the sense of asymmetry changes from one range to another. In one case an asymmetry reversal takes place along trend, from northeast directed to southwest directed. This geometric similarity to the pattern of thrust plates is taken to signify a common genesis for the thrust and fold structures. These reversals along the trend of a particular range are inadequately explained, but the close geometric relation between reversals and transverse faults suggests an interrelated origin dependent on longitudinal shortening in conjunction with lateral shortening.

Most of the northern Franklin Mountains appear to be floored by a décollement zone in shale and evaporite beds of the Cambrian Saline River Formation. Structures above the zone probably are accentuated by tectonic thickening of Saline River. The décollement is assumed to extend beneath the Colville Hills about 175–200 mi northeast of the Mackenzie Mountain Front. In the McConnell Range on the south and the Mackenzie Mountains on the southeast, the décollement zone must be at a lower stratigraphic level, because beds older than Saline River Formation are exposed in structures.

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