Major dextral transcurrent displacements along the Northern Rocky Mountain Trench and related lineaments in north-central British Columbia

Abstract

The Northern Rocky Mountain Trench and a number of other prominent lineaments, along and east of the eastern margin of the Intermontane Belt, mark faults along which dextral transcurrent movements have been dominant. Offsets of shelf to off-shelf facies boundaries in lower Paleozoic rocks indicate a cumulative displacement of at least 750 km, and probably >900 km, within the system of faults related to those in the Northern Rocky Mountain and the Tintina Trenches. Farther west, another system of faults appears to offset plutons and stratigraphic assemblages along the eastern margin of the Intermontane Belt by as much as 300 km. These faults, including the Kutcho and the Pinchi, connect in part with the Teslin Suture Zone in Yukon Territory and probably with the Fraser River-Straight Creek fault zone in southern British Columbia. Although dextral transcurrent faulting may have taken place between the Middle Jurassic and early Cenozoic, the most convincing evidence points to middle Cretaceous and particularly to early Cenozoic (Eocene?) displacements. The Eocene(?) movements were temporally related to plutonism, volcanism, lamprophyre dike emplacement, high heat flow, sedimentation in grabens, and rapid uplift of northwesterly trending elongate ranges. Climactic episodes of granite emplacement, particularly in and near the northern Omineca Crystalline Belt, at ∼100 m.y., 70 m.y., and 50 m.y. ago may have been facilitated by changes from dominantly compressional to dominantly transcurrent and related tensional strain.