Columbia River fault zone: southeastern margin of the Shuswap and Monashee complexes, southern British Columbia

Abstract

The Columbia River fault zone extends for 250 km from south of Nakusp, through Revelstoke, to north of Bigmouth Creek. It is a composite fault zone, which dips 20–30° easterly and separates major tectonic elements. The structurally lowest element is the Monashee Complex, which includes the culminations of Pinnacle Peaks, Thor–Odin, and Frenchman Cap. At Hoskins Creek, the Monashee décollement splays westward from the fault zone and then runs southward along the western margin of the Monashee Complex. On the east side, the Selkirk allochthon is a composite of four tectonic slices. Its western part consists of Clachnacudainn, Goldstream, and French Creek slices forming the hanging wall of the Columbia River fault zone. The remainder of the allochthon forms the highest and largest Illecillewaet slice, which may be composite.The fault zone retains evidence of a long history of movement extending from the mid-Mesozoic to Eocene. Early deformation formed a mylonite zone up to 1 km wide in which rocks recrystallized under greenschist facies conditions. The displacement truncated major folds and metamorphic isograds that had developed in the Middle Jurassic. Orientation of slickensides, fiber growth, and strain features in the mylonite indicates normal, dip-slip displacement with the slices of the hanging wall moving eastward. South of Revelstoke, the Galena Bay stock, dated at 150 Ma, apparently intruded the zone and gives a minimum age for early displacement that must be in the Late Jurassic.Late displacement caused intense fracturing, folding of mylonite, and development of gouge zones. These features are well exposed at the Revelstoke damsite, continue north of Revelstoke, but diminish in importance southward. Late movement was again normal, dip-slip with the hanging wall moving eastward; it probably ended in the Eocene. No fault scarps or disrupted drainages have been observed, and at several localities glacial sediments lie undisturbed across the fault zone, indicating a lack of postglacial movement.Metamorphic zones, juxtaposed along the fault, imply a minimum dip-slip displacement of 15–25 km. Displacement in this range poses stratigraphic and metamorphic problems, which are alleviated if displacement is in excess of 80 km. The tectonic slices east of the Columbia River fault zone are part of an allochthonous cover that was transported at least tens of kilometres eastward over the Shuswap and Monashee complexes during the Late Jurassic.

Formation of the Shuswap metamorphic core complex during late-orogenic collapse of the Canadian Cordillera: Role of ductile thinning and partial melting of the mid-to lower crust

“…4). This sequence, referred to as the mantling or cover gnei ses, has been interpreted as a shelf or platform sedimentary sequence correlated with either Lower Paleozoic or Lower Mesozoic formations (Reesor & Moore, 1971;Read, 1980;Brown, 1980;Read & Brown, 1981;Okul itch, 1984;Scam mel & Brown, 1990;Carr, ) 991 b, 1992 geology of the Shuswap MCC, and illustrate the relationship between partial melting and deformation at the latitude of the Thor-Odin dome. We propose a model for the formation of the Shuswap MCC, where late-orogenic gravitational collapse of the Canadian Cordillera i accommodated by normal faulting of the brittle upper crust and ductile thinning of the mid-to lower crust coeval with partial melting and the formation of migmatite domes ( fig.…”

Exhumation of orogenic crust: Diapiric ascent versus low-angle normal faulting

“…The Shuswap core complex is bounded by detachment faults to the east and west (Brown and Journeay, 1987;Parrish et al, 1988;Carr, 1992). The footwall consists of migmatitic metamorphic rocks, including diatexites in the Thor-Odin dome, located in the footwall adjacent to the eastern detachment (Read and Brown, 1981) (Fig. 1B).…”

The Himalayan Orogenic Segment

“…The timing of the normal faulting, as in the case of other mountain ranges such as the Alps or the Canadian cordillera (Read & Brown, 1981), is posterior to the thrusting along the MCT and the accompanying metamorphism. It postdates the crystallization of the leucogranites but it is cut by the system of N-S normal faults responsible for the recent Tibetan grabens.…”