Figure 2.1

Simplified terrane map of the Canadian Cordillera (Gabrielse and Yorath, 1989; Wheeler et al., 1991).

Figure 2.2

Contemporary plate tectonic regime of the Canadian Cordillera and adjacent Pacific Ocean basin (Riddihough and Hyndman, 1991, Figs. 13.1 and 13.2A) showing in blue the direction (arrows) and rate (in mm/a = km/Ma) of displacement of offshore plates relative to North America.

Figure 2.3

Space and time relations between the suspect terranes of the southern Canadian Cordillera and the North American craton (see Fig. 2.1 for present distribution of terranes). Figure shows: 1) depositional time interval spanned by each terrane, 2) gaps between columns indicating unknown spatial relations among terranes, 3) ages of intrusive bodies that stitch terranes together, 4) depositional time intervals of overlap assemblages that define Insular and Intermontane superterranes, 5) light brown area showing westward growth of the western margin of North America by terrane accretion, and 6) spatial relations of Canadian Cordilleran morphogeological belts to terrane accretion. The coincidence of the Omineca Belt and Coast Belt with suture zones between lntermontane Superterrane and North American rocks, and Insular Superterrane and Intermontane Superterrane, respectively, indicate that these tectonic welts are at least partly collisional in origin (modified after Monger, Price and Tempelman-Kluit, 1982; Price, Monger and Roddick, 1985).

Figure 2.4

Biogeographic reconstruction of accreted terranes based on Pliensbachian (Lower Jurassic) faunal assemblages (after Smith and Tipper, 1991): a. present latitudinal distribution of terranes relative to North America; b. latitudinal distribution of terranes relative to North America in the Pliensbachian as deduced from variations in faunal assemblages.

Figure 2.5

Stages in the evolution of the Rocky Mountain Foreland Thrust and Fold Belt along 49° 45' N latitude (the line of section W-E of Fig. 2.6), balanced section with no vertical exaggeration (after Price, 1986). a. Crustal-scale palinspastic section derived from section W-E of Figures 2.6 and 2.7; extension faults of Middle Proterozoic, Late Proterozoic and early Paleozoic age are shown schematically, as is the abrupt change in thickness between the cratonic platform and the miogeocline. b. Paleozoic rocks and underlying Proterozoic rocks of the outboard part of the miogeocline are deformed, synkinematically metamorphosed and intruded by granite at depths of more than 20 km beneath the allochthonous Intermontane Superterrane in the Middle Jurassic at 171 Ma (Archibald et al., 1983). c. A reversal of tectonic vergence in the Jurassic resulted in tectonic wedging of Intermontane Superterrane between the Cordilleran miogeocline and its basement, and delamination and tectonic thickening of the miogeocline while it was still outboard of the edge of the cratonic platform. The crosscutting, high-level mid-Cretaceous granitic plutons establish a minimum age for thrust and fold structures in the Purcell Anticlinorium and in the suture zone between Intermontane Terrane and the North American rocks. d. The final stage in the evolution of the foreland thrust and fold belt terminated at the end of the Paleocene after the miogeocline had been displaced over the edge of the craton, producing about 10 to 15 km of crustal thickening and about 10 km of isostatic subsidence of the underlying Lower Proterozoic continental crust and lithospheric mantle.

Figure 2.6

Simplified geological map of the Rocky Mountain Foreland Thrust and Fold Belt along the Canada-U.S.A. boundary (modified after Price, 1981). W-E, line of section of Figure 2.7; SW-NE, line of section of Figure 2.8d; white numbers in black circles, locations for time-thickness curves of Figure 2.8. Symbols identifying the more important faults are as follows: Bo, Bourgeau; BR, Bull River; Co, Columbia River; FI, Flathead; Ha, Hall Lake; Ho, Hope; Le, Lewis; Li, Livingstone, Mo, Moyie; Ne, Newport; Pu, Purcell; RMT, Rocky Mountain Trench; StM, St Mary. Symbols identifying batholiths are as follows: By, Bayonne; F, Fry Creek; Ka, Kaniksu; Ku, Kuskanax; N, Nelson; W, White Creek. The Valhalla metamorphic complex is identified by the symbol, V.

Figure 2.7

Structure section (lower) and palinspastic section (upper) along line W-E of Figure 2.6 (modified after Price, 1981). The thickness of the supracrustal rocks below the Late Jurassic horizontal sea-level datum in the palinspastic section defines the depth to the Early Proterozoic crystalline basement immediately prior to tectonic subsidence that resulted from the load imposed on the lithosphere by tectonic thickening of the supracrustal rocks during thrusting and folding. In the palinspastic section, the thick Cambrian to Devonian shaly facies of the miogeocline, and the underlying thick sequence of Proterozoic rocks occupy nested rift basins west of the present locus of the Purcell anticlinorium and the Kootenay Arc.

Figure 2.8

Conceptual model for formation of the foreland basin by regional isostatic flexure of the continental lithosphere in response to loading imposed by tectonically thickened supracrustal rocks of the thrust and fold belt (after Price, 1973). Di, initial depth to basement; Df, final depth to basement; Df - Di, amount of subsidence.

Figure 2.9

Times and rates of subsidence in the southern Canadian Rocky Mountains in the Crowsnest Pass area. a, b, and c are time-depth (= cumulative stratigraphic thickness) curves for the Devono-Mississippian Exshaw Formation at: a. Fernie, B.C. (location 1 in Fig. 2.6); b. the Pacific-Atlantic Flathead well at Sage Creek, B.C. (location 2 in Fig. 2.6), dashed lines show subsidence under Lewis thrust sheet and uplift due to unroofing by normal faulting; and c. eastern edge of the foothills north of Pincher Creek, Alberta (location 3 in Fig. 2.6), dashed line shows thickness of foreland basin sequence that was eroded, as deduced from moisture content of coals (Nurkowski, 1984). d. A SW-NE structure section through the Pacific-Atlantic Flathead well (modified after P.L. Gordy in Gordy et al., 1977), see SW-NE in Figure 2.6 for location of section. Preservation of the Lower Cretaceous Blairmore group below Upper Eocene-Lower Oligocene fanglomerates in Flathead valley graben implies that the Lewis thrust sheet was still more than 8 km thick at the end of the Eocene (37 Ma), more than 20 Ma after the termination of thrusting and folding at 58 Ma. e. The superimposition of curves a, b, and c illustrates the eastward migration of depo-axis of the foreland basin.

Figure 2.10

Tintina Trench (TT) - Northern Rocky Mountain Trench (NRMT) fault zone and Fraser River (FR)-Straight Creek (SC) fault zone in stereographic projection centred on axis of best fitting small-circle (green) for TT-NRMT fault zone. Numbered ticks along the red fault traces are points along TT-NRMT and FR-SC fault zones that were used to calculate the best fitting small-circles. Long green dashed line is best fitting small-circle curve for points 1-34; its axis is at lat. 35.4° N, long. 158.7° W, and its radius is 3430 km (apical half-angle = 31.2°). Short green dashed curve is drawn about the same axis, but with a radius of 3350 km (apical half-angle = 30.5°), which corresponds to the mean distance between points 48 to 57 on FR-SC fault zone and best fitting small-circle through points 1 to 34 on TT-NRMT fault zone (after Price and Carmichael, 1986).

Figure 2.11

Transforms, thrusts and normal faults in the southeastern Canadian Cordillera (after Price, in Price et al., 1985). Large, solid black arrows indicate direction of compression during interval from 75 to 59 Ma, and direction of extension during interval from 58 to 42 Ma.

Figure 2.12

Regional tectonic map of the Canadian Cordillera (after Price, 1986) showing locations of structure sections 1 to 5 of Figure 2.13.

Figure 2.13

Net subsidence of the basement (widely spaced vertical ruling) and net uplift of the surface (closely spaced vertical ruling) due to formation of the Rocky Mountain thrust and fold belt in southwestern Alberta, as estimated by superimposing the palinspastic sections (upper panels) on the structure sections (middle panels) using the present-day sea level of the structure section and the Late Jurassic horizontal sea-level datum of the palinspastic section as a common datum. The difference in depth to the basement at the present time and in Late Jurassic time is the net subsidence (i.e., the total subsidence less the amount of erosion and isostatic uplift that has occurred since the thrusting and folding). The net uplift of the surface is the difference between the present topographic profile and the Late Jurassic sea-level datum. a. Section 1 of Figure 2.12 (after Price, 1981). b. Section 2 of Figure 2.12 (after Price, 1981). c. Section 3 of Figure 2.12 (after Price and Mountjoy, 1970). d. Section 4 of Figure 2.12 (after Mountjoy, 1980). e. Section 5 of Figure 2.12 (after Thompson, 1981).

Figure 2.14

End of Late Cretaceous and Paleocene tectonic regime of right-lateral transpression: major faults are restored to 58 Ma; heavy broken lines mark locus of future Early and Middle Eocene faults; heavy solid lines mark Tintina-Northern Rocky Mountain Trench fault system with 100 km of Early and Middle Eocene right-lateral strike-slip displacement eliminated; isopachs in the plains show the main locus of Late Cretaceous and Paleocene foreland basin subsidence adjacent to restraining bend in Tintina-Northern Rocky Mountain Trench right-lateral fault system.

Figure 2.15

End of Middle Jurassic to mid-Cretaceous tectonic regime of terrane collision and accretion: major right-lateral transform faults and the horizontal convergence across the foreland thrust and fold belt are restored to 90 Ma; heavy broken lines mark locus of future right-lateral transform faults; isopachs show main locus of foreland basin subsidence during deposition of the Lower Cretaceous (Aptian) Bullhead Group and equivalents.

Figure 2.16

Three stages in the tectonic evolution of the Canadian Cordillera:

a. end of Early Cretaceous and Late Jurassic regime of terrane collision, indentation and lateral escape;

b. end of Late Cretaceous and Paleocene regime of left-lateral transpression;

c. end of Early and Middle Eocene regime of left-lateral transtension.