Precambrian Basement of the Western Canada Sedimentary Basin in Northern Alberta

The crystalline basement of northern Alberta is part of western Laurentia and is mostly covered by Phanerozoic strata of the Western Canada Sedimentary Basin (WCSB). The Early Proterozoic Athabasca Group covers a limited portion of the basement south of Lake Athabasca; north of Lake Athabasca, the crystalline basement is exposed in the northeastern corner of the province. Existing geological information on the sub-WCSB crystalline basement of northern Alberta has been variously assembled to support several, partly conflicting, Proterozoic terrane-accretion models. These tectonic models and the currently available geological and geophysical information are briefly reviewed herein.

Basement subdivisions of northern Alberta that have been inferred from potential field data, particularly aeromagnetic data, include, from east to west, the Taltson, Buffalo Head, Chinchaga, Ksituan and Nova domains. The Great Slave Lake Shear Zone and the Snowbird Tectonic Zone roughly bound these domains to the northwest and southwest, respectively. The aeromagnetic domains are routinely interpreted as basement terranes and Early Proterozoic subduction-related magmatic arcs, although the petrological, geochemical and geochronological constraints are rather loose.

The Bouguer gravity anomaly, long-wavelength gravity data and deep seismic data do not contribute substantially to the accreted-terrane model for northern Alberta. Except for the Great Slave Lake Shear Zone, geophysical and geological data obtained from drillcore cannot be corroborated to convincingly support cryptic sutures between the distinct terranes that have been previously postulated in northern Alberta. The Early Proterozoic terrane-accretion model for the northern Alberta basement requires further investigation and testing.

Phanerozoic reactivation of the sub-WCSB basement, documented in the Peace River Arch area and along the Great Slave Lake Shear Zone, may also characterize other shear zones that extend beneath the Phanerozoic cover. Basement reactivation is of critical importance for understanding the role of basement structure in controlling sedimentation and diagenetic patterns in the WCSB basin, as well as in the development of hydrocarbon traps and reservoirs, and of pathways for mineralizing fluids in the Phanerozoic stratigraphy.