Lithosphere seismic reflection structure of the southeastern Canadian cordillera: Initial results

Nearly 270 km of crustal seismic reflection data obtained by Lithoprobe in the southern Canadian Cordillera provide a geometric link between the Rocky Mountain foreland thrust and fold belt, the Purcell anticlinorium, and the extensional regime superimposed on the crystalline core zone. Autochthonous North American basement and its overlying deformed and transported cover can be traced from the thrust and fold belt, beneath the Rocky Mountain trench, to 20 km depth beneath the central part of the Purcell anticlinorium. The Purcell anticlinorium is cored by foreshortened Proterozoic supracrustal rocks that were carried northeastward on a series of west dipping imbricate thrust faults. These faults crop out within and east of the anticlinorium and converge downward with subhorizontal detachments above the autochthonous North American basement. Beneath the western Purcell anticlinorium and Kootenay Arc, reflections associated with the Purcell stratigraphy and its underlying crystalline basement terminate at about 20 km depth and may be truncated against the east dipping Eocene Slocan Lake fault zone. The Slocan Lake fault zone is clearly imaged from the surface to about 12 km depth and can probably be followed discontinuously to about 25 km depth. A west-dipping, high amplitude reflection from beneath the Valhalla gneiss complex outlines the domal geometry of the complex and is probably related to an east verging compressional shear zone.