Geophysical review of the continental margins of eastern and western Canada

Abstract

The evolution and geophysical features of the continental margins of eastern and western Canada are reviewed in light of recent plate-tectonic concepts. The two margins are very different in age, structure, and origin. The eastern margins were formed either by rifting or by transform motion during the latest separation of the continents around the Atlantic that occurred from Jurassic to Tertiary times. Studies of these margins centre around a reconstruction of plate motions, the inception of which occurred over 70 Ma ago, and on subsequent processes such as subsidence and sedimentation. The subsidence of the margin is explicable in terms of cooling of the lithosphere and sediment loading. Deep crustal features are inferred from seismic, gravity, and magnetic data. The recognition of the ocean–continent boundary at these margins involves consideration of edge effects, magnetic quiet zones and rifting mechanisms. The western Canadian margins are present active plate boundaries. Recent geophysical studies of these margins centre around the detailed definition of the present plate boundaries and relative plate motions, and those of the recent past (about the past 10 Ma), and involve spreading ridges, transform faults, and subduction zones. The plate convergence predicted by offshore geophysical data has a pronounced effect on the continental crust and upper mantle extending several hundred kilometres inland from the coast. In southwestern Canada patterns characteristic of subduction zones are seen in seismic structure, the gravitational and magnetic fields, heat flow, and deep electrical structure.