Plateau uplift in western Canada caused by lithospheric delamination along a craton edge

Continental plateaux, such as the Tibetan Plateau in Asia and the Altiplano-Puna Plateau in South America, are thought to form partly because upwelling, hot asthenospheric mantle replaces some of the denser, lower lithosphere(1-4), making the region more buoyant. The spatial and temporal scales of this process are debated, with proposed mechanisms ranging from delamination of fragments to that of the entire lithosphere(1-4). The Canadian Cordillera is an exhumed ancient plateau that abuts the North American Craton(5). The region experienced rapid uplift during the mid-to-late Eocene, followed by voluminous magmatism(6), a transition from a compressional to extensional tectonic regime(7) and removal of mafic lower crust(8). Here we use Rayleigh-wave tomographic and thermochronological data to show that these features can be explained by delamination of the entire lithosphere beneath the Canadian Cordillera. We show that the transition from the North American Craton to the plateau is marked by an abrupt reduction in lithospheric thickness by more than 150 km and that asthenosphere directly underlies the crust beneath the plateau region. We identify a 250-km-wide seismic anomaly about 150-250 km beneath the plateau that we interpret as a block of intact, delaminated lithosphere. We suggest that mantle material upwelling along the sharp craton edge(9) triggered large-scale delamination of the lithosphere about 55 million years ago, and caused the plateau to uplift.