Résumé
Several recent seismic velocity models of the upper mantle in western Canada indicate a sharp transition from the high velocities associated with Archean cratons to low velocities beneath the Phanerozoic Canadian Cordillera. Most of those models are obtained from the analysis of surface wave data and suggest that the thick lithosphere of the Canadian Shield variably underlies a portion of the Cordillera. Here we use relative delay time tomography derived from teleseismic body-waves to investigate the geometry of the transition zone between the Phanerozoic lithosphere of the Cordillera and the juxtaposed cratonic lithosphere, as well as the extent of the Canadian Shield lithosphere beneath the Canadian Arctic Archipelago. Our new body-wave tomography models are based on two independent inversions of P- and S-wave relative delay times from teleseismic earthquakes. Our seismic tomography model expands from our recent work on the Slave Craton, and provides a much greater coverage of western Canada compared to previous studies thanks to the recent installation (since 2013) of several new broadband seismograph networks (e.g., Transportable Array, Yukon-Northwest Seismograph Network, Yukon Observatory network, Banks Island Seismic Network, etc.). The new version of the model will therefore include the Canadian Cordillera and the Beaufort Sea region, in addition to our model for the Canadian Shield region. In this study, we present preliminary results on the structure of the upper mantle underlying western Canada.