Geodynamic models allow insights into the processes that control lithosphere structure and evolution. Here, we highlight geodynamic studies along a profile through southwestern Canada, from the Cascadia subduction zone into the Laurentian craton. Geophysical and geological observations show distinct changes in thermal structure along this profile. One major change is between the cool forearc and hot volcanic arc. This marks the transition from (1) a stagnant forearc mantle that is cooled by the subducting Juan de Fuca Plate to (2) an advection-dominated arc region, where high temperatures arise from mantle flow driven by the subducting plate (corner flow). High temperatures occur for 400-500 km east of the arc to the Rocky Mountain Trench (RMT), where lithosphere thickness increases from 60-70 km below the Cordillera to >200 km below the craton. The timing of Cordillera lithosphere thinning is debated. A long-lived (>100 Ma) thin lithosphere inherited from earlier tectonics requires vigorous convection of a weak, hydrated mantle. Conversely, thinning may have occurred through gravitational removal of the lower lithosphere in the Eocene. Models show that a removal event only allows for a short-lived thin lithosphere (~25 Myr), owing to conductive cooling. Even if there was Eocene delamination, the present-day thin lithosphere requires small-scale convection in the Cordillera mantle. The thermal contrast across the RMT is enhanced by edge-driven convection at the Cordillera-craton lithosphere step. The step itself is an enigmatic feature, and its long-term preservation requires that the craton mantle lithosphere is strong (dry) with moderate chemical depletion.

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Geophysical imaging reveals significant changes in mantle properties from the Southern Canadian Cordillera to the Laurentian Craton in southwestern Canada. We examine mantle structure using shear wave velocity (VS) from seismic tomography and electrical resistivity from magnetotellurics. Independent analyses of VS and resistivity are poorly constrained because of the number of free parameters. To overcome these limitations, we conduct a joint analysis of VS and resistivity to quantify temperature and olivine water content at 75–150 km depth, corresponding to the cordillera asthenosphere and craton mantle lithosphere. For the cordillera, there is a trade‐off between temperature and water content; the observations are consistent with either warm, hydrated, and melt‐free mantle (∼1,240°C; ∼1,600 ppm H/Si in olivine) or hotter, less hydrated mantle (∼1,370°C; ∼600 ppm H/Si) with some melt at 75 km depth. In contrast, the craton mantle lithosphere is ∼350°C cooler and drier (<300 ppm H/Si). Temperatures depend strongly on the seismic attenuation model. If this is known, the temperature uncertainty is <100°C. There is significant uncertainty in olivine water content (>500 ppm H/Si), owing to observation uncertainties, the resistivity model, and mantle composition. Our results indicate that the cordillera asthenosphere has a low viscosity (1019–1021 Pa s) and is susceptible to small‐scale convection. Approximately below the Rocky Mountain Trench, there is a subvertical eastward increase in lithosphere thickness. The cratonic mantle lithosphere viscosity is 1022–1024 Pa s and the western edge of the craton may be unstable, suggesting that the present‐day geometry is a transient feature.