We propose a passive broad-band seismic experiment in northwestern Canada, a setting in which fundamental questions regarding the structure and dynamics of the mantle's upper and lower boundary layers can be uniquely addressed. Characterized by a series of crustal terranes welded together in order of increasing age from west to east and spanning ~4.0 Ga of Earth's history, the region represents the most nearly complete and continuous age transect of continental lithosphere on the planet and is the ideal location for investigation of the modes and temporal variation of lithospheric assembly and craton stabilization. Our goal is to produce a systemic, 3D determination of volumetric heterogeneity, anisotropy, and discontinuity structure in the upper mantle.