Channelized lithospheric erosion shapes the western North American craton margin.

Modification of craton margins influences topographic evolution, magmatism, and mineralization, though the scales, geometries, and driving mechanisms remain debated. Previous studies of the western North American craton margin focused primarily on the Colorado Plateau, invoking hydration by the subducting slab as the controlling factor. Here we construct a high-resolution 3-D shear-wave velocity model of this margin using full-wave ambient noise tomography. Our model reveals a distinct inward retreat of the high-velocity cratonic keel with depth along the entire margin, not limited to the edge of the Colorado Plateau, as previously thought. Two laterally confined (150-200 km wide) low-velocity zones, reflecting channelized lithospheric weakening, extend 500-600 km into the craton, reaching the Black Hills in two opposite directions. Their spatial correlation with strong mantle flows suggests that this flow can erode the craton itself. Kimberlite and basalt geochemistry data suggest that this entire margin undergoes progressive and laterally heterogeneous lithospheric erosion and may eventually delaminate, facilitating progressive inward and lateral lithospheric thinning. This progressive erosion process drives the migration of volcanism and regional topographic uplifts. Our findings provide insights into the detailed characteristics and mechanisms of lithospheric modification at craton margins, shaping the long-term evolution of cratonic lithosphere.