Kimberlite magmas are volatile-rich, potassic, and ultramafic, and they are host to most of the world’s diamond deposits. A continental-scale kimberlite magmatic belt (the central Cretaceous kimberlite corridor [CCKC]) is found in the interior of the North American continent. Parallel to and coeval with the CCKC, the Cretaceous Omineca magmatic belt (OMB) is located in the Cordilleran orogen. Cordilleran magmatism, including the OMB, is commonly explained through long-lived east-dipping subduction beneath the western margin of the continent. However, this does not explain the temporal and spatial relationships between the OMB and CCKC. We suggest that west-dipping subduction of North American lithosphere beneath the eastern side of the Cordillera explains both. In this model, subduction resulted in arc magmatism of the OMB. The contemporaneous CCKC was formed by extensional stress acting on the continent as it flexed upon entry into the trench. Using a semi-infinite elastic beam model, we show that flexure of a subducting continental plate (elastic thickness = 120 km) produces tensile stresses in the deep continental lithosphere, coincident with the location of the CCKC.