Constraining Cretaceous subduction polarity in eastern Pacific from seismic tomography and geodynamic modeling

Abstract Interpretation of recent mantle seismic images below the America ignited a debate on the Cretaceous subduction polarity in the eastern Pacific Ocean. The traditional view is that the massive vertical slab wall under eastern North America resulted from an eastward Farallon subduction. An alternative interpretation attributes this prominent seismic structure to a westward subduction of the North American Plate against a stationary intraoceanic trench. Here I design quantitative subduction models to test these two scenarios, using their implied plate kinematics as velocity boundary conditions. Modeling results suggest that the westward subduction scenario could not produce enough slab volume as seismic images reveal, as is due to the overall slow subduction rate (~2.5 cm/yr). The results favor the continuous eastward Farallon subduction scenario, which, with an average convergence rate of >10 cm/yr prior to the Eocene, can properly generate both the volume and the geometry of the imaged lower mantle slab pile. The eastward subduction model is also consistent with most Cretaceous geological records along the west coast of North America.