Kinematics of the East Pacific Rise Retrodicted From Pacific and Farallon/Nazca Subduction‐Related Torques: Support for Significant Deep Mantle Buoyancy Controlling EPR Spreading

Abstract

AbstractSlab‐pull together with other boundary‐related torques of the Pacific and Farallon/Nazca plates are reconstructed from paleo‐agegrid datasets over the past 80 Ma in the no‐net rotation (NNR) frame of reference. The resulting reconstructions of both the retrodicted Pacific‐Farallon/Nazca age distribution and relative motion history of the East Pacific Rise (EPR) are compared with global plate kinematic reconstructions of these same aspects of Pacific basin evolution. There are mismatches between the predicted and observed age distributions and relative motion history of the EPR. Slab‐pull related torques mostly retrodict west to east motion of the EPR, whereas global kinematics result in south to north motions, orthogonal to each other. Slab‐pull torques are augmented with estimates of subduction and transform resistances together with spatially variable viscosities to assess their potential contributions to Pacific‐Farallon/Nazca relative motions and EPR motions in the NNR frame of reference. We argue that the discrepancies between these different reconstructed histories result from contributions associated with basal tractions acting on the Pacific and Farallon/Nazca plates resulting from deep mantle buoyancy. We propose that the latter has controlled the EPR evolution over the past 80 Ma and significantly contributed to driving plate motions at least in the Pacific basin.