Pacific Plate Motion Linked to Changes in Deformation at the Plate Margins

Recent studies document many changes along the Pacific-North American plate boundary in latest Miocene-earliest Pliocene time. Basin and Range extension changed from E-W to NW-SE; the Pacific plate velocity changed clockwise to a more northerly direction with respect to North America; plate boundary motion was localized in the Gulf of California. The microplate capture events that initiated extension along this part of the plate boundary at 12-14 Ma cannot explain these younger events. We model the boundary forces on the Pacific plate before and after the cessation of subduction along the northern Melanesian arc system, to test for expected changes in Pacific plate kinematics. The collision of the Ontong Java plateau with the arc and the subsequent slab break-off led to sudden changes in the plate boundary forces and in the Pacific plate's direction of motion. These changes are evaluated at three locations on the edge of the Pacific plate, far from the Ontong-Java Plateau: western North America, the South Island of New Zealand and the Pitman transform fault. The kinematics of these major transform boundaries at the edges of the Pacific plate are shown to be in reasonable agreement with this model.