Pliocene change in Pacific-plate motion

Abstract

The absolute motion of the Pacific plate has been nearly constant during the past 15 Myr, but Epp¹ recognized that some change took place between 15 Myr and the present, and tentatively chose 1 Myr for the time of the change. Cox and Engebretson² found a change in Pacific absolute motion based on hotspot tracks and a change in Pacific–Antarctic relative motion. The Pliocene deformation in California and the Juan de Fuca rotations led them to postulate a 5-Myr age for the change. The manner and timing of the change are explored more thoroughly here, and we put the time for the change in motion of the Pacific plate at between 5 and 3.2 Myr, basing the younger limit on the correlation of computed hotspot tracks with Pacific and Nazca hotspot traces. The change may explain several observations on the neighbouring continental and oceanic plate boundaries, including direct adjustments at the Pacific spreading ridges. A likely mechanism for the change is a large clockwise torque caused by acceleration of the sinking slab beneath the Kurile trench, where a fossil spreading ridge is inferred to have been subducted.