Viscous coupling at mid-oceanic ridges explaining puzzling Pacific Plate motions

Motions of subducting tectonic plates are explained by slab pull, ridge push, and possibly mantle drag1,2. Non-subducting oceanic plates are surrounded by only ridges and transform faults and are expected to move much slower than subducting plates, if moving at all. Surprisingly, however, the Pacific Plate was non-subducting for most of its first ~140 million years while attaining plate speeds of 5-9 cm/yr6,7. These rates are even faster than those of many subducting plates and the physical driver of this large motion remains puzzling. Here we show by 3D numerical modeling experiments that oceanic plates appear to be viscously coupled across the mid-ocean ridge to their oceanic neighbor such that plate motion can be transferred despite active ridge spreading. The plate coupling occurs underneath the weak magmatic ridge where the stronger depleted underlying mantle transfers plate stress and motion. Such viscous plate coupling provides a novel explanation why the early Pacific Plate trailed its fastest-moving subducting northern neighbors5 by being pulled NNW across their shared mid-oceanic ridge. A global implication of such stress transfer between adjacent oceanic plates is that a large regional change in the forcing of one plate will propagate globally, offering a conceptual explanation for global plate reorganizations.