Dynamics of abrupt change in the Pacific Plate motion at 50 Ma

Abstract:

Global plate circuits and the Hawaiian-Emperor Seamount Bend (HEB) show the Pacific Plate abruptly changed motion from north to west-north-west at around 50 Ma. Several possibilities for explaining the change in Pacific Plate motion have emerged, including initiation of Izu-Bonin-Mariana (IBM) and Tonga-Kermadec subduction, which have been dated to 50 Ma based on analysis of recently acquired deep sea drilling cores, or demise of the spreading center between the Izanagi and Pacific Plates which putatively merged with the trench of the long-lasting subduction zone along the eastern margin of Asia from about 60 to 50 Ma. Although computationally challenging, it is now possible to capture the fundamental physics of subduction in global models of plate motions and we test the prevailing ideas of the change in Pacific Plate motion -- Izanagi Ridge demise and IBM initiation. We find the reconstruction with Izanagi Plate subduction and subsequent demise of the Izanagi-Pacific ridge incapable of pulling Pacific Plate northward before 50 Ma or causing any sudden change. By reconstructing intra-oceanic subduction from Late Mesozoic to early Cenozoic in northern Pacific, we build high-resolution global subduction and flow models. Slab pull from Kronotsky intra-oceanic subduction drives the Pacific plate to the north while its Eocene demise leads to a sudden change in plate motion. The 52 Ma initiation of Izu-Bonin-Mariana only progressively pulls the Pacific to the west over the next five million years and may have been a consequence of changing plate dynamics.