The linkage between the sudden change in Cenozoic Pacific Plate motion and underlying convective flow with forward and adjoint models

The bend in the Hawaiian-Emperor Seamount Chain has been at least partially attributed to the sudden change in Cenozoic Pacific Plate motion. Coeval with the plate motion change is the initiation of the Izu-Bonin-Mariana (IBM) and the Tonga-Kermadec trenches. These events highlight a dramatical interval of change in plate tectonic forces which intimately relate to the underlying mantle. Yet, the dynamics of the whole system and the causal relationship between events remain uncertain. We are untangling these issues with state-of-the-art geodynamic methods. Ancient mantle structure is constructed by combining upper mantle slabs built with the kinematics of the earlier plate history of subduction with long-wavelength lower mantle structure obtained by inverting present-day seismic tomography backward in time. The combined mantle thermal structure acts as an input for a high-resolution geodynamic model with a realistic non-linear rheology, and with ancient plate motion as a prediction (or as a constraint). We use forward and adjoint models to better explore and constrain the parameter space. By varying the thermal structure and the strength of plate interfaces and comparing the predicted and observed plate motion, we systematically investigate the mechanisms for the Pacific Plate motion change, including the formation of the IBM subduction zone, subduction of the Pacific-Izanagi ridge, changes in plate coupling, and changes in mantle upwellings such as Pacific LLSVP. The causal relationship between the Pacific Plate motion change and the initiation of the Tonga-Kermadec trench will also be discussed.