Kerguelen Plume Drives the Eocene Directional Change in Australian Plate Motion

Abstract Australia undergoes a directional plate motion change from westward to northward motion in the early Cenozoic that is associated with Australia/Antarctica separation. At the same time, there is evidence for early Cenozoic growing dynamic topography in the western part of the continent, which we infer by mapping geological hiatus—suggesting a high-pressure source in the upper mantle to the west of Australia. Plate motion changes can be used to better constrain the torques that drive plate tectonics. Such changes in motion need adjustments in either the torques exerted at plate boundaries or basal shear stresses. Furthermore, changes in the direction plate motion are useful to pinpoint torque locations. In particular, basal shear stresses can be understood in terms of Poiseuille flow. In this context, active driving asthenosphere torques arise from pressure gradients in the asthenosphere. Thus, Poiseuille flow inherently connects both horizontal and vertical plate motions, including dynamic topography. Mantle plumes generate positive pressure gradients in the asthenosphere, which is evident from elevated dynamic topography in regions with plume activity. Here, we apply a simple Poiseuille flow model to demonstrate that the Kerguelen plume is precisely located to provide the torque to initiate the early Cenozoic directional change of Australian plate motion; these results are entirely consistent with the hiatus occurrence in the western half of the continent at that time. Our findings point out the feasibility of identifying torque sources from active upper mantle flow that can account for shifts in the direction of plate motions.