NEW CONSTRAINTS ON TEMPORAL VARIATIONS IN HAWAIIAN PLUME BUOYANCY FLUX

The Hawaiian Ridge provides a 50 million year record of the interaction between a plume of hot rock rising through the mantle and the northwestward motion of the Pacific plate. One feature related to the plume-lithosphere interaction, known as the ‘swell’, is a broad region of elevated bathymetry dynamically supported by the thermal buoyancy of plume material accumulating beneath the lithosphere. Prior studies have examined changes in swell dimensions to estimate fluctuations in the rate at which mass and heat are transported by the Hawaiian plume (buoyancy flux) to the base of the lithosphere. To improve upon these efforts, we propose a new method to constrain Hawaiian plume buoyancy flux using a model of plume spreading that assumes non-Newtonian rheology, while accounting for changes in the velocity of the Pacific plate and subsidence of the swell attributed to heat loss. Buoyancy flux over time is constrained along the swell axis by fitting model predictions of swell dimensions to cross-axis profiles of swell bathymetry corrected for sediment loading, lithospheric cooling, and surface volcanism. Our results show that the buoyancy flux of the Hawaiian plume has more than doubled between ~50 Ma and the present, with a maximum at ~15 Ma. Comparisons to the history of erupted magma flux and other measures of plume activity suggest that our results of increased buoyancy flux could be achieved by increases in either the material flux or excess temperature of the plume. We suggest our method as an improved means to estimate plume buoyancy flux from swell dimensions.