Tracking Temporal Variations in Hawaiian Plume Flux Using Evolving Swell Topography

For more than 50 million years the Hawaiian hotspot has supported the growth and evolution of the Hawaiian Ridge. As the hot and buoyant Hawaiian Plume, ascends and pools beneath the Pacific plate, it spreads laterally and is dragged westward along with plate motion. Lateral spreading beneath the lithosphere is dependent on both the rheology and total density heterogeneity of the accumulated plume material. Total density heterogeneity of the plume can be observed on the surface, as it causes isostatic uplift of the seafloor to form the 3000km long and 1000km wide bathymetric feature known as the ';Hawaiian Swell'. Recent models of the Hawaiian plume have begun to use bathymetric variations in the swell to constrain temporal changes in plume parameters that were previously held as constants. To expand upon these studies, we use variation in the dimensions of the swell to constrain temporal variations in the rate of material flux feeding the Hawaiian plume. To begin we developed a model for swell bathymetry, based on the non-Newtonian rheological plume model of [Asadi et al., 2011] and the swell profile relation of [Wessel & Keating, 1994]. We compare modeled cross-axial profiles of the swell to geographically paired profiles of swell bathymetry corrected for ocean sediment thicknesses and seafloor subsidence. This procedure constrains plume flux as a function of time, as the Hawaiian swell forms over the hotspot and moves away down the axis of plate motion. During the last 35 million years our model suggests that plume flux has experienced large-scale oscillations with peak to trough amplitudes in the range of ~40-60 m^3/s, (~10 - 20% of mean plume flux), occurring over periods of 5 - 10 million years. While traditional geochemical studies of variations in Hawaiian plume flux suggest a clear and dramatic increase in rates toward the present day, our model suggests that the current peak in plume flux is part of a long-term oscillatory pattern, rather than an exponential one. This swell analysis method shows promise for application to other hotspot swells, to gain understanding into oscillatory behavior of mantle plumes. We also extend this analysis of the Hawaiian ridge to the bend in the Hawaiian chain at 50 Ma, and to earlier times, to gain better insight into the long-period cycles of the Hawaiian plume.