Mantle Viscosity: A Comparison of Models from Postglacial Rebound and from the Geoid, Plate Driving Forces, and Advected Heat Flux

Models of the radial variation of effective viscosity inferred from the Earth’s response to surface loads associated with Pleistocene deglaciation are compared to structures inferred from models of geodynamic phenomena associated with convection - the geoid, plate driving forces, and advected heat flux. While observations of the Earth’s response to surface loads do not have sufficient resolution to justify more than two viscous layers, adequately matching the observed long-wavelength geoid anomalies associated with density contrasts in the lower mantle (inferred from seismic tomography) and in the upper mantle (inferred from a model of subducted slabs) requires more structure. It is possible to explain the geoid, observed plate velocities, the advected heat flux in the lower mantle, and relative sea level variations in oceanic regions, all with a mantle with a high-viscosity/elastic lid, an asthenospheric channel of 2 x 1019 Pa s from 100 to 400 km depth, a 6 x 1020 Pa s transition zone, and a lower mantle of 6 x 1021 Pa s. The uplift history of Australia, Fennoscandia, and Laurentia can be explained with an asthenospheric viscosity less than a factor of 10 higher. Lateral variations in lower mantle viscosity are not required. Transient creep appears to be unimportant for the recent response to surface loads from Pleistocene deglaciation.

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