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true polar wander, geoid, mantle circulation models, density anomalies, strong core heating, viscosity

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Growing evidence points to a substantial heat flow across the core‐mantle boundary (CMB), but the rotational stability of strongly bottom heated mantle flow with prominent upwelling plumes is poorly known. Here we calculate polar motion for the past 100 Myr induced in a new class of isochemical high‐resolution mantle circulation models (MCMs) with Earth‐like convective vigor and up to 12 TW core heat flux. Our MCMs include internal heating and a simple three‐layer viscosity profile associated with the lithosphere (1023 Pa s) and the upper (1021 Pa s) and the lower mantle (1023 Pa s), separated at 100 and 650 km depth, respectively. A published mantle mineralogy model in the pyrolite composition, consistent with our assumption of whole mantle flow, allows us to relate thermal to density variations in a thermodynamically self‐consistent way. All models yield modest polar motion on the order of 0.5° Myr−1 or less, in accordance with paleomagnetic data and agreeing with a number of studies that demonstrate the stabilizing effect of the rotational bulge. Although a substantially reduced lower mantle viscosity would increase this rate, the good agreement between MCM and seismic mantle heterogeneity lends independent support for our viscosity profile, as otherwise, slabs in the MCM would rapidly sink to depth levels where they are tomographically not observed. In general, there is good agreement between the long‐wavelength geoids predicted from our MCMs and recent satellite derived models of Earth's geoid (correlation coefficient of around 0.4), but noticeable differences at intermediate wavelengths, for example, in the western Pacific and in Africa, suggest the use of gravity data to distinguish between competing plate reconstruction models.

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Geochemistry, Geophysics, Geosystems, v. 10, issue 11, art. Q11W04

Copyright 2009 by the American Geophysical Union.