Earth's CMB topography and mantle convection

Better understanding topography on Earth's core-mantle boundary (CMB) may provide important constraints on mantle dynamics, specifically the style of mantle convection, and on lower mantle heterogeneity. For example, the origin of large, lowermost mantle low shear wave velocity provinces beneath the central Pacific and Africa is not well constrained, but are likely related to both mantle dynamics and CMB topography. Two competing hypotheses for these anomalies are: thermal upwellings (e.g., plume clusters) or large intrinsically dense piles of primitive mantle material (e.g., thermochemical piles). Here we discuss the results from our current 3D investigation of CMB topography in two styles of mantle convection: 1) an isochemical mantle with plume clusters, and 2) a thermochemical mantle with large, intrinsically dense piles. In this study, we numerically investigate 3D spherical models of mantle convection and calculate maps of topography (CMB and surface, with self-gravitation included) and geoid (CMB and surface). Maps of CMB topography and geoid (CMB and surface) are produced, and compared to observed CMB topography (e.g., Morelli and Dziewonski, 1987; Boschi and Dziewonski, 2000; Sze and van der Hilst, 2003) and surface geoid (e.g., Earth Geopotential Model, 1996). Our predicted surface geoid maps provide a key image of how CMB topography, for any given model, will affect the geoid. The results of this work emphasize the importance in using a suite of observables (in this case, topography and geoid maps for CMB and surface) to constrain whole mantle dynamics and lower mantle structure.