THERMAL AND CHEMICAL HETEROGENEITY IN THE MANTLE - A SEISMIC AND GEODYNAMIC STUDY OF CONTINENTAL ROOTS

Chemical differences in the mantle below continents and oceans are investigated in the context of a recent seismic model of three-dimensional mantle structure. This analysis of the existence and magnitude of deep continent-ocean chemical differences is based on a model of a viscous flowing mantle and it suggests that this continent-ocean heterogeneity is internally supported and thus produces little flow. This stabilization reduces the vertical flow of mass and heat across the upper mantle and results in a large continent-ocean signal in the surface gravity and topography fields. The stabilization of continent-ocean heterogeneity also provides an explanation for the large amplitude of the nonhydrostatic ellipticity in the Earth's geoid.