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 inv estigated in the context of a recent seismic model of three-dimensiona l mantle structure. This analysis of the existence and magnitude of de ep continent-ocean chemical differences is based on a model of a visco us flowing mantle and it suggests that this continent-ocean heterogene ity is internally supported and thus produces little flow. This stabil ization reduces the vertical flow of mass and heat across the upper ma ntle and results in a large continent-ocean signal in the surface grav ity and topography fields. The stabilization of continent-ocean hetero geneity also provides an explanation for the large amplitude of the no nhydrostatic ellipticity in the Earth's geoid.