COMPARISONS BETWEEN SEISMIC EARTH STRUCTURES AND MANTLE FLOW MODELS BASED ON RADIAL CORRELATION-FUNCTIONS

Three-dimensional numerical simulations were conducted of mantle conve ction in which flow through the transition zone is impeded by either a strong chemical change or an endothermic phase change. The temperatur e fields obtained from these models display a well-defined minimum in the vertical correlation length at or near the radius where the barrie r is imposed, even when the fields were filtered to low angular and ra dial resolutions. However, evidence for such a feature is lacking in t he shear-velocity models derived by seismic tomography. This compariso n suggests that any stratification induced by phase or chemical change s across the mid-mantle transition zone has a relatively small effect on the large-scale circulation of mantle material.