Post-Archeozoic large-scale convection in the earth's mantle

Abstract

Static models of the lower mantle do not easily accommodate a cooling of the core on a terrestrial time scale. Moreover, merely shallow flows do not readily explain the present distribution of sial. Therefore, a still active, overall and occasionally reversing mantle convection is proposed that is consistent with the spasmodic character of orogenesis. This convection is compatible with modern estimates of pertinent parameters in a hydrodynamic theory of convection within spherical shells. It bears on the geomagnetic dynamo and helps to explain a correlation that has been suggested between changes in earthquake activity and in the earth's rotation. Apart from tidal dissipation within the mantle, a cooling of a radio-inactive core, on the order of 600°C during the last two and a half to three billion years, seems to be required to complete about a dozen successive mantle overturns.