Abstract: A convection mechanism for explaining episodicity of magmatism and orogeny

Abstract

A convection mechanism for explaining episodicity of magmatism and orogeny

The hypothesis is developed that convection takes place continuously in the upper
mantle and episodically also in the lower mantle. The reason for the latter assumption is seen in the
temperature dependence of the viscosity. By radioactive heating of the lower mantle the viscosity
gradually decreases until the critical Rayleigh number is achieved. The lower mantle convection initiated
in this way, however, disappears after sufficient heat has been transferred to the exterior. This heat
transfer becomes evident by an increase of igneous and tectonic activities in the crust.