Phase changes and convection in the Earth’s mantle

Abstract

A phase change may hinder or enhance convection, depending on its characteristics. Univariant transformations such as may occur in the mantle constitute a barrier to convection unless the motion starts at some distance above or below the transition level; an initial temperature gradient in excess of the adiabatic value is also required. Multivariant transformations only require, in the transformation zone, an initial gradient slightly greater than the adiabatic value for a homogeneous layer. The effect on convection of transformation rates is not likely to be serious.