Chemical differentiation of a convecting planetary interior - Consequences for a one plate planet such as Venus

Simple models of the thermal and chemical evolution of a planetary interior are developed to explore the possible consequences of a chemically buoyant depleted mantle layer for planetary evolution. As the depleted layer thickens the melting temperature at the top of the underlying convecting mantle also increases and the degree of partial melting of the mantle added to the depleted layer decreases. As the less depleted mantle with less positive compositional buoyancy is added, the negative thermal buoyancy of the layer eventually exceeds its positive compositional buoyancy. The depleted layer then sinks into and mixes with the convecting interior. On Venus the population of impact craters is indistinguishable from a random distribution over the surface and gives a surface age of about 500 Myr. It is suggested that the above mechanism may explain this episodic global resurfacing of Venus.