Dynamical layering in planetary mantles

The thermal history of the Earth, it’s chemical differentiation and also the reaction of the interior with the

atmosphere is largely determined by convective processes within the Earth’s mantle. A simple physical model,

resembling the situation,shortly after core formation, consists of a compositionally stable stratified mantle, as

resulting from fractional crystallization of the magma ocean. The early mantle is subject to heating from below

by the Earth’s core and cooling from the top through the atmosphere. Additionally internal heat sources will

serve to power the mantle dynamics. Under such circumstances double diffusive convection will eventually lead

to self organized layer formation, even without the preexisting jumps is material properties. We have conducted

2D and 3D numerical experiments in Cartesian and spherical geometry, taking into account mantle realistic

values, especially a strong temperature dependent viscosity and a pressure dependent thermal expansivity . The

experiments show that in a wide parameter range. distinct convective layers evolve in this scenario. The layering

strongly controls the heat loss from the core and decouples the dynamics in the lower mantle from the upper

part. With time, individual layers grow on the expense of others and merging of layers does occur. We observe

several events of intermittent breakdown of individual layers. Altogether an evolution emerges, characterized by

continuous but also spontaneous changes in the mantle structure, ranging from multiple to single layer flow. Such

an evolutionary path of mantle convection allows to interpret phenomena ranging from stagnation of slabs at

various depth to variations in the chemical signature of mantle upwellings in a new framework