Double-diffusive layering during the evolution of planetary mantles

Abstract

Summary The degree of layering during planetary mantle evolution has been a key issue and is still heavily debated, especially since the observation of seismic discontinuities within the Earth mantle and their correlation to phase transitions within the mantle mineral assemblage and the detection of geochemical differences in mantle derived basalts (Mid Ocean Ridge Basalts and Ocean Island Basalts). We present the phenomenon of double-diffusive layering in a fluid with strongly temperature dependent viscosity, as relevant for planetary mantle material, to study the influence of an initial compositional gradient with regard to the thermal and chemical evolution of a planet. The numerical experiments show that in a wide parameter range distinct layers are formed self-organized from a continuously stratified state by dynamical fractionation and are thus likely to appear as a generic. Considering this as a plausible model for planetary mantle evolution it provides a dynamical explanation for the existence of distinct chemical reservoirs within the history of a planet's mantle.