The role of light elements at the core-mantle boundary – partitioning, demixing, and transport

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The possible presence of a stagnant layer below the core-mantle boundary raises a number of important geophysical and geochemical questions for the deep Earth. In the proposed project, we plan to explore the possibility of this layer being caused by a distinct chemical composition, i.e., the accumulation of light elements there, initially brought to the core at higher temperature during core segregation. To this avail we will perform ab-initio simulations on different aspects that may lead to the formation and stability of such a light element enriched layer, and determine dynamically important physical properties of it. For the geodynamo and thermal evolution considerations in other projects proposed within the focus program, density, viscosity and thermal conductivity are of significance. We have agreed to collaborate with two other projects, Wicht and Zhu for the geodynamo, Tosi et al. for thermal evolution simulations. As an additional driving force for the geodynamo, especially in the young Earth, we will explore the possible exsolution of SiO2 from the initial core composition. In a more geochemical context, we will consider the transport of light elements to the core during its formation by equilibration between the magma ocean and metal, as well as the possible chemical equilibration of the chemical boundary layer with the overlying mantle. Methodologically, we will perform large-scale molecular dynamics simulation using both density functional theory and machine learning potentials, and – based on molecular dynamics simulations – compute thermodynamic potentials of candidate reaction products to quantitatively determine partitioning of light elements between liquid iron-alloys (the core) and solid (the mantle) and liquid silicates (the magma ocean) at relevant high pressures and temperatures.