Layering processes in the evolution of planetary mantle

• Applicant: Professor Dr. Ulrich Hansen
• Subject Area: Geophysics
• Term: from 2013 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 252309337

Layer formation is a prominent feature in many natural systems. Distinct layers are stacked and separated by sharp interfaces. They are on the scale of magma chambers and intrusions or on grandeur dimension; the Earth's oceans and the mantle of planetary bodies. The internal structure of the Earth's mantle, i.e. the separation of the upper and lower mantle, has always been and remains highly debated and the presence of additional layers is considered to be likely, despite a still missing proof. Pure thermal convection is not sufficient to generate separately convecting layers. It has been assumed that the endothermic phase change from spinel to perovskite at a depth of 670km is a potential mechanism to separate the convective flows in the upper and lower mantle. But considering earth-like conditions early numerical studies showed, that complete layering is not expected for geological timescales. Taking into account at least two components that influence the density and have different diffusivities, distinct layers can evolve dynamically. Such systems are called double diffusive systems (d.d.c). Identifying one component as heat and the other as chemical composition (e.g. heavy material) it seems to be likely that d.d.c. plays a significant role in the dynamics of a planetary mantle, especially for the formation of distinct layers in the Earth's mantle.Within the scope of the submitted proposal we want to research the process of layering due to double diffusive convection and the consequences for the evolution of the Earth's mantle. The main focus of attentions is the formation and evolution of self-organised layers in the presence of an endothermic phase change. At first a pre-existing numerical double diffusive model will be improved by the effect of a phase change. Another key aspect will then be the investigation of layering with respect to an earth-relevant rheology. This will be an essential step and will help to get a better understanding for the evolution of the Earth's mantle and the today's observed surface features like plate tectonics, geochemistry, surface heat flow, etc.. To our knowledge this kind of study has never been done by any other work group.

• DFG Programme: Research Grants