Crystallizing the terrestrial magma ocean: thermo- and geodynamics

• Applicants: Dr. Gerd Steinle-Neumann; Dr. Nicola Tosi
• Subject Area: Geophysics ; Mineralogy, Petrology and Geochemistry
• Term: from 2015 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 276817549

Cooling and crystallization of the magma ocean that likely originated from the Moon-forming impact set the initial thermal and chemical structure of the solid mantle and thus the conditions for the subsequent evolution of the interior controlled by thermo-compositional convection. Modelling of the composition resulting from magma ocean crystallization requires a detailed description of the liquidus and phase diagram - over the entire mantle pressure-range-, of the distribution coefficients of major elements between crystals and melts, and of the density of residual liquids and newly formed solids. We will extend thermodynamic models of melting phase relations in the MgO-SiO2 system to the FeO-MgO-SiO2 (FMS) and CaO-MgO-SiO2 (CMS) systems by performing targeted multianvil high-pressure experiments. The focus will be on better constraining the liquidus on the MgSiO3 side of the eutectic in the presence of FeO and to obtain reliable data on the eutectic in the CMS system in which all major phase of the lower exists: periclase, bridgmanite and Ca-perovskite. These experiments will also be used to establish partition coefficients, in particular of Fe, between the melt and lower mantle phases. The additional constraints will be incorporated into a model of fractional crystallization of the magma ocean, establishing the crystallization sequence and the density structure of the terrestrial magma ocean. Newly obtained MD results on melt densities in the CMS, the FMS and Al2O3-bearing mantle compositions will be included to compute buoyancy of crystallizing lithologies. The resulting density stratification will provide us with a physically and chemically consistent picture of the thermal and compositional state of the mantle immediately after its solidification and will serve as a novel starting point for numerical models of the dynamics of the interior. We will employ these models to simulate the coupled evolution of the mantle and core over the entire history of the Earth and characterize from a new perspective fundamental processes such as the onset and maintenance of plate tectonics and magnetic field generation, and the formation and subsequent mixing of large scale geochemical reservoirs.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1833: Building a Habitable Earth
• Cooperation Partners: Professorin Dr. Doris Breuer; Dr. Sylvain Petitgirard; Dr. Ana-Catalina Plesa; Professor Dr. David Rubie