C2 - Modelling giant impacts and the subsequent thermochemical evolution of liquid metal in a convecting magma ocean

Research areas: Geophysics

Summary

Giant impacts on Earth heavily influenced core formation and may have contributed to late accretion of material, but exactly to what extent the present day geochemical signature of Earth’s mantle reflects the processes of core formation and late accretion and how much of the delivered material was incorporated into the core remains unclear. To better understand these processes it is key to comprehend how the material delivered by giant impacts was dispersed upon impact, and how the metal (or sulphide) settled in a global or partial magma ocean.

The first issue knowing the distribution of the impactor material is important because the way in which the impact-delivered metal interacts with the ambient magma strongly depends on the size–frequency distribution of particles or clumps the impactor is dispersed into. The second issue the settling of impactor material  also strongly depends on the thermodynamic convection state of the magma ocean. Thus, understanding how the magma ocean interacted with the sinking metal particles is crucial for understanding core formation. For example, we must understand how both of these factors particle size and convection state of the ambient magma affected the material’s sinking speed: while metal particles that sink quickly leave little time for chemical equilibration, those that sink sufficiently slowly could allow time for equilibration between metal and silicate materials, potentially shaping the chemical signatures we see in Earth’s mantle today.

Therefore, we propose to investigate, by means of numerical experiments, how impactors and, in case of differentiated bodies, their cores were dispersed during the penetration into a magma ocean, how the size–frequency distribution of droplets, chunks, or large clumps depends on impact parameters (impact velocity, relative size to the depth of the magma ocean, rheology of the impactor and target) and how the flow style of the magma ocean affects the interaction of metal and silicates. By combining impact modelling with sophisticated models of the magma ocean that account for solidification processes, we expect to gain a better understanding of the changing reaction of the magma ocean to impacts and the changing nature of the sedimentation during its evolution.