On the fate of impact-delivered metal in a terrestrial magma ocean

Impacts on Earth crucially influenced core formation and the subsequent evolution of Earth's mantle and may have contributed to late accretion of material. However, 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 material delivered by giant impacts and by impacts of smaller projectiles during late accretion was incorporated into the core remains unclear. To improve the insight into these processes, it is of key importance to comprehend how impact-delivered metal droplets are dispersed and subsequently settle in a terrestrial magma ocean. Settling and mixing are potentially strongly influenced by the convective and rotational state of the magma ocean. Therefore, by means of numerical experiments in spherical geometry, we study how the convective state of the magma ocean and the potentially strong planetary rotation affect the settling of impactdelivered material in a deep global magma ocean. We reveal crucial differences in metal dispersion and in settling history depending on the impactor's target latitude. For an impact at either pole, the metal dispersion within the magma ocean is spatially limited while the metal droplets settle fast. Impacts at lower latitudes allow for a higher degree of dispersion, being accompanied by a slower metal settling. Consequently, metal-silicate equilibration may differ depending on the target latitude, being limited to certain localized domains of the magma ocean. We further demonstrate that the volume fraction undergoing metal-silicate equilibration seems to depend linearly on the impactor's diameter and may be largely underestimated in previous studies. Overall, we present a possible mechanism for heterogeneous metal-silicate equilibration and the generation of chemical heterogeneities and isotopic anomalies in Earth's mantle due to the influence of planetary rotation, potentially shaping the geochemical signatures that are observed today. (C) 2020 The Authors. Published by Elsevier B.V.

Automated summary

Numerical experiments were conducted to study the settling of impact-delivered material in a global magma ocean, showing crucial differences in metal dispersion and settling history depending on the latitude of the impactor's target. Impacts at the poles result in limited metal dispersion and fast settling, while impacts at lower latitudes allow for higher dispersion and slower settling, potentially leading to differences in metal-silicate equilibration in localized domains of the magma ocean.