[S-IT20] Deep Earth Sciences

[SIT20-P06] Iron percolation and its effect on the convective vigor

*Sogen Kitamura¹, John W. Hernlund¹, Kang Wei Lim² (1.Institute of Science Tokyo, 2.Institut de Physique du Globe de Paris)

Keywords:Mantle convection, Two phase system, early Earth

Metallic Fe can exist in the lower mantle due to the self-oxidation of iron (3Fe2+ = Fe + 2Fe3+). Close to the core-mantle boundary (CMB), a two-phase system comprising molten Fe and solid silicates/oxides can coexist during the Earth’s early history, which subsequently allows for the molten Fe to percolate towards the core with the aid of compaction. Since Fe is much denser than mantle materials, Fe loss in the mantle can affect the vigor of mantle convection. Moreover, the expected short timescale of percolation relative to mantle convection can significantly influence the geochemical and geodynamical characteristics of the mantle. In this study, we model and analyze the effects of mantle Fe loss on convection.
Our results show this percolation could have two competing effects: efficient percolation creates a dense Fe layer at the CMB which inhibits convection, while less dense portions due to Fe loss promotes convection. Because of these effects, the convection onset is mainly controlled by the growth of the thermal boundary layer. Moreover, melt fraction in the molten region could converge to the critical fraction in the case of efficient percolation. This suggests that molten Fe could be removed quickly from the mantle and accumulate at the CMB, which subsequently changes the mantle redox state.