Centrifugal force drives the formation of the antipodal basal mantle structures

Large low shear-wave velocity provinces (LLSVPs) are degree-2, antipodal structures in Earth’s lowermost mantle that may play a key role in mantle convection and plate tectonics. However, the origin and timing of their degree-2 configuration remain poorly understood due to the lack of geological constraints (McNamara, 2019). Tidal evolution models predict that Earth’s length of day (L.O.D) increased from ~6 h to 24 h over geological time (Farhat et al., 2022), suggesting that centrifugal force could have significantly influenced early LLSVPs evolution. Here, we investigate this mechanism using 3D self-consistent thermochemical mantle convection models that incorporate centrifugal force, implemented with the code StagYY. In our models, L.O.D increases linearly from 6 h to 24 h over the full 4.56 Gyrs model time. We assume that LLSVPs originate from a uniform basal dense layer that are results of either magma ocean crystallization (Labrosse et al., 2007) or the Moon-forming giant impact (Yuan et al., 2023). We find that centrifugal force substantially accelerates the formation of degree-2 basal mantle structures. A subduction girdle centered at the equator and two basal mantle structures centered at the poles are observed in our models. These degree-2 structures emerge consistently across experiments with varying yield stresses and corresponding plate tectonic configurations. Thus, our simulations demonstrate that centrifugal force drives the formation of antipodal LLSVPs, further suggesting that the polar LLSVPs may subsequently migrate through true polar wander. References:Farhat, M., Auclair-Desrotour, P., Boué, G., Laskar, J., 2022. The resonant tidal evolution of the Earth-Moon distance. Astronomy & Astrophysics 665.Labrosse, S., Hernlund, J.W., Coltice, N., 2007. A crystallizing dense magma ocean at the base of the Earth’s mantle. Nature 450, 866-869.McNamara, A.K., 2019. A review of large low shear velocity provinces and ultra low velocity zones. Tectonophysics 760, 199-220.Yuan, Q., Li, M., Desch, S.J., Ko, B., Deng, H., Garnero, E.J., Gabriel, T.S.J., Kegerreis, J.A., Miyazaki, Y., Eke, V., Asimow, P.D., 2023. Moon-forming impactor as a source of Earth’s basal mantle anomalies. Nature 623, 95-99.