Influence of deep mantle thermal conductivity on the thermochemical evolution of Earth's mantle and core

Recent mineral physics studies of lower mantle thermal conductivity predict substantially different values of thermal conductivity under core-mantle boundary (CMB) conditions, which might be expected to result in different CMB heat fluxes and thermal histories of Earth's mantle and core. We test this prediction using mantle convection simulations coupled with a parameterised core evolution model. Our results demonstrate that differences in lower mantle thermal conductivity do not lead to proportional changes in CMB heat flux. Instead, there is a self-regulation of CMB heat flux that results in similar present-day values: higher thermal conductivity results in more rapid core cooling, reducing the temperature drop across the CMB thermal boundary layer; and also promotes the formation of larger basaltic piles above the CMB, which further lower the local and global CMB heat flux. The upper and lower mantle follow different thermal evolution paths due to partial layering caused by the “basalt barrier” at the mantle transition zone. The modelled mantle temperatures at 4.5 Gyr are similar across models with different lower mantle thermal conductivity. The upper mantle thermal evolution is broadly consistent with petrological constraints. These findings highlight the importance of considering thermochemical feedback mechanisms when modelling Earth's thermal evolution. • CMB heat flux becomes similar regardless of the deep mantle thermal conductivity. • Size of basaltic piles above CMB is affected by thermal conductivity. • Upper/lower mantle temperatures evolve differently due to mid-mantle basalt barrier. • Present-day mantle temperature remains similar regardless of the deep mantle thermal conductivity.