Grain boundary diffusion cannot explain the W isotope heterogeneities of the deep mantle

Abstract The depletion of ¹⁸²W associated with the enrichment of ³He in some ocean island basalts likely fed by deep-rooted mantle plumes may derive from the Earth's core through long-term core-mantle interactions. It has been proposed that the grain boundary diffusion of siderophile elements is an efficient mechanism for core-mantle interaction and may effectively modify the W isotopic compositions of the plume-source mantle. In this study, we perform large-scale molecular dynamics simulations driven by machine learning potentials of ab initio quality to investigate the diffusion of W along ferropericlase grain boundaries and in (Mg,Fe)O liquid. Our findings suggest that the diffusion of W is sluggish under core-mantle boundary conditions, and thus is unlikely to have observable impacts on the W isotopic compositions of terrestrial igneous rocks.