Fig. 3: The efficiency of grain boundary diffusion in transporting W isotope signals across the core-mantle boundary.
From: Grain boundary diffusion cannot explain the W isotope heterogeneities of the deep mantle
a The effective diffusion distance of W as a function of grain size over 4.54 Gyr, calculated from effective diffusivities under 4000–5000 K and 140 GPa. The orange shading corresponds to the grain size predicted for the average lower mantle94. b The μ182W value of OIB samples as a function of the height of the plume generation zone after the diffusive isotopic exchange over 4.54 Gyr. The blue shading represents the values calculated from effective diffusion coefficients (5.0 × 10−16 m2 s−1 to 6.2 × 10−15 m2 s−1, calculated from Eq. (5) in Methods) under 4000–5000 K and 140 GPa. The green curve is calculated from the effective diffusion coefficient (7.1 × 10−14 m2 s−1) assuming W diffusivity in (Mg,Fe)O liquid at 5000 K is the upper bound of grain boundary diffusivity. The grain size of 0.1 mm is considered. The lowest height of observable ultra-low velocity zones (ULVZs) is shown for reference62. The histogram showing the frequency distribution of previously reported μ182W measured in OIB natural samples5 is shown for comparison. Source data are provided as a Source Data file.
