Geochemistry and Distribution of Recycled Domains in the Mantle Inferred From Nd and Pb Isotopes in Oceanic Hot Spots: Implications for Storage in the Large Low Shear Wave Velocity Provinces

Abstract

AbstractSubduction of continental and oceanic crust is thought to give rise to geochemically distinct reservoirs in the mantle called EM (enriched mantle) and HIMU (high μ = 238U/204Pb), respectively. However, the locations of EM and HIMU domains in the Earth's interior are poorly constrained. We explore the geographic distribution of extreme EM (143Nd/144Nd ≤ 0.512630) and HIMU (206Pb/204Pb ≥ 20) geochemical signatures in ocean island basalts erupted at hot spots, highlighting three observations. First, hot spots geographically associated with the two large low shear wave velocity provinces (LLSVPs) have a similar range of EM compositions. If these hot spots are sourced by the LLSVPs via upwelling plumes, this observation is consistent with the hypothesis that the LLSVPs formed by similar processes and have similar geodynamic histories. Second, the EM and HIMU domains exhibit different latitudinal zonation: oceanic hot spots with the most extreme EM compositions (143Nd/144Nd < 0.5125) are concentrated in the Southern Hemisphere (14°S to 52°S latitude), while oceanic hot spots hosting HIMU compositions are found primarily near the tropical latitudes (38°N to 29°S). Third, all 13 oceanic hot spots with EM compositions (143Nd/144Nd ≤ 0.512630) are geographically associated with the LLSVPs; oceanic hot spots located far from the LLSVPs exhibit only non‐EM (143Nd/144Nd > 0.512630) compositions. In contrast, the HIMU domains do not show a clear geographic association with the LLSVPs. Therefore, EM and HIMU domains in the Earth's mantle exhibit different spatial distributions. This may reflect differences in subduction inputs of these two components, or differences in how they segregate or accumulate in the deep Earth.