Mantle plume–stagnant slab interaction controls the generation of a mixed mantle source for continental intraplate basalts

Abstract

Continental intraplate basalts from southeastern Eurasia show ocean island basalt-like geochemical signatures and heterogeneous isotopic compositions suggesting mixing between isotopically enriched and depleted end-member sources. Although the isotopically enriched end-member(s) in these basalts which are related to oceanic crustal recycling have been investigated, the nature of the isotopically depleted end-member(s) remains unclear. We present geochemical characteristics of the southeast Cambodia basalt and compare them with other Cenozoic intraplate basalts in the South China Sea region. All these basalts contain a component with low Ce/Pb and Nb/Th ratios, moderate 87Sr/86Sr (~0.7040) and εNd (~ + 5), high εHf (~ + 9.5), and slightly positive ΔεHf value. These chemical and isotopic signatures are not consistent with the depleted local asthenosphere. We suggest a FOZO-like component, which is most likely derived from lower mantle material, represents the low-Ce/Pb component. Combined with geophysical observations, we propose that the interaction between the upwelling mantle plume and the stagnant slabs controls the formation of these intraplate basalts from the South China Sea region. This study highlights the important role of stagnant slabs in the mantle transition zone in modifying the compositions of mantle plumes, ultimately resulting in upper mantle heterogeneity.