The metasomatic alternative for ocean island basalt chemical heterogeneity

Cantal basalt compositions may be used to constrain the trace element variation generated by the evolution of a metasomatic agent within the lithosphere. Reconstruction of compositions in different parts of the lithosphere indicates significant heterogeneities in Th / Pb, U / Pb and Sm / Nd resulting from the metasomatic process. Subduction and isolation of this metasomatic lithosphere generates over 1-1.8 Ga, Nd and Pb isotopic variations similar to those observed in oceanic island basalts. Moreover, these isotopic variations are correlated with variations in trace element ratios commonly interpreted as the product of mixing between different end-member mantle components (HIMU and EM). The model calculations suggest that isotopic and trace element variations observed in OIB may more likely be the result of melting metasomatised subducted oceanic lithosphere rather than a mixture of chemically distinct mantle sources that formed and evolved independently from one another.