Upper Mantle abundance data

Fresh, Cenozoic oceanic basalts typically span a narrow range in 5 O ( 5 to 7 %o for whole rocks), restricting the abundance of subducted crust in their mantle sources and crustal contaminants added to them during differentiation to amounts less than 10 wt %. Furthermore, these data suggest that isotopic fractionations during melting, metasomatism, and metamorphism in the upper mantle are small... 

The lower mantle Ar and Xe isotope compositions cannot be well constrained by available data and are taken as unknowns. Therefore, the isotopic compositions, and so nonradiogenic isotope abundances, are unknowns. However, these are calculated from the balance of fluxes into the upper mantle (see below). 

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