The evolution of Nd isotopes with time

The evolution of Nd/ isotopes with rime in the mande, the continental crust and the bulk earth. Relative to the bulk Earth (CHUR) in which the fractionation of Sm/Nd is normalized to unity, the depleted mande (DM) has a high Sm/Nd ratio and shows higher Nd. The continental crust has lower Sm/Nd and shows a retarded Nd/ Nd evolution with time. Enriched mantle (EM) shows some affinity with the continental crust inasmuch as it also has a retarded evolution. Note that in the Sm-Nd system 

Othman et al. (1984), reduces to an epsilon value of +2.5 at 4.0 Ga. Some support for depleted mantle very early in the history of the earth comes from the work of CoUerson et aL (1991). 

Brevart tfr a/. (1986) use Pb isotope initial ratios to demonstrate mantle heterogen ty at 2.7 Ga and have constructed a depleted mantle curve from 2.7 Ga to the present day from the initial ratios of komatiites and basalts on a isotope evolution diagram. 

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