Is there an ultradepleted mantle?

A number of researchers have reported experimental data on the Sm-Nd isotop ic system of garnet and clinopyroxene from xenoliths in the kimberlite pipe s of southern Africa and Yakutia. In the majority of cases, they do not agr ee with the real values of xenolith ages and the initial Nd-143/(144) Nd. C onsequently, they cannot be considered evidence for the existence of an ult radepleted mantle reservoir and its evolution beginning from 4.5 Ga.