Tungsten-182 evidence for an ancient kimberlite source.

Globally distributed kimberlites with broadly chondritic initial Nd-Hf isotopic systematics may be derived from a chemically homogenous, relatively primitive mantle source that remained isolated from the convecting mantle for much of the Earth's history. To assess whether this putative reservoir may have preserved remnants of an early Earth process, we report W/W and Nd/Nd data for "primitive" kimberlites from 10 localities worldwide, ranging in age from 1,153 to 89 Ma. Most are characterized by homogeneous μW and μNd values averaging -5.