Tungsten-182 evidence for an ancient kimberlite source

Significance Kimberlites are igneous rocks derived from deep mantle sources. Recent studies have suggested that certain kimberlites originated from a mantle source with relatively primitive chemical composition that was created by early Earth processes. We present W isotope data for a global suite of kimberlites with variable formation ages and find their mantle source(s) to be characterized by 182 W/ 184 W averaging ∼6 ppm lower than the upper mantle ratio. This result is consistent with derivation of some kimberlites from one or more early formed mantle reservoirs. The low 182 W/ 184 W of these kimberlites is indicative of an ancient mantle source modified by some form of core–mantle interaction, an early silicate fractionation event, an overabundance of late-accreted materials, or a combination of these.