Tungsten-182 evidence for an ancient kimberlite source
Nao Nakanishi, Andrea Giuliani, Richard W. Carlson, M. F. Horan, Jon Woodhead, D. Graham Pearson, R. J. Walker
Abstract
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.