View article

The carbon isotope composition (δ¹³C) of primary graphite from 28 mantle derived eclogite xenoliths from kimberlites in southern Africa and USA range from ‐14.31 to ‐2.84%_PDB, with a mean value of ‐6.2%. Both Group I and Group II eclogites are represented by anomalously low carbon isotope ratios. There is no simple correlation between isotopic composition and depth of origin, demonstrating carbon isotopic heterogeneity in the shallow upper mantle not previously recognized, but known from the deeper eclogite diamond population. Interpreted in the light of recent geochemical evidence supporting a subduction origin for some mantle eclogites and their diamonds, low δ¹³C graphite‐bearing eclogites could represent some of the earliest material emplaced beneath the cratons by subduction.