A fresh isotopic look at Greenland kimberlites: Cratonic mantle lithosphere imprint on deep source signal

The North Atlantic craton in West Greenland and northern Labrador has been subjected to deep volatile-rich melting events between ca. 610 and 550 Ma that produced compositionally diverse diamond-bearing kimberlite and aillikite magmas. Whereas kimberlite dyke intrusions appear to be restricted to the Maniitsoq area in the craton interior between 568 and 553 Ma, aillikite/carbonatite intrusives preferentially occur at Paleoproterozoic mobile belts such as in the Sarfartoq area (605–550 Ma) of West Greenland. Although there is an overlap between the major and trace element compositions of the exceptionally fresh Maniitsoq kimberlites and Sarfartoq aillikites, the latter typically show higher TiO 2, Al 2O 3, and K 2O, as well as higher Zr, Hf, Cs and Rb contents. Furthermore, the Sarfartoq aillikites are displaced toward lower ε Hf by ~ 3 epsilon units at similar ε Nd compared with the isotopically depleted Maniitsoq kimberlites and their garnet and ilmenite megacrysts. The generally lower ε Hf of aillikites corresponds to lower CO 2/K 2O and points to the involvement of a K-rich melt component in aillikite genesis, most likely derived from a cratonic metasome. In contrast, the Maniitsoq kimberlite compositions, in particular the high CO 2 as well as low Al 2O 3 and K 2O contents, resemble published carbonate-rich melt compositions that were produced experimentally from carbonated peridotite in excess of 6 GPa, i.e., under sublithospheric conditions. By utilizing published high-pressure carbonated peridotite/melt trace element partition coefficients, we demonstrate that many of the hallmark geochemical features of kimberlites, such as relative Zr–Hf depletions, can be produced by low-degree partial melting of carbonated fertile peridotite within the asthenosphere. For the Greenland-Labrador Diamond Province, we propose that a common asthenosphere-derived carbonated silicate melt component must have been present throughout the North Atlantic craton base at 610-to-550 Ma. This widespread carbonate-rich melt component variably interacted with old phlogopite-bearing cratonic metasomes, giving rise to diverse suites of aillikites, i.e., hybrid carbonated potassic-silicate magmas, that locally separated out carbonate fractions to form intrusive carbonatites at crustal levels. The kimberlites, however, appear to be mixtures of this asthenosphere-derived carbonate-rich melt component and entrainment of materials from the refractory cratonic mantle lithosphere, with l