Isotopic characteristics and petrogenesis of the lamproites and kimberlites of central west Greenland

Kimberlites which intruded the Sisimiut (formerly Holsteinsborg) region of central west Greenland during the Early Palaeozoic have initial ⁸⁷Sr/⁸⁶Sr between 0.7028 and 0.7033 and ε_Nd between + 1.3 and + 3.9. Mid-Proterozoic potassic lamproites from the same region have initial ⁸⁷Sr/⁸⁶Sr between 0.7045 and 0.7060, ε_Nd between −13 and −10 and unradiogenic initial Pb isotopic compositions. The isotopic data favour an asthenospheric mantle source for the kimberlite magmas, in common with “basaltic” kimberlites from other localities, whereas the lamproite magma sources evolved in isolation from the convecting mantle for > 1000 Ma, probably within the subcontinental lithospheric mantle of the Greenland craton, prior to emplacement of the lamproites.