Chemical and isotopic (C, O, Sr, Nd) characteristics of the Xiluvo carbonatite (central-western Mozambique)

The Xiluvo complex of central Mozambique is made up of coarse- to fine-grained calciocarbonatites (soevites and alvikites), heavily altered lamprophyres and syenitic rocks that intruded the Precambrian basement ca. 120 Ma ago. The carbonatites have fractionated rare earth element patterns (chondrite-normalized La/Yb=30-80) and markedly negative Rb, K, P, Zr and Ti anomalies in mantle-normalized incompatible element diagrams. The δ18O (+7 to +8), δ13C (-5), and the age-corrected 87Sr/86Sr (0.7032-0.7033) and 143Nd/144Nd (0.51263-0.51262) indicate an origin in the mantle. A few carbonatitic samples have higher δ18O (+13), indicating interaction with high- δ18O crust or late-stage fluids. The chemical and isotopic compositions of the Xiluvo carbonatites and nearby carbonatites of similar age in Malawi indicate very similar sources, characterized by time-integrated depletion of Rb with respect to Sr and of Sm with respect to Nd. These characteristics point to a source similar in many respects to those of other East African carbonatites and to those of some ocean island basalts, with the additional influx of components possibly located in the African lithospheric mantle. (author)