Isotopic fingerprints of recycled eclogite facies sediments in the generation of the Huanglongpu carbonatite, central China

Abstract

Carbonatites are the most important sources of global niobium (Nb) and rare earth element (REE) resources, particularly the light REEs. The Huanglongpu carbonatite in central China is unique for the enrichment of molybdenum (Mo) and heavy REEs. Till now, the source nature of the Huanglongpu carbonatites is still poorly understood. In this contribution, we present elemental and C-O-Sr-Nd-Pb isotopic data of calcite to constrain the source signatures of the Huanglongpu carbonatite. Elemental geochemistry and C-O isotopes of the calcite vein-networks in the carbonatite reveal that the Huanglongpu carbonatites is of igneous genesis and originated from mantle-derived carbonatitic melts. The negative εNd(t) values (−8.03–−5.05) and elevated initial 87Sr/86Sr ratios (0.7049–0.7056) indicate considerable contribution of recycled crustal components in the mantle source. Combination of O-Sr-Nd-Pb isotopes suggests that over 10 wt% of recycled sediments might have been involved into the depleted mantle, accounting for the source of the Huanglongpu carbonatite. Considering the enrichment of heavy REE, REE distribution simulation indicates that the Huanglongpu carbonatite might be from the 30% partial melting of eclogite facies sediments. Accordingly, we infer that the Huanglongpu carbonatite might have been derived from the partial melting of a hybridized mantle source modified by recycled sediments of eclogite facies. The enrichment of Mo and heavy REEs plausibly resulted from the contribution of garnet/pyroxene from the eclogitic sediments within the subducted slab.