U-Pb ages, geochemistry, C-O-Nd-Sr-Hf isotopes and petrogenesis of the Catalão II carbonatitic complex (Alto Paranaíba Igneous Province, Brazil): implications for regional-scale heterogeneities in the Brazilian carbonatite associations

The Catalão II carbonatitic complex is part of the Alto Paranaíba Igneous Province (APIP), central Brazil, close to the Catalão I complex. Drill-hole sampling and detailed mineralogical and geochemical study point out the existence of ultramafic lamprophyres (phlogopite-picrites), calciocarbonatites, ferrocarbonatites, magnetitites, apatitites, phlogopitites and fenites, most of them of cumulitic origin. U-Pb data have constrained the age of Catalão I carbonatitic complex between 78 ± 1 and 81 ± 4 Ma. The initial strontium, neodymium and hafnium isotopic data of Catalão II (87Sr/86Sri = 0.70503-0.70599; ?Ndi = -6.8 to -4.7; 176Hf/177Hf = 0.28248-0.28249; ?Hfi = -10.33 to -10.8) are similar to the isotopic composition of the Catalão I complex and fall within the field of APIP kimberlites, kamafugites and phlogopite-picrites, indicating the provenance from an old lithospheric mantle source. Carbon isotopic data for Catalão II carbonatites (?13C = -6.35 to -5.68 ?) confirm the mantle origin of the carbon for these rocks. The origin of Catalão II cumulitic rocks is thought to be caused by differential settling of the heavy phases (magnetite, apatite, pyrochlore and sulphides) in a magma chamber repeatedly filled by carbonatitic/ferrocarbonatitic liquids (s.l.). The Sr-Nd isotopic composition of the Catalão II rocks matches those of APIP rocks and is markedly different from the isotopic features of alkaline-carbonatitic complexes in the southernmost Brazil. The differences are also observed in the lithologies and the magmatic affinity of the igneous rocks found in the two areas, thus demonstrating the existence of regional-scale heterogeneity in the mantle sources underneath the Brazilian platform.