Crustal contamination in the Niquelandia Complex, Central Goias, Brazil: Sr-Nd isotopes and trace-element geochemistry.

The Niquelândia stratiform complex is constituted by two main superposed sequences, separated by a high T shear zone. The lower unit (LS), at the eastern, includes gabbros, peridotites and pyroxenites, and the upper unit (US), at the western part of the body comprises gabro-norites and amphibolites. US is bordered by the volcano-sedimentary Proterozoic Indaianopolis sequence, and LS is in tectonic contact with the terrains of the Archaean basement. The 143Nd/144Nd – 147Sm/144Nd plot do not provide good geochronological data. However LS and US arrays suggest two parallel 870 Ma reference lines, which were used for correlations between Sm-Nd isotopic data and trace-element geochemistry. These diagrams indicate that the Niquelândia complex originates from a depleted mantle source and experienced crustal contamination. The variation fields of US and LS in the 143Nd/144Nd – 87Sr/86Sr diagram, using the least contaminated gabbro as a proxy of the parental melt, indicate distinct arrays for the units. AFC modeling using the Juscelândia volcano-sedimentary sequence as the enriched end-member reproduces successfully the LS variation, whereas the US arrays is compatible with a contaminant characterized by low to moderate 87Sr/86Sr and low 147Nd/144Nd values. This study shows that LS and US may be cogenetic and coeval, if melts underwent contaminations from different components.