Nd isotopes from the Ribeira Belt in the Rio Paraíba do Sul region, SE Brazil: significance for its Neoproterozoic evolution

H. L. Roig, E.L. Dantas, and P.R Meneses

A systematic Nd isotope study carried out along the border between São Paulo and Rio de Janeiro states, in SE Brazil, enabled the recognition of different tectonostratigraphic domains originated during the diachronous collisional events that formed the Brasília and the Ribeira fold belts during the Brasiliano orogeny. Each domain has a characteristic Nd isotopic signature. A dominant Paleoproterozoic source, with TDM model ages varying between 1.6 to 1.9 Ga and 2.0 to 2.2 Ga, characterizes the supracrustal sequences of the Embu and Andrelândia Domains, respectively, whereas a mixture of Neoproterozoic and older sources is recorded in rocks of the Costeiro Domain, with TDM model ages varying between 1.2 and 1.4 Ga. A new occurrence of basement rocks was identified along the tectonic contact between the Andrelândia and Embu Domains showing TDM model ages between 2.7 and 3.2 Ga, suggestive of an Archean source. Neoproterozoic granites across the Ribeira Belt also show multiple sources, covering values between 1.4 and 2.4, but no systematic distribution across the domain boundaries could be found. The isotopic data add to the discussion about the presence of suture zones between terranes in the Ribeira Belt and helps to understand the Neoproterozoic evolution of this segment in the South America platform.