The Syn-Orogenic Rhyacian/Orosirian Costa Sena Basin, Southeastern Brazil

The Costa Sena metavolcanosedimentary sequence outcrops as a basement inlier within the Araçuaí fold-and-thrust belt, Minas Gerais State, Brazil. Although some studies have been carried out on this sequence, it’s origin and evolution are still controversial. In order to provide insights into its understanding, new whole-rock geochemical and zircon U-Pb (LA-ICPMS) geochronologic data were obtained for schists from the base of the sequence, as well as for metabreccia from the top of the sequence. When normalized to Cl chondrites, the schists can be classified in (i) porphyroclastic schists, with or without lazulite, that show the same REE signature as its basement; (ii) schists of dominant alkaline source; (iii) schists of dominant leucogranite source. Macroscopically, (iv) schists can be fine grained and banded; and (v) kyanite and/or tourmaline rich. Together with the alkaline nature of the samples, detrital zircon age spectra for the Barão do Guaicuí schists and Bandeirinha metabreccia suggest that the sequence was deposited in a foreland basin, under collisional tectonic settings. The Bandeirinha metabreccia sample yielded maximum depositional age peak at 2093 ± 9 Ma (25%), with important contribution peak at 2656 Ma (52%). The youngest zircon spot of the population (n=98) yielded an age of 2000 ± 40 Ma. Therefore, as originally defined, we suggest the maintenance of the Bandeirinha Formation inside the Costa Sena metavolcanosedimentary sequence, representing a change to arid environmental condition after epicontinental water regression. The concordant detrital zircon data from a schist (sample CSOV-08) of the Barão do Guaicuí Formation shows last population peak at 2112 ± 7 Ma, although schist sample CSOV-06A show a younger population at 2070 ± 23 Ma (Discordia line age). As foreland basins are the sedimentary record of orogenetic processes, this work contributes to the understanding of the Paleoproterozoic evolution of the São Francisco-Congo Paleocontinent.