An example of a Neoproterozoic hyperextended margin: An integrated perspective of the basic magmatism recorded in the Andrelândia Basin, central Ribeira Orogen, SE-Brazil

Abstract

Deformed amphibolite to granulite-facies metasedimentary rocks of Andrelândia and Raposos Group, associated metabasic rocks witnessed the evolutionary stage of the Andrelândia sedimentary basin, within Central Ribeira orogen, bordering the southern São Francisco Craton. Despite detailed geological maps and provenance studies, there is still a knowledge gap and debate on the stratigraphic pile and the age of sedimentation in the Andrelândia basin. New data regarding metabasic rocks interlayered in Andrelândia basin is presented, including detailed geological mapping, lithogeochemistry, Sm-Nd and Rb-Sr isotopes and LA-ICPMS U-Pb zircon geochronology. The metabasic rocks occur as centimetric to metric lenses with sharp contacts with the metasedimentary country rocks, displaying the same ca. 620–580 Ma age span of metamorphism and deformation. Geochemical results indicate high-TiO2 within-plate to low-TiO2 MORB to E-MORB signatures for lower and upper units of the distal Raposos Group. Additionally, only low-titanium MORB-like metabasites were found in the most proximal unit, Andrelândia Group. One sample within the Raposos Group yielded crystallization age of ca. 653 Ma, metamorphic overprint at ca. 579 Ma and Paleo to Mesoproterozoic inherited zircon grains. The metabasic rocks interleaved in the Andrelândia Group, Nd TDM model ages are between 1.10 and 1.90 Ga, with εNd (653 Ma) varying between −8 to + 2.1 and 87Sr/86Sr (653 Ma) values between 0.7144 and 0.7033. Nd TDM model ages are between 1.80 and 2.0 Ga, with negative εNd (653) −14 to −0.2 and initial 87Sr/86Sr between 0.7157 and 0.7043. The results indicate an isotopic similarity with the biotite schists of the Santo Antônio Unit, previously considered as arc-derived in an active margin setting. Together with previously published isotopic and geochronology data, and with the structural distribution of the units and tectonic interleaved basement slices in the distal Raposos Group, we envisage a tectonic model with syn-to-late depositional basic magmatism between ca. 760 to 653 Ma. The proposed model compares the evolution of Andrelândia-Raposos basin with modern hyper-extended magma poor rifted continental margin sedimentary basins as plausible tectonic setting. Finally, the results are compared with those from the Araçuaí orogen, the Northern part of the Araçuaí-Ribeira Orogenic System, displaying similarities in ages and composition.