The Southern Brasília Belt

Abstract

This chapter presents a review of the main tectonic features of the Southern Brasilia belt with emphasis on its relationships with the southwestern margin of the São Francisco craton in the context of the Neoproterozoic Brasiliano orogenic collage of West Gondwana. The belt is characterized by a stack of W-vergent nappes of passive margin units bounded to the west by the Archean-Paleoproterozoic Goiás microcontinent and the Neoproterozoic Mara Rosa, Goiás and Arenápolis magmatic arcs. The protracted history of the passive margin development initiated with Mesoproterozoic rifting events that led to a final Tonian continental break up and development of a wide continental margin basin. Minimum sedimentation ages of the sedimentary units involved are given by subduction-related regional metamorphism between 650 and 610 Ma. An older sedimentary phase of the passive margin is represented by the Paranoá Group, the Jequitaí Formation (Bambuí Group), the Vazante and Canastra groups, the Cubatão Formation (Ibiá Group) and part of the Araxá Group, whose youngest detrital zircons were dated between 1.0 and 0.9 Ga. The orogenic phase of the southern Brasilia belt started with progressive subduction of distal to proximal passive margin units at 650–630 Ma and development of recumbent folds associated with a regionally penetrative foliation and medium to high-pressure metamorphic parageneses. Post-metamorphic peak nappe exhumation took place around 610– 605 Ma (monazite U-Pb) and final cooling at 600–580 Ma, as indicated by K-Ar ages on white mica and biotite. The syn-orogenic Neoproterozoic sedimentary units show detrital zircons as young as 600 Ma, with mixed cratonic/arc-related sedimentary provenance, represented by the Bambuí Group, Rio Verde Formation (Ibiá Group) and upper thrust sheets of the Araxá Group.