Characterization and Geological Meaning of the Crystalline Basement Occurrence in the Unaí Region, Minas Gerais State (Central Brasilia Belt)

Abstract

Granitoid rocks petrographically and compositionally characterized as tonalite, monzonite granodiorite and granite were observed in restricted areas in the central portion of the external zone of the Brasilia Belt. These outcrops of peraluminous rocks were interpreted as the sialic basement of the region, associated with paleogeographic highs prior to the deposition of the Proterozoic sedimentary cover. U-Pb zircon age of 2.14 Ga and geochemical analysis are compatible with other Paleoproterozoic bedrock areas observed mainly in the north Brasilia Belt. The existence of a basement bulkhead conditioned the Neoproterozoic deformation, causing the inflection of regional structures from NNW to N60-70W and over again to the NNW regional trend. The absence of contact metamorphism along the adjacent supracrustal rocks, regional foliation attitude that is different from that observed in the granitoids (tonalite, granotiorite, monzonite and granite) and the older age, show that these rocks represent basement windows and not younger intrusive bodies, as previously interpreted. The rocks studied in this research are correlated to the Aurumina Suite, which represents the main basement rock set in the North Brasília Belt.