The Northern Brasilia Belt

The Brasilia belt is a well-preserved Neoproterozoic orogenic belt within the Tocantins Province, central Brazil. Its northern segment strikes N-S, and verges eastwards to the Sao Francisco craton. The northern Brasilia belt external zone is a fold-thrust belt of low-grade passive margin metasedimentary rocks as well as syn-orogenic sedimentary sequences related to a magmatic arc. The internal zone includes deep sea sediments associated to an ophiolite mlange, arc-type calc-alkaline volcanics and intrusives, and S-type collisional granites. Metamorphic grade increases westwards from non-metamorphic and low-grade rocks, in the east, to high-temperature amphibolite facies rocks, culminating in ultrahigh-T granulites in the metamorphic core. The belt is the result of convergence of the Amazonian, Sao Francisco and Paranapanema paleocontinents and involved the subduction of a wide oceanic lithosphere and development of primitive island arc systems. Convergence also entrapped the Goias massif, an exotic continental fragment, comprising Archean granite-greenstone terrains, Paleoproterozoic granite-gneiss, Neoproterozoic layered complexes, and Proterozoic cover rocks, exposed between the magmatic arc and the metamorphic core in the central part of the belt, and the external zone farther north.