The Archaean terranes of central eastern Brazil: a review

Abstract

This paper compiles and describes several lithostratigraphic sequences which have characteristics typical of granite-greenstone and granite-gneiss terranes. The Archaean high-grade metamorphic assemblages are also described and are considered to form part of the mobile belt areas. Three major Archaean domains appear to be present in central eastern Brazil, i.e., the São Francisco Craton and the Jequié and Goiás Mobile Belts. In addition, several other small, but no less important, ancient nuclei occur within the Tocantins Province, especially in central Goiás. The São Francisco Craton is mostly covered by thick platform sequences of Proterozoic age, and as a result it can be examined only around the margins where granite-greenstone terranes are partially exposed. There appears to be sufficient evidence to recognise a stable Archaean basement domain, except in the northeast where the craton has been largely affected by the Transamazonian cycle (2.2-1.8 Ga) and, therefore, may represent a separate province. The available data for the Jequié and Goiás belts suggest that these domains have been subjected to high-grade regional metamorphism, chiefly granulite facies, during the Jequié tectono-thermal event of ∼2.7 Ga, equivalent to the Liberia-Limpopo events in Africa. The differentiated mafic to ultramafic complexes of central Goiás, of uncertain age, may also be related to the evolution of the Goiás Mobile Belt. In general, the Archaean terranes described here appear to display a rather fragmentary pattern with poorly defined boundaries due to substantial reworking, which makes them partially different from better preserved, major ancient domains in other continents.