The major precambrian terranes of eastern south america: a study of their regional and chronological evolution

Abstract

Abstract The Archaean of South America comprises two types of domain, the low-grade granite-greenstone assemblages of cratonic type, and the high-grade granulite-gneiss terranes of mobile zones related to the ∼ 2.7 Ga old Jequie event, equivalent to the Limpopo-Liberia event in Africa. The geological evolution of the Proterozoic terranes of eastern South America is intimately linked to three major tectogenetic cycles and their related tectono-thermal events, i.e. the Transamazonian, the Uruscuano and the Brasiliano cycles, of early, middle, and late Proterozoic age, respectively. The first, equivalent to the Eburnian of Africa, is characterized by the reworking of Archaean crust and accompanied by intense magmatism. Several major geotectonic provinces, such as the Amazonian Province, the Sao Luis Province, the Paramirim Province and the Rio de la Plata Province, were stabilized after this event. The Uruacuano Belt seems to have been the only mobile zone active during the middle Proterozoic, and consequently the Uruacuano cycle (equivalent to the Kibaran of Africa) has a relatively restricted regional imprint over the South American platform. Conversely, the late Precambrian Brasiliano cycle (equivalent to the Pan-African) affected extensive areas adjacent to the Atlantic Coast, and in central Brazil. The development of all these major mobile zones appears to be related to ensialic intracratonic processes, including intense reworking of pre-existing crust, and within them there seems to be an almost complete absence of oceanic volcanism, except for minor basaltic to andesitic volcanics found in the Ribeira belt of late Precambrian age.