Early Precambrian basic rocks of South America

Abstract

Precambrian mafic–ultramafic igneous rocks of South America are diverse in composition, age and origin. They include greenstone belts, layered complexes, and anorogenic volcanics and dyke swarms, exposed on the three main cratonic regions: the Amazonian Craton, the São Francisco Craton and the Goiá Massif (Figure 17.1). The geology of these regions has been reviewed in Almeida et al (1981), Gibbs and Barron (1983), Almeida and Hasui (1984), Hasui and Almeida (1985) and Cordani et al. (1988). The geology has been interpreted in terms of a number of orogenic cycles, notably the Guriense (> 3 Ga), Jequié (2.7Ga), Transamazonian (2.0Ga), Uruaçuano–Espinhago (1.5–1.1 Ga) and Brasiliano (1.1–0.5 Ga) Cycles (see Wernick, 1981), during which the Precambrian crust progressively accreted. It has been estimated that 80% of the Precambrian of South America had formed by the end of the Transamazonian (Cordani et al, 1988).