Archean granitoid magmatism in the Canaã dos Carajás area: Implications for crustal evolution of the Carajás province, Amazonian craton, Brazil

Abstract

Geological mapping, geochemical, and geochronological studies undertaken in the Archean granitoids of the Canaã area in the Carajás province, Amazonian craton, Brazil, led to the identification of new granitoid units. Two compositional groups of granitoids were recognized: (1) minor tonalitic-trondhjemitic units which are both geochemically different (Campina Verde and Pedra Branca) or similar to Archean TTGs (Rio Verde) and (2) major granitic units encompassing calc-alkaline (Canaã dos Carajás, Bom Jesus, and Serra Dourada), transitional (Cruzadão) and alkaline (Planalto) granites. These granitoids form four age groups from Mesoarchean to Neoarchean. (1) The protolith of the Pium complex, the Bacaba tonalite and other coeval rocks, as indicated by the presence of inherited zircons, were formed at 3.05–3.0Ga; (2) at 2.96–2.93Ga, the Canaã dos Carajás granite and the older rocks of the Rio Verde trondhjemite were crystallized; (3) at 2.87–2.83Ga, the Campina Verde tonalitic complex, the Rio Verde trondhjemite, and the Cruzadão, Bom Jesus and Serra Dourada granites were formed; (4) in the Neoarchean, at 2.75–2.73Ga, the Planalto and Pedra Branca suites and charnockite rocks were crystallized. The granitic units cover more than 60% of the Canaã surface. The Canaã area differs from the Rio Maria and other granite-greenstone terranes by the scarcity of TTGs, dominance of granites, and absence of sanukitoids. The evolution of the Canaã area started at least at 3.2Ga and was different from that of the juvenile Rio Maria terrane (2.98–2.86Ga), because of indicating a contribution from pre-existing crust. The Mesoarchean Canaã crust was strongly reworked during the Neoarchean (2.75–2.70Ga) and was probably the substratum of the Neoarchean Carajás basin. The evolution of the Carajás province differs from those of Dharwar and Karelian cratons. It approaches the evolution described in the Limpopo belt, in the sense that the Neoarchean granitoid magmatism was generated in hot zones of the deep crust, possibly due to collisional tectonic processes.