1.76 Ga volcano-plutonism in the southwestern Amazonian craton, Aripuanã-MT, Brazil: tectono-stratigraphic implications from SHRIMP U–Pb zircon data and rock geochemistry

Paleoproterozoic felsic and mafic volcanic rocks, extrusive and hypabyssal quartz porphyry, and high-K, A-type epizonal granites dominate the Aripuanã region in the southwestern Amazonian craton in the Mato Grosso state of Brazil. The extrusive and intrusive felsic rocks display similar major and trace elements abundanceʹs and equivalent SHRIMP U–Pb ages of 1762–1755 Ma; contacts between them in the field occur gradually. The felsic volcanic activity occurred predominantly as explosive subaqueous volcanism. Various features such as absence of plate collision evidences, lack of any sign of oceanic crust, lack of complete trends of magmatic differentiation, and bimodal characteristics suggest that the magmatism was intracratonic. The characteristically undeformed felsic igneous rocks were formed by extensional events, probably triggered by mantle activation in an intracratonic ‘anorogenic’ or post-collisional environment. Throughout the Amazonian craton there are wide areas displaying similar magmatism responsible for the generation of distinctive A-type granites. These A-type granites and associated volcanic rocks yield ages of ∼1.76 Ga, suggesting that they are genetically linked and that there was a unique tectonic mechanism of widespread action in this craton.