K-Ar and Rb-Sr age determinations for rocks of the Serra dos Carajás area, northern Brazil, indicate that the rocks were affected by the Transamazonian orogenic cycle, whose syntectonic phase is supposed to have taken place at about 1,960 m.y. ago. Posttectonic activity in the region is related to some granitic intrusions about 1,800 m.y. old, followed by the accumulation of postorogenic sedimentary and associated volcanic rocks. One of the anorogenic bodies is about 1,400 m.y. old. A late Paleozoic magmatic episode is indicated by diabase dike intrusions. Events prior to the Transamazonian orogeny have been also recognized in the area between Serra do Cinzento and Serra Buritirama.

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