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The São Francisco craton in eastern Brazil is one of the major shield areas in South America. In the Quadrilátero Ferrífero area (southern sector of the craton) the Archean Rio das Velhas greenstone belt is surrounded by granite–gneiss terrane and is overlain by Proterozoic sedimentary successions. The Bonfim Metamorphic Complex is the only area of the granite–gneiss terrane adjacent to the greenstone belt that has been mapped. It comprises two gneissic units, tonalites, and late granitic dykes, which crosscut the regional north–south shear fabric. Samples of gneiss, two tonalites and a granitic dyke were dated by U–Pb. A zircon core from the Alberto Flores gneiss yielded a minimum age of 2920 Ma, whereas the overgrowth is concordant at 2772 ± 6 Ma. Two tonalites from the vicinity of Serra da Moeda are [Formula: see text] old, and a late dyke yielded an age of [Formula: see text]. These data, together with previously published U–Pb ages, show that (i) greenstone belt volcanism was coeval with granitoid intrusion and with metamorphism of older units in the granite–gneiss terrane at ca. 2780 Ma and (ii) the main crust-forming event in the Quadrilátero Ferrífero area is about 2780 Ma old. Clear evidence is now available indicating that older magmatism is 2.8–3.2 Ga old. In addition, the last Archean deformation must have occurred in the interval 2780–2703 Ma. Finally, the presence of 2774 ± 6 Ma titanite in the tonalites indicates that the metamorphism associated with the Trans-Amazonian orogeny (ca. 2.0 Ga) did not reach amphibolite facies in the study area.

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The Quadrilátero Ferrífero has some of the largest iron and gold deposits in the world and is a major geotectonic unit of the São Francisco Craton in Brazil. U-Pb zircon SHRIMP geochronology of six detrital sedimentary and metasedimentary rocks (114 zircon crystals, 118 spot analyses) has improved the understanding of the sedimentary processes and provenance ages of both rocks and the associated iron formation. The age of deposition of the iron formation is constrained between 2.58 and 2.42 Ga. The presence of an old Paleoarchean crust is dated in detrital zircon crystals, including the oldest zircon in South America (3809G3 Ma). Only high-Th/U, magmatic zircon crystals are present in the dated sedimentary rocks, and these indicate that the crust of the region was formed mostly during the Jequié cycle (six age peaks between 3055 and 2635 Ma). This time span of w420 m.y. is similar to the duration of a long-lived Wilson cycle. Most of the Rio das Velhas Basin was filled during approximately 30 m.y. between 2746 and 2717 Ma, though volcanism probably started earlier. The youngest detrital zircon age from the Minas Supergroup indicates that the intracratonic basin fill, including the iron formation, was deposited after 2580 Ma. Therefore, the crust was cratonized shortly after the intrusion of minor granitic bodies at around 2.62-2.58 Ga. A large gap in orogenic activity is indicated by the absence of zircon ages of 2580-2182 Ma. q

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