U?Pb ages and Hf-isotope data of detrital zircons from the late Neoarchean-Paleoproterozoic Minas Basin, SE Brazil.

Because of its world-class iron ore deposits and promising Au and U mineralizations, the late Neoarchean to Paleoproterozoic Minas Basin (Minas Supergroup, SE of Brazil) is one of the best-studied basins in South America. However, the lack of datable interlayered volcanic rocks prevented discourse over ages of the strata, the sources and the nature of its ore deposits. In this paper, we present detrital zircon U? Pb age patterns coupled with Lu?Hf data for 18 samples, representing different stages of the Minas Basin evolution ( 2000 analyzed zircons). Age spectra for the main basal unit (Moeda Formation) show a classic rift-related detrital zircon pattern, characterized by multiple autochthonous sources, which in turn are much older than the age of deposition. Maximum age for the rifting event is constrained at ca. 2600 Ma. Detritus accumulated at the base of the Minas Supergroup were derived from Archean source rocks and their sedimentation was marked by differential uplift of the Archean crust, shortly after the 2730?2600 Ma high-K calc-alkaline magmatism (Mamona Event). The age of the BIF deposits is younger than 2600 Ma, most likely coinciding with the great oxygenation event between 2400 and 2200 Ma and the precipitation of banded iron deposits worldwide. Detrital zircons from the topmost units of the Minas strata suggest that tectonic inversion and closure of the basin took place at ca. 2120 Ma with the deposition of the synorogenic Sabar? Group. Rhyacian zircon supply showing juvenile Hf signatures gives evidence of a late Rhyacian amalgamation between the Mineiro Belt and the craton. The eHf signatures support the hypothesis that the Archean crystalline crust of the craton was mostly built by crust?mantle mixing processes, with a successive decrease of eHf values in zircons crystallized after 3250 Ma and minor mantle-like additions after Paleoarchean times. Regionally, our dataset supports previous interpretations of a long-lived evolution of the southern S?o Francisco Craton comprising a succession of convergent island arcs, small microplate collisions, and developmen

The Archeane-Paleoproterozoic evolution of the Quadril?tero Ferr?fero, Brasil : current models and open questions.

The Quadril atero Ferr?fero is a metallogenic district (Au, Fe, Mn) located at the southernmost end of the S~ao Francisco craton in eastern Brazil. In this region, a supracrustal assemblage composed of Archean greenstone and overlying NeoarcheanePaleoproterozoic sedimentary rocks occur in elongated keels bordering domal bodies of Archean gneisses and granites. The tectonomagmatic evolution of the Quadril atero Ferr?fero began in the Paleoarchean with the formation of continental crust between 3500 and 3200 Ma. Although this crust is today poorly preserved, its existence is attested to by the occurrence of detrital zircon crystals with Paleoarchean age in the supracrustal rocks. Most of the crystalline basement, which is composed of banded gneisses intruded by leucogranitic dikes and weakly foliated granites, formed during three major magmatic events: Rio das Velhas I (2920e2850 Ma), Rio das Velhas II (2800e2760 Ma) and Mamona (2760e2680 Ma). The Rio das Velhas II and Mamona events represent a subduction-collision cycle, probably marking the appearance of a modern-style plate tectonic regime in the Quadril atero Ferr?fero. Granitic rocks emplaced during the Rio das Velhas I and II events formed by mixing between a magma generated by partial melting of metamafic rocks with an end member derived by recycling gneissic rocks of older continental crust. After deformation and regional metamorphism at ca. 2770 Ma, a change in the composition of the granitic magmas occurred and large volumes of high-K granitoids were generated. The ca. 6000 m-thick Minas Supergroup tracks the opening and closure of a basin during the NeoarcheanePaleoproterozoic, between 2600 and 2000 Ma. The basal sequence involves continental to marine sediments deposited in a passive margin basin and contain as a marker bed the Lake Superiortype Cau^e Banded Iron Formation. The overlying sediments of the Sabar a Group mark the inversion of the basin during the Rhyacian Minas accretionary orogeny. This orogeny results from the collision between the nuclei of the present-day S~ao Francisco and Congo cratons, generated the fold-and thrust belt structure of the Quadril atero Ferr?fero. Afterwards, the post- orogenic collapse resulted in the deposition of the Itacolomi Group and in the genesis of the dome-and-keel structure. In this paper, we review current knowledge about the 1500 Ma long-lasting tectonomagmatic and structural evolution of the Quadril atero Ferr?fero identifying the most compelling open questions and future challenges