The Archeane-Paleoproterozoic evolution of the Quadrilátero Ferrífero, Brasil : current models and open questions.

Abstract

The Quadril atero Ferrífero 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 Ferrífero 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 Ferrífero. 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 Ferrífero. 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 Ferrífero identifying the most compelling open questions and future challenges.