Proterozoic contraction/extension tectonics of the southern SÃO Francisco Region, Minas Gerais, Brazil

摘要

The southern São Francisco region comprises the southern portion of the São Francisco craton, which is underlain by Archean basement, and its fringing Proterozoic orogenic belts. Included in this region are three geologic provinces: the Quadrilátero Ferrífero (QF), the São Francisco Basin, and the Cordilheira do Espinhaço. We synthesize preliminary results of ongoing structural analysis, reconnaissance field studies, and published reports to provide a concise review of the geology of the region and to propose a working tectonic model for its Proterozoic evolution. Interpretation of superimposed folds, faults, and foliations leads to the conclusion that the southern São Francisco region records the effects of four principal tectonic events that occurred subsequent to deposition of the Lower Proterozoic Minas Supergroup. The first event resulted in formation of a northwest‐verging fold‐thrust belt. The second event led to development of high‐angle reverse faults, open folds, and basement uplift. The third event is manifested in the QF by the formation of normal faults and by the intrusion of mafic dikes; these extensional structures may be associated with formation of the sedimentary basins east and south of the São Francisco craton. The final event resulted in formation of a west‐verging fold‐thrust belt that affected the QF, the Cordilheira Espinhaço, and the São Francisco basin. The events that we describe can be tentatively associated with regionally recognized orogenic periods (Trans‐Amazonian, U