Geometry and evolution of the Manhua?u-Santa Margarida shear zone system, Ara?uai Orogen, MG.

O Feixe de Zonas de Cisalhamento Manhua?u-Santa Margarida de orienta??o geral NS estende-se por, aproximadamente, 300 km na regi?o leste de Minas Gerais. Como uma das principais estruturas do n?cleo cristalino do Or?geno Ara?ua?, ? constitu?do por um conjunto de zonas de cisalhamento d?cteis, que, em mapa, mostram tra?os sigmoidais. O seu segmento norte ? composto por zonas de cisalhamento reversas que promovem o transporte de material em dire??o a oeste e, subordinadamente, por zonas transcorrentes dextrais. Os segmentos central e sul s?o dominados por zonas transcorrentes dextrais. O desenvolvimento do feixe deu-se em quatro fases deformacionais neoproteroz?icas. A primeira fase promoveu a nuclea??o do conjunto de zonas reversas, que ficaram parcialmente preservadas no segmento norte do feixe. Durante a segunda fase, as zonas preexistentes experimentaram, de norte para sul, uma rota??o progressiva para a vertical e para a dire??o NE-SW, al?m de intensa reativa??o transcorrente dextral. A terceira fase gerou zonas de cisalhamento normais de ocorr?ncia restrita ao segmento norte. Na quarta fase, formaram-se falhas transversais e juntas. Em sua termina??o sul, o feixe, dominado por zonas transcorrentes dextrais, rotaciona-se at? confundir-se com as estruturas da por??o NW da Faixa Ribeira. Tal fato implica que as estruturas dessa por??o do feixe s?o de mesma idade, ou algo mais velhas que as transcorr?ncias dextrais, que marcam o quadro tect?nico do segmento NW da Faixa Ribeira.The N-S trending Manhua?u-Santa Margarida shear zone system extends for ca. 300 km in eastern Minas Gerais. As one of the main structures of the crystalline core of the Neoproterozoic Ara?ua? Orogen, the Manhua?u-Santa Margarida system is made up of a series of ductile shear zones, which show a sigmoidal trace in map view. The northern segment of the system mainly consists of west-verging thrusts and subordinate dextral strike-slip shear zones. The central and southern segments are dominated by dextral strike-slip shear zones. The development of the Manhua?u-Santa Margarida system occurs in four distinct Neoproterozoic deformation phases. During the first phase, the system nucleated as a series of thrust shear zones, which remain preserved in the northern segment. During the second phase, the thrust zones experienced a clockwise rotation coupled with an intensive strike-slip reactivation, becoming vertical and NE-striking in the southern portion of the orogen. The third deformation phase generated normal-sense shear zones, observed only in the northern segment of the system. Brittle deformation along WNW-striking fault zones and jointing are the manifestations of the fourth and youngest deformation phase. The southern segment of the Manhua?u-Santa Margarida system, dominated by dextral strike-slip zones, rotates progressively to a NE orientation and merges with the structures of the northwestern segment of the Ribeira belt. Therefore, the structures of the southern termination of the Manhua?u-Santa Margarida system are of the same age or slight older than the dextral strike-slip shear zones that characterize the tectonic grain of the northwestern portion of the Ribeira Belt