A Formação Salinas, Orógeno Araçuaí (MG): história deformacional e significado tectônico

Abstract

The Salinas Formation, made up of metasandstones, metapelites and metaconglomerates, occurs mainly in the surroundings of the town of Salinas, northern Minas Gerais. In this region, rocks of the Salinas Formation lie unconformably on top of the Macaubas Group on the west, and are intruded by Neoproterozoic and Cambrian granites on the east. Four generations of deformational structures were documented in this region, three of them affecting the Salinas rocks. The structures of the oldest phase, D D, representing an episode of syn-sedimentary deformation, include folds, faults and convolute bedding. The subsequent phases, D1, D2 and D G are related to the development of the Aracuai orogen. The D1 phase, represented by folds, shear zones, and a whole series of small-scale elements, took place during the Brasiliano event (585 to 560 Ma) and was associated to regional metamorphism in the green schist to amphibolite facies conditions. The D2 phase, corresponding to the extensional collapse of the orogen (520 to 500 Ma), is recorded by fold trains that cascade down to ESE. These structures are associated to a crenulation cleavage and normal-sense shear zones, which affect only the metasediments of the Macaubas Group. The D G phase, related to the emplacement of granite bodies, caused folding and contact metamorphism in the Salinas rocks. The nature, age, deformation history and tectonic setting of Salinas Formation in the Aracuai orogen point out to a deposition in a syn-collisional basin - a flysch basin -, developed between a passive margin and an orogenic front.