Abstract
The present paper is a result of geological mapping of an area of about 3 000 km 2 situated in the South of Minas Gerais. Geologically the area is underlain by the Pinhal Group, Amparo Group and the Silvianopolis Complex of Brasiliano, Trans-Amazonic and Archaean ages respectively. On the basis of structural analysis the effects of superposed folding in the area assignable to four phases of deformation were identified. The oldest of these is designated Fn followed by Fn+1, Fn+2 and Fn+3. The Fn phase represents the culmination of a pre-Trans-Amazonic event involving migmatization and formation of granulites and is recognisable solely in the rocks of the Silvianopolis Complex. The Fn+1 phase characterized by isoclinal folding, which affected both the Amparo Group and the Silvianopolis Complex, took place in the Trans-Amazonic orogeny. The subsequent Fn+2 phase caused isoclinal folding of the Fn+1 folds with fold axes and axial planes in a north-westerly direction and vergence to the northeast. Crescent shaped interference figures of type 2 were formed in this phase as a result of interference consequent on the refolding of the Fn+1 folds. This phase is provisionally correlated with the Uruacuano Cycle. Finally, the Fn+ folding affected the Fn+1 and Fn+2 structures resulting in flexural or open folds with northeast fold axes and axial surfaces without any definable vergence. Type 3 interference figures originated by the superposition of the Fn+3 on Fn+1 folds and are characterized by approximate coaxial refolding. The Fn+3 deformation is tentatively related to the Brasiliano Cycle.
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