Interferência entre duas faixas móveis neoproterozóicas: o caso das faixas Brasília e Ribeira no Sudeste do Brasil

Abstract

Neoproterozoic metasedimentary successions of the Andrelândia Sequence, gneisses of the Guaxupe Massif and Paleoproterozoic ortogneisses, with igneous zircon of 2.088_26 Ma, constitute the Precambrian units in the Tres Coracoes region, southern Minas Gerais State. Deformational structures and metamorphic associations indicate two collisional events related to the Neoproterozoic orogeny, that originated the Brasilia and Ribeira fold belts.Two continuous deformational phases (DB1 and DB2) and a relatively high pressure metamorphic event (MB) were related to the Brasilia fold belt. Superposed and related to the Ribeira fold belt, two deformational phases (DR1 and DR2) and a lower pressure metamorphic event (MR) are recognized. DB1 and DB2 produced nappes with movement to ESE, E and ENE. MB metamorphism started during DB1, as indicated by metamorphic isograds that are dislocated by DB1 and DB2 structures. K-feldspar-in/muscovite-out and sillimanite-in isograds related to the granulite facies are concordant with DB2 thrust faults, showing that the MB peak was sin-DB2. Folds with steep axial planes and axes plunging toWSWwere produced during DR1 that folded the nappes lateraly. The fact that metamorphic isograds related to theMRmetamorphic event cutMBisogrades and pre-existing structures shows the superimposition of this event on the Brasilia fold belt evolution. Finally, the last deformational phase DR2 produced dextral transcurrent ductile-brittle shear zones with SW-NE strike, that cut structures and metamorphic isograds of both fold belts.