CONTRASTE DE ESTILOS ESTRUTURAIS E METAMÓRFICOS NA FAIXA DOBRADA SERGIPANA

EMANUEL FERRAZ JARDIM DE SÁ, JEAN-MICHEL LEGRAND, PETER CHRISTIAN HACKSPACHER

Resumo


The Sergipe fold belt can be divided in two segments. The metasediments in the southern one (Miaba and Vaza Barris groups) were deformed mostly by a WNW-trending folding phase associated with high-angle thrusts (F1). The metamorphism is monophasic, of greenschist or prehnite-pumpellyite facies and probably of intermediate pressure type. Later deformation episodes include kinks, crenulation (F2) and WNW transcurrent shear zones with steep plunging folds (F3). The supracrustals in the northern segment (Macururé Group) were deformed by three phases of macroscopic folds. The first one(F1) is characterized by tight to isoclinal, originally recumbent and transposed folds with southern vergence. A metamorphic event ranged from greenschist to high amphibolite facies (reaching sillimanite and anatexis isograds to the North), probably in a low pressure regime(M1). A second phase was responsible for SE-verging, closed to tight, overturned or inclined folds (F2). A new metamorphic recrystallization episode (M2)proceeded from greenschist to amphibolite facies, with kyanite or andaluzite present. A third deformation event (F3) can be detected, with northern-verning inclined folds. The associated metamorphism reached the kyanite isograd. Small and large scale interference patterns were defined by superimposition of the different phases. Structural correlations across the two segments suggest that the main folding in the south - (F1)s - can be equated with the third one to the north - (F3)N. The southern metasediments have been correlated with the upper Proterozoic Bambuí Group based on lithological grounds. A few radiometric dates support the assumption of a middle or lower Proterozoic age for the northern supracrustals, and their similarities with the other schist belts in the Northeast region are striking. Although a coeval evolution cannot be excluded at this stage, we favour the interpretation that the northern segment behaved as a basement unit, and was rejuvenated during the Brasiliano event, characterized by the development of an ensialic fold beld represented by the southern segment.


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