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Tectonic evolution of the Sergipano Fold Belt, NE Brazil, during the Brasiliano orogeny

1989; Elsevier BV; Volume: 45; Issue: 4 Linguagem: Inglês

10.1016/0301-9268(89)90068-5

1872-7433

Ian Davison, Reginaldo Alves dos Santos,

Geochemistry and Geologic Mapping

Abstract The Sergipano Fold Belt (SFB) represents the southern segment of a Brasiliano-age (∼600 Ma) continental collision zone which extends over NE Brazil and continues into Central Africa as the North Equatorial Fold Belt. Major sinistral transcurrent fault/shear zones and thrusts separate domains with individual lithological, tectonometamorphic and magmatic characteristics. The principal steeply-dipping strike slip zones trend east-west to WNW-ESE. Lithological correlations across the shears have not proved possible, which suggests that displacements were probably large, but as yet, are unquantified. Major folding and thrusting affected all the domains. Folds have a southerly vergence with NW-SE to WNW-ESE, trends, consistent with a NE-SW to NNE-SSW shortening direction; although small differences in shortening trends exist between individual domains. The southernmost allochthonous domain of carbonate to clastic shelf-slope sediments was subject to a single phase of folding and thrusting onto the Sao Francisco Craton, accompanied by greenschist-facies metamorphism. North of this domain lies the Macurure Domain, which is separated from the southernmost allochthonous domain by the major Sao Miguel do Aleixo transpressive shear zone. Polyphase deformation, amphibolite facies metamorphism and massive granitic intrusion characterize this domain. North of the Macurure Domain lie the migmatites and granites of the Poco Redondo Domain, which represent a deeper crustal level. They are separated from the Macurure Domain by the Belo Monte Shear. A late tectonic leucogranite in the Poco Redondo Domain yields a 600 Ma Rb/Sr isochron. Finally, the Poco Redondo Domain was overthrust from the north by the Caninde Gabbroic Complex, associated with carbonates, pelites and amphibolites metamorphosed to greenschist and upper amphibolite facies; this has previously been interpreted as an ophiolite sequence. Although the relative movements or absolute ages of the domains are unknown, their distinct geological differences suggest that they are separate crustal blocks which underwent large lateral movement during the Brasiliano collision.