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A história de inversão do aulacógeno do Paramirim contada pela sinclinal de Ituaçu, extremo sul da Chapada Diamantina (BA)

2007; Sociedade Brasileira de Geologia; Volume: 37; Issue: 4 Linguagem: Inglês

10.5327/rbg.v37i4.1328

2317-4889

Simone Cerqueira Pereira Cruz, Fernando F. Alkmim,

Geography and Environmental Studies

The Paramirim aulacogen located in the northern Sao Francisco craton is a partially inverted rift, which represents the depositional site of two major craton cover units, the Espinhaco and Sao Francisco Supergroups of paleo/mesoproterozoic and neoproterozoic ages, respectively. Inversion of the aulacogen resulted in a system of NNW-SSE-trending faults and folds that dominates its structural picture. The age of inversion and its driving mechanism persist over the years as matter of debate in the Brazilian geological literature. Located in the southern end of the aulacogen, the Ituacu syncline is a synformal depression that belongs to set of the dominant inversion structures. Besides basement, the Ituacu syncline involves all Proterozoic sedimentary units in very good exposure conditions. Because of that, the Ituacu syncline can be viewed as a miniature of the Paramirim aulacogen, thereby representing a natural laboratory for both analysis of inversion structures and test of hypothesis concerning its tectonic evolution. A detailed and field based structural investigation performed in the syncline area allows us to document two distinct families of inversion structures. The older family, Da, consists of a system of thin-skinned faults and folds, which shows a general WNW-ESE orientation and a systematic NNE-directed vergence. The younger family, Dp, comprises a very rich and diverse set of NNW-SSE-trending and ENE-verging fabric elements, associated with thin-skinned and basement-involved faults and folds, among them the Ituacu syncline as a whole. Both families of structures affect the carbonates of the Salitre Formation, the youngest among the aulacogen fill units, indicting thus a maximum late Neoproterozoic age for the inversion of the southern Paramirim aulacogen. We interpret the Da structures as a consequence of the migration of Brasiliano deformation front further north, into the aulacogen trough, in the same way as document in many other areas close to Sao Francisco craton boundaries. The Dp structures clearly reflect the frontal closure of the aulacogen, due to an overall WSW-ENE oriented compression, which was probably induced by the collisions the Sao Francisco craton became involved during the Brasiliano-PanAfrican tectonic collage.