The Jeremoabo transpressional transfer fault, Recôncavo-Tucano Rift, NE Brazil.

Abstract

The Jeremoabo fault, located in the Early Cretaceous Recôncavo–Tucano Rift, northeastern Brazil, represents an example of transfer fault. A field-based structural analysis along 20 km of exposures revealed an E–W-trending and steeply dipping reverse-sinistral fault that resulted from transpressional reactivation of a pre-existent weak zone. The fault is associated with a 5-km-wide footwall deformation zone, in which sandstone layers are folded and locally overturned becoming parallel to the fault. The deformation zone contains a pervasive system of NE- and NNW-trending conjugate Riedel shear fractures of outcrop to kilometer scale. A paleostress analysis based on these Riedel fractures indicated σ1 and σ3 trending, respectively, 016° and 108°, and σ2 subvertical, consistent with transpression and local switch between σ1 and σ2 relative to the regional paleostress field. The Jeremoabo fault links smaller rift border faults and has sense of slip consistent with the mapped offset of the basin border. Its transfer function is attested by linkage with a major dextral transfer fault and a transfer zone during the rifting period. By acting together these structures accommodated the change in asymmetry between the two major half-grabens of the rift.