O papel das falhas na evolução de bandas de deformação na bacia do Rio do Peixe

Abstract

The fragile reactivation of continental scale pre-cambrian ductile shear zones and the development of rifte basins in northeastern Brazil occurred in the Cretaceous. These basins commonly exhibit subseismic structures, such as deformation bands. The objective of this study is to analyze the influence of early rift architecture and associated master faults on the occurrence and attributes of deformation bands. Shuttle radar topography, aeromagnetic, and gravity data were used to unravel the rift structure and identify master fault segments. In addition, an unmanned aerial vehicle (UAV) were used and a field study to map deformation bands close to the main rift faults. The results indicated that the Rio do Peixe Basin was formed along the reactivation of the Malta fault and the Portalegre fault.. Deformation bands occur in poorly sorted, medium to very coarse sandstones within ~70 m wide hanging wall damage zones at the master border faults. The deformation bands occur as single bands or unified bands, called clusters, as far as 5 km from Portalegre Fault master faults, as far as 2.5km from Malta Fault and they are widespread in a structural high bounded by two relay ramps. The deformation bands follow the strike or are oblique to the master rift faults and become slip surfaces when a zone of deformation bands causes a zone of weakness that forms faults. The slip surfaces kinematics are consistent with those of extensional rift faults. In addition, a decrease in deformation band frequency occurs away from the master faults. The deformation band frequencies peak close to the fault core with values as high as 22- 48 bands/m. These observations indicate the influence of reactivated rift faults on the deformation band pattern and evolution, and they contribute to the prediction of the location, strike, and kinematics of deformation bands in continental extensional settings.