Basement control on fault formation and deformation band damage zone evolution in the Rio do Peixe Basin, Brazil

摘要

The objective of this study is to analyze the influence of brittle reactivations of continental-scale Precambrian ductile shear zones on the evolution of deformation band damage zones. Our results indicate that the Rio do Peixe Basin was formed by the Cretaceous reactivation of its basement EW- and NE-SW-striking major fault segments. These fault segments are composed of a footwall with Precambrian crystalline mylonites and a hanging wall with Cretaceous fine to coarse sandstones. In the hanging wall, deformation bands occur in poorly sorted, fine to very coarse sandstones. These deformation bands occur as single bands or clusters mostly within damage zones similar to 84 m from the basement faults and are widespread in structural highs. Our data plot slightly above the medium fault displacement vs. the damage zone width solution but falls within the point cloud of global patterns. The slip surfaces strike EW- and NE-SW and are parallel or slightly oblique to the basement rift faults. The kinematics of slip surfaces are consistent with those of the reactivated basement faults. In addition, a logarithmic decrease in deformation band frequency occurs away from the basement slip surface. The deformation band frequencies peak close to the fault core with values as high as 22-48 bands/m. The lithology grain size also influences deformation as clusters of deformation bands and slip surfaces are only observed in coarse sandstones. This new case of deformation bands in damage zones of basement faults is characterized by a strong attitude and geometric and kinematic inheritance but follows the deformation band frequency of global patterns.