Late Cenozoic deformation in the Central Andes: fault kinematics from the northern Puna, northwestern Argentina and southwestern Bolivia

Abstract Fault kinematics from the northern Puna region of the central Andean Plateau show two phases of deformation. The older deformation involved thrusting on NNE-SSW striking faults prior to about 9 Ma. This produced an average shortening direction (120°±20°) which does not overlap the Miocene-to-Recent convergence direction between the Nazca and South American Plates (82°±4°). Reactivation of normal faults associated with a Cretaceous rift and strike-slip faulting in the weakened magmatic arc can explain the ∼40° discrepancy. Deformation younger than 9 Ma is on normal and strike-slip faults that indicate diverse Plio-Quaternary strain orientations, possibly due to the influence of both gravitational and subduction forces. While the normal faults are minor, five orogen parallel (NS) strike-slip faults are marked by ten- to sixty-kilometer-long scarps. Striae indicate right-lateral strike-slip with minor normal displacement. At least two of these faults reactive older thrusts. By analogy with trench-linked forearc strike-slip faults, the kinematics of these back-arc strike-slip faults can be explained by the decoupling of oblique foreland convergence into two mutually orthogonal components.