Salar Grande pull-apart basin, Atacama Fault System, northern Chile

Abstract The Salar Grande basin is a ‘poly-history’ strike-slip basin along the north-trending Atacama Fault System in northern Chile (21°S, 70°W). It exhibits a range of structures that indicate a complex evolution with multiple deformation styles. This paper presents a new interpretation of Salar Grande as a strike-slip pull-apart basin with three stages of evolution. In the first stage (Oligocene to Early Miocene), the basin opened as a sinistral strike-slip pull-apart structure at a left-stepping releasing jog of the Atacama Fault System. At the end of this stage, the basin had a rhomboidal geometry with dimensions of about 35 km length and 10 km width, bounded by a series of linked oblique-extensional basin-sidewall faults. The western sidewall faults linked to the northern fault strand of the Atacama Fault System whereas the eastern sidewall faults linked to the southern strand. The basin interior was a series of tilted fault blocks forming half-grabens. During the second stage (Oligocene to Early Miocene) a NNW-SSE basin short-cut fault developed, dissecting the basin with 6 km of sinistral offset. In the third stage (Pleistocene-Recent), NNW-SSE strike-slip faults were dextrally reactivated with displacements of up to 1 km. The understanding of field examples such as Salar Grande provides new insights into the geometries and evolution of complex multi-phase strike-slip terranes. The geometries recognized in Salar Grande compare well with analogue modelling studies of strike-slip fault systems.