The Salina del Fraile pull-apart basin, northwest Argentina

Abstract The Salina del Fraile in northwest Argentina is a Pliocene to Recent pull-apart basin developed at a releasing stepover along the NNE-SSW-trending El Fraile sinistral strike-slip fault. The basin is 35 km long and 12 km wide with a characteristic rhomboidal shape and is starved of synkinematic sediments thus providing unique 3D exposures. Prominent basin side-wall fault systems form scarps 700 m high and large tilted fault blocks form a terraced system along the southwest basin sidewall. A short-cut, basin-floor fault transects the pull-apart basin connecting the northwest strand of the El Fraile Fault to the southeast strand. An anticlinal positive flower structure in the northwest of the basin is a relict of early, segmented, fault growth typical of strike-slip fault evolution. Extension faults in the basin floor indicate a NE-SW intrabasinal extension direction during the Pliocene to Recent. The pull-apart basin accommodates an estimated 7.7 km of sinistral displacement along the El Fraile fault system. The morphology and fault architecture of the Salina del Fraile pull-apart can be directly compared to scaled sandbox models of strike-slip pull-apart basins. This first detailed analysis of the Salina del Fraile pull-apart basin provides a model for 3D architecture and evolution of similar pull-apart basins, and may serve as a template for the interpretation of other pull-apart systems.