Deep seismic reprocessing of industrial lines, combined with surface geologic and structural data, provides the basis of a new tectonic interpretation of the northern Sierras Pampeanas at 27S latitude. These basement mountain blocks, uplifted during an episode of shallowing of the subduction zone, show an active double-wedge thrusting. Deep seismic data indicate the different vergences of the western and eastern sectors of the Sierra de Aconquija, in the western Sierras Pampeanas at this latitude. Neotectonic evidence reveals that both systems are active, although the western sector has been active since at least middle to late Miocene times and recorded a much greater uplift and horizontal displacement than did the east. The eastern sector, although presently active, recorded only minor uplift and displacement. These facts enable correlation of the events in the northern Sierras Pampeanas with analog and numerical models that predict the behavior of double-wedge thrusting.

A by-product of this analysis is the knowledge that a middle Miocene Atlantic transgression covered the entire region, prior to the uplift of the Sierra de Aconquija. Based on correlation of the foreland basin deposits on both sides of the range, two stages of development are recognized. A single foreland basin covered the study area at an early stage, during the marine transgression (13.5 Ma), and at a late stage, a broken foreland basin developed.