The Agrio and Chos Malal thrust and fold belts develop over more than 200 km in the northwestern sector of the Neuquén Basin. In their frontal sector, the eastern flank of ramp related anticlines behaves as tectonic wedges, inserting along evaporitic related detachments. The multiple occurrence of those detachments determines the occurrence of several packages with distinctive structural styles ("structural levels"). In the northern part of the analyzed thrust and fold belt, the participation of deformed units of the Mendoza Group within these structural levels add complexity to the frontal area, and led to the occurrence of commercial oil accumulations. To the south, the Mendoza Group remains undeformed at the front of the belt, and the deformation concentrates within alternating saltclastic levels located higher in the stratigraphic column (Huitrín and Rayoso formations). The seismic recorded there allows to recognize a wide duplex structure, sandwiched between detachment levels located at the base and top of that package. This duplex structure is characterized by the replication of discrete horses (mainly hinterland dipping), in a clear passive roof configuration. The duplex belt spreads along 150 km with a maximum wide of about 40 km. The frontal boundary of the duplex structure is a blind line, where no thin-skinned deformation is present to the east. This blind line represents the real deformation front of the analyzed thrust and fold belts.