The southern Central Andes of Argentina between 35° and 39°S latitude can be divided into two sectors with contrasting geological histories. The boundary between the sectors coincides with the Cortaderas lineament. North of the Cortaderas lineament, the Andes record a foreland expansion of arc magmatism that is associated with contractional deformation in the Malargüe fold-and-thrust belt, and subsidence of the Río Grande foreland basin between 15 and 5 Ma. The peak expansion of deformation into the foreland occurred as late Miocene magmatic arc rocks erupted more than 500 km east of the trench and the San Rafael basement block was uplifted in central Mendoza. This stage was followed by the collapse of the basement uplift by normal faulting, the retreat of the magmatic arc, and the eruption of widespread late Pliocene to early Pleistocene within-plate lava flows in the Payenia region. Extensive Quaternary calderas and rhyolitic domes along the axis of the main Andes reflect crustal melting associated with basaltic underplating. In contrast, the structural evolution of the sector south of the Cortaderas lineament is dominated by the Late Cretaceous development of the Agrio fold-and-thrust belt, which underwent minor reactivations in the Eocene and the late Miocene. The post-Miocene Guañacos fold-and-thrust belt that has since developed along the axis of the main Andes concentrates neotectonic contraction. Arc magmatism in this sector is largely restricted to the axial area of the Andes. Both the sectors north and south of the Cortaderas lineament show evidence of an important episode of extension during the Oligocene to early Miocene, and for renewed extension in the Pliocene and the Pleistocene. The contrasting geological histories north and south of the Cortaderas lineament reflect differences in the geometry of the subducting plate, variations in crustal rheologies inherited from a more restricted distribution of Mesozoic rifts in the northern than the southern segment, and variations in the trench roll-back velocity through time.

Teleseismic earthquakes recorded within the ISSA (Integrated Seismological Experiment in the Southern Andes) temporary seismic experiment in the Southern Andes between 36° and 40°S latitude have been used to construct receiver function images of the crust and upper mantle. The oceanic Moho of the subducted Nazca plate is observed down to a depth of ∼100 km, corresponding well with the Wadati-Benioff zone seismicity and wide-angle seismic reflections. Beneath the volcanic arc, the slab begins to be invisible with P-to-S converted waves, implying the completion of the gabbroeclogite transformation in the oceanic crust at that depth. The continental Moho has been imaged at depth of ∼40 km beneath the main cordillera and shallows toward the eastern end of the profile beneath the Neuquén Basin to ∼35 km depth. Beneath the Loncopué graben, the Moho is locally uplifted to 30 km depth, possibly resulting from the backarc spreading beginning in the Pliocene-Pleistocene. An anomalously high Poisson's ratio beneath the volcanic arc may indicate partial melting in the upper-plate crust.

The eastern slope of the Andes between 36°S and 39°S shows contrasting behavior north and south of 37.5°S to 38°S. The region is notable for a mixed contractional and extensional tectonic regime in the last 5 m.y. that has led to the formation of four broad extensional depocenters and the Guañacos fold-and-thrust belt. The post–late Miocene tectonic evolution of the eastern slope of the Andes south of 37.5°S has been dominated by the development of the Bío Bío–Aluminé and the Loncopué troughs, which have undergone extensional collapse in association with abundant mafic volcanism. The formation of these troughs postdates the middle to late Miocene contractional deformation that inverted the early Miocene Cura Mallín basin. At the same latitude, the forearc has been uplifted by underthrusting and basal accretion. The distribution of late Pliocene to Quaternary deformation along the forearc, arc, and retroarc in this region is typical of a subduction system governed by a negative roll-back velocity. North of 37.5°S, post–late Miocene extensional collapse has occurred in the Las Loicas trough, which extends southeastward from the frontal arc near 35°S to the Tromen region in the retroarc near 37.5°S, and in the Sierra de Reyes trough in the eastern retroarc. The extensional collapse of these basins occurred in a more restricted region than in the troughs south of 37.5°S. The retroarc extension, which is locally accommodated by transtension, postdates late Miocene deformation in the Chos Malal and Malargüe fold-and-thrust belts. To the west, uplift related to shortening has produced the young Guañacos fold-and-thrust belt in the Main Cordillera, which is antithetic to the Benioff zone. This contractional belt is considered to be out-of-sequence in the sense that deformation occurred to the west of the Cretaceous to Miocene fold-and-thrust belt. The structural contrasts north and south of 37.5°S to 38°S are difficult to explain in the context of the modern tectonic setting in which relative convergence parameters, subducting oceanic slab age, and climate are similar. The differences are better explained as responses to contrasting changes in the late Miocene to Holocene geometry of the Benioff zone north and south 37.5°S to 38°S.