In this classic segment, many tectonic processes, like flat-subduction, terrane accretion and steepening of the subduction, among others, provide a robust framework for their understanding. Five orogenic cycles, with variations in location and type of magmatism, tectonic regimes and development of different accretionary prisms, show a complex evolution. Accretion of a continental terrane in the Pampean cycle exhumed lower to middle crust in Early Cambrian. The Ordovician magmatic arc, associated metamorphism and foreland basin formation characterized the Famatinian cycle. In Late Devonian, the collision of Chilenia and associated high-pressure/low-temperature metamorphism contrasts with the late Palaeozoic accretionary prisms. Contractional deformation in Early to Middle Permian was followed by extension and rhyolitic (Choiyoi) magmatism. Triassic to earliest Jurassic rifting was followed by subduction and extension, dominated by Pacific marine ingressions, during Jurassic and Early Cretaceous. The Late Cretaceous was characterized by uplift and exhumation of the Andean Cordillera. An Atlantic ingression occurred in latest Cretaceous. Cenozoic contraction and uplift pulses alternate with Oligocene extension. Late Cenozoic subduction was characterized by the Pampean flat-subduction, the clockwise block tectonic rotations in the normal subduction segments and the magmatism in Payenia. These processes provide evidence that the Andean tectonic model is far from a straightforward geological evolution.

The southern Andes were created by two main cycles of shallow to flat subduction settings that were followed by steepening subduction zones starting in Late Cretaceous times. The first wave of contractional deformation and Andean uplift migrated through the continental interior as a result of two shallow subduction zones, one developed between 36 and 39°S and the other between 40 and 46°S, associated with the expansion of arc magmatism. In latest Cretaceous to Eocene times, its northernmost segment flattened, increasing the compression and uplift of mountains in the far foreland area, whereas, to the south, a steepening subduction zone provoked extensional collapse of vast sectors of the fold and thrust belt followed by within-plate magmatism. The whole area between 36 and 44°S retreated as a large steepening zone in late Oligocene times, inducing asthenosphere injection and the formation of large within-plate plateaux in the foreland zone, as well as narrow extensional basins induced by the incipient collapse of the fold and thrust belt hinterland zone. The late Miocene was characterized by the development of three shallow subduction zones that expanded differentially between 34°30′ and 50°S. These were again associated with arc expansions and lateral construction of the fold and thrust belt. Their evolution finished in Pliocene to Quaternary times with the eruption of within-plate plateaux and widespread extensional deformation that still governs important sectors of the present retroarc area. Finally, an incipient shallow subduction setting could have been developing between 35 and 39°S in the last 3 Ma associated with renewed Andean uplift at these latitudes. Cyclic shallow subduction in the southern Andes, and therefore repeated behaviour of constructional stages followed by collapsing ones associated with voluminous volcanism, could be the consequence of the cycle imposed by the docking of seismic ridges, one achieved in latest Cretaceous (?) to Eocene times and the other in late Miocene times. Other factors, such as the collision of highly serpentinized and therefore isostatically buoyant plateaux, associated with fracture oceanic zones, are also considered to trigger shallow subduction settings.Los Andes del Sur fueron creados a través de dos ciclos principales en los cuales la zona de subducción se subhorizontalizó y posteriormente se empinó en diferentes segmentos comenzando en el Cretácico superior. La primer fase contraccional en los Andes del Sur migró desde el borde de placas hacia el interior continental en relación al desarrollo de dos zonas de subducción subhorizontal, una desarrollada entre los 36°y los 39°S y la otra entre los 40°y los 46°S, ambas relacionadas a la expansión oriental del magmatismo del arco volcánico. En el Cretácico más alto hasta el Eoceno, la sección subhorizontal más septentrional siguió acentuándose asociándose así al levantamiento de relieves montañosos lejanos al límite de placas, al tiempo que el sector meridional se empinó rápidamente lo que provocó el colapso extensio...

The Chos Malal and Agrio fold and thrust belts are located in the western part of the Neuquén basin, an Andean retroarc basin of central-western Argentina. Both belts show evidence of tectonic inversion at the western part during Late Cretaceous times. The eastern part is dominated by late Miocene deformation which also partially reactivated the western structures. This work focuses on the study of the regional structure and the deformational event that shaped the relief of this part of the Andes. Based on new field work and structural data and previously published works a detailed map of the central part of the Neuquén basin is presented. Three regional structural cross sections were surveyed and balanced using the 2d Move TM software. In order to define a more accurate uplift history, new apatite fission track analyses were carried on selected structures.These data was used for new thermal history modeling of the inner part of the Agrio and Chos Malal fold and thrust belts. The results of the fission track analyses improve the knowledge of how these fold and thrust belts have grown trough time. Two main deformational events are defined in Late Cretaceous to Paleocene and Late Miocene times. Based on this regional structural analysis and the fission track data the precise location of the orogenic front for the Late Cretaceous-Paleocene times is reconstructed and it is proposed a structural evolution of this segment of the Andes. This new exhumation data show how the Late Cretaceous to Paleocene event was a continuous and uninterrupted deformational event.