ABSTRACT The Argentinean and Bolivian sub-Andean fold-and-thrust belt is located in the orogenic front between 18–23°S and 64–63°W and immediately to the east of the Puna-Altiplano system and Eastern Cordillera. This fold-and-thrust belt is characterized by thin-skinned structures detached in Lower Paleozoic sequences. The compressional stage that affected this part of the orogen began in late Miocene and is ongoing. Examining the morphology of the folds and thrusts by combining digital elevation models, geological maps, and field observations allows us to present tectonic and geomorphological data on lateral fold growth and spatially linked shortening along the San Antonio range. The crest of this fold chain shows multiple culminations, slightly right-stepping, that merge to form the full San Antonio structural trend. Forked drainage patterns and the presence of wind gaps suggest recent fold amplification and lateral growth from these culminations. Linear and stepped linkage geometries are found between single structures. A northward increase in surface elevation and fluvial erosion follows the south to north increase in fold amplitude, aspect ratio, and change in structural style from folding to thrusting. The observed along-strike alternation of topographic highs and lows correlates well with the locations of subsurface hydrocarbon traps and saddle spill points indicating that the shallow and deep deformation patterns are coupled as a single structural feature.

ABSTRACT The analysis of the pre-Andean history of the Central Andes shows a complex tectonic evolution. The basement of the Andean continental margin was formed by the accretion of Precambrian blocks during the formation of Rodinia in late Mesoproterozoic times. There are two magmatic arcs of Grenvillian age, one developed on the margin of the craton, known as the Sunsas belt, and another on the accreted terranes. The suture between these blocks with the Amazonian craton has been continuously reactivated by tectonic and magmatic processes. The terranes of Paracas and Arequipa, both of Grenvillian age, have a contrasting Paleozoic evolution. The Arequipa terrane amalgamated to the craton by the end of the Mesoproterozoic, and during the Paleozoic its suture acted as a crustal weakness zone. This zone concentrated the extension and the formation of a large platform in the retro-arc basin, where the Eopaleozoic sediments accumulated. The Famatinian magmatic arc of Ordovician age (475–460 Ma) is preserved in this segment along the continental margin. The Eopaleozoic extension that affected the Paracas terrane reopened the old suture and formed oceanic crust between Amazonia and Paracas. The subduction of this oceanic crust developed a magmatic arc over the cratonic margin, which is preserved in the Eastern Cordillera of Peru as orthogneisses associated with metamorphic rocks of Famatinian age. There are ophiolitic assemblages, paired metamorphic belts, and intense deformation associated with the Paracas collision (~460 Ma)against the Amazonian craton. In northern Eastern Cordillera of Peru the late Paleozoic orogen has within-plate granitic belts and was far away from the active margin. The orogen was deformed and uplifted in two phases (336–285 Ma and 280–235 Ma) known as the early and late Gondwanide orogenies. They are preserved as medium grade metamorphic belts developed along the Paracas segment. Further south along the Arequipa segment in southern Peru and Bolivia, the late Paleozoic–Triassic rocks are represented by granites and acidic volcanic rocks, which are not metamorphosed and are associated with sedimentary rocks. Relics of a magmatic arc are exposed as tonalites and metamorphic rocks (~260 Ma) along the northern continental margin of Peru and in the near offshore platform. The extensional regime that dominated most of the Mesozoic developed rift basins in the hanging-wall of the terrane sutures, which controlled the structural highs and basin margins. The Peruvian Late Cretaceous orogeny produced the emplacement of the Coastal batholith, the beginning of deformation along the coast, and the first foreland basins. The giant Ayabacas submarine syn-tectonic collapse is also controlled by previous sutures. The Cenozoic Andean evolution was dominated by a wave of shallowing of the subducted slab, the migration of the magmatism to the foreland, the steepening of the oceanic plate, and the consequent “inner arc” magmatism. The “inner arc” plutonic and volcanic rocks are the expression of deep crustal melts, associated with crustal delamination and lithospheric mantle removal. The flattening of the oceanic slab is related to ablative subduction and shortening in the Altiplano and Eastern Cordillera. The steepening is associated with rapid removal of mantle lithosphere and crustal delamination, expressed at surface by the “inner arc” magmatism. The suture crustal weakness zones between different terranes partially controlled the location of the delaminated blocks and the “inner arc” magmatism. Both processes triggered the lower crust ductile shortening and subsequent upper crustal brittle development of the sub-Andean fold-and-thrust belt.