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| Incaic orogeny | |
|---|---|
| Name | Incaic orogeny |
| Type | Orogenic episode |
| Location | Central Andes, South America |
| Age | Late Cretaceous–Paleogene |
| Orogenic belt | Andes |
| Coordinates | -15°S, -70°W |
Incaic orogeny is a major orogenic episode that shaped the central Andes during the Late Cretaceous through Paleogene, producing mountain building, crustal shortening, magmatism, and metallogenesis across western South America. It represents a key phase in the long-term evolution of the Andes and affected terranes from northern Peru through central Chile, interacting with pre-existing structures, sedimentary basins, and subduction dynamics beneath the South American Plate.
The Incaic orogeny marks a pronounced phase of crustal deformation and magmatic activity in the central Andes associated with intensified convergence between the Nazca Plate and the South American Plate, contemporaneous with regional events such as the uplift of the Altiplano-Puna plateau and reorganization of forearc and backarc systems. It is invoked to explain widespread folding in the Cordillera Occidental, thrusting in the Cordillera Oriental, and emplacement of volcanic arcs that affected provinces including Arequipa, Cusco, and Antofagasta. Key figures in the study of Andean orogeny include researchers affiliated with institutions such as the Geological Society of America, Servicio Geológico Colombiano, and universities like Universidad Nacional Mayor de San Marcos and Universidad de Chile.
The timeframe for the Incaic episode is generally placed from the Late Cretaceous (Campanian–Maastrichtian) into the Paleogene (Paleocene–Eocene), overlapping with plate reorganizations recorded in marine sections of the Peru-Chile Trench and terrestrial successions in the Altiplano. Stratigraphic markers include equivalents to the Pisco Formation in southern Peru and the Moquegua Basin sequences, alongside intrusive suites correlated with Andean magmatic belts studied in the Atacama Desert and the Central Volcanic Zone. Regional correlations have been proposed linking deformation with events recorded in the Yumaque Basin and the Chaco Basin margin.
Convergence-driven shortening, flat-slab subduction segments, and slab rollback are central tectonic mechanisms attributed to the Incaic deformation, with coupling between the Nazca Plate and South America modulated by oceanic plateaus such as the Nazca Ridge and the Inca Plateau (hypothetical) invoked in some models. Lateral variations in deformation are explained by interaction with cratonic blocks like the Brazilian Shield and orogenic fabrics inherited from the Grenville Orogeny and Brasiliano orogeny. Kinematic indicators include thrust faults, fold-and-thrust belts, and hinterland shortening recorded adjacent to volcanic arcs analogous to processes observed in the Saint Elias orogen and interpreted through analogs used by research groups at Smithsonian Institution and University of California, Berkeley.
Stratigraphic successions deformed during the Incaic include Mesozoic marine sequences, continental clastics, and Cenozoic synorogenic deposits preserved in basins such as the Moquegua Basin, Tarapacá Basin, and the Coquimbo Basin. Structural architectures comprise thin-skinned thrusting in foreland domains, thick-skinned uplift of basement blocks in the Eastern Cordillera, and major south-north-trending fault systems comparable to the Pallatanga Fault and Atacama Fault. Fold styles range from box folds and vergent ramp-flat systems to basement-involved uplifts similar to structures documented in the Puna and Sierras Pampeanas.
Metamorphic grades elevated across the orogen include greenschist to amphibolite facies in mid-crustal levels, with localized high-pressure episodes recorded in rocks exhumed in the Central Andes; metamorphism was synchronous in places with magmatism forming calc-alkaline to high-K volcanic and plutonic suites. Magmatic products linked to the Incaic span batholith emplacement, andesitic-dacitic volcanism, and porphyritic intrusions akin to those in the Cordillera de la Costa and the Bolivian Altiplano volcanic province. Petrogenetic studies reference isotopic systems such as U-Pb zircon geochronology performed by groups at Arizona State University and Universidad de Concepción.
Paleogeographic reconstructions depict contractional deformation driving uplift, erosion, and development of foreland basins that captured synorogenic sedimentation, with depositional systems ranging from deep-marine turbidites to fluvial megafans and lacustrine facies. Basin evolution models invoke flexural response of the lithosphere to loading by thrust sheets and magmatic arcs, producing depocenters analogous to the Maracaibo Basin and shelf-margin systems compared with exposures in Norte Chico. Provenance studies cite recycled orogens and cratonic sources including the Amazon Craton, using detrital zircon datasets generated by labs at Massachusetts Institute of Technology and Universidad de Buenos Aires.
The Incaic orogeny is linked to concentration of metallogenic provinces hosting porphyry copper, epithermal gold-silver, and polymetallic vein systems that underpin mining districts in Antofagasta Region, Oruro, and La Paz. Ore-forming processes include magmatic-hydrothermal fluid circulation associated with batholith emplacement and structural brecciation along thrusts and faults, producing deposits comparable to Chuquicamata, Escondida, and Potosí (mining)-style mineralization. Exploration strategies by companies such as Codelco and research by institutions like the Instituto Geológico y Minero de España draw on tectono-metallogenic models tied to this orogenic phase.
The Incaic orogeny represents a pivotal chapter in the protracted Andean orogenic cycle that established the major elevation gradients, drainage reorganizations, and metallogenic architecture of western South America, setting the stage for later Neogene uplift and climatic interactions that influenced Amazon Basin drainage capture and sediment flux to the Sierra de la Ventana. Its imprint is preserved in structural corridors, magmatic belts, and basin fills studied by international collaborations involving the International Union of Geological Sciences and national geological surveys across Peru, Bolivia, and Chile.
Category:Orogenies Category:Geology of the Andes