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| Andean magmatic arc | |
|---|---|
| Name | Andean magmatic arc |
| Location | South America |
| Range | Andes |
| Type | Volcanic arc |
| Age | Cenozoic |
Andean magmatic arc The Andean magmatic arc is the major Cenozoic continental volcanic arc associated with the subduction of the Nazca Plate beneath the South American Plate along the western margin of South America, producing widespread magmatism from Colombia to Tierra del Fuego. The arc links a chain of volcanic centers and intrusive complexes including the Northern Volcanic Zone (NVZ), Central Volcanic Zone (CVZ), and Southern Volcanic Zone (SVZ), and interacts with crustal structures such as the Altiplano and the Patagonian Andes. Research on the arc involves collaborations among institutions like the Smithsonian Institution, United States Geological Survey, Consejo Nacional de Ciencia y Tecnología (CONACyT), and universities in Chile, Argentina, and Peru.
The arc sits above the convergent margin formed by the ongoing subduction of the Nazca Plate and the younger segments of the Antarctic Plate beneath the South American Plate, with plate interactions recorded by the Peru–Chile Trench, the Chile Ridge, and the Juan Fernández Ridge. Tectonic drivers include slab dip changes, flat-slab segments such as beneath Peru linked to the Nazca Ridge and the Juan Fernández hotspot, and crustal shortening expressed in the Andean orogeny, the Bolivian Orocline, and the uplift of the Altiplano–Puna plateau. Lithospheric architecture incorporates accreted terranes like the Chilean Coastal Cordillera, pre-Andean cratons including the Guiana Shield and the Cuyania terrane, and major faults such as the Atacama Fault System and the Liquiñe-Ofqui Fault Zone.
Magma generation reflects metasomatism and partial melting above the subducting slab influenced by slab-derived fluids and melts from hydrated oceanic crust and sediments inferred from geochemical signatures reported by studies in SERNAGEOMIN, Servicio Geológico Minero Argentino (SEGEMAR), and international projects with isotopic work on Sr, Nd, Pb and Hf. Primary magmas show contributions from mantle wedge peridotite modified by fluids from the subducting Nazca Plate and interaction with continental lower crust such as the Precambrian shields of South America and the Palaeozoic basins; petrogenetic processes include fractional crystallization, crustal assimilation, and magma mixing documented at centers like Ojos del Salado, Llullaillaco, and Nevado Ojos del Salado. Evidence from xenoliths, melt inclusions, and experimental petrology connects arc magmas to slab-derived components similar to arcs studied at the Kermadec Arc and the Cascades Volcanic Arc.
The arc is segmented into well-defined volcanic zones—NVZ (Colombia–Ecuador?), CVZ (Bolivia–Chile–Argentina), SVZ (Chile–Argentina), and the Austral volcanic provinces—controlled by subduction angle, slab age, and lithospheric thickness, as shown by variations between northern segments near the Caribbean Plate and southern segments adjacent to the Scotia Plate. Along-strike variations manifest in compositions from basaltic andesite to rhyolite, crustal thickness contrasts between the Puna plateau and the Coastal Cordillera, and magmatic flare-ups associated with events like the Miocene ignimbrite provinces and the Pliocene–Quaternary volcanic belts. Structural segmentation aligns with major tectonic features such as the Bolivian Orocline, the Loncopan–Valdivia Fault Zone and the subducting plate geometry near the Nazca fracture zones and the Chilean Flat Slab.
Volcanic activity in the arc spans from Paleogene to ongoing Holocene eruptions at stratovolcanoes and calderas including Lascar, Puyehue-Cordón Caulle, Puyehue, and Villarrica, with eruptive styles ranging from effusive basaltic eruptions akin to Mauna Loa to large explosive ignimbrites comparable to deposits studied at Yellowstone and Toba. Eruption histories are constrained by methods developed at institutions like USGS, Istituto Nazionale di Geofisica e Vulcanologia (INGV), and regional geochronology labs, documenting major ignimbrite flare-ups during the Miocene–Pliocene associated with calderas such as the Altiplano–Puna volcanic complex and cluster volcanism at the Maricunga Belt.
Arc magmatism generated world-class ore deposits including porphyry copper–molybdenum systems of the Chilean Iron Belt and the Peruvian metallogenic provinces, epithermal gold–silver deposits in the Colca and Zacatecas analogues, and skarn and IOCG systems related to intrusive centers like El Teniente, Escondida, Cerro Negro, and Antofagasta. Metallogenic patterns reflect magmatic differentiation, hydrothermal circulation along structures such as the Atacama Fault and fluid pathways tied to arc magmatism studied by mining companies like Codelco, Barrick Gold, and BHP, and by national geological surveys.
High-precision geochronology from U–Pb zircon dating, 40Ar/39Ar sanidine and biotite ages, and (U–Th)/He thermochronology have resolved pulses of magmatic activity, including Miocene ignimbrite flare-ups, Pliocene–Pleistocene arc migration, and Quaternary volcanism at centers such as Llullaillaco and Tupungatito. Integrating geochronology with geochemistry and isotopic tracers demonstrates episodic magmatic evolution controlled by slab rollback events like those inferred for the Miocene Chilean flat-slab episodes and by crustal shortening phases recorded in the Eastern Cordillera and Cordillera Real.
Arc volcanism has sculpted landscapes including the Altiplano–Puna plateau, generated large ignimbrite sheets that altered topography and drainage networks such as the Desaguadero River basin, and influenced paleoclimate through ash dispersal affecting regions like the Atacama Desert and the Amazon Basin. Volcanic hazards include explosive eruptions, lahars impacting urban centers like Arequipa, Antofagasta, and Santiago, and long-term hazards from active calderas monitored by agencies including SERNAGEOMIN and INGEMMET with hazard mitigation linked to international frameworks like the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI). The arc’s magmatic activity continues to affect resources, hazards, and tectonic evolution across South America.
Category:Volcanic arcs Category:Andes Category:Geology of South America