in the
Tierra del Fuego. The Andes range is about wide throughout its length, except in the
Bolivian flexure where it is about wide.|alt=Mountains with snowy peaks|left The Andes are an
orogenic belt of mountains along the
Pacific Ring of Fire, a zone of
volcanic activity that encompasses the Pacific rim of the Americas as well as the
Asia-Pacific region. The Andes are the result of
tectonic plate processes extending during the
Mesozoic and
Tertiary eras, caused by the
subduction of
oceanic crust beneath the
South American Plate as the
Nazca Plate and South American Plate converge. These processes were accelerated by the effects of climate. As the uplift of the Andes created a rain shadow on the western fringes of
Chile,
ocean currents and prevailing winds carried moisture away from the
Chilean coast. This caused some areas of the subduction zone to be sediment-starved, which in turn prevented the subducting plate from having a well lubricated surface. These factors increased the rate of contractional coastal uplift in the Andes. The main cause of the rise of the Andes is the contraction of the western rim of the
South American Plate due to the subduction of the
Nazca Plate and the
Antarctic Plate. To the east, the Andes range is bounded by several
sedimentary basins, such as the
Orinoco Basin, the
Amazon Basin, the
Madre de Dios Basin, and the
Gran Chaco, that separate the Andes from the ancient
cratons in eastern South America. In the south, the Andes share a long boundary with the former
Patagonia Terrane. To the west, the Andes end at the
Pacific Ocean, although the
Peru–Chile Trench can be considered their ultimate western limit. " in the
Puna de Atacama,
Salta (
Argentina)|leftThe Andean orogen has a series of bends or
oroclines. The
Bolivian Orocline is a seaward-concave bending in the coast of
South America and the Andes Mountains at about 18° S. At this point, the orientation of the Andes turns from northwest in
Peru to south in
Chile and
Argentina. The Bolivian Orocline area overlaps with the area of the maximum width of the
Altiplano Plateau, and according to Isacks (1988) the Orocline is related to
crustal shortening. The specific point at 18° S where the
coastline bends is known as the
Arica Elbow. Further south lies the Maipo Orocline, a more subtle orocline between 30° S and 38°S with a seaward-concave break in the trend at 33° S. Near the southern tip of the Andes lies the Patagonian Orocline.
Orogeny and
Illimani in
Bolivia, two prominent peaks formed by the tectonic uplift caused by the
Andean orogeny and plate
subduction.|left The western rim of the
South American Plate has been the place of several pre-Andean
orogenies since at least the late
Proterozoic and early
Paleozoic, when several
terranes and
microcontinents collided and amalgamated with the ancient
cratons of eastern South America, by then the South American part of
Gondwana. The formation of the modern Andes began with the events of the
Triassic, when
Pangaea began the breakup that resulted in developing several
rifts. The development continued through the
Jurassic Period. It was during the
Cretaceous Period that the Andes began to take their present form, by the
uplifting,
faulting, and
folding of
sedimentary and
metamorphic rocks of the ancient cratons to the east. The rise of the Andes has not been constant, as different regions have had different degrees of tectonic stress, uplift, and
erosion. Across the
Drake Passage lie the mountains of the
Antarctic Peninsula south of the
Scotia Plate, which appear to be a continuation of the Andes chain. The far east regions of the Andes experience a series of changes resulting from the Andean orogeny. Parts of the
Sunsás Orogen in
Amazonian craton disappeared from the surface of the earth, being
overridden by the Andes. The
Sierras de Córdoba, where the effects of the ancient
Pampean orogeny can be observed, owe their modern uplift and relief to the
Andean orogeny in the
Tertiary. Further south in southern
Patagonia, the onset of the Andean orogeny caused the
Magallanes Basin to evolve from being an
extensional back-arc basin in the
Mesozoic to being a contractional
foreland basin in the
Cenozoic.
Seismic activity Tectonic forces above the
subduction zone along the entire west coast of South America where the
Nazca Plate and a part of the
Antarctic Plate are sliding beneath the
South American Plate continue to produce an ongoing
orogenic event resulting in minor to major
earthquakes and
volcanic eruptions to this day. Many high-magnitude earthquakes have been recorded in the region, such as the
2010 Maule earthquake (M8.8), the
2015 Illapel earthquake (M8.2), and the
1960 Valdivia earthquake (M9.5), which as of 2024 was the strongest ever recorded on seismometers. The amount, magnitude, and type of seismic activity varies greatly along the subduction zone. These differences are due to a wide range of factors, including friction between the plates, angle of subduction, buoyancy of the subducting plate, rate of subduction, and hydration value of the mantle material. The highest rate of seismic activity is observed in the central portion of the boundary, between 33°S and 35°S. In this area, the angle of subduction is very low, meaning the subducting plate is nearly horizontal. Studies of mantle hydration across the subduction zone have shown a correlation between increased material hydration and lower-magnitude, more frequent seismic activity. Zones exhibiting dehydration instead are thought to have a higher potential for larger, high-magnitude earthquakes in the future. The mountain range is also a source of shallow intraplate earthquakes within the South American Plate. The largest such earthquake (as of 2024)
struck Peru in 1947 and measured 7.5. In the Peruvian Andes, these earthquakes display normal (
1946), strike-slip (1976), and reverse (
1969, 1983) mechanisms. The Amazonian Craton is actively underthrusted beneath the sub-Andes region of Peru, producing thrust faults. In Colombia, Ecuador, and Peru, thrust faulting occurs along the sub-Andes due in response to contraction brought on by subduction, while in the high Andes, normal faulting occurs in response to gravitational forces. In the extreme south, a major
transform fault separates
Tierra del Fuego from the small
Scotia Plate.
Volcanism , an area of intense geothermal activity with
fumaroles and
geysers, Bolivia shows the high plains of the Andes Mountains in the foreground, with a line of young volcanoes facing the much lower Atacama Desert The Andes range has many active volcanoes distributed in four volcanic zones separated by areas of inactivity. The Andean volcanism is a result of the
subduction of the Nazca Plate and Antarctic Plate underneath the South American Plate. The belt is subdivided into four main volcanic zones that are separated from each other by volcanic gaps. The volcanoes of the belt are diverse in terms of activity style, products, and morphology. Although some differences can be explained by which volcanic zone a volcano belongs to, there are significant differences inside volcanic zones and even between neighboring volcanoes. Despite being a typical location for
calc-alkalic and subduction volcanism, the Andean Volcanic Belt has a large range of volcano-tectonic settings, such as rift systems, extensional zones,
transpressional faults, subduction of
mid-ocean ridges, and
seamount chains apart from a large range of crustal thicknesses and
magma ascent paths, and different amount of crustal assimilations.
Ore deposits and evaporites The Andes Mountains host large
ore and
salt deposits, and some of their eastern
fold and thrust belts act as traps for commercially exploitable amounts of
hydrocarbons. In the forelands of the
Atacama Desert, some of the largest
porphyry copper mineralizations occur, making Chile and Peru the first- and second-largest exporters of
copper in the world. Porphyry copper in the western slopes of the Andes has been generated by
hydrothermal fluids (mostly water) during the cooling of
plutons or volcanic systems. The porphyry mineralization further benefited from the dry climate that reduced the disturbing actions of
meteoric water. The dry climate in the central western Andes has also led to the creation of extensive
saltpeter deposits that were extensively mined until the invention of synthetic
nitrates. Yet another result of the dry climate are the
salars of
Atacama and
Uyuni, the former being the largest source of
lithium and the latter the world's largest reserve of the element. Early Mesozoic and
Neogene plutonism in Bolivia's Cordillera Central created the
Bolivian tin belt as well as the famous, now mostly depleted, silver deposits of
Cerro Rico de Potosí.
Climate The Andes Mountains is connected to the climate of South America, particularly through the hyper-arid conditions of the adjacent
Atacama Desert. The Atacama Bench, a prominent low-relief feature along the Pacific seaboard, serves as a key geomorphological record of the long-term interplay between Andean tectonics and Cenozoic climate. While the initial uplift and shortening of the Andes were driven by the subduction of the Nazca Plate beneath the South American Plate, arid climate acted as an important feedback mechanism. Reduced erosion rates in the increasingly arid Atacama region may have effectively stopped tectonic activity in certain parts of the mountain range. This lack of erosion could have facilitated the eastward propagation of deformation, leading to the widening of the Andean orogen over time. Thus, the Atacama Desert and its geological features, like the Atacama Bench, offer critical insights into the coupled evolution of the Andes Mountains and the changing regional climate. ==History==