The geology of Chile is a characterized by processes linked to subduction, such as volcanism, earthquakes, and orogeny. The building blocks of Chile's geology were assembled during the Paleozoic Era when Chile was the southwestern margin of the supercontinent Gondwana. In the Jurassic, Gondwana began to split, and the ongoing period of crustal deformation and mountain building known as the Andean orogeny began. In the Late Cenozoic, Chile definitely separated from Antarctica, and the Andes experienced a significant rise accompanied by a cooling climate and the onset of glaciations. The subduction interactions shaped four main morphostructures of Chile: the Andes, the Intermediate Depression, the Coast Range, and the Peru–Chile Trench off the coast. Since Chile is on an active continental margin, it has many volcanoes. Almost the entire country is subject to earthquakes arising from strains in the Nazca and Antarctic plates or shallow strike-slip faults. Northern Chilean mineral resources are a major economic resource, and the country is the leading producer of copper, lithium and molybdenum. Most of these mineral deposits were created from magmatic hydrothermal activity, and the water required to form those deposits derived from the subducted slab of the oceanic crust beneath the Andes. The Chilean Easter Island and Juan Fernández Archipelago are volcanic hotspot islands in the eastward-moving Nazca plate. The geology of the Chilean Antarctic Territory has various commonalities with that of mainland Chile.
General characteristics
The three primary morphological features derived from the Andes are the Andes Mountains proper, the Chilean Coast Range and the Chilean Central Valley, also known as the Intermediate Depression and the Longitudinal Valley. The mountains run parallel in a north–south direction from Morro de Arica to Taitao Peninsula, making up most of Chile's land surface. South of Taitao, only the Andes Mountains are present. North of the Taitao Peninsula, the Peru–Chile Trench subduction zone is the boundary between the South American and Nazca plates. At Taitao, the Chile triple junction and the Nazca plate subduct the South American plate.
The Andes
In Norte Grande the mountains form a series of plateaus, such as Puna de Atacama and the Altiplano. At a south latitude of 27 degrees, Chile's highest mountain (Ojos del Salado) reaches a height of 6,893 metres (22,615 ft). Below 42 degrees south, the Andes split into a fjord landscape and the highest mountain is Monte San Valentin at 4,058 metres (13,314 ft) at north of Northern Patagonian Ice Field. As the mountains ebb, the snow line lowers; in the Llanquihue it is at 1,200 metres (3,900 ft), and 900 metres (3,000 ft) in the Magallanes.
Intermediate Depression
The Intermediate Depression, a series of faults running north to south, separates the Andes from the Coast Range with a steady decrease in altitude as the latitude increases. In Norte Grande the Intermediate Depression is partially covered by a series of salt flats, and has the world's largest potassium nitrate deposits. In Norte Chico, the depression disappears briefly before reappearing in a narrow valley at Santiago. From the narrows southward the valley widens until it is interrupted near Loncoche by the Bahía Mansa Metamorphic Complex (part of the Coast Range), then widening at Los Llanos (near Paillaco). In central and southern Chile (33°–42° south), the landscape is partially covered with glacial sediments from the Andes. In Zona Austral (south of 42° south) the depression dips below sea level, appearing occasionally in islands such as Chiloé. Its southern end is the Isthmus of Ofqui.
Chilean Coast Range
The Chilean Coast Range runs southward along the coast (parallel to the Andes) from Morro de Arica to Taitao Peninsula, ending at the Chile triple junction. The range, a combined horst, forearc high and accretionary wedge, was separated from the Andes during the Tertiary rise due to the subsidence of the Intermediate Depression.
Geologic history
Paleozoic Era The oldest rocks in Chile are micaceous schists, phyllites, gneisses and quartzites, many examples of which are found in the Coast Range of south-central Chile. The schists of southern Chile were initially formed by sediment in the proto-Pacific Ocean, and later metamorphosed in the forearc wedge of the Peru–Chile Trench.
Mesozoic Era
During the Triassic Period about 250 million years ago Chile was part of the supercontinent Pangaea, which concentrated the world's major land masses. Africa, Antarctica, Australia and India were near Chile. When Pangaea began to split apart during the Jurassic period, South America and the adjacent land masses formed Gondwana. Floral affinities among these now-distant landmasses date from the Gondwanaland period. South America separated from Antarctica and Australia 27 million years ago with the development of the Drake Passage. Across the 1,000-kilometre (620 mi)-wide Drake Passage lie the mountains of the Antarctic Peninsula, south of the Scotia plate, which appear to be a continuation of the Andes. In the extreme south, the Magallanes–Fagnano Fault separates Tierra del Fuego from the small Scotia plate. The formation of the Andes began during the Jurassic. During the Cretaceous, the Andes began to assume their present form by the uplifting, faulting and folding of sedimentary and metamorphic rocks of ancient cratons. Tectonic forces along the subduction zone along the west coast of South America continue to their orogenesis, resulting in earthquakes and volcanic eruptions to this day.
Cenozoic Era The Altiplano plateau was formed during the Tertiary, with several mechanisms proposed; all attempt to explain why the topography of the Andes incorporates a large area of low relief at high altitude (high plateau):
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