Thegeology of Chile is a characterized by processes linked tosubduction, such asvolcanism,earthquakes, andorogeny. Thebuilding blocks of Chile's geology wereassembled during thePaleozoic Era when Chile was the southwestern margin of the supercontinentGondwana. In theJurassic, Gondwana began to split, and the ongoing period ofcrustal deformation andmountain building known as theAndean orogeny began. In theLate Cenozoic, Chile definitely separated from Antarctica, and the Andes experienced a significant rise accompanied by a cooling climate and the onset ofglaciations.
The subduction interactions shaped four mainmorphostructures of Chile: theAndes, theIntermediate Depression, theCoast Range, and thePeru–Chile Trench off the coast. Since Chile is on an activecontinental margin, it has manyvolcanoes. Almost the entire country is subject to earthquakes arising from strains in theNazca andAntarctic plates or shallowstrike-slip faults. Northern Chilean mineral resources are a major economic resource, and the country is the leading producer ofcopper,lithium andmolybdenum. Most of these mineral deposits were created frommagmatichydrothermal activity, and the water required to form those deposits derived from the subducted slab of the oceanic crust beneath the Andes.
The ChileanEaster Island andJuan Fernández Archipelago are volcanichotspot islands in the eastward-moving Nazca plate. The geology of theChilean Antarctic Territory has various commonalities with that of mainland Chile.
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 fromMorro de Arica toTaitao 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 Trenchsubduction zone is the boundary between the South American and Nazca plates. At Taitao, theChile triple junction and theNazca plate subduct the South American plate.
InNorte Grande the mountains form a series ofplateaus, such asPuna de Atacama and theAltiplano. 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 afjord landscape and the highest mountain isMonte San Valentin at 4,058 metres (13,314 ft) at north ofNorthern Patagonian Ice Field. As the mountains ebb, thesnow line lowers; in theLlanquihue it is at 1,200 metres (3,900 ft), and 900 metres (3,000 ft) in theMagallanes.
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. InNorte Grande the Intermediate Depression is partially covered by a series ofsalt flats, and has the world's largestpotassium nitrate deposits. InNorte Chico, the depression disappears briefly before reappearing in a narrow valley atSantiago. From the narrows southward the valley widens until it is interrupted nearLoncoche by theBahía Mansa Metamorphic Complex (part of the Coast Range), then widening atLos Llanos (nearPaillaco). In central and southern Chile (33°–42° south), the landscape is partially covered with glacialsediments from the Andes. InZona Austral (south of 42° south) the depression dips belowsea level, appearing occasionally in islands such asChiloé. Its southern end is theIsthmus of Ofqui.
TheChilean Coast Range runs southward along the coast (parallel to the Andes) fromMorro de Arica toTaitao Peninsula, ending at theChile triple junction. The range, a combinedhorst,forearc high andaccretionary wedge, was separated from the Andes during theTertiary rise due to thesubsidence of the Intermediate Depression.
The oldest rocks in Chile aremicaceousschists,phyllites,gneisses andquartzites, many examples of which are found in theCoast Range of south-central Chile. The schists ofsouthern Chile were initially formed by sediment in the proto-Pacific Ocean, and later metamorphosed in theforearc wedge of the Peru–Chile Trench.
During theTriassic Period about 250 million years ago Chile was part of thesupercontinentPangaea, which concentrated the world's major land masses.Africa,Antarctica,Australia andIndia were near Chile. When Pangaea began to split apart during theJurassic period, South America and the adjacent land masses formedGondwana. 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 theDrake Passage. Across the 1,000-kilometre (620 mi)-wide Drake Passage lie the mountains of theAntarctic Peninsula, south of the Scotia plate, which appear to be a continuation of the Andes. In the extreme south, theMagallanes–Fagnano Fault separatesTierra del Fuego from the smallScotia plate.
The formation of the Andes began during the Jurassic. During theCretaceous, the Andes began to assume their present form by the uplifting,faulting andfolding ofsedimentary andmetamorphic rocks of ancientcratons. Tectonic forces along thesubduction zone along the west coast of South America continue to theirorogenesis, resulting in earthquakes and volcanic eruptions to this day.
TheAltiplanoplateau was formed during theTertiary, 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):
TheQuaternaryglaciations left visible marks in most parts of Chile, particularlyZona Sur andZona Austral. These includeice fields,fjords,glacial lakes and u-shaped valleys. During theSanta María glaciation glaciers extended into the Pacific Ocean at 42° south, dividing theChilean Coast Range and creating what is nowChacao Channel.Chiloé, part of the Chilean Coast Range, became an island. South of Chacao Channel, Chile's coast is split by fjords, islands and channels; these glaciers createdmoraines at the edges of the Patagonian lakes, changing their outlets to the Pacific and shifting thecontinental divide. The remnants of thePatagonian Ice Sheet which covered large parts of Chile andArgentina are theNorthern and theSouthern Patagonian Ice Fields.
It has been suggested that from 1675 to 1850 theSan Rafael Glacier advanced during theLittle Ice Age. The first documented visit to the area was made in 1675 by the Spanish explorerAntonio de Vea, who enteredSan Rafael Lagoon throughRío Témpanos ("Ice Floe River") without mentioning the manyice floes for which the river is named. De Vea also wrote that theSan Rafael Glacier did not reach far into the lagoon. In 1766 another expedition noticed that the glacier did reach the lagoon and hadcalved intoicebergs.Hans Steffen visited the area in 1898, noting that the glacier now penetrated far into the lagoon. As of 2001, the glacier has retreated behind its 1675 border due to climate change.[1]
Easter Island is avolcanic island consisting of three extinct volcanoes:Terevaka, at an altitude of 507 metres (1,663 ft), forms the bulk of the island. Two other volcanoes (Poike andRano Kau) form the eastern and southern headlands, giving the island its triangular shape. There are numerous lesser cones and other volcanic features: the craterRano Raraku, thecinder conePuna Pau and many volcanic caves (includinglava tubes).
Easter Island and its surrounding islets, includingMotu Nui andMotu Iti, form the comminuted apex of a large volcanic mountain rising over 2,000 metres (6,600 ft) from the seabed. It is part of the Sala y Gómez Ridge, a mostly-submarine mountain range with dozens ofseamounts.Pukao andMoai are two seamounts west of Easter Island, extending 2,700 km (1,700 mi) east to theNazca Seamount. Pukao, Moai and Easter Island were formed during the last 750,000 years, with the last eruption a little over 100,000 years ago. These are the youngest mountains of the Sala y Gómez Ridge, which was formed by theNazca plate floating over theEaster hotspot.[2] Only on Easter Island is the Sala y Gómez Ridge dry land.
ThevolcanicJuan Fernández Islands were created by ahotspot in the Earth's mantle penetrating theNazca plate. The islands were carried eastward as the plate subducted theSouth American continent.Radiometric dating indicates that Santa Clara is the oldest of the islands (at 5.8 million years), followed by Robinson Crusoe (3.8–4.2 million years) and Alexander Selkirk (1.0–2.4 million years). Robinson Crusoe is the largest of the islands at 93 square kilometres (36 sq mi), and its highest peak (El Yunque) is 916 metres (3,005 ft) high. Alexander Selkirk covers 50 square kilometres (19 sq mi), and its highest peak is Los Innocentes at 1,319 metres (4,327 ft). Santa Clara covers 2.2 square kilometres (540 acres), reaching an elevation of 350 metres (1,150 ft).
Chile has the world's largestcopper reserves, and is the largest producer and exporter of the metal.[3] Notable copper mines includeChuquicamata andEscondida. Chile accounts for five percent of the Western Hemisphere'sgold production, of which 41 percent is a by-product ofcopper extraction.[3] The country holds the largest world reserves ofrhenium[3] andpotassium nitrate, and its reserves ofmolybdenum are estimated to be the third-largest in the world.[3] Most of Chile's mineral resources are inthe north;gas,coal andoil reserves, in the southernMagallanes Region, are sufficient for local needs.Guarello Island, in the Magallanes Region, has the world's southernmostlimestone mine.
Since 2000, geothermal exploration and concessions have been regulated by theLaw of Geothermal Concessions (Spanish:Ley de Concesiones de Energía Geotérmica). The Chilean company Geotermia del Pacífico, with support fromCORFO, is exploring a location inCuracautín as a site for ageothermal power plant. Geotermia del Pacífico's studies indicated that two geothermal fields near Curacautín could be used for energy production, with a combined capacity to supply 36,000 homes in 2010. One area to be developed is located near theTolhuaca hot springs, and the other is in Río Blanco Springs.[4] Another area under consideration for geothermal production isCordón Caulle.
Although geology-focused tourism is rare, there are some sites in which the local geology is a major attraction (for example, the copper mine atChuquicamata).
Earthquakes,volcanic eruptions andmass ground movements are frequent occurrences. The subduction zone along Chile's coast has produced the most powerful earthquake ever recorded, the1960 Valdivia earthquake. Earthquakes are notorious for triggering volcanic eruptions, such as the1960 Cordón Caulle eruption. Chilean earthquakes have produced tsunamis.
Landslides occur frequently in the Andes, most following earthquakes. The2007 Aysén Fjord earthquakes produced several landslides along the Fjords Mountains, spawning a tsunami.Lahars are among the most lethal volcanic hazards in Chile; a lahar destroyed the original site ofCoñaripe.
Major earthquakes in Chile occur in a small number of source areas. Those affecting coastal regions are generally aligned offshore from Concepción southward, with the major epicenters producing a predictable pattern of seismic and tsunami effects.[5] The first systematic seismological recordings in Chile began afteran earthquake and fire devastated Valparaiso in 1906.[6]
Earthquakes in northern Chile are known to have caused bothuplift andsubsidence of the continent. Large earthquakes ofMagnitude 8 or more are associated with subsidence and drowning of the Chilean coast, except peninsulas and offshore islands. Magnitude 7 to 8 earthquakes with a source area near an internal boundary of the Earth known as theMoho are known to result in uplift of the coast. Earthquakes near the Moho may account for permanentdeformation of the western edge ofSouth American plate that accumulates into a long-term net uplift of the continent.[7]
Although the most powerful six quakes recorded were clustered in two time periods (a 12-year span from 1952 to 1964 and a seven-year span from 2004 to 2011), this is considered a statistical anomaly.[8] The phenomenon of comparably-large quakes on the same (or neighboring) faults within months of each other may be explained by geological mechanisms, but this does not fully demonstrate a relationship between events separated by longer periods and greater distances[9]
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| Faults | |
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| Terranes | |
