Geology of Chile
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The Geology of Chile is a result of the Andean and preceding orogenies present in the convergent boundary of South America's western coast. During the Paleozoic and Precambrian periods, this boundary was shaped by terranes and microcontinents, finally developing into a pure subduction zone. The subduction shaped four massive geological features: (1) the Andes; (2) the Intermediate Depression—a graben and foreland basin; (3) the Coast Range—an accretionary wedge and horst; and (4) the Peru-Chile Trench off the coast. As Chile is located in an active continental margin, it hosts a large number of volcanoes. Nearly all of the territory of Chile 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 export. Chile is a leading producer of copper, lithium and molybdenum. Most of these minerals were created from volcanic and magmatic activity, which is sustained by an arid climate that has prevailed over the Atacama Desert for millions of years.
The Chilean territories of Easter Island and Juan Fernández Archipelago are volcanic hotspot islands in the eastward-moving Nazca plate. The Antarctic Peninsula, claimed as part of the Chilean Antarctic Territory, shares characteristic features with the southern Andes.
- 1 General characteristics
- 2 Geologic history
- 3 Pacific islands
- 4 Economic geology
- 5 Geological hazards
- 6 See also
- 7 Notes
- 8 References
- 9 External links
The three major morphological features derived from the Andes are the Andes Mountains proper, the Chilean Coast Range and the Chilean Central Valley—also called the Intermediate Depression and Longitudinal Valley. These ranges 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 the Nazca Plates. At Taitao, both the Chile Triple Junction and the Nazca Plate subduct under the South American Plate.
In Norte Grande the mountains form a series of plateaus, such as Puna de Atacama and Altiplano. At a latitude of 27° S, Chile's highest mountain, Ojos del Salado, reaches 6,893 metres. Below 42° S latitude, the Andes are split into a fjord landscape; the highest mountain is Monte San Lorenzo at only 3,706 m. As the mountains diminish, the snow line becomes lower; in the Llanquihue it is at 1,200 m, and at Magallanes only 900m.
The Intermediate Depression, a series of faults running north to south, separates the Andes from the Coast Range, with a steady decrease in altitude at greater latitudes. In Norte Grande the Intermediate Depression is partly covered by a series of salt flats and has the world's largest potassium nitrate deposits. In Norte Chico, the depression disappears briefly before reappreaing in a narrow valley at Santiago. From the narrows southward, the valley widens but is interrupted near Loncoche by the Bahía Mansa Metamorphic Complex, part of the Coast Range. The valley becomes still wider at Los Llanos near Paillaco. In central and southern Chile (33°-42° S) the landscape is partly covered with glacifluvial sediments from the Andes. In Zona Austral, south of 42° S, the depression dips below sea level, appearing occasionally in the islands, such as Chiloé. Its southern extreme is marked by the Isthmus of Ofqui.
Chilean Coast Range
The Chilean Coast Range is a mountain range that runs southward along the coast parallel with the Andean Mountains, from Morro de Arica to Taitao Peninsula, ending at the Chile Triple Junction. This range is a combined horst, forearc high and accretionary wedge structure and was separated from the Andes proper during the Tertiary rise due to the subsidence of the Intermediate Depression.
The oldest rocks in Chile are micaceous schists, phyllites, gneisses, and quartzites. Many examples are found in the Coast Range of south-central Chile. The schist of southern Chile were initially formed by sediment in the proto-Pacific Ocean and later metamorphized in the forearc wedge of the Peru-Chile Trench.
During the Triassic Period some 250 million years ago, Chile was part of the supercontinent Pangea which concentrated all major land masses in the world. Africa, Antarctica, Australia, and India were in close proximity to Chile. When Pangea 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 (see also: Antarctic Floristic Kingdom). 27 million years ago South America separated from Antarctica and Australia with the genesis of the Drake Passage. Across the 1,000 km (620 mi) wide Drake Passage lies the mountains of the Antarctic Peninsula, south of the Scotia Plate, which appear to be a continuation of the Andes chain. 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 period. During the Cretaceous period, the Andes began to assume their present form by the uplifting, faulting and folding of sedimentary and metamorphic rocks of the ancient cratons. Tectonic forces along the subduction zone along the entire west coast of South America continue to produce an ongoing orogenic event, resulting in minor to major earthquakes and volcanic eruptions to this day.
The Altiplano plateau was formed during the Tertiary and several mechanisms were proposed as responsible. All aim to explain why the topography in the Andes incorporates this large area of low relief at high altitude (high plateau) within the orogen:
- Existence of weaknesses in the Earth's crust prior to tectonic shortening. Such weaknesses would cause the partition of tectonic deformation and uplift into eastern and western cordillera, leaving the necessary space for the formation of the Altiplano basin.
- Magmatic processes rooted in the asthenosphere might have contributed to uplift the plateau.
- Climate controlled the spatial distribution of erosion and sediment deposition, creating the lubrication along the Nazca Plate subduction and hence influencing the transmission of tectonic forces into South America.
- Climate also determined the formation of internal drainage (endorheism) and sediment trapping within the Andes, potentially blocking tectonic deformation in the area between the two cordilleras.
The Quaternary glaciations left visible marks in most parts of Chile, particularly in Zona Sur and Zona Austral. These include ice fields, fjords, glacial lakes and u-shaped valleys. During the Santa María glaciation glaciers penetrated into the Pacific Ocean at 42° S, dividing the Chilean Coast Range, and creating what is now Chacao Channel. Chiloé, which used to be a continuous 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 created moraines at the edges of the Patagonian lakes, changing their outlets to the Pacific, and then shifting the continental divide.
It has been suggested that between 1675 and 1850 the San Rafael Glacier advanced considerably during the Little Ice Age. The first documented visit to the area was made in 1675 by the Spanish explorer Antonio de Vea, who entered San Rafael Lagoon through Río Témpanos (Spanish for Ice Floe River) without mentioning the many ice floes for which the river is currently named. De Vea also stated that the San Rafael Glacier did not reach far into the lagoon. In 1766 another expedition noticed that the glacier did reach the lagoon and calved into large icebergs. Hans Steffen visited the area in 1898, noting that the glacier now penetrated far into the lagoon. As of 2001, the border of the glacier has retreated back beyond the borders of 1675 due to climate change.
Easter Island is a volcanic high island, consisting of three extinct volcanoes: Terevaka (altitude 507 metres) forms the bulk of the island. Two other volcanoes, Poike and Rano Kau, form the eastern and southern headlands, giving the island its approximately triangular shape. There are numerous lesser cones and other volcanic features: the crater Rano Raraku, the cinder cone Puna Pau and many volcanic caves including lava tubes.
Easter Island and surrounding islets such as Motu Nuiand Motu Iti are the comminuted apex of a large volcanic mountain which rises over two thousand metres from the sea bed. It is part of the Sala y Gómez Ridge, a (mostly submarine) mountain range with dozens of seamounts. There are Pukao and then Moai, two seamounts to the west of Easter Island, extending 2,700 km (1,700 mi) east to the Nazca Seamount.. Pukao, Moai and Easter Island were formed in the last 750,000 years, with the last eruption a little over a hundred thousand years ago. These are the youngest mountains of the Sala y Gómez Ridge, which has been formed by the Nazca Plate floating over the Easter hotspot. Only at Easter Island does the Sala y Gómez Ridge form dry land.
The Juan Fernández Islands are of volcanic in origin, and were created by a hotspot in the Earth's mantle that broke through the Nazca Plate. The islands were carried eastward as the Nazca Plate subducted the South American continent. Radiometric dating indicates that Santa Clara is the oldest of the islands, at a venerable 5.8 million years old, followed by Robinson Crusoe, 3.8-4.2 million years old, and Alexander Selkirk, 1.0-2.4 million years old. Robinson Crusoe is the largest of the islands, at 93 km² and the highest peak, El Yunque, is 916 meters. Alexander Selkirk is 50 km² ; its highest peak is Los Innocentes at 1319 meters. Santa Clara is 2.2 km², and reaches 350 meters.
Chile has the world's largest copper reserves and is also the largest producer and exporter of the metal. Some well-known copper mines are Chuquicamata and Escondida. Chile accounts for 5% of the western hemisphere's gold production of which 41% is a by-product of copper extraction. Chile holds the largest world reserves of rhenium and potassium nitrate. Chile's reserves of molybdenum are estimated to be the third largest in the world. Most of Chile’s mineral resources are in the north; the gas, coal and oil reserves are in southern Magallanes Region enough for local needs.
Since 2000, geothermal exploration and concessions have been regulated by the Law of Geothermal Concessions (Spanish: Ley de Concesiones de Energía Geotérmica). Currently the Chilean company Geotermia del Pacífico, with support of CORFO, is exploring a locality in Curacautín as a site for a geothermal power plant. Geotermia del Paícifco's studies show that two geothermal fields near Curacautín could be used for energy production with combined capacity of supplying 36,000 homes in 2010. One of the geothemal areas to be developed is located close to the Tolhuaca hotsprings and the other in Río Blanco Springs.
Another area being considered geothermal energy production is Cordón Caulle.
Tourism focused on geology is scarce, considering the natural landmarks that draw visitors to Chile are a direct result of geological processes. There are some sites where the local geology is a major attraction; e.g, tourism in the copper mine at Chuquicamata.
Earthquakes, volcanic eruptions and mass ground movements are frequent occurrences. The subduction zone along Chile's coast has produced the most powerful earthquake ever recorded, the 1960 Valdivia earthquake. Earthquakes are notorious for triggering volcanic eruptions, such as the 1960 with Cordón Caulle. Chilean earthquakes have produced tsunamis.
Landslides occur with a degree of frequency in the Andes, with most events happening after earthquakes. The 2007 Aysen Fjord earthquake produced several landslides along the Fjords Mountains, spawning a tsunami.
Major earthquakes in Chile generally occur in a small number of source areas. Those that affect coastal regions are generally aligned offshore from Concepción southward. The major epicenters produce a predictable pattern of seismic and tsunami effects.
The first systematic seismological recordings in Chile began after an earthquake and fire devastated Valparaiso in 1906.
Significant seismic events of the last hundred and twenty years:
- 1906 Valparaiso earthquake. The 8.8 Chilean quake in August was preceded by the Ecuador-Colombia quake (8.8 magnitude) in January and the San Francisco quake (7.9 magnitude) in April.
- 1960 Valdivia earthquake. The 9.5-magnitude quake in Chile (largest in modern history) was comparable in scale to earthquakes in Alaska (2nd largest) and the Kamchatka Peninsula (5th largest).
- 2010 Chile earthquake. The 8.8-magnitude quake in Chile (6th largest) was comparable in scale to undersea seismic events near Indonesia in 2004 (3rd largest) and near Japan in 2011 (4th largest).
- 2003 Coquimbo event—specific data
The Coquimbo earthquake occurred on June 20, 2003 at 6:30 am local time (13:30 UTC) on the coast of the Coquimbo Region, Chile. It was rated 6.8 on the moment magnitude scale. There were no injuries, but there were landslides in some areas and a partial loss of electricity to the region.
|Date||20 June 2003|
|Magnitude||6.8 Mw |
|Depth||33 kilometers (21 mi)|
|Max. intensity||VI MM|
- List of Shocks (Only shocks 5.0 or greater)
|2003-06-20||04:39:30||23.0 km (14 mi)||5.0 (Mw)|
|2003-06-20||06:30:41||8.1 km (5 mi)||7.5 (Mw)|
|2003-06-20||07:07:31||4.1 km (3 mi)||5.6 (Mw)|
|2003-06-20||09:20:28||15.5 km (10 mi)||6.1 (Mw)|
|2003-06-20||09:25:19||10.9 km (7 mi)||5.2 (Mw)|
|2003-06-21||17:00:12||10.1 km (6 mi)||5.1 (Mw)|
|2010-06-24||03:31:03||20.0 km (12 mi)||5.1 (Mw)|
|2010-06-24||15:31:00||12.0 km (7 mi)||5.0 (Mw)|
|2010-06-27||13:05:06||14.0 km (9 mi)||5.0 (Mw)|
|2010-06-27||16:26:11||11.0 km (7 mi)||5.0 (Mw)|
- 2007 Tocopilla earthquake—specific data
- 2007 Puchuncaví event—specific data
|Date||15 December 2007|
|Depth||10 kilometers (6.2 mi)|
|Max. intensity||VI MM|
The 2007 Puchuncaví earthquake occurred on December 15, 2007 at 15:22 local time (18:22 UTC) on the coast of the Valparaíso Region, Chile; and had a magnitude of 6.7 on the Richter scale. Landslides occured which left minor cracks in stuctures of the city of Puchuncaví. The maximum intensity of the earthquake on the Mercalli scale was VI.
The most powerful six quakes ever recorded appear to be clustered in two time periods: a 12-year span between 1952 and 1964 and a 7-year span between the 2004 and 2011; however, this is understood as a statistical anomaly
The phenomenon of comparably large quakes happening on the same or neighboring faults within months of each other can be explained by geological mechanisms; but this does not fully demonstrate a relationship between events separated by longer periods and greater distances
- The Petrogenetic Evolution of Lavas from Easter Island and Neighbouring Seamounts, Near-ridge Hotspot Volcanoes in theSE Pacific
- U.S. Geological Survey (2005). Minerals Yearbook 2005.
- CHILE COULD HAVE GEOTHERMAL ENERGY BY 2010 Santiago Times
- Lomitz, Cinna; "Major earthquakes and tsunamis in Chile during the period 1535 to 1955"; International Journal of Earth Sciences, Vol. 59, No. 3; abstract.
- Moreno, Teresa. (2006). The Geology of Chile, p. 264., p. 264, at Google Books
- "Chile 1906 Valparaiso Earthquake Centennial," CNRS International Magazine (France). 2006.
- Phillips, Campbell; "The 10 biggest earthquakes in history"; Australian Geographic, 14 March 2011.
- Pappas, Stephanie. "Sumatra, Japan, Chile: Are Earthquakes Getting Worse?"; LiveScience; 11 March 2011.
- National Geophysical Data Center. "Significant earthquake". Retrieved 7 November 2012.
- Brahic, Catherine; "The mega-quake connection: Are huge earthquakes linked?"; New Scientist; UK; 16 March 2011.
- Brüggen, Juan. Fundamentos de la geología de Chile, Instituto Geográfico Militar 1950.
- Duhart, Paul et al. El Complejo Metamórfico Bahía Mansa en la cordillera de la Costa del centro-sur de Chile (39°30'-42°00'S): geocronología K-Ar, 40Ar/39Ar y U-Pb e implicancias en la evolución del margen sur-occidental de Gondwana
- Moreno, Teresa and Wes Gibbons. (2006). The Geology of Chile. London: Geological Society of London. 13-ISBN 9781862392199/10-ISBN 1862392196; OCLC 505173111
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