La Pacana

Last updated

Pacana Caldera
Salar de Pujsa con Acamarachi.jpg
Viewing from inside the caldera towards the western margin
Highest point
Elevation 4,500 m (14,800 ft)
Listing List of volcanoes in Chile
Coordinates 23°13′11″S67°27′58″W / 23.21972°S 67.46611°W / -23.21972; -67.46611 Coordinates: 23°13′11″S67°27′58″W / 23.21972°S 67.46611°W / -23.21972; -67.46611 [1]
Geography
Relief Map of Chile.jpg
Red triangle with thick white border.svg
Pacana Caldera
Northern Chile
Geology
Mountain type Caldera
Volcanic arc/belt Altiplano–Puna volcanic complex
Last eruption 2 mya

La Pacana is a Miocene age caldera in northern Chile's Antofagasta Region. Part of the Central Volcanic Zone of the Andes, it is part of the Altiplano-Puna volcanic complex, a major caldera and silicic ignimbrite volcanic field. This volcanic field is located in remote regions at the Zapaleri tripoint between Chile, Bolivia and Argentina.

The Miocene is the first geological epoch of the Neogene Period and extends from about 23.03 to 5.333 million years ago (Ma). The Miocene was named by Charles Lyell; its name comes from the Greek words μείων and καινός and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene is preceded by the Oligocene and is followed by the Pliocene.

A caldera is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber/reservoir in a volcanic eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is lost. The ground surface then collapses downward into the emptied or partially emptied magma chamber, leaving a massive depression at the surface. Although sometimes described as a crater, the feature is actually a type of sinkhole, as it is formed through subsidence and collapse rather than an explosion or impact. Only seven caldera-forming collapses are known to have occurred since 1900, most recently at Bárðarbunga volcano, Iceland in 2014.

Chile Republic in South America

Chile, officially the Republic of Chile, is a South American country occupying a long, narrow strip of land between the Andes to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far south. Chilean territory includes the Pacific islands of Juan Fernández, Salas y Gómez, Desventuradas, and Easter Island in Oceania. Chile also claims about 1,250,000 square kilometres (480,000 sq mi) of Antarctica, although all claims are suspended under the Antarctic Treaty.

Contents

La Pacana along with other regional volcanoes was formed by the subduction of the Nazca Plate beneath the South American Plate in the Peru-Chile Trench. La Pacana is situated in a basement formed by various Paleozoic formations and Tertiary ignimbrites and volcanoes. Several major faults cross the region at La Pacana and have influenced its volcanic activity.

Subduction A geological process at convergent tectonic plate boundaries where one plate moves under the other

Subduction is a geological process that takes place at convergent boundaries of tectonic plates where one plate moves under another and is forced to sink due to gravity into the mantle. Regions where this process occurs are known as subduction zones. Rates of subduction are typically in centimeters per year, with the average rate of convergence being approximately two to eight centimeters per year along most plate boundaries.

Nazca Plate Oceanic tectonic plate in the eastern Pacific Ocean basin

The Nazca Plate, named after the Nazca region of southern Peru, is an oceanic tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction, along the Peru–Chile Trench, of the Nazca Plate under the South American Plate is largely responsible for the Andean orogeny. The Nazca Plate is bounded on the west by the Pacific Plate and to the south by the Antarctic Plate through the East Pacific Rise and the Chile Rise respectively. The movement of the Nazca Plate over several hotspots has created some volcanic islands as well as east-west running seamount chains that subduct under South America. Nazca is a relatively young plate both in terms of the age of its rocks and its existence as an independent plate having been formed from the break-up of the Farallon Plate about 23 million years ago. The oldest rocks of the plate are about 50 million years old.

South American Plate A major tectonic plate which includes most of South America and a large part of the south Atlantic

The South American Plate is a major tectonic plate which includes the continent of South America as well as a sizable region of the Atlantic Ocean seabed extending eastward to the African Plate, with which it forms the southern part of the Mid-Atlantic Ridge.

La Pacana is a supervolcano and is responsible for the eruption of the giant Atana ignimbrite, which reaches a volume of 2,451–3,500 cubic kilometres (588–840 cu mi) and constitutes the fifth-largest explosive eruption known. The Atana ignimbrite was erupted 3.8 ± 0.1 and 4.2 ± 0.1 million years ago, almost simultaneously with the much smaller (volume of 180 cubic kilometres (43 cu mi)) Toconao ignimbrite. The Pujsa ignimbrite was erupted by La Pacana before the Atana/Toconao ignimbrites, and the Filo Delgado and Pampa Chamaca/Talabre ignimbrites afterwards.

Supervolcano Volcano that has erupted 1000 cubic km in a single eruption

A supervolcano is a large volcano that has had an eruption of magnitude 8, which is the largest value on the Volcanic Explosivity Index (VEI). This means the volume of deposits for that eruption is greater than 1,000 cubic kilometers.

Explosive eruption type of volcanic eruption

In volcanology, an explosive eruption is a volcanic eruption of the most violent type. A notable example is the 1980 eruption of Mount St. Helens. Such eruptions result when sufficient gas has dissolved under pressure within a viscous magma such that expelled lava violently froths into volcanic ash when pressure is suddenly lowered at the vent. Sometimes a lava plug will block the conduit to the summit, and when this occurs, eruptions are more violent. Explosive eruptions can send rocks, dust, gas and pyroclastic material up to 20 km (12 mi) into the atmosphere at a rate of up to 100,000 tonnes per second, traveling at several hundred meters per second. This cloud may then collapse, creating a fast-moving pyroclastic flow of hot volcanic matter.

Geography and structure

La Pacana lies in the Antofagasta Region of Chile, in the Andes [1] just north of the Tropic of Capricorn. [2] The border between Chile and Bolivia crosses the northern sector of the caldera. [3] The area of La Pacana is largely uninhabitated; [1] small settlements such as Socaire, Talabre and Toconao [4] exist close to the Salar de Atacama, where streams descend the mountain slopes to the salar. [1] The caldera was discovered during mapping efforts in the region between 1980–1985. [5]

Antofagasta Region Region of Chile

The Antofagasta Region is one of Chile's sixteen first-order administrative divisions. It comprises three provinces, Antofagasta, El Loa and Tocopilla. It is bordered to the north by Tarapacá and by Atacama to the south and is the second-largest region of Chile. To the east it borders Bolivia and Argentina. The capital of the region is the port city of Antofagasta, another important city being Calama. The main economic activity is copper mining in the giant porphyry copper systems located inland.

Andes Mountain range in South America

The Andes or Andean Mountains are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The Andes also have the 2nd most elevated highest peak of any mountain range, only behind the Himalayas. The range is 7,000 km (4,300 mi) long, 200 to 700 km wide, and has an average height of about 4,000 m (13,000 ft). The Andes extend from north to south through seven South American countries: Venezuela, Colombia, Ecuador, Peru, Bolivia, Chile and Argentina.

Tropic of Capricorn Line of southernmost latitude at which the sun can be directly overhead

The Tropic of Capricorn is the circle of latitude that contains the subsolar point on the December solstice. It is thus the southernmost latitude where the Sun can be directly overhead. Its northern equivalent is the Tropic of Cancer.

La Pacana is part of the Central Volcanic Zone, [2] one of the four volcanic zones that make up the Andean Volcanic Belt and which are separated from each other by gaps without ongoing volcanic activity. [6] A number of stratovolcanoes and ignimbrite-forming centres have erupted in the Central Volcanic Zone since the Miocene, [7] about 50 of which are considered to be active. [8] In addition, the Central Volcanic Zone features about 18 minor volcanic fields. The largest historical eruption of the Andes occurred in 1600 at Huaynaputina in Peru in the Central Volcanic Zone, and the most active volcano of the Central Volcanic Zone is Láscar in Chile. [6]

Andean Volcanic Belt Volcanic belt in South America

The Andean Volcanic Belt is a major volcanic belt along the Andean cordillera in Argentina, Bolivia, Chile, Colombia, Ecuador, and Peru. It is formed as a result of 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. While some differences can be explained by which volcanic zone a volcano belongs to, there are significant differences within volcanic zones and even between neighboring volcanoes. Despite being a type location for calc-alkalic and subduction volcanism, the Andean Volcanic Belt has a broad range of volcano-tectonic settings, as it is a rift systems and extensional zones, transpressional faults, subduction of mid-ocean ridges and seamount chains apart from a large range on crustal thicknesses and magma ascent paths, and different amount of crustal assimilations.

Stratovolcano Tall, conical volcano built up by many layers of hardened lava and other ejecta

A stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava, tephra, pumice and ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and periodic intervals of explosive eruptions and effusive eruptions, although some have collapsed summit craters called calderas. The lava flowing from stratovolcanoes typically cools and hardens before spreading far, due to high viscosity. The magma forming this lava is often felsic, having high-to-intermediate levels of silica, with lesser amounts of less-viscous mafic magma. Extensive felsic lava flows are uncommon, but have travelled as far as 15 km (9.3 mi).

Ignimbrite A variety of hardened tuff

Ignimbrite is a variety of hardened tuff. Ignimbrites are igneous rocks made up of crystal and rock fragments in a glass-shard groundmass, albeit the original texture of the groundmass might be obliterated due to high degrees of welding. The term ignimbrite is not recommended by the IUGS Subcommission on the Systematics of Igneous Rocks.

La Pacana has a diameter of 60 by 35 kilometres (37 mi × 22 mi) with a north-south elongation. [9] This is one of the best exposed and largest calderas in the world; [10] the largest caldera known is Toba in Sumatra with a maximum length of 100 kilometres (62 mi). [11] La Pacana might not be a single caldera; some reconstructions imply that the northern parts of the caldera are actually a separate collapse structure. [12] The floor of the caldera lies at an elevation of 4,200–4,500 metres (13,800–14,800 ft), the central uplift and the caldera rim are higher and reach 5,200 metres (17,100 ft). The caldera rim is well exposed except in the northern and western sides, where later volcanism has buried it. [9] After the formation of the caldera, sediments and [13] tuffs within the caldera were uplifted [14] over an angular area of 350 square kilometres (140 sq mi), forming the 1 kilometre (0.62 mi) high resurgent dome known as Cordón La Pacana. [15] This resurgent dome is cut by numerous faults and features a poorly developed graben on its summit. [13] Originally it was believed that the present-day calder rim did not coincide with the caldera ring fault, [9] which was instead identified to coincide with margins of the resurgent dome; later research however indicates the present-day topographic margin as the caldera edge. [16] The resurgent dome is separated from the caldera rim by a 2–10 kilometres (1.2–6.2 mi) wide moat that makes up about two thirds of the entire surface of the caldera, [17] but is interrupted on the northern side of the caldera by the "hinge" of the caldera collapse, which assumed the form of a trap-door. [18] The moat is filled by sediments formed by erosion and by [19] alluvial, evaporite and lacustrine sediments left behind by lakes. [15]

Lake Toba Crater Lake located in Sumatra, Indonesia

Lake Toba is a large natural lake in Sumatra, Indonesia occupying the caldera of a supervolcano. The lake is located in the middle of the northern part of the island of Sumatra, with a surface elevation of about 900 metres (2,953 ft), the lake stretches from 2.88°N 98.52°E to 2.35°N 99.1°E.The lake is about 100 kilometres long, 30 kilometres (19 mi) wide, and up to 505 metres (1,657 ft) deep. It is the largest lake in Indonesia and the largest volcanic lake in the world.Lake Toba Caldera is one of the nineteen Geopark in Indonesia, which is proposed to be included in the UNESCO Global Geopark.

Sumatra island in western Indonesia, westernmost of the Sunda Islands

Sumatra is a large island in western Indonesia that is part of the Sunda Islands. It is the largest island that is located entirely in Indonesia and the sixth-largest island in the world at 473,481 km2.

Tuff Rock consolidated from volcanic ash

Tuff, also known as volcanic tuff, is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is compacted into a solid rock in a process called consolidation. Tuff is sometimes erroneously called "tufa", particularly when used as construction material, but properly speaking, tufa is a limestone precipitated from groundwater. Rock that contains greater than 50% tuff is considered tuffaceous.

The Guayaques volcanic group Guayaques volcanic group chile ii region.jpg
The Guayaques volcanic group

The collapse of the caldera cut through older volcanic centres, exposing the Ceja Alta and Quilapana porphyry deposits. Other older volcanic centres exposed in the walls of the caldera are the Cerro Aguas Calientes stratovolcano in the eastern wall and the Cerro Gigantes in the western wall. [20] Volcanic activity resumed within the caldera and at the edge of the resurgent dome, forming lava domes between 4.1 and at least 1.6 million years ago. [14] These volcanic centres include the Corral de Coquena crater and the lava domes of Morro Negro east, Cerro Bola and Purifican west and Cerros de Guayaques north of the resurgent dome. The Arenoso, Chamaca and Chivato Muerto lava domes in the southern wall of the caldera were originally considered to be pre-caldera; [20] later these three domes were identified as post-caldera domes. [21] Stratovolcanoes inside the caldera include the cones associated with the Cerros de Guayaques lava domes and the volcanoes Cerro Incaguasi, Cerros de Pili, Cerros Negros and Huailitas. [20]

Some extant hot springs within the caldera may indicate that there is still a geothermal system associated with La Pacana, although not a very important one considering their low temperature (less than 25 °C (77 °F)). [11] A few lakes such as the spring-fed Laguna de Chivato Muerto, Laguna Trinchera and Ojos del Rió Salado, [11] as well as salt pans such as Salar de Aguas Calientes Norte, Salar de Aguas Calientes Sur, Salar de Pujsa and Salar de Quisquiro have developed within the moat. [22] Streams such as Río de Pili and Río Salado complete the hydrology of the caldera. [11]

Gravimetric observations have been conducted on La Pacana. A large negative anomaly (an anomaly with less-than-expected mass crust) coincides with the surface of the La Pacana caldera and extends past its borders; it may be a consequence of the caldera being infilled with low-density material. Positive anomalies (anomalies with more-than-expected mass in the crust) are found in the areas surrounding the caldera and dot discrete zones within it; the former represent the dense basement and the latter may be intrusions associated with individual vents. [12]

Geology

In the Peru-Chile Trench, the Nazca Plate subducts beneath the South American Plate at a rate of about 7–9 centimetres per year (2.8–3.5 in/year), [6] leading to volcanic activity at distances of 130–160 kilometres (81–99 mi) from the trench. [7]

Research indicates that subduction has been ongoing since the Jurassic 200 million years ago but accelerated 26 million years ago. [23] After a phase of andesitic volcanism lasting from the late Tertiary to the Miocene, [24] large scale ignimbritic volcanism commenced about 23 million years ago and is still ongoing. [25] It began north of 21° southern latitude with the 23-18 million years old Oxaya formation and the 15–17 million years old Altos de Pica formation. Later the San Bartolo and Silapeti groups were generated, ending by the early Pleistocene. [24] Volcanic activity at La Pacana is more recent than elsewhere in the region, with the oldest volcanic rocks that crop out in La Pacana being between 11 and 7.5 million years old. [7] Large scale ignimbritic activity continued until 2 million years ago. [12]

Regional

The Central Andes are the site of extensive ignimbrites that were erupted from large calderas usually located within the adjacent Altiplano, east of the principal volcanic arc. Many of these calderas are part of the Altiplano-Puna volcanic complex, a large volcanic complex covering a surface area of 70,000 square kilometres (27,000 sq mi) with about 30,000 cubic kilometres (7,200 cu mi) of ignimbrites. La Pacana is the largest caldera of the Altiplano-Puna volcanic complex. [10] [14] The ignimbrites form a surface that lies at an average elevation of 4,000 metres (13,000 ft). [23] Stratovolcanoes developed on top of these ignimbrite sheets and today form the most clear expression of volcanic activity in the region, [8] with some of them exceeding the height of 6,000 metres (20,000 ft) above sea level. [23] The long-lasting dry climate means that traces of volcanic activity can be recognizable over long timeframes. [24]

The Altiplano-Puna volcanic complex is underpinned by a large seismic velocity anomaly at a depth of 20 kilometres (12 mi), which may be the largest structure consisting of near-molten (10–20%) rock on Earth. [14] This partial melt zone was formed by the injection of mafic magmas into the lower crust; a major episode of overturning before 10.6 million years ago caused crustal anatexis and started the onset of ignimbritic volcanism. [26] Magmas formed within this melt zone rose into the upper crust and differentiated between depths of 8–4 kilometres (5.0–2.5 mi) to form the ignimbrite-forming secondary magmas. [27] Presently, the inferred margin of this partially molten zone coincides fairly well with a negative gravimetric anomaly that clusters around the tripoint between Argentina, Bolivia and Chile and with the extent of the Altiplano-Puna volcanic complex. [28]

Local

The basement beneath La Pacana is formed by sediments of Ordovician age, Devonian-Permian quartzites, the mixed Salta formation also of Permian age and sediments of Cretaceous-Tertiary age. [29] At the eastern margin of La Pacana in Argentina, they overlay an even older Precambrian basement. [7] Most of this original basement however is covered by Miocene ignimbrites from centres that may coincide with the La Pacana caldera. [29] Two of these older ignimbrites are known as the Pampa Múcar and Antigua Chacaliri ignimbrites. [30]

La Pacana together with the Cerro Guacha and Purico Complex calderas forms the La Pacana Complex. Guacha experienced two major eruptions, of which one occurred 4.1 million years ago. The Purico complex began erupting 1.3 million years ago; it is the youngest centre of the La Pacana Complex with the youngest eruptions occurring during the Holocene. [26] Additional volcanic centres west and southwest of La Pacana are Acamarachi, Láscar, Colachi and Cordón de Puntas Negras. [4]

A number of faults transect the region at La Pacana, including the north-south Miscanti Lineament and the Socompa and Quisiquiro lineaments. These lineaments or faults have influenced volcanism and geomorphology in the region, with volcanoes and vents aligning along these lineaments. [7]

Composition

The Toconao and Atana ignimbrites are formed by rhyolite and dacite-rhyodacite, respectively. They form a potassium-rich calc-alkaline suite. Both contain pumices, three different types of which are found in the Atana ignimbrite. Phenocrysts within the ignimbrite are chiefly formed by plagioclase. [14]

Both the Atana and the Toconao ignimbrite include minerals like allanite, apatite, biotite, epidote, hornblende, ilmenite, magnetite, monazite, orthopyroxene, plagioclase, quartz, sanidine, titanite and zircon. Not all of these minerals are found in both ignimbrites, and not always in the same phase (crystals or matrix). [14]

Ultimately, the magmas at La Pacana are the products of mantle melts interacting with various crustal domains deep in the crust, within the partially molten zone that has been found at depths of c.20 kilometres (12 mi) beneath the Altiplano-Puna volcanic complex. [14]

Various geothermometers indicate that the Toconao ignimbrite was colder than the Atana ignimbrite; temperatures have been estimated at 730–750 °C (1,350–1,380 °F) and 750–790 °C (1,380–1,450 °F) respectively. While the depth at which the Toconao ignimbrite formed is unknown, the Atana ignimbrite formed at a depth of 7–8.5 kilometres (4.3–5.3 mi). Such a formation depth is comparable to depths estimated for other magmatic systems such as Fish Canyon, Long Valley and Yellowstone. [14]

Climate and biota

Weather records are available for the Salar de Aguas Calientes. There, an average temperature of 1 °C (34 °F) and average precipitation of 150 millimetres per year (5.9 in/year) have been recorded. [31]

There is little vegetation in the dry Altiplano. Nevertheless a number of animal species are found, such as Andean moles, rheas, vicuñas and vizcachas. Ducks, geese and flamingos frequent waterbodies and salars. [1]

Eruption history

La Pacana has erupted two ignimbrites which differ in composition and were emplaced one shortly after the other: The dacitic Atana ignimbrite and the rhyolitic Toconao ignimbrite. [14] The Atana ignimbrite was once considered part of the Guaitiquina ignimbrite, which was later split off, [2] while the Puripicar ignimbrite may be correlated with the Atana instead. [13] Also, some of the ignimbrites erupted by La Pacana originally were attributed to Cerro Guacha. [10] Both ignimbrites originated from different parts of the same magma chamber and their origin in the La Pacana caldera is established by isotope ratios of the rocks and the geographical distribution of their outcrops. [14]

Before the eruption of the Toconao and Atana ignimbrites, early activity generated the Pujsa ignimbrite [7] between 5.8 ± 0.1 and 5.7 ± 0.4 million years ago and some stratovolcanoes and porphyries that are cut by the caldera walls. [20] The Pujsa ignimbrite resembles the Atana ignimbrite and like the Toconao ignimbrite is mainly exposed on the western side of the caldera. [7]

The first large eruption, which took place between 4 ± 0.9 and 5.3 ± 1.1 million years ago, formed the Toconao ignimbrite. [14] The Toconao ignimbrite crops out mainly west of the caldera; [7] only later were units of the Toconao identified on the eastern side of La Pacana. [32] This ignimbrite has a volume of approximately 180 cubic kilometres (43 cu mi) and is formed by a lower un-indurated and an upper indurated subunit. Tube pumices are contained in the lower subunit and in a less than 10 centimetres (3.9 in) Plinian deposit that was emplaced beneath the Toconao ignimbrite. [14]

The formation of the caldera coincided with the eruption of the Atana ignimbrite; the eruption was still underway when the terrain subsided [9] to a depth of 2–3 kilometres (1.2–1.9 mi) beneath the previous surface in the northwestern segment of La Pacana. [12] Dates obtained on the Atana ignimbrite are between 3.8 ± 0.1 and 4.2 ± 0.1 million years ago, which is not clearly distinguishable from the dates of the Toconao ignimbrite seeing as there is no indication that a pause occurred between the eruption of the two ignimbrites. This ignimbrite is considerably larger than the Toconao ignimbrite, [14] reaching a volume of 2,451–3,500 cubic kilometres (588–840 cu mi) [33] and a volcanic explosivity index of 8. This makes the Atana eruption the fifth-largest explosive eruption known and La Pacana a supervolcano. [12] The Atana ignimbrite forms a flow sheet that extends from within the caldera to the outside in the form of a 30–40 metres (98–131 ft) thick structure. [14] This flow sheet originally probably covered a surface area of about 7,700 square kilometres (3,000 sq mi), part of which was later eroded away. [13] The Atana ignimbrite is fairly welded, rich in crystals and poor in lithics. It is underlaid by pumice and ash deposits. [14] Pumice is also found as fragments within the ignimbrite, ranging from white rhyolite to gray andesite. [34] After its eruption, wind and water driven erosion occurred on the Atana ignimbrite, carving valleys and yardangs into it. [3]

Some differences exist between the facies of the ignimbrite inside and outside of the caldera, as well as between the western and eastern outcrops. Such differences concern the degree of welding of the ignimbrite, the occurrence or absence of devitrification and the jointing patterns. [35] In fact, a segment of the northern Atana ignimbrite was later considered to not be actually part of the Atana ignimbrite at all because of the different facies and petrology. [36] This separate ignimbrite was christened to be an upper and a lower Tara ignimbrite, possibly erupted by the Cerro Guacha caldera. [37] The Tara ignimbrite fills part of the La Pacana caldera. [38] The total volume of the La Pacana ignimbrites proper is estimated to be about 3,400–3,500 cubic kilometres (820–840 cu mi), on the basis of gravimetric information about the volume of the caldera and the infill ignimbrites. [12]

The most likely theory for the origin of both Atana and Toconao ignimbrites is that they formed by crystal fractionation within a magma chamber, where the Toconao magma was extracted from convecting dacitic magma that was undergoing crystallization. This volatile-rich and crystal-poor extracted magma erupted first as a Plinian eruption. Then a tectonic event, most likely a movement along a fault cutting through the caldera, prompted the rise and eruption of the Atana ignimbrite. [14] Two potential vents have been found at the northern and western margins of the caldera, where breccia deposits occur within the Atana ignimbrite. [39] Some of the magma that gave rise to the Atana ignimbrite was erupted after the ignimbrite; the lava domes formed after the caldera collapse were generated by this magma. [14] This category of dependent postcaldera volcanism includes Corral de Coquena and Morro Negro; other postcaldera volcanic centres have different compositions and thus probably formed from different sources than the Atana magma. [40]

Ignimbrite eruptions continued after the formation of the caldera. The Filo Delgado ignimbrite was erupted at some time during the Pliocene from the Huailitas volcano. [20] Its volume is about 0.1 cubic kilometres (0.024 cu mi). [17] 2.4 ± 0.4 million years ago, the Pampa Chamaca ignimbrite filled the moat between the resurgent dome and the caldera rim. [20] The Pampa Chamaca or Talabre [27] ignimbrite was erupted from a vent probably buried beneath the present-day Cordon de Puntas Negras [17] or the Salar de Aguas Calientes [41] and reached a volume of about 0.5 cubic kilometres (0.12 cu mi). [17]

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Cerro Blanco is a caldera in the Andes of the Catamarca Province in Argentina. Part of the Central Volcanic Zone of the Andes, it is a volcano collapse structure located at an altitude of 4,670 metres (15,320 ft) in a depression. The caldera is associated with a less well defined caldera to the south and several lava domes.

Cerro Chao

Cerro Chao is a lava flow complex associated with the Cerro del León volcano in the Andes. It is the largest known Quaternary silicic volcano body and part of the most recent phase of activity in the Altiplano–Puna volcanic complex.

Cerro Guacha

Cerro Guacha is a Miocene caldera in southwestern Bolivia's Sur Lípez Province. Part of the volcanic system of the Andes, it is considered to be part of the Central Volcanic Zone (CVZ), one of the three volcanic arcs of the Andes, and its associated Altiplano-Puna volcanic complex (APVC). A number of volcanic calderas occur within the latter.

Cerro Chascon-Runtu Jarita is a complex of lava domes located inside, but probably unrelated to, the Pastos Grandes caldera. It is part of the more recent phase of activity of the Altiplano-Puna volcanic complex.

Cerro Panizos mountain in Bolivia

Panizos is a Late Miocene era caldera in the Potosí Department of Bolivia and the Jujuy Province of Argentina. It is part of the Altiplano-Puna volcanic complex of the Central Volcanic Zone in the Andes. 50 volcanoes active in recent times are found in the Central Volcanic Zone, and several major caldera complexes are situated in the area. The caldera is located in a logistically difficult area of the Andes.

Coranzuli is a back-arc caldera in the Andes, related to the Altiplano-Puna volcanic complex.

Corral de Coquena is a volcanic spatter rampart in the Andes, over the Tropic of Capricorn. The rampart at its highest point is 4,572 metres (15,000 ft) high.

Incapillo

Incapillo is a Pleistocene caldera, a depression formed by the collapse of a volcano, in the La Rioja province of Argentina. Part of the Argentine Andes, it is considered the southernmost volcanic centre in the Central Volcanic Zone of the Andes with Pleistocene activity. Incapillo is one of several ignimbritic or calderic systems that, along with 44 active stratovolcanoes, are part of the Central Volcanic Zone.

Kari-Kari is a Miocene caldera in the Potosi department, Bolivia. It is part of the El Fraile ignimbrite field of the Central Volcanic Zone of the Andes. Volcanic activity in the Central Volcanic Zone has generated 44 volcanic centres with postglacial activity and a number of calderas, including the Altiplano-Puna volcanic complex.

Cerro Bitiche is a volcanic field in Argentina. It is located east of the Central Volcanic Zone away from the volcanic arc within the Altiplano-Puna volcanic complex (APVC), close to Zapaleri volcano.

Pairique volcanic complex is a volcanic complex in the Jujuy Province, Argentina.

Pastos Grandes

Pastos Grandes is the name of a caldera and its crater lake in Bolivia. The caldera is part of the Altiplano-Puna volcanic complex, a large ignimbrite province that is part of the Central Volcanic Zone of the Andes. Pastos Grandes has erupted a number of ignimbrites through its history, some of which exceeded a volume of 1,000 cubic kilometres (240 cu mi). After the ignimbrite phase, the lava domes of the Cerro Chascon-Runtu Jarita complex were erupted close to the caldera and along faults.

Vilama (caldera) mountain

Vilama is a Miocene caldera in Bolivia and Argentina. Straddling the border between the two countries, it is part of the Central Volcanic Zone, one of the four volcanic belts in the Andes. Vilama is remote and forms part of the Altiplano-Puna volcanic complex, a province of large calderas and associated ignimbrites that were active since about 8 million years ago, sometimes in the form of supervolcanoes.

Tata Sabaya mountain

Tata Sabaya is a 5,430-metre (17,810 ft) high volcano in Bolivia. It is part of the Central Volcanic Zone, one of several volcanic belts in the Andes which are separated by gaps without volcanic activity. This section of the Andes was volcanically active since the Jurassic, with an episode of strong ignimbritic volcanism occurring during the Miocene. Tata Sabaya lies in a thinly populated region north of the Salar de Coipasa salt pan.

References

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Sources

Further reading