complex Complex commonly refers to: * Complexity, the behaviour of a system whose components interact in multiple ways so possible interactions are difficult to describe ** Complex system, a system composed of many components which may interact with each ...

Andes The Andes ( ), Andes Mountains or Andean Mountain Range (; ) are the List of longest mountain chains on Earth, longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range ...

Altiplano The Altiplano (Spanish language, Spanish for "high plain"), Collao (Quechuan languages, Quechua and Aymara language, Aymara: Qullaw, meaning "place of the Qulla people, Qulla") or Andean Plateau, in west-central South America, is the most extens ...

highland Highlands or uplands are areas of high elevation such as a mountainous region, elevated mountainous plateau or high hills. Generally, ''upland'' refers to a range of hills, typically from up to , while ''highland'' is usually reserved for range ...

subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...

Nazca Plate The Nazca plate or Nasca plate, named after the Nazca region of southern Peru, is an oceanic list of tectonic plates, tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction, along the Peru– ...

South American Plate 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 ...

Andean Volcanic Belt 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 Americ ...

latitude In geography, latitude is a geographic coordinate system, geographic coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from −90° at t ...

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

Bolivia Bolivia, officially the Plurinational State of Bolivia, is a landlocked country located in central South America. The country features diverse geography, including vast Amazonian plains, tropical lowlands, mountains, the Gran Chaco Province, w ...

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58mya),

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcanic eruption. An eruption that ejects large volumes of magma over a short period of time can cause significant detriment to the str ...

s erupted

felsic In geology, felsic is a grammatical modifier, modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz.Marshak, Stephen, 2009, ''Essentials of Geology,'' W. W. Norton & Company, 3rd ed. It is contrasted ...

ignimbrite Ignimbrite is a type of volcanic rock, consisting of hardened tuff. Ignimbrites form from the deposits of pyroclastic flows, which are a hot suspension of particles and gases flowing rapidly from a volcano, driven by being denser than the surrou ...

s in four distinct pulses separated by periods of low levels of activity. At least three volcanic centres ( Guacha caldera, La Pacana, Pastos Grandes, Vilama) had eruptions of a Volcanic Explosivity Index (VEI) of 8, as well as smaller scale eruptive centres. Activity waned after 2 mya, but present-day geothermal activity and volcanoes dated to the

Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...

, as well as recent ground deformation at Uturunku volcano indicate still-extant present-day activity of the system.

Geography

The

Andes The Andes ( ), Andes Mountains or Andean Mountain Range (; ) are the List of longest mountain chains on Earth, longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range ...

mountain chain originated from the subduction of the

Nazca Plate The Nazca plate or Nasca plate, named after the Nazca region of southern Peru, is an oceanic list of tectonic plates, tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction, along the Peru– ...

below the South American Plate and was accompanied by extensive volcanism. Between 14° S and 28° S lies one volcanic area with over fifty recently active systems, the Central Volcanic Zone (CVZ). Since the late

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

between 21° S and 24° S a major

ignimbrite Ignimbrite is a type of volcanic rock, consisting of hardened tuff. Ignimbrites form from the deposits of pyroclastic flows, which are a hot suspension of particles and gases flowing rapidly from a volcano, driven by being denser than the surrou ...

province formed over thick crust, the Altiplano–Puna volcanic complex, between the Atacama and the

Altiplano The Altiplano (Spanish language, Spanish for "high plain"), Collao (Quechuan languages, Quechua and Aymara language, Aymara: Qullaw, meaning "place of the Qulla people, Qulla") or Andean Plateau, in west-central South America, is the most extens ...

. The Toba volcanic system in

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...

and

Taupō Taupō (), sometimes written Taupo, is a town located in the central North Island of New Zealand. It is situated on the edge of Lake Taupō, which is the largest freshwater lake in New Zealand. Taupō was constituted as a borough in 1953. It h ...

in New Zealand are analogous to the province. The APVC is located in the southern Altiplano-Puna plateau, a surface plateau wide and long at an altitude of , and lies east of the volcanic front of the Andes. Deformational belts limit it in the east. The Altiplano itself forms a block that has been geologically stable since the

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

; below the Atacama area conversely recent extensional dynamics and a weakened crust exist. The Puna has a higher average elevation than the Altiplano, and some individual volcanic centres reach altitudes of more than . The basement of the northern Puna is of

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

to

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

age.

Geology

The APVC is generated by the

subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...

of the

Nazca Plate The Nazca plate or Nasca plate, named after the Nazca region of southern Peru, is an oceanic list of tectonic plates, tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction, along the Peru– ...

beneath the

South American Plate 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 ...

at an angle of nearly 30°. Delamination of the crust has occurred beneath the northern Puna and southern Altiplano. Below depth, seismic data indicate the presence of melts in a layer called the Altiplano–Puna low velocity zone or Altiplano Puna magma body. Regional variations of activity north and south of 24°S have been attributed to the southwards moving subduction of the Juan Fernández Ridge. This southwards migration results in a steepening of the subducting plate behind the ridge, causing

decompression melting Igneous rock ( ), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial ...

. Between 1:4 to 1:6 of the generated melts are erupted to the surface as

ignimbrite Ignimbrite is a type of volcanic rock, consisting of hardened tuff. Ignimbrites form from the deposits of pyroclastic flows, which are a hot suspension of particles and gases flowing rapidly from a volcano, driven by being denser than the surrou ...

s.

Mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...

rocks are associated with

strike-slip fault In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

s and normal faults and are found in the southern Puna and Altiplano. The southern Puna has calc-alkaline

andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomina ...

s erupted after 7 mya, with the least

evolved Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

magmas being the 6.7 mya Cerro Morado and 8–7 m Rachaite complex flows.

Basaltic Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron ( mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% ...

over shoshonitic (both 25 and 21 m) to

andesitic Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomina ...

(post-

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

) lavas are found in the southern Altiplano. Ignimbrites deposited during eruptions of APVC volcanoes are formed by "boiling over" eruptions, where magma chambers containing viscous crystal-rich volatile-poor magmas partially empty in tranquil, non-explosive fashion. As a result, the deposits are massive and homogeneous and show few size segregation or fluidization features. Such eruptions have been argued to require external triggers to occur. There is a volume-dependent relationship between homogeneity of the eruption products and their volume; large volume ignimbrites have uniform mineralogical and compositional heterogeneity. Small volume ignimbrites often show gradation in composition. This pattern has been observed in other volcanic centres such as the Fish Canyon Tuff in the United States and the Toba ignimbrites in

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...

. Petrologically, ignimbrites are derived from dacitic– rhyodacitic magmas.

Phenocryst image:montblanc granite phenocrysts.JPG, 300px, Granites often have large feldspar, feldspathic phenocrysts. This granite, from the Switzerland, Swiss side of the Mont Blanc massif, has large white phenocrysts of plagioclase (that have trapezoid sh ...

s include

biotite Biotite is a common group of phyllosilicate minerals within the mica group, with the approximate chemical formula . It is primarily a solid-solution series between the iron- endmember annite, and the magnesium-endmember phlogopite; more al ...

, Fe– Ti-oxides,

plagioclase Plagioclase ( ) is a series of Silicate minerals#Tectosilicates, tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continu ...

and

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

with minor

apatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of Hydroxide, OH−, Fluoride, F− and Chloride, Cl− ion, respectively, in the crystal. The formula of the admixture of ...

and titanite. Northern Puna ignimbrites also contain

amphibole Amphibole ( ) is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is ...

, and clinopyroxene and orthopyroxene occur in low- Si magmas, while higher Si magmas also contain

sanidine Sanidine is the high temperature form of potassium feldspar with a general formula K(AlSi3O8). Sanidine is found most typically in felsic volcanic rocks such as obsidian, rhyolite and trachyte. Sanidine crystallizes in the monoclinic crystal sys ...

. These magmas have temperatures of and originate in depths of . The ignimbrites are collectively referred to as San Bartolo and Silapeti Groups. Since the Miocene, less silicic magmas containing

olivine The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...

,

plagioclase Plagioclase ( ) is a series of Silicate minerals#Tectosilicates, tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continu ...

and  clinopyroxene have been erupted by the APVC as well. These "mafic" magmas form various monogenetic volcanoes, inclusions in more silicic magmas and lava flows which sometimes occur in isolation and sometimes are linked to

stratovolcano A stratovolcano, also known as a composite volcano, is a typically conical volcano built up by many alternating layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with ...

es. Eruptions are affected by the local conditions, resulting in high altitude eruption columns that are sorted by westerly stratospheric winds. Coarse deposits are deposited close to the vents, while fine ash is carried to the Chaco and eastern cordillera. The highest volcanoes in the world are located here, including high

Ojos del Salado Nevado Ojos del Salado is a Dormant volcano, dormant complex volcano in the Andes on the Argentina–Chile border. It is the highest volcano on Earth and the highest peak in Chile. The upper reaches of Ojos del Salado consist of several overlapp ...

and high Llullaillaco. Some volcanoes have undergone flank collapses covering as much as . Most calderas are associated with fault systems that may play a role in caldera formation.

Scientific investigation

The area's calderas are poorly understood and some may yet be undiscovered. Some calderas were subject to comprehensive research. Research in this area is physically and logistically difficult. Neodym,

lead Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...

and

boron Boron is a chemical element; it has symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the boron group it has three ...

isotope analysis has been used to determine the origin of eruption products. The dry climate and high altitude of the

Atacama Desert The Atacama Desert () is a desert plateau located on the Pacific Ocean, Pacific coast of South America, in the north of Chile. Stretching over a strip of land west of the Andes Mountains, it covers an area of , which increases to if the barre ...

has protected the deposits of APVC volcanism from

erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...

, but limited erosion also reduces the exposure of buried layers and structures. Evidence of volcanic activity and cyclic variation has been obtained from remote fallout deposits as well.

Geologic history

The APVC area before the upper Miocene was largely formed from

sedimentary Sedimentary rocks are types of rock formed by the cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or deposited at Earth's surface. Sedime ...

layers of

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

to Miocene age and deformed during previous stages of Andean orogeny, with low volume volcanics. Activity until the late

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

was effusive with

andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomina ...

as the major product. After a volcanic pause related to flat slab subduction, starting from 27 mya volcanism increased suddenly. Ignimbrites range in age from 25 mya to 1 mya. In the late

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

, more evolved

andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomina ...

magmas were erupted and the crustal components increased. In the late

Tertiary Tertiary (from Latin, meaning 'third' or 'of the third degree/order..') may refer to: * Tertiary period, an obsolete geologic period spanning from 66 to 2.6 million years ago * Tertiary (chemistry), a term describing bonding patterns in organic ch ...

until the

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), as well as the current and most recent of the twelve periods of the ...

, a sudden decrease of

mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...

volcanism coupled with a sudden appearance of rhyodacitic and dacitic

ignimbrite Ignimbrite is a type of volcanic rock, consisting of hardened tuff. Ignimbrites form from the deposits of pyroclastic flows, which are a hot suspension of particles and gases flowing rapidly from a volcano, driven by being denser than the surrou ...

s occurred. During this flare-up it erupted primarily

dacite Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite. ...

s with subordinate amounts of

rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture (geology), texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained matri ...

s and andesites. The area was uplifted during the flare-up and the crust thickened to . This triggered the formation of

evaporite An evaporite () is a water- soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as oce ...

basins containing

halite Halite ( ), commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride ( Na Cl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, pi ...

,

boron Boron is a chemical element; it has symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the boron group it has three ...

and

sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...

and may have generated the

nitrate Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...

deposits of the

Atacama Desert The Atacama Desert () is a desert plateau located on the Pacific Ocean, Pacific coast of South America, in the north of Chile. Stretching over a strip of land west of the Andes Mountains, it covers an area of , which increases to if the barre ...

. The sudden increase is explained by a sudden steepening of the subducting plate, similar to the Mid-Tertiary ignimbrite flare-up. In the northern Puna, ignimbrite activity began 10 mya, with large-scale activity occurring 5 to 3.8 Ma in the arc front and 8.4 to 6.4 Ma in the back arc. In the southern Puna, backarc activity set in 14–12 Ma and the largest eruptions occurred after 4 Ma. The start of ignimbritic activity is not contemporaneous in the entire APVC area; north of 21°S the Alto de Pica and Oxaya Formations formed 15–17 and 18–23 mya respectively, whereas south of 21°S large scale ignimbrite activity didn't begin until 10.6 mya. Activity waned after 2 mya, and after 1 mya and during the

Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...

, activity was mostly

andesitic Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomina ...

in nature with large ignimbrites absent. Activity with composition similar to ignimbrites was limited to the eruption of

lava dome In volcanology, a lava dome is a circular, mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano. Dome-building eruptions are common, particularly in convergent plate boundary settings. Around 6% of eruptions ...

s and flows, interpreted as escaping from a regional sill high at depth. The APVC is still active, with recent unrest and ground inflation detected by InSAR at Uturuncu volcano starting in 1996. Research indicates that this unrest results from the intrusion of dacitic magma at or more depth and may be a prelude to caldera formation and large scale eruptive activity. Other active centres include the El Tatio and Sol de Mañana geothermal fields and the fields within Cerro Guacha and Pastos Grandes calderas. The latter also contains <10 ka

rhyolitic Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals ( phenocrysts) in an otherwise fine-grained groundmass. The miner ...

flows and domes. The implications of recent

lava dome In volcanology, a lava dome is a circular, mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano. Dome-building eruptions are common, particularly in convergent plate boundary settings. Around 6% of eruptions ...

s for future activity in the APVC are controversial, but the presence of

mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...

components in recently erupted volcanic rocks may indicate that the magma system is being recharged.

Extent

The APVC erupted over an area of from ten major systems, some active over millions of years and comparable to Yellowstone Caldera and

Long Valley Caldera Long Valley Caldera is a Depression (geology), depression in eastern California that is adjacent to Mammoth Mountain. The valley is one of the Earth's largest calderas, measuring about long (east-west), wide (north-south), and up to deep. Lo ...

in the United States. The APVC is the largest ignimbrite province of the

Neogene The Neogene ( ,) is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period million years ago. It is the second period of th ...

with a volume of at least , and the underlying magmatic body is considered to be the largest

continent A continent is any of several large geographical regions. Continents are generally identified by convention (norm), convention rather than any strict criteria. A continent could be a single large landmass, a part of a very large landmass, as ...

al melt zone, forming a

batholith A batholith () is a large mass of intrusive rock, intrusive igneous rock (also called plutonic rock), larger than in area, that forms from cooled magma deep in the Earth's crust. Batholiths are almost always made mostly of felsic or intermediate ...

. Alternatively, the body revealed by seismic studies is the remnant mush of the magma accumulation zone. Deposits from the volcanoes cover a surface area of more than . La Pacana is the largest single complex in the APVC with dimensions , including the caldera. Magma generation rates during the pulses are about , based on the assumption that for each of arc there is one caldera. These rates are substantially higher than the average for the Central Volcanic Zone, . During the three strong pulses, extrusion was even higher at . Intrusion rates range from and resulted in plutons of volume beneath the calderas.

Source of magmas

Modelling indicates a system where

andesitic Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomina ...

melts coming from the mantle rise through the crust and generate a zone of

mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...

volcanism. Increases in the melt flux and thus heat and volatile input causes partial melting of the crust, forming a layer containing melts reaching down to the Moho that inhibits the ascent of mafic magmas because of its higher

buoyancy Buoyancy (), or upthrust, is the force exerted by a fluid opposing the weight of a partially or fully immersed object (which may be also be a parcel of fluid). In a column of fluid, pressure increases with depth as a result of the weight of t ...

. Instead, melts generated in this zone eventually reach the surface, generating felsic volcanism. Some mafic magmas escape sideward after stalling in the melt containing zone; these generate more mafic volcanic systems at the edge of the felsic volcanism, such as

Cerro Bitiche 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. The field is formed by seven scoria cone ...

. The magmas are mixtures of crust derived and mafic mantle-derived melts with a consistent petrological and chemical signature. The melt generation process may involve several different layers in the crust. Another model requires the intrusion of

basaltic Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron ( mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% ...

melts into an amphibole crust, resulting in the formation of hybrid magmas. Partial melting of the crust and of hydrous basalt generates

andesitic Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomina ...

– dacitic melts that escape upwards. A residual forms composed from

garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. Garnet minerals, while sharing similar physical and crystallographic properties, exhibit a wide range of chemical compositions, de ...

pyroxenite at a depth of . This residual is denser than the mantle

peridotite Peridotite ( ) is a dense, coarse-grained igneous rock consisting mostly of the silicate minerals olivine and pyroxene. Peridotite is ultramafic, as the rock contains less than 45% silica. It is high in magnesium (Mg2+), reflecting the high pr ...

and can cause delamination of the lower crust containing the residual. Between 18 and 12 mya the Puna-Altiplano region was subject to an episode of flat subduction of the

Nazca Plate The Nazca plate or Nasca plate, named after the Nazca region of southern Peru, is an oceanic list of tectonic plates, tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction, along the Peru– ...

. A steepening of the subduction after 12 mya resulted in the influx of hot asthenosphere. Until that point, differentiation and crystallization of rising mafic magmas had mostly produced andesitic magmas. The change in plate movements and increased melt generation caused an overturn and anatexis of the melt generating zone, forming a density barrier for mafic melts which subsequently ponded below the melt generating zone. Dacitic melts escaped from this zone, forming

diapir A diapir (; , ) is a type of intrusion in which a more mobile and ductilely deformable material is forced into brittle overlying rocks. Depending on the tectonic environment, diapirs can range from idealized mushroom-shaped Rayleigh–Taylor ...

s and the magma chambers that generated APVC ignimbrite volcanism. Magma generation in the APVC is periodical, with pulses recognized 10, 8, 6, and 4 mya. The first stage included the Artola, Granada, Lower Rio San Pedro and Mucar ignimbrites. The second pulse involved the Panizos, Sifon and Vilama ignimbrites and the third was the largest, with a number of ignimbrites. The fourth pulse was weaker than the preceding ones and involved the Patao and Talabre ignimbrites among others. The magmas beneath the APVC are noticeably rich in

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

derived from the subduction of water-rich rocks. A volume ratio of about 10-20% of water has been invoked to explain the pattern of electrical conductivity at a depth of . The total amount of water has been estimated to be , comparable to large lakes on Earth.

Tomographic studies

Seismic tomography is a technique that uses

seismic wave A seismic wave is a mechanical wave of acoustic energy that travels through the Earth or another planetary body. It can result from an earthquake (or generally, a quake), volcanic eruption, magma movement, a large landslide and a large ma ...

s produced by earthquakes to gather information on the composition of the crust and mantle below a volcanic system. Different layers and structures in the Earth have different propagation speeds of seismic waves and

attenuate In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at variable at ...

them differently, resulting in different arrival times and strengths of waves travelling in a certain direction. From various measurements 3D models of the geological structures can be inferred. Results of such research indicate that a highly hydrated slab derived from the

Nazca Plate The Nazca plate or Nasca plate, named after the Nazca region of southern Peru, is an oceanic list of tectonic plates, tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction, along the Peru– ...

– a major source of melts in a collisional volcanism system – underlies the Western Cordillera. Below the Altiplano, low-velocity zones indicate the presence of large amounts of partial melts that correlate with volcanic zones south of 21° S, whereas north of 21° S thicker lithospheric layers may prevent the formation of melts. Next to the Eastern Cordillera, low-velocity zones extend farther north to 18.5° S. A thermally weakened zone, evidenced by strong attenuation, in the crust is associated with the APVC. This indicates the presence of melts in the crust. A layer of low velocity (shear speed of ) thick is assumed to host the APVC magma body. This body has a volume of about and a temperature of about . Other seismological data indicate a partial delamination of the crust under the Puna, resulting in increased volcanic activity and terrain height.

Subsystems

* Aguas Calientes caldera () * Alto de los Colorados () *

Cerro Bitiche 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. The field is formed by seven scoria cone ...

* Cerro Blanco caldera () * Cerro Chanka () * Cerro Chao () * Cerro Chascon () * Cerro Chillahuita () * Cerro Galán () * Cerro Morado () * Cerro Panizos () * Chipas caldera * Coranzulí caldera () * Delmedio () * El Morro-Organullo * Granada complex () * Guacha caldera () * Huayra Huasi volcanic complex () * Kapina caldera () * Laguna Amarga caldera () * La Torta () * La Pacana () * Lascar * Negra Muerta volcanic complex () * Pairique volcanic complex () * Pastos Grandes * Pocitos () * Purico Complex () * Quevar () * Rachaite complex () * Ramadas volcanic complex () * Rincon volcanic complex () * Tastil volcano () * El Tatio * TulTul () * Uturuncu () * Vallecito caldera () * Vilama ()

Ignimbrites

* Abra Grande Ignimbrite, 6.8 mya. * Acay Ignimbrite, 9.5–9.9 mya. * Antofalla Ignimbrite, 11.4–9.6 mya. * Arco Jara Ignimbrite, 11.3 mya. * Artola/Mucar Ignimbrite, 9.4–10.6 mya. * Atana Ignimbrite, 4.11 mya. * Blanco Ignimbrite, . * Caspana Ignimbrite, 4.59–4.18 mya. * Cerro Blanco Ignimbrite, 0.5–0.2 mya. * Cerro Colorado, 9.5–9.8 mya. * Cerro Lucho lavas, 10.6 mya. * Cerro Panizos Ignimbrite, 6.7–6.8 mya. * Chuhuilla Ignimbrite, 5.45 mya. * Cienago Ignimbrite, 7.9 mya. * Cueva Negra/Leon Muerto Ignimbrites, 3.8–4.25 mya. * Cusi Cusi Ignimbrite, >10 mya. * Galan Ignimbrite, 2.1 mya. * Granada/Orosmayo/Pampa Barreno Ignimbrite, 10-10.5 mya. * Grenada Ignimbrite, 9.8 mya. * Guacha Ignimbrite, 5.6–5.7 mya. * Guaitiquina Ignimbrite, 5.07 mya. * Laguna Amarga Ignimbrite, 3.7–4.0, 5.0 mya. * Laguna Colorada Ignimbrite, 1.98 mya. * Laguna Verde Ignimbrite, 3.7–4.0 mya. * Las Termas Ignimbrite 1 and 2, 6.45 mya. * Los Colorados Ignimbrite, 7.5–7.9 mya. * Merihuaca Ignimbrites, 5.49–6.39 mya. * Morro I Ignimbrite, 12 mya. * Morro II Ignimbrite, 6 mya. * Pairique Chico block and ash, 10.4 mya. * Pampa Chamaca, 2.52 mya. * Pitas/Vega Real Grande Ignimbrites, 4.51–4.84 mya. * Potrero Grande Ignimbrite, 9.8–9 mya. * Potreros Ignimbrite, 6.6 mya. * Purico Ignimbrite, 1.3 mya. * Puripicar Ignimbrite, 4.2 mya. * Rachaite volcanic complex, 7.2–8.4 mya. * Rosada Ignimbrite, 6.3–8.1 mya. * Sifon Ignimbrite, 8.3 mya. * Tajamar/Chorrillos Ignimbrite, 10.5–10.1 mya. * Tamberia Ignimbrite, 10.7–9.5 mya. * Tara Ignimbrite, 3.6 mya. * Tatio Ignimbrite, 0.703 mya. * Toba 1 Ignimbrite, 7.6 mya. * Toconao

pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of extremely vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicula ...

, 4.65 mya. * Vallecito Ignimbrite, 3.6 mya. * Verde Ignimbrite, 17.2 mya. * Vilama Ignimbrite, 8.4–8.5 mya. * Vizcayayoc Ignimbrite, 13 mya.

References

Bibliography

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External links

Volcano World

{{DEFAULTSORT:Altiplano-Puna volcanic complex Volcanism of Chile Andean Volcanic Belt Plate tectonics Miocene volcanism Pliocene volcanism Pleistocene volcanism Geology of Bolivia Geology of Chile Geology of Argentina Miocene South America Neogene South America Pleistocene South America Quaternary South America Miocene geology Pleistocene geology Pliocene geology Geology of South America Puna de Atacama