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 Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...

Altiplano The Altiplano (Spanish for "high plain"), Collao (Quechua and Aymara: Qullaw, meaning "place of the Qulla") or Andean Plateau, in west-central South America, is the most extensive high plateau on Earth outside Tibet. The plateau is located at the ...

highland Highlands or uplands are areas of high elevation such as a mountainous region, elevated mountainous plateau or high hills. Generally speaking, upland (or uplands) refers to ranges of hills, typically from up to while highland (or highlands) is ...

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 American ...

latitude In geography, latitude is a 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 the south pole to 90° at the north pol ...

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...

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 in the geologic time scale that extends from 5.333 million to 2.58mya),

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...

s erupted felsic

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 surro ...

s in four distinct pulses separated by periods of low levels of activity. At least three volcanic centres ( Guacha caldera,

La Pacana 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 f ...

, Pastos Grandes, Vilama) had eruptions of a Volcanic Exposivity 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 geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togeth ...

, as well as recent

ground deformation Ground may refer to: Geology * Land, the surface of the Earth not covered by water * Soil, a mixture of clay, sand and organic matter present on the surface of the Earth Electricity * Ground (electricity), the reference point in an electrical c ...

at Uturunku volcano indicate still-extant present-day activity of the system.

Geography

The

Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...

mountain chain originated from the subduction of the Nazca Plate 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 surro ...

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

Atacama The Atacama Desert ( es, Desierto de Atacama) is a desert plateau in South America covering a 1,600 km (990 mi) strip of land on the Pacific coast, west of the Andes Mountains. The Atacama Desert is the driest nonpolar desert in the w ...

and the

Altiplano The Altiplano (Spanish for "high plain"), Collao (Quechua and Aymara: Qullaw, meaning "place of the Qulla") or Andean Plateau, in west-central South America, is the most extensive high plateau on Earth outside Tibet. The plateau is located at the ...

. The

Toba Toba may refer to: Languages * Toba Sur language, spoken in South America * Batak Toba, spoken in Indonesia People * Toba people, indigenous peoples of the Gran Chaco in South America * Toba Batak people, a sub-ethnic group of Batak people from N ...

volcanic system in

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...

and Taupo 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 ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...

; 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, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...

to

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

age.

Geology

The APVC is generated by the subduction of the Nazca Plate beneath the South American Plate at an angle of nearly 30°.

Delamination Delamination is a mode of failure where a material fractures into layers. A variety of materials including laminate composites and concrete can fail by delamination. Processing can create layers in materials such as steel formed by rolling a ...

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 The Juan Fernández Ridge is a volcanic island and seamount chain on the Nazca Plate. It runs in a west–east direction from the Juan Fernández hotspot to the Peru–Chile Trench at a latitude of 33° S near Valparaíso. The Juan Fernánde ...

. This southwards migration results in a steepening of the subducting plate behind the ridge, causing

decompression melting Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...

. 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 surro ...

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 incl ...

rocks are associated with strike-slip faults and normal faults and are found in the southern Puna and Altiplano. The southern Puna has

calc-alkaline The calc-alkaline magma series is one of two main subdivisions of the subalkaline magma series, the other subalkaline magma series being the tholeiitic series. A magma series is a series of compositions that describes the evolution of a mafic m ...

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 predo ...

s erupted after 7 mya, with the least

evolved Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

magmas being the 6.7 mya

Cerro Morado Cerro Morado is a monogenetic volcanic field, in Argentina. It is part of a group of mafic volcanic centres in the Altiplano-Puna region, which is dominated by silicic rocks such as dacitic - rhyolitic rocks. The field was formed during eruptions ...

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% of a ...

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 predomin ...

(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 The Fish Canyon Tuff is the large volcanic ash flow or ignimbrite deposit resulting from one of the largest known explosive eruptions on Earth, estimated at . (see List of largest volcanic eruptions). The Fish Canyon Tuff eruption was centred at th ...

in the United States and the

Toba Toba may refer to: Languages * Toba Sur language, spoken in South America * Batak Toba, spoken in Indonesia People * Toba people, indigenous peoples of the Gran Chaco in South America * Toba Batak people, a sub-ethnic group of Batak people from N ...

ignimbrites in

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...

. Petrologically, ignimbrites are derived from

dacitic 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 rhyol ...

–

rhyodacitic Rhyodacite is a volcanic rock intermediate in composition between dacite and rhyolite. It is the extrusive equivalent of those plutonic rocks that are intermediate in composition between monzogranite and granodiorite. Rhyodacites form from rapid ...

magmas.

Phenocryst 300px, feldspathic phenocrysts. This granite, from the Switzerland">Swiss side of the Mont Blanc massif, has large white plagioclase phenocrysts, triclinic minerals that give trapezoid shapes when cut through). 1 euro coins, 1 euro coin (diameter ...

s include biotite, Fe– Ti-oxides,

plagioclase Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more pro ...

and

quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...

with minor apatite and

titanite Titanite, or sphene (from the Greek ''sphenos'' (σφηνώ), meaning wedge), is a calcium titanium nesosilicate mineral, Ca Ti Si O5. Trace impurities of iron and aluminium are typically present. Also commonly present are rare earth metals ...

. Northern Puna ignimbrites also contain amphibole, and

clinopyroxene The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe I ...

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 with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...

,  plagioclase and  clinopyroxene have been erupted by the APVC as well. These "mafic" magmas form various

monogenetic volcano A monogenetic volcanic field is a type of volcanic field consisting of a group of small monogenetic volcanoes, each of which erupts only once, as opposed to polygenetic volcanoes, which erupt repeatedly over a period of time. The small monogeneti ...

es, inclusions in more silicic magmas and lava flows which sometimes occur in isolation and sometimes are linked to stratovolcanoes. 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 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 overlapping lava domes, ...

and high

Llullaillaco Llullaillaco () is a dormant stratovolcano at the border of Argentina (Salta Province) and Chile (Antofagasta Region). It lies in the Puna de Atacama, a region of tall volcanic peaks on a high plateau close to the Atacama Desert, one of the dri ...

. 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 with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...

and boron 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 ( es, Desierto de Atacama) is a desert plateau in South America covering a 1,600 km (990 mi) strip of land on the Pacific coast, west of the Andes Mountains. The Atacama Desert is the driest nonpolar desert in th ...

has protected the deposits of APVC volcanism from

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is dis ...

, 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 that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

layers of

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...

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 predo ...

as the major product. After a volcanic pause related to

flat slab subduction Flat slab subduction is characterized by a low subduction angle (<30 degrees to horizontal) beyond the

seismogenic layer

, 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 predo ...

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

Tertiary Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...

until the Quaternary, 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 incl ...

volcanism coupled with a sudden appearance of

rhyodacitic Rhyodacite is a volcanic rock intermediate in composition between dacite and rhyolite. It is the extrusive equivalent of those plutonic rocks that are intermediate in composition between monzogranite and granodiorite. Rhyodacites form from rapid ...

and

dacitic 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 rhyol ...

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 surro ...

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 rhyolites 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 ocean ...

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, p ...

, boron 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 deposits of the

Atacama Desert The Atacama Desert ( es, Desierto de Atacama) is a desert plateau in South America covering a 1,600 km (990 mi) strip of land on the Pacific coast, west of the Andes Mountains. The Atacama Desert is the driest nonpolar desert in th ...

. The sudden increase is explained by a sudden steepening of the subducting plate, similar to the

Mid-Tertiary ignimbrite flare-up The Mid-Tertiary ignimbrite flare-up, was a dramatic period of volcanic eruptions in mid-Cenozoic time, approximately 25–40 million years ago, centered in the western United States. These eruptions are seen today as deposits of ignimbrite, the ...

. 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 geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togeth ...

, 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 predomin ...

in nature with large ignimbrites absent. Activity with composition similar to ignimbrites was limited to the eruption of lava domes 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 Interferometric synthetic aperture radar, abbreviated InSAR (or deprecated IfSAR), is a radar technique used in geodesy and remote sensing. This geodetic method uses two or more synthetic aperture radar (SAR) images to generate maps of surface defo ...

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 mineral ...

flows and domes. The implications of recent lava domes 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 incl ...

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 The Yellowstone Caldera, sometimes referred to as the Yellowstone Supervolcano, is a volcanic caldera and supervolcano in Yellowstone National Park in the Western United States. The caldera and most of the park are located in the northwest corn ...

and

Long Valley Caldera Long Valley Caldera is a 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. Long Valley was formed ...

in the United States. The APVC is the largest ignimbrite province of the Neogene 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 landmasses. Generally identified by convention rather than any strict criteria, up to seven geographical regions In geography, regions, otherwise referred to as zones, lands or territories, are areas t ...

al melt zone, forming a batholith. 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 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 f ...

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 In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

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 predomin ...

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 incl ...

volcanism. Increases in the melt flux and thus heat and volatile input causes

partial melting Partial melting occurs when only a portion of a solid is melted. For mixed substances, such as a rock containing several different minerals or a mineral that displays solid solution, this melt can be different from the bulk composition of the soli ...

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 an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the ...

. 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 cones ...

. The magmas are mixtures of crust derived and mafic mantle-derived melts with a consistent

petrological Petrology () is the branch of geology that studies rocks and the conditions under which they form. Petrology has three subdivisions: igneous, metamorphic, and sedimentary petrology. Igneous and metamorphic petrology are commonly taught together ...

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% of a ...

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 predomin ...

–

dacitic 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 rhyol ...

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. All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different s ...

pyroxenite Pyroxenite is an ultramafic igneous rock consisting essentially of minerals of the pyroxene group, such as augite, diopside, hypersthene, bronzite or enstatite. Pyroxenites are classified into clinopyroxenites, orthopyroxenites, and the we ...

at a depth of . This residual is denser than the mantle peridotite 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. 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 Anatexis (via Latin from Greek roots meaning "to melt down") is the partial melting of rocks. Traditionally, anatexis is used specifically to discuss the partial melting of crustal rocks, while the generic term "partial melting" refers to the par ...

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 diapirs 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 (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...

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 wave of acoustic energy that travels through the Earth. It can result from an earthquake, volcanic eruption, magma movement, a large landslide, and a large man-made explosion that produces low-frequency acoustic energy ...

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 vari ...

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 Slab or SLAB may refer to: Physical materials * Concrete slab, a flat concrete plate used in construction * Stone slab, a flat stone used in construction * Slab (casting), a length of metal * Slab (geology), that portion of a tectonic plate tha ...

derived from the Nazca Plate – 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 Delamination is a mode of failure where a material fractures into layers. A variety of materials including laminate composites and concrete can fail by delamination. Processing can create layers in materials such as steel formed by rolling a ...

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 cones ...

* Cerro Blanco caldera () * Cerro Chanka () *

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 Chao ...

() * Cerro Chascon () * Cerro Chillahuita () * Cerro Galán () *

Cerro Morado Cerro Morado is a monogenetic volcanic field, in Argentina. It is part of a group of mafic volcanic centres in the Altiplano-Puna region, which is dominated by silicic rocks such as dacitic - rhyolitic rocks. The field was formed during eruptions ...

() *

Cerro Panizos Panizos is a Late Miocene 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 ...

() * 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 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 f ...

() *

Lascar A lascar was a sailor or militiaman from the Indian subcontinent, Southeast Asia, the Arab world, British Somaliland, or other land east of the Cape of Good Hope, who was employed on European ships from the 16th century until the middle of the ...

* Negra Muerta volcanic complex () * Pairique volcanic complex () * Pastos Grandes *

Pocitos :''Pocitos is also the colloquial name for the city of Salvador Mazza, Salta Province, Argentina'' Pocitos is an upscale beach '' barrio'' (neighbourhood or district) in Uruguay's capital city, Montevideo. Location This area is located along the ...

() * Purico Complex () * Quevar () * Rachaite complex () * Ramadas volcanic complex () *

Rincon volcanic complex Rincon volcanic complex is a volcano in Argentina. This volcanic complex is formed by a southwest–northeast trending long series of volcanoes that contain amphitheatres. The volcanoes are formed mainly by lava flows; pyroclastic material has onl ...

() * 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 highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular v ...

, 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