Cerro Guacha is a

Miocene The Miocene ( ) is the first 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 means "less recen ...

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 ...

in southwestern

Bolivia , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...

Sur Lípez Province Sur Lípez or Sud Lípez is a province in the Potosí Department in Bolivia. The seat of the province is San Pablo de Lípez. Location Sur Lípez is one of sixteen provinces in the Potosí Department. Also the southwesternmost point of Bolivia ...

. Part of the volcanic system of 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 ...

, it is considered to be part of the

Central Volcanic Zone 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 ...

(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 Guacha and the other volcanoes of that region are formed from the

subduction Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

of the

Nazca plate The Nazca Plate or Nasca 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 Na ...

beneath the

South America 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-A ...

. Above the subduction zone, the crust is chemically modified and generates large volumes of melts that form the local caldera systems of the APVC. Guacha is constructed over a basement of sediments. Two major ignimbrites, the 5.6-5.8 mya Guacha ignimbrite with a volume of and the 3.5-3.6 mya Tara ignimbrite with a volume of were erupted from Cerro Guacha. More recent activity occurred 1.7 mya and formed a smaller ignimbrite with a volume of . The larger caldera has dimensions of with a rim altitude of . Extended volcanic activity has generated two nested calderas, a number of lava domes and lava flows and a central resurgent dome.

Geography and structure

The caldera was discovered in 1978 thanks to

Landsat The Landsat program is the longest-running enterprise for acquisition of satellite imagery of Earth. It is a joint NASA / USGS program. On 23 July 1972, the Earth Resources Technology Satellite was launched. This was eventually renamed to Lan ...

imagery. It lies in

next to the

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 ...

an frontier. The terrain is difficult to access being located at altitudes between . The caldera is named after Cerro Guacha, a feature named as such by local topographic maps. Later research by the Geological Service of Bolivia indicated the presence of three welded

tuff 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 lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock cont ...

Paleogene The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period, geologic period and system that spans 43 million years from the end of the Cretaceous Period million yea ...

red beds and

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

sediments form the basement of the caldera. Cerro Guacha is part of the Altiplano-Puna volcanic complex, an area of extensive

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 ...

volcanism in the Central Andes between 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 ...

and 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 associated with the

of the Andes. Several large caldera complexes are found within this area, formed by crustal magma chambers generated by magmas derived from the melting of deep crustal layers. Present day activity is limited to geothermal phenomena in

El Tatio El Tatio is a geothermal field with many geysers located in the Andes Mountains of northern Chile at above mean sea level. It is the third-largest geyser field in the world and the largest in the Southern Hemisphere. Various meanings have bee ...

Sol de Manana Sol or SOL may refer to: Astronomy * The Sun Currency * SOL Project, a currency project in France * French sol, or sou * Argentine sol * Bolivian sol, the currency of Bolivia from 1827 to 1864 * Peruvian sol, introduced in 1991 * Peruvian sol ( ...

and Guacha, with recent activity encompassing the extrusion of

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). It follows the Neogene Period and spans from 2.58 million years ...

lava domes and flows.

Deformation Deformation can refer to: * Deformation (engineering), changes in an object's shape or form due to the application of a force or forces. ** Deformation (physics), such changes considered and analyzed as displacements of continuum bodies. * Defo ...

in the area occurs beneath

Uturuncu Uturuncu is a dormant volcano in the Sur Lípez Province of Bolivia. It is high, has two summit peaks, and consists of a complex of lava domes and lava flows with a total volume estimated to be . It bears traces of a former glaciation, even t ...

volcano north of the Guacha centre. A westward-facing semicircular scarp () contains subvertically banded Guacha ignimbrite layers rich in lithic clasts and is the presumable vent of the Guacha ignimbrite. The resulting caldera formed like a trapdoor and with a volume of is among the largest known. Volcanic structures are aligned along the eastern moat of this structure, which is filled by

lacustrine A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...

deposits and welded ignimbrites. Another eastern collapse was generated by the Tara Ignimbrite eruption, with dimensions of . The margins of the caldera-graben structure are about high while the caldera floors are about lower. Probably dacitic lava domes are found on the northern caldera rim, with the caldera floor possibly containing lava flows. The caldera contains a

resurgent dome In geology, a resurgent dome is a dome formed by swelling or rising of a caldera floor due to movement in the magma chamber beneath it. Unlike a lava dome, a resurgent dome is not formed by the extrusion of highly viscous lava onto the surfac ...

, the western part of it is formed by the Tara ignimbrite while the eastern is part of the Guacha ignimbrite. This dome was cut by the Tara collapse, exposing of Guacha ignimbrites. The resurgent dome in the caldera rises about above the caldera floor. A second resurgence episode occurred inside the Tara caldera. The caldera is filled up to thick with ignimbrites. Three lava domes, roughly coeval with the Tara ignimbrite, are constructed on the northern side of the resurgent dome. The western dome is named Chajnantor and is the most

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

-rich of the domes. Rio Guacha in the middle is more

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 rhyolite ...

. The Puripica Chico lavas on the western side of the caldera are not associated with a collapse. Dark coloured lava flows are found to the southwest of the caldera. Some geothermal activity occurs within the caldera. Laudrum ''et al.'' suggested that the heat from Guacha and

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 ...

may be transferred to the

geothermal system to the west.

Geology

Guacha is part of a volcanic complex in the

back-arc A back-arc basin is a type of geologic basin, found at some convergent plate boundaries. Presently all back-arc basins are submarine features associated with island arcs and subduction zones, with many found in the western Pacific Ocean. Most of ...

region of the

in Bolivia. The Central Andes are underlaid by the

Paleoproterozoic The Paleoproterozoic Era (;, also spelled Palaeoproterozoic), spanning the time period from (2.5–1.6 Ga), is the first of the three sub-divisions (eras) of the Proterozoic Eon. The Paleoproterozoic is also the longest era of the Earth's ...

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

Arequipa-Antofalla Arequipa-Antofalla is a basement unit underlying the central Andes in northwestern Argentina, western Bolivia, northern Chile and southern Peru. Geologically, it corresponds to a craton, terrane or block of continental crust. Arequipa-Antofalla ...

terrane In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust fragment formed on a tectonic plate (or broken off from it) and accreted or " sutured" to crust lying on another plate. The crustal block or fragment preserves its own ...

. The Central Andes started to form 70 mya. Previously, the area was formed from a

marine basin with some early volcanics. Since the

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

has been occurring on the western margin of present-day

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...

, resulting in variable amounts of volcanic activity. A short interruption of volcanism, associated with a flattening of the subducting plate, occurred in the

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

35-25 mya. Subsequently, renewed melt generation modified the overlying crust until major volcanism, associated with a "flare up" of ignimbritic volcanism occurred 10 mya. beneath the local volcanic zone lies the

Benioff zone Benioff is a surname. Notable people with the surname include: *David Benioff (born 1970), American writer, screenwriter and television producer *Hugo Benioff (1899–1968), American seismologist and academic **Wadati–Benioff zone *Marc Benioff ( ...

of the subducting

. Recently a change in volcanic activity away from ignimbritic towards cone-forming volcanism has been observed.

Local

Guacha caldera is part of the Altiplano-Puna volcanic complex (APVC), an igneous province in the central

covering a surface area of . Here on an average altitude of between 10 and 1 mya roughly of ignimbrites were erupted. Gravitic research indicates the presence of a low density area centered beneath Guacha. The magmatic body underpinning the APVC is centered beneath Guacha. Guacha caldera is also closely linked to the neighbouring

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, Altiplano-Puna volcanic complex, a major caldera and silicic ignimbri ...

caldera. The Guacha caldera forms a structure with the neighbouring

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 ...

, Coranzulí and Vilama calderas associated with a fault named the Lípez lineament. Activity along this lineament commenced with the Abra Granada volcanic complex 10 mya ago and dramatically increased more than a million years later. Volcanic activity is linked to this fault zone and to the thermal maturation of the underlying crust. After 4 million years ago activity waned again in the Altiplano-Puna volcanic complex.

Geologic record

The Guacha system was constructed over a timespan of 2 million years with a total volume of . Eruptive activity occurred at regular intervals. Calculations indicate that the Guacha system was supplied by magmas at a rate of . Located at a high altitude in an area of long term arid climate has preserved old volcanic deposits over time. Thus, unlike in other areas of the world such as the

Himalayas The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest. Over 100 ...

where water erosion governs the landscape the morphology of the Altiplano-Puna volcanic complex is mostly tectonic in origin.

Composition and magma properties

The Guacha Ignimbrite is

rhyodacite 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 rich in crystals. The Chajnantor lava dome contains

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 system ...

while Rio Guacha of

composition contains

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 A ...

and

pyroxene 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 II) ...

. The Tara ignimbrite has a composition intermediary to that of these two domes, being

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 ...

- rhyolithic. The Guacha Ignimbrite contains 62-65% SiO₂, Puripicar 67-68% and the Tara Ignimbrite 63%.

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 prope ...

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 form ...

are found in all ignimbrites. Geological considerations indicate that the Guacha ignimbrite was stored at a depth of and the Tara ignimbrite at a depth of .

Zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of the r ...

temperatures are , and for Guacha, Tara and Chajnantor respectively.

Climate

The climate of the Central Andes is characterized by extreme aridity. The eastern mountain chain of the Andes prevents moisture from the

Amazon Amazon most often refers to: * Amazons, a tribe of female warriors in Greek mythology * Amazon rainforest, a rainforest covering most of the Amazon basin * Amazon River, in South America * Amazon (company), an American multinational technology c ...

from reaching the Altiplano area. The area is also too far north for the precipitation associated with the

Westerlies The westerlies, anti-trades, or prevailing westerlies, are prevailing winds from the west toward the east in the middle latitudes between 30 and 60 degrees latitude. They originate from the high-pressure areas in the horse latitudes and trend to ...

to reach Guacha. This arid climate may go back to the

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...

and was enhanced by geographical and orogenic changes during the

Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...

Oxygen isotope There are three known stable isotopes of oxygen (8O): , , and . Radioactive isotopes ranging from to have also been characterized, all short-lived. The longest-lived radioisotope is with a half-life of , while the shortest-lived isotope is ...

analysis indicates that the Guacha caldera ignimbrites have had little influence from meteoric waters. This is consistent with the climate of the Guacha region displaying long-term

aridity A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and development of plant and animal life. Regions with arid climates tend to lack vegetation and are called xeric or desertic. Most ar ...

for the last 10 mya as well as with the scarcity of pronounced geothermal systems in the APVC which are essentially limited to the

and

fields.

Eruptive history

Guacha has been the source of eruptions with volumes of more than

dense rock equivalent Dense-rock equivalent (DRE) is a volcanologic calculation used to estimate volcanic eruption volume. One of the widely accepted measures of the size of a historic or prehistoric eruption is the volume of magma ejected as pumice and volcanic ash, k ...

s. These eruptions in Guacha's case have a Volcanic explosivity index of 8. The close succession of multiple large scale eruptions indicates that

pluton 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 ...

s feeding such eruptions are assembled over millions of years. The Guacha ignimbrite (including the Lowe Tara Ignimbrite, Chajnantor Tuff, Pampa Guayaques Tuff and possibly the Bonanza Ignimbrite) was first considered part of another ignimbrite named Atana Ignimbrite. It has a minimum volume of and covers a surface area of at least . Several different dates have been determined on the basis of argon-argon dating, including 5.81±0.01 on

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 alumino ...

and 5.65±0.01 mya on

, which is the preferred age. Various samples are separated by distances of up to , making this ignimbrite among the most widespread in the Andes. One stream spreads northwards past

Uturunku Uturuncu is a dormant volcano in the Sur Lípez Province of Bolivia. It is high, has two summit peaks, and consists of a complex of lava domes and lava flows with a total volume estimated to be . It bears traces of a former glaciation, eve ...

volcano along the Quetena valley until Suni K'ira. Some ash deposits in the northern

Chilean Coast Range The Chilean Coastal Range ( es, Cordillera de la Costa) is a mountain range that runs from north to south along the Pacific coast of South America parallel to the Andean Mountains, extending from Morro de Arica in the north to Taitao Peninsula, ...

are linked to the Guacha eruption. The Guacha ignimbrite was also known as Lower Tara at first. The later Tara ignimbrite (including the Upper Tara Ignimbrite, the Filo Delgado Ignimbrite and the Pampa Tortoral Tuff) forms the western dome of the Guacha caldera and spreads mostly north and southeast, between

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 ...

and

. It has a minimum volume of and covers a surface area of at least in Chile and in Bolivia where it was at first not recognized. Some outflows are more than thick. Several different dates have been determined on the basis of argon-argon dating, including 3.55±0.01 on

and 3.49±0.01 mya on

, which is the preferred age. The Chajnantor lavas and the Rio Guacha dome in the caldera have been K-Ar dated at 3.67±0.13 and 3.61±0.02 mya respectively. This ignimbrite ponded inside the Guacha caldera, and one particularly thick layer (>) is found beneath

Zapaleri Zapaleri is a volcano whose summit is the tripoint of the borders of Argentina, Bolivia and Chile. A number of railways are in the area. It is part of Potosí Department (Bolivia), Jujuy Province (Argentina), and Antofagasta Region (Chile). The ...

stratovolcano. This ignimbrite was formerly known as Upper Tara. Geological considerations indicate that this ignimbrite formed from pre-existent melts and an influx of

magma. The Puripica Chico ignimbrite is known for having formed the Piedras de Dali hoodoos, named like that by tourists because of their surreal landscape. It has a volume of and it was apparently erupted at the hinge of the Guacha caldera. It has been argon-argon dated at 1.72±0.01 mya, making it the youngest Guacha caldera volcanite. The Puripicar ignimbrite has a volume of and is 4.2 mya old. After research indicated that it was different from another ignimbrite named Atana, it was originally linked to the Guacha caldera but Salisbury ''et al.'' in 2011 linked the Tara ignimbrite to Guacha instead. Another ignimbrite associated with Guacha is the Guataquina Ignimbrite named after Paso de Guataquina. It covers an area of and has an approximate volume of . It was later interpreted to be a combination of the Guacha, Tara and non-Guacha Atana ignimbrites.

References

External links

* {{DEFAULTSORT:Guacha, Cerro Volcanoes of Potosí Department Andean Volcanic Belt Supervolcanoes VEI-8 volcanoes Calderas of Bolivia Miocene calderas Miocene South America