Aucanquilcha

Coordinates: 21°11′S 68°35′W / 21.183°S 68.583°W / -21.183; -68.583
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Aucanquilcha
Quechua: Auqa/aukka; "cruel"/"enemy", kichka/khiska; "spine"; "cruel spine"[4]
PronunciationOW-kahn-KEEL-chuh
Geography
Aucanquilcha is located in the northernmost part of Chile
Aucanquilcha is located in the northernmost part of Chile
Aucanquilcha
Central Volcanic Zone
Last eruption240,000 ± 50,000 years ago (Pleistocene)[5]

Aucanquilcha is a massive

glaciation, resulting in the formation of moraines and cirques
.

The cluster has generated lava ranging in composition from andesite to dacite, with the main volcano being exclusively of dacitic composition. Systematic variations in temperature, crystal and biotite content have been recorded during the evolution of the cluster.

At Aucanquilcha volcano there is some

aerial cableway was employed to transport the sulfur to the town of Amincha
. To bring the sulfur down, a road network to the summit was constructed in 1972, although it is now impassable.

In 1986, four men were reported to be living at an altitude of 5,900 metres (19,400 ft), making them the highest permanent residents on Earth.

Geography and geology

Regional setting

Main articles: Andean Volcanic Belt and Altiplano–Puna volcanic complex

Aucanquilcha is part of the

compound volcanoes and has generated over 3,000 cubic kilometres (720 cu mi) of eruption products over 28 million years.[5]

The Aucanquilcha complex lies northwest of the

seismic velocity zone that has been linked to the presence of 15–25% of partial melts in the zone. The Aucanquilcha complex is much smaller volumetrically than the APVC ignimbrites, but the duration of activity and the location indicate that Aucanquilcha is a subcomponent of the APVC complex.[6]

The long-term magma output of Aucanquilcha is comparable to the magma output of other long-term active volcanoes in the central Andes such as

lithostatic load imposed by the edifices on the magma chambers and the increased travel distance of the magma through the edifice.[5]

Local setting

Topographic map of the Chile-Bolivia frontier.
In this topographic map of the region, the white surface in the upper left is Aucanquilcha.

Aucanquilcha is part of a cluster of volcanoes located between the

vents. It is likely that two small lava domes (Cerro Cumbre Negra and Summit 5867) on the northwest flank occupy flank vents.[5] To the north lies the 3.3 mya old andesite Cerro Tres Monos ridge; to the west lies the east-west Cerro Polan and La Luna ridge.[5]

The volcanic cluster of which Aucanquilcha is a part contains about 19–20 volcanoes and has generated about 340 cubic kilometres (82 cu mi) of andesite and

alluvial deposits. On its southern side lies the Cerro Chela volcano.[6][7] The cluster lies on a 70-kilometre (43 mi) thick crust,[6] and arid conditions since the Miocene have preserved its structures. Its volcanoes are arranged in north-south and northwestern alignments, which may indicate a rupture of the crust above shallow magma reservoirs.[7]

Aucanquilcha underwent a northwestward flank collapse, generating a debris avalanche deposit. The debris avalanche descended 2,100 metres (6,900 ft) and ran for 17 kilometres (11 mi) with an

Mount St Helens avalanche of 1980 and one-third of the surface area of the Ollagüe avalanche. A volume of 0.35 cubic kilometres (0.084 cu mi) is assumed based on a probable thickness of 10 metres (33 ft).[5][7]

Petrographically, the composition of the cluster ranges from andesite to dacite with

orthopyroxene+amphibole (hornblende and pargasite) or amphibole+biotite+minor amounts of pyroxene are subordinate components. Apatite, ilmenite, magnetite and zircon can also be found. There is evidence of magma mixing and mingling.[5][6]

Rocks have a porphyritic texture.[5] Basaltic andesites typically contain less than 10% crystals while dacites generally have more than 20% crystals. The Alconcha group lavas of the first one million years are crystal-poor and lack biotite; later lavas contain biotite and more crystals. Based on geothermometric data, the highest temperatures occurred during phases of high activity and lower temperatures are associated with low output periods.[10] It is likely that crustal feedback and increased deep crustal influx of mantle-derived basalts drive increased magmatic flux. During the time of the Polan eruption on the west flank, magma output was spatially segregated with the peripheral Miño Volcano generating andesite lavas and the more central volcanos generating dacites.[7]

Various parts of the main volcano have been subjected to

talus deposits.[5] The central part of the complex is heavily altered by fumarole activity.[3] Hydrothermal alteration may be driven by the formation of a deep magma reservoir and resulting hydrothermal circulation in overlying rocks.[7]

Eruptive history

Eruption rates increased 6 million years ago, coinciding with magmas becoming more uniform in composition and the onset of strong hydrothermal alteration. It is possible that solidification of magmas below the volcano insulated the feeding channels from heat loss and caused the temperatures in the system to increase. Activity waned again 2 million years ago, with magma and included crystals being drawn from depths of 3 to 23 kilometres (1.9 to 14.3 mi) and forming the Aucanquilcha volcano proper.[6][10] The 10-million-year duration of activity of the Altiplano–Puna volcanic complex systems is comparable to the duration of Aucanquilcha activity.[11] The age of the lava flows ranges from heavily glaciated andesite flows overlying less-eroded ones to possibly postglacial lava flows that may be tens of thousands of years old.[3]

Aucanquilcha cluster

Aucanquilca

The Aucanquilcha cluster formed in four stages, each corresponding to a group. The Alconcha group, with seven volcanoes, is constructed from pyroxene, andesite and dacite and formed 11–8 mya. It is constructed from two northern

dated 10.96–10.51 mya), and five lava domes on the northeastern side of the cluster. Alconcha has a large breach on the southern side of its crater that is likely the product of a flank collapse but the avalanche deposit may be buried beneath younger material. Lavas within the breach are dated 10.78–10.43 mya. The centres of Volcan Tuco and Alconcha are heavily eroded, and Alconcha's lavas and scoria lie on top of Tuco. The Ujina ignimbrite was erupted 9.4 mya from an unknown vent and has a volume of 2 cubic kilometres (0.48 cu mi) of dacite. While the vent location is unknown, the composition of the ignimbrite, and its dating and distribution, indicate an association with this group. The domes are poorly researched, with the Coscalito dome dated 8.9–8.7 mya and Cerro Amincha 8.01. The total volume of this group is 46 cubic kilometres (11 cu mi), indicating a flux rate of 0.013 cubic kilometres per millennium (0.0031 cubic miles per millennium).[7]

The Gordo group, which erupted 6–4 mya following a probable 2-million-year hiatus, is located in the southern and western parts of the cluster. Cerro Gordo itself (5.49

stratocone with a lava-filled crater, and layers of scoria and agglutinated lavas dip from it. Volcan Pabellón (4.14–4.12 mya) sits southwest of the Puquíos-Negro ridge. The Las Bolitas lava field (5.23–5.13 mya) is associated with the Gordo group but the vent locations are unknown. The total volume of this group is 55 cubic kilometres (13 cu mi), indicating a flux rate of 0.027 cubic kilometres per millennium (0.0065 cubic miles per millennium).[7]

The 3.6–2.3 mya Polan group, with ten dispersed volcanoes including Miño Volcano, is the largest group in the cluster and includes Tres Monos, La Luna, Cerro Polan, Chaihuiri, Miño Volcano and the lavas of the Aucanquilcha platform. Cerro Polan's (3.5–3 mya) eastern side is deeply dissected, and the exposed materials are heavily altered in the deeper sections. Lava fields to Polan's west and southwest (2.6 mya on one western field) are associated with it. La Luna (2.97–2.57) lies just east of Polan; these two volcanoes were probably one volcano in the past. La Luna has a lava dome surrounded by a glaciated but unaltered lava table. Cerro Tres Monos (3.4–2.78 mya) forms a northbound 14-kilometre (8.7 mi) long ridge with at least six vents. Hydrothermal alteration has affected some lavas and pyroclastics from Tres Monos, and the western side has lateral and terminal moraines. The Aucanquilcha platform (3.6–2.7 mya) sits underneath the main Aucanquilcha volcano, and its lava mostly flowed north. Its southern side is a 4,500-metre (14,800 ft) table with one hill, Cerro Campana, dated to 3.3 mya. The platform presumably forms one third of the total volume of the Aucanquilcha cluster and may have originated from a part of the ridge of the La Luna-Polan trend, now buried beneath Aucanquilcha. Chaihuiri (2.39 mya) is a lava dome with moraines and two short lava flows; it is the youngest Polan group volcano. The total volume of this group is 154 cubic kilometres (37 cu mi), indicating a flux rate of 0.077 cubic kilometres per millennium (0.018 cubic miles per millennium).[7]

After the four main phases, some

basaltic composition, including Poruñita and Luna de Tierra, formed between Aucanquilcha and Ollagüe.[10]

Aucanquilcha proper

Landscape view

The main Aucanquilcha volcano formed in four stages. Between 1.04–0.92

glacial erosion. The total volume is 21.1 cubic kilometres (5.1 cu mi), indicating a flux rate of 0.16 cubic kilometres per millennium (0.038 cubic miles per millennium). This volcano was probably an isolated cone, but the existence of a previous stage cannot be excluded.[5]

The second stage, named Rodado, lasted from 0.95 to 0.85 mya. It formed on the eastern slopes of the Azufrera volcano, with one vent at the 6,073 metres (19,925 ft) summit. Rodado stage lavas are blocky and platy and usually thicker than Azufrera stage lavas. Some of the summit vent lavas are among the most

solfataric alteration. The Cerro Chinchillas lavas are the oldest of this stage; erupted from an unknown vent, they lack amphiboles. The total volume is 9.1 cubic kilometres (2.2 cu mi), indicating a flux rate of 0.09 cubic kilometres per millennium (0.022 cubic miles per millennium). A flank collapse, possibly triggered by a large earthquake, occurred during this stage.[5]

The third stage is the Cumbre Negra stage, named after the westernmost summit and principal vent of this stage, Cerro Cumbre Negra (5,670 metres (18,600 ft)). The time course of its activity is less defined than the previous two stages; it may have occurred between 1–0.47 mya, but most likely 0.6–0.5 mya based on

potassium–argon dating. Four lava flows derived from the main vent, all less than one kilometre long and 40–60 metres (130–200 ft) thicker than previous stages. They all have hydration rinds but no native sulfur deposits. This stage generated Aucanquilcha's only pyroclastic flow during a lava dome collapse as occurred on Merapi in Indonesia. The total volume of this stage is 0.7 cubic kilometres (0.17 cu mi), indicating a flux rate of 0.005 cubic kilometres per millennium (0.0012 cubic miles per millennium).[5]

The youngest stage, known as Angulo, lasted from 0.66 to 0.24 mya. It was centered between the Azufrera and Rodado stage edifices 0.35–0.23 mya. Most lava flows from this stage originate on a 1-kilometre (0.62 mi) long ridge that includes Aucanquilcha's highest summit. One crater on the northeast side of the ridge fed lavas to the north. Other than that, most flows extend southwards 4 to 9 kilometres (2.5 to 5.6 mi) from the vent, and with the exception of a due south flow 50 metres (160 ft) thick they are thin, with thicknesses of 15–20 metres (49–66 ft). One of the oldest flows has been compared in length to the 50% longer Chao Dacite flow but is much thinner. The flows from this stage are weakly weathered and partially overlie glacial deposits. The total volume is 5.8 cubic kilometres (1.4 cu mi), indicating a flux rate of 0.015 cubic kilometres per millennium (0.0036 cubic miles per millennium).[5]

There is no evidence of Holocene activity[12] but the volcano has active fumaroles though the low-temperature fumaroles are not visible through short wavelength infrared data from satellites.[13] Fumarole activity was observed in 1962[14] and is most conspicuous in the trenches dug during sulfur mining operations. Lava flow emissions and minor explosive activity, confined to the edifice of the volcano, are the most important risks from renewed activity.[15]

Glaciation and hydrology

The volcano is currently not glaciated despite its height, due to the

Rio Loa are on Aucanquilcha[17] and it drains the western and northwestern sides of the volcano; the eastern side drains into the Salar de Ollagüe salt pan, the northeastern into the Salar de Laguani, and the southeastern into the Salar de Carcote. Most valleys only intermittently transport water, if at all,[18] but it forms the headwaters of the Rio Loa.[19]

The volcanic cluster was modestly glaciated during the

glacial striations and moraines at elevations above 4,500 metres (14,800 ft),[7] and shows evidence of glaciers both on the main volcano and its subsidiaries. At least two distinct glacier stages took place.[19] The western Azufrera edifice was heavily glaciated in the past. At least three moraine stages have been mapped on that edifice, and on its southern side is found a modest cirque with glacially polished lavas on the floor. The Rodado stage edifice has several moraine stages on its southern slopes. Another small cirque with a moraine has been found in the northeastern side of the Cerro Cumbre Negra summit next to an Azufrera stage lava flow. A small moraine lies on the south side of the Angulo edifice; some lavas from that edifice overlie glacial deposits.[5]

Human activity and mining

Tracks in a sulfur mine on Aucanquilcha
A sulfur mine on Aucanquilcha
Aucanquilcha camp

A famous

trucks. The sulfur was then transported to Chuquicamata to be converted into sulfuric acid[20][25] or to Antofagasta to be shipped.[20] The mine was active from 1950 to 1992.[26] In 1977 other sulfur mines were present to the west between Cerro Polan and Cerro Gordo and south of the main Aucanquilcha massif.[18] Amincha was closed in 1992;[27] the last reported mining activity on the mountain was in 1994[5] and during the 1980s[27]-1990s the worker camps were abandoned.[24]

The cableway, of which ruins are still standing,

mining camp (5,300 metres (17,400 ft)) and from there to Amincha (3,900 metres (12,800 ft))[28] where the sulfur was refined during the 1950s.[20] The road leading up to the mine is dated 1972 and is now impassable because of rock falls.[28] There is still a relic network of roads leading up to 5,900 metres (19,400 ft)[5] as well as ruins of the Amincha and El Ángulo stations.[20]

epithermal mineralization above deep porphyry copper mineralization.[29] The sulfur itself formed at temperatures of 450 °C (842 °F) in a now extinct fumarole.[30]

Altitude and habitation

The sulfur mine is notable for being the highest mine in the world at 5,950 metres (19,520 ft)[28] and the highest permanently inhabited area.[8] An expedition in 1935, part of the International High Altitude Expedition, found that miners lived at an altitude of 5,300 metres (17,500 ft) in the town of Quilcha and reached the higher mine on foot. The expedition found that an even higher abandoned village at 5,639 metres (18,501 ft) existed, but miners refused to live there. The conclusion taken from the expedition was that 5,334 metres (17,500 ft) was the highest habitable altitude.[28]

West in 1986 reported that a few miners permanently lived in the mine area.[31] A small group of men, caretakers of the mine, has lived at an altitude of 5,900 metres (19,500 ft) in a galvanized iron hut. One of them reportedly had spent two years there.[32] These are considered to be the highest human inhabitants on Earth.[33] Research performed on Aymara miners of the Aucanquilcha mine indicates that they are fully acclimatized to the altitude, with less hyperventilation and higher hemoglobin than acclimatized people from lower areas.[34] Their families are born and raised at lower altitudes, however.[33]

See also

References

  1. ^
    ISSN 0022-1430
    .
  2. ^ "Aucanquilcha". Andes Specialists. Retrieved 2020-04-12.
  3. ^
    ISBN 978-3-642-77355-6
    .
  4. ^ (in Spanish) Cerro Aucanquilcha
  5. ^
    S2CID 140668081
    .
  6. ^
    ISSN 0091-7613
    .
  7. ^
    S2CID 129122958
    .
  8. ^
    S2CID 128824938
    .
  9. S2CID 128974452
    .
  10. ^
    S2CID 129808417
    .
  11. ISSN 0016-7606
    .
  12. ISBN 978-0-12-818082-2
    .
  13. ISSN 0148-0227
    .
  14. S2CID 128979648
    .
  15. ISSN 0717-7305. Archived from the original
    (PDF) on June 29, 2021. Retrieved 20 August 2021.
  16. ISSN 0717-7356
    .
  17. PMID 34690508
    .
  18. ^
    Salar de Ascotan. Archived from the original (jpg) on 11 November 2010. Retrieved 6 September 2015. Alt URL
  19. ^
    ISBN 3906151034
    .
  20. ^
    S2CID 213428375
    .
  21. PMID 11809089
    .
  22. ISBN 978-1-4381-0963-3
    .
  23. ^ González, José Antonio (2010). "The mining industry in Antofagasta and the Bolivian immigration during the nitrate cycle. Study notes". Revista Si Somos Americanos (in Spanish). 10 (2).
  24. ^
    S2CID 216492401 – via ResearchGate
    .
  25. ISBN 978-0-19-973107-7
    .
  26. ISBN 978-956-00-0010-1
    .
  27. ^
    doi:10.1080/02757206.2020.1862106
    .
  28. ^
    PMID 12631426
    .
  29. ISBN 978-3-642-88284-5
    .
  30. ISBN 978-3-642-36833-2
    .
  31. ISBN 978-1-4684-5481-9
    .
  32. PMID 3305469
    .
  33. ^
    ISBN 978-1-139-48535-7
    .
  34. PMID 2506621
    .

Further reading

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