Incapillo

Coordinates: 27°53′24″S 68°49′12″W / 27.89000°S 68.82000°W / -27.89000; -68.82000
Source: Wikipedia, the free encyclopedia.

Incapillo
A dark lake in a fairly deep crater; the terrain is in part covered by snow, in part rocky, with no vegetation
View inside the caldera
Highest point
Elevation5,750 or 5,386 m (18,865 or 17,671 ft)[1]
Coordinates27°53′24″S 68°49′12″W / 27.89000°S 68.82000°W / -27.89000; -68.82000[2]
Geography
Incapillo is located in west-central Argentina, which lies on the southeastern coast of South America.
Incapillo is located in west-central Argentina, which lies on the southeastern coast of South America.
Incapillo
The South American country of Argentina
LocationCentral
mya

Incapillo is a

Central Volcanic Zone (CVZ) that erupted during the Pleistocene. Incapillo is one of several ignimbrite[a] or caldera systems that, along with 44 active stratovolcanoes
, are part of the CVZ.

Subduction of the Nazca Plate beneath the South American Plate is responsible for most of the volcanism in the CVZ. After activity in the volcanic arc of the western Maricunga Belt ceased six million years ago, volcanism commenced in the Incapillo region, forming the high volcanic edifices Monte Pissis, Cerro Bonete Chico and Sierra de Veladero. Later, a number of lava domes were emplaced between these volcanoes.

Incapillo is the source of the Incapillo ignimbrite, a medium-sized deposit comparable to the

hydrothermal
activity.

Geography and structure

Incapillo, located in Argentina's La Rioja province,[4] is the highest caldera stemming from explosive volcanism in the world. The name Incapillo means 'Crown of the Inca' in Quechua;[5] it is also known as Bonete caldera,[2] Corona del Inca[6] or Inca Pillo.[7] The surrounding mountain peaks were visited by pre-Hispanic people.[8] The crater is marketed as a tourist destination, with visits possible between December and April.[9]

Incapillo is part of the Andean

Southern Volcanic Zone at 33° southern latitude.[12]

A mountain with snow patches rises above a smaller hill, which in turn rises above a plain covered with sparse yellow plants
Cerro Bonete Chico

Incapillo is a caldera with a diameter of 5 by 6 kilometres (3.1 mi × 3.7 mi) and lies at an elevation of 5,750 metres (18,860 ft)

lava domes.[5] The caldera is about 400 metres (1,300 ft) deep[7] and its walls reach heights of 250 metres (820 ft).[14] The pumice-containing Incapillo ignimbrite forms the bulk of the caldera walls.[15]

Forty lava domes surround the caldera,

rhyodacitic domes were eroded after caldera formation;[5] these were formerly considered erosional remnants.[15] Older domes have reddish oxidised colours in satellite images.[19] The total combined volume of the domes is about 16 cubic kilometres (3.8 cu mi).[20]

A blue lake in a crater, with the terrain covered in rocks and no vegetation
Laguna Corona del Inca, with a lava dome to the right[17]

The Laguna Corona del Inca, considered to be the highest navigable lake in the world,

hydrothermal activity persists in the lake.[15] The lake is fed by meltwater;[23] its surface area declined between 1986 and 2017.[24] Other lakes occur in topographic depressions.[25]

Geology

The Nazca plate is subducting beneath the South American plate in the area of the CVZ at a speed of 7–9 centimetres (2.8–3.5 in) per year. The subduction results in volcanism along the Occidental Cordillera 240–300 kilometres (150–190 mi) east of the trench formed by the subduction.[10]

Incapillo is one of at least six different ignimbrite or caldera volcanoes that are part of the CVZ in Chile, Bolivia and Argentina. The CVZ is one of four different volcanic arcs in the Andes.[10] The Maricunga Belt, about 50 kilometres (31 mi) west of Incapillo, is where volcanism started 27 million years ago. Phases of ignimbritic and stratovolcanic activity occurred, including Copiapo volcano, until activity ceased with the last eruption of Nevado de Jotabeche 6 million years ago. South of Incapillo, the Pampean flat slab region is associated with tectonic deformation and lack of volcanic activity until Tupungatito volcano farther south.[5]

S. L. de Silva and P. Francis suggested in their 1991 book Volcanoes of the Central Andes that the CVZ should be subdivided into two systems of volcanoes: one in Peru and another in Chile, on the basis of the orientation (northwest–southeast versus north–south). Charles R. Stern notes that C.A. Wood, G. McLaughlin and P. Francis in a 1987 paper at the American Geophysical Union instead suggested a subdivision into nine different groups.[10]

Local

Incapillo is on crust that is 70-kilometre (43 mi) thick – among the thickest in volcanic regions of Earth.[5] Several studies indicate that trends in the isotope ratios of Incapillo's volcanic rocks are because of a thickening crust and increased contribution thereof to the magmas.[26] At the latitude of Incapillo, the northern Antofalla terrane borders the Cuyania terrane. The terranes have distinct origins and were attached to South America during the Ordovician[b].[28]

At the latitude of Incapillo, subduction of the Nazca Plate beneath the South American Plate abruptly shallows towards the south. This shallowing forms the limit between the volcanically active CVZ and the magmatically inactive Pampean flat slab region farther south.[29] This magmatic inactivity occurs because the flat slab removes the asthenospheric wedge.[4]

Incapillo is part of a volcanic system active between 3.5 and 2 million years ago that includes Ojos del Salado and

Cerro Galan and Cerro Blanco.[32] This trend may be related to delamination of the lower crust. Also, these centres are located between two domains of different rigidity, an Ordovician sedimentary domain of low rigidity and a higher rigidity basement.[33]

The formation of the older lava domes may have been influenced by buried faults or the supply systems of the older Pissis and Bonete Chico volcanoes.

seismic velocity anomaly beneath the principal mountain range may be linked to its waning activity.[36]

Composition

The Incapillo ignimbrite is formed by

alkali feldspar. Older domes have higher amphibole and lower quartz content than younger domes. Post-caldera domes are strongly hydrothermally altered.[38]

Rocks from Incapillo are rich in

alumina than almost all Central Andes siliceous volcanic rocks.[42]

The composition of the lava domes suggests that they were formed by degassed magma left behind by the caldera-forming eruption.[43] The pre-caldera lava domes were generated either directly from a common magma chamber or indirectly through secondary chambers.[34] The lead isotope ratios indicate that the volcano formed at the edge of an area of granite and rhyolite of Paleozoic age.[44] Incapillo magmas probably formed as adakitic high-pressure mafic magmas derived from the crust, either directly by anatexis or indirectly from dragged-down crustal fragments.[45] The magmas were then modified by crustal contamination and fractional crystallisation.[46] As the subducting slab shallowed, crustal garnet-containing lherzolite and granulite-eclogite—contributed both from the crustal basis and forearc rocks that were dragged down by the subducting slab—became an increasingly important component of erupted magmas.[47] Eventually, the Incapillo magma chamber was disconnected from the mantle and lower crust.[45]

The Incapillo ignimbrite contains xenoliths with sizes of 0.5–4 centimetres (0.2–1.6 in) formed by amphibolite. Amphibole is the dominant component.[48] Amphibole crystals are enclosed in intersitital plagioclase crystals and sometimes contain secondary biotite crystals.[49] Raw sulfur deposits occur on the volcano.[7]

Climate, hydrology and vegetation

Incapillo as a high altitude location has an alpine climate, with low temperatures and low oxygen, high winds and predominantly summer precipitation. Incapillo itself has no weather stations and thus exact climate data are not available; however, Laguna Brava farther south has an average precipitation of 300 millimetres (12 in) and an average temperature of 0–5 °C (32–41 °F).[50] The Desaguadero River (Río Desaguadero) originates on Bonete.[23]

Vegetation varies depending on water supply and altitude, reaching up to elevations of 4,300–5,000 metres (14,100–16,400 ft); below that, the vegetation takes the form of a scrub steppe. Grasses at 5,000 metres (16,000 ft) include Festuca, Stipa and in wetter areas also genera like Calamagrostis. Scrub like Adesmia and Nototriche copon occasionally form dense patches.[23]

Geologic history

Activity at Incapillo commenced shortly after the end of the Maricunga Belt volcanism and occurred first at Monte Pissis between 6.5 and 3.5 million years ago (mya). Further volcanism occurred south of Incapillo 4.7±0.5 mya, at Sierra de Veladero 5.6±1 – 3.6±0.5 mya, and in the region of Cerro Bonete Chico 5.2±0.6 – 3.5±0.1 mya.

rhyolitic volcanism formed ignimbrites and lava domes 2.9±0.4 – 1.1±0.4 mya,[4] with the youngest pre-caldera dome being 0.873±0.077 mya old.[52] The lava domes formed through non-explosive extrusion.[34]

The Incapillo ignimbrite is unwelded

dense rock equivalent volume is about 14 cubic kilometres (3.4 cu mi).[48] The volume of the Incapillo ignimbrite is comparable to that of the Katmai ignimbrite.[34] The Incapillo ignimbrite was probably formed from a low-height fountaining eruption without a high eruption column,[54] forming a base surge first and pyroclastic flows later.[34] The change from lava dome to ignimbrite-forming eruptions may have been triggered by the injection of hotter magmas into the magma chamber. A less likely theory is that the shift was caused by changes in the tectonic context. During the eruption, a piston-like collapse formed the caldera.[20]

Later, a debris flow named Veladero (also known as Quebrada de Veladero Ignimbrite) occurred in a glacier valley south of the caldera. It is rich in lithics and pumice.[53] These lithics are derived from Sierra de Veladero, Cerro Bonete Chico, and Pircas Negras lavas. The debris flow ranges from 15 to 25 metres (49 to 82 ft) in thickness 5 kilometres (3.1 mi) south of the caldera to 10 to 15 metres (33 to 49 ft) farther south, the total volume being 0.7–0.5 cubic kilometres (0.17–0.12 cu mi). The debris flow does have a different composition from the main Incapillo ignimbrite as it contains red-brown dacite and clasts. It has a massive ungraded composition and is likely a lahar or debris flow deposit, probably influenced by glacial or crater lake water. Wind-driven effects have generated hummocky ridges.[17]

There are no dates available for post-caldera lava domes, which probably arose from magma ascending through the caldera-forming conduits, as these domes are found only inside the caldera. The elevated temperatures of the caldera lake suggest that hydrothermal activity still occurs beneath Incapillo.[20] Seismic tomography has identified the presence of an at least partially molten structure beneath the volcano.[55]

Notes

  1. ^ Ignimbrites are volcanic rocks formed when hot gas and rocks emitted during an eruption consolidate to form a rock.[3]
  2. ^ Between 485.4±1.9 and 443.8±1.5 million years ago.[27]

References

  1. ^ a b c "Incapillo". Global Volcanism Program. Smithsonian Institution. Retrieved 27 July 2023.
  2. ^ a b Guzmán et al. 2014, p.176
  3. ^ Chen et al. 2020, Ignimbrite
  4. ^ a b c d Kay and Mpodozis 2000, p.626
  5. ^ a b c d e Goss et al. 2009, p.392
  6. ^ Guzmán, Silvina; Grosse, Pablo; Martí, Joan; Petrinovic, Iván A.; Seggiaro, Raúl E. (2017). Calderas cenozoicas argentinas de la zona volcánica central de los Andes – procesos eruptivos y dinámica: una revisión [Argentine Cenozoic calderas of the Central Volcanic Zone of the Andes – eruptive processes and dynamics: a review] (Report) (in Spanish). p. 530. Archived from the original on 16 January 2021. Retrieved 13 January 2021.
  7. ^
    ISSN 0328-2333. Archived
    from the original on 15 January 2021. Retrieved 13 January 2021.
  8. ISSN 0717-7356. Archived
    from the original on 15 April 2023. Retrieved 15 April 2023.
  9. ^ "Crater Corona del Inca" [Corona del Inca Crater]. Turismo Villa Unión del Talampaya (in Spanish). 8 April 2015. Archived from the original on 24 October 2022. Retrieved 24 October 2022.
  10. ^
    doi:10.4067/S0716-02082004000200001
    .
  11. ^ Goss et al. 2009, p.389
  12. ^ Kay and Mpodozis 2013, p.304
  13. Bibcode:2003AGUFM.S41D0123G
    .
  14. ^ a b Guzmán et al. 2014, p.186
  15. ^ a b c d e f Goss et al. 2009, p.393
  16. ^ Kay and Mpodozis 2013, p.310
  17. ^ a b c Goss et al. 2009, p.395
  18. ^ Goss et al. 2009, p.396
  19. ^ Goss et al. 2009, p.397
  20. ^ a b c Goss et al. 2009, p.402
  21. ISSN 1852-0006. Archived
    from the original on 4 September 2023. Retrieved 13 January 2021.
  22. ^ Casagranda et al. 2018, p.1740
  23. ^ a b c d Morello et al. 2012, p.34
  24. ^ Casagranda et al. 2018, p.1744
  25. ^ Abels and Prinz 1995, p.192
  26. ^ Kay and Mpodozis 2013, p.323
  27. ^ "International Chronostratigraphic Chart" (PDF). International Commission on Stratigraphy. August 2018. Archived from the original (PDF) on 31 July 2018. Retrieved 22 October 2018.
  28. ^ Kay and Mpodozis 2013, p.322
  29. ^ Mulcahy et al. 2014, p.1636
  30. ^ Kay and Mpodozis 2013, pp.307, 310
  31. ^ a b Kay and Mpodozis 2013, p.329
  32. ^ Guzmán et al. 2014, pp.177–178
  33. ^ Guzmán et al. 2014, p.183
  34. ^ a b c d e f Goss et al. 2009, p.400
  35. ^ Mulcahy et al. 2014, p.1644
  36. S2CID 244635436
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  37. ^ a b Goss et al. 2009, p.394
  38. ^ Goss et al. 2009, pp.396–397
  39. ^ Kay and Mpodozis 2013, pp.314–320
  40. ^ Kay and Mpodozis 2000, pp.626–627
  41. ^ Goss, Kay and Mpodozis 2010, p.124
  42. ^ Goss, Kay and Mpodozis 2010, p.111
  43. S2CID 37724809. Archived
    from the original on 29 April 2019. Retrieved 1 December 2019.
  44. ^ Kay and Mpodozis 2013, p.320
  45. ^ a b Goss, Kay and Mpodozis 2010, p.123
  46. ^ Goss, Kay and Mpodozis 2010, p.125
  47. ^ Kay and Mpodozis 2000, pp.628–629
  48. ^ a b Goss, Kay and Mpodozis 2010, p.104
  49. ^ Goss, Kay and Mpodozis 2010, p.120
  50. ^ Morello et al. 2012, p.33
  51. doi:10.1016/j.epsl.2008.12.035
    .
  52. ^ Goss et al. 2009, p.399
  53. ^ a b Guzmán et al. 2014, p.187
  54. ^ Goss et al. 2009, p.401
  55. PMID 28831089
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Sources

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