Jotabeche is a Miocene- Pliocene

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 the Atacama Region of Chile. It is part of the volcanic Andes, more specifically of the extreme southern end 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). This sector of the Andean Volcanic Belt contains about 44 volcanic centres and numerous more minor volcanic systems, as well as some caldera and ignimbrite systems. Jotabeche is located in a now inactive segment of the CVZ, the Maricunga Belt. Jotabeche 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, like the other volcanoes in the CVZ and the Andean Volcanic Belt. In the region of Jotabeche, during the late Miocene and Pliocene a change in the subduction geometry has caused volcanism to end, with volcanism shifting eastwards to the

Incapillo Incapillo is a Pleistocene caldera, a depression formed by the collapse of a volcano, in the La Rioja province of Argentina. Part of the Argentine Andes, it is considered the southernmost volcanic centre in the Central Volcanic Zone of the Andes ...

volcanic centre. The crust beneath Jotabeche is thick, which has had effects on the rock composition of the volcano. Jotabeche has erupted two major ignimbrites between 8,500,000 and 5,900,000 years ago. The first ignimbrite was the larger one and is named Negro Francisco and the second is called Jotabeche proper. A caldera and some

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

s are also part of the complex. Volcanism ceased 5 million years ago.

Geography and structure

Jotabeche is located at the extreme southern end of the Central Volcanic Zone (CVZ) of the Andes. The Central Volcanic Zone is one of the four volcanic zones of the Andean Volcanic Belt. In this belt, ongoing subduction of the Antarctica plate,

and its precursor the Farallon plate are responsible for ongoing volcanic activity, including such volcanoes as Villarrica and Nevado del Ruiz. The Central Volcanic Zone sub-belt itself contains about 44 volcanic centres and over five major

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 ...

caldera and ignimbrite complexes. The so-called Abancay deflection separates the CVZ in the north from the Peruvian flat subduction segment where no volcanic activity occurs, while the southern limit is marked by a seismic discontinuity around 27° S. Jotabeche is a high volcano with a caldera. A

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 ...

dome formed inside of the caldera. The Jotabeche complex reaches a thickness of when including ignimbrite, lava domes and lavas. The high and wide Jotabeche Norte

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

is found northeast of Jotabeche and is surrounded by pyroclastic flows. The Santa Cecilia lava domes () have diameters of and sit along a long fault. The Miocene volcanic complex branches out in four chains stretching in east-west direction, the Cadillal, Aguas Blancas, Jotabeche Norte and Cordon de Yeguas Heladas. N-S to NE-SW trending faults border the volcanic complex and have allowed the intrusion of diorite

porphyries Porphyry ( ) is a textural term for an igneous rock consisting of coarse-grained crystals such as feldspar or quartz dispersed in a fine-grained silicate-rich, generally aphanitic matrix or groundmass. The larger crystals are called phenocr ...

. The resulting hydrothermally altered rocks are the sites of mineral deposits and prospects. These faults include the Yeguas Heladas, Rio La Gallina and Rio Astaburuaga and form a hexagonal structure which partly forms the margin of the caldera. Otherwise, only little erosion has taken place at Jotabeche; stronger erosion though has exposed a > thick hydrothermally altered complex at Aldebaran-Cerro Casale. Other hydrothermally altered areas are found within depressions. The crust beneath Jotabeche reaches a thickness of .

Geology

Jotabeche is a volcanic centre in the 26-6

mya Mya may refer to: Brands and product names * Mya (program), an intelligent personal assistant created by Motorola * Mya (TV channel), an Italian Television channel * Midwest Young Artists, a comprehensive youth music program Codes * Burmese ...

old and long Maricunga belt. Some stratovolcanoes in the belt include Copiapó-Azufre, Cerros Bravos, Doña Inés, La Laguna, Lagunillas, Ojos del Maricunga, Santa Rosa and Cadillal-Yeguas Heladas. Volcanic activity in this belt has also generated porphyry deposits containing silver, gold and copper. This belt is bordered by

graben In geology, a graben () is a depressed block of the crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German, meaning 'ditch' or 'trench'. The word was first used in the geologic contex ...

and horst tectonic structures that have generated the Salar de Maricunga and the Laguna de Negro Francisco. Jotabeche is located at the southern end of the Maricunga belt, which was active starting from 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 ...

until the Pliocene. The formation of this volcanic belt was influenced by the changes in the subduction of the Nazca plate, which included the shallowing of the subducting plate and the formation of the Puna plateau. Jotabeche, belonging to the fourth stage of Maricunga belt activity after the third stage of Copiapo, is the youngest eruption of the Maricunga belt, whose activity ended with the Jotabeche caldera forming eruption. Volcanism afterwards shifted eastwards. Jotabeche is one of the largest volcanoes in the Maricunga belt. Volcanic activity at Jotabeche is coeval with the last mineralization phase of the Vallecito system in the El Indio belt.

Local

Jotabeche is part of the so-called Cordillera de Darwin segment of the Andes. The basement in the area consists of various sedimentary-volcanic formations dating back to the Paleozoic Chinches formation but also including the Jurassic Lautaro formation and the Cretaceous Quebrada de Monardes formation. Of the volcanic formations, the Pantanoso rhyolitic formation of the Paleozoic and the thick andesitic-dacitic lava flows of the mesozoic Rio Aguas Blancas formation are the most important. During the Cretaceous, local extension formed a number of small faults in the area. The oldest of these sequences crops out east of Jotabeche at the Chilean-

Argentine Argentines (mistakenly translated Argentineans in the past; in Spanish (masculine) or (feminine)) are people identified with the country of Argentina. This connection may be residential, legal, historical or cultural. For most Argentines, s ...

frontier.

Composition

Jotabeche has generated rhyodacite rocks. The Negro Francisco ignimbrite is rhyolitic while the Jotabeche ignimbrite itself is of rhyodacitic composition. Specific concentrations are 65–70% for Negro Francisco while the caldera complex has 68–72%. The Jotabeche Norte stratovolcano has a concentration of 60% and is considered to be hornblende andesite in terms of composition. Overall, all rocks fit the potassium-rich calc alkaline pattern. Gold-rich porphyry deposits are found on Jotabeche's flanks. Diorites are also found but the only weak erosion and thick late Miocene rock cover bury them. Other mineralizations are found between Jotabeche and the Salar de Maricunga. The chemistry of Jotabeche ignimbrites is distinct from other Tertiary volcanic rocks in the Andes. The rocks of Jotabeche have lanthanum,

strontium Strontium is the chemical element with the symbol Sr and atomic number 38. An alkaline earth metal, strontium is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is ex ...

and yttrium concentrations which fit an eclogitic trend, similar to other Andean volcanoes Pircas Negras, Tortolas and Vallecito. More generally, the geochemistry is indicative of the volcanic activity being influenced both by a thick crust and other factors of crustal contamination. Other composition data are indicative of a drop in mantle water content above the shallowing slab. The crust above the Jotabeche ignimbrite source region was thick enough to permit the stability of garnet in said source region.

Glaciation

Jotabeche does not currently display any perennial snow, only during summer is snow observed in the area. Likewise,

rock glacier Rock glaciers are distinctive geomorphological landforms, consisting either of angular rock debris frozen in interstitial ice, former "true" glaciers overlain by a layer of talus, or something in-between. Rock glaciers are normally found at high ...

s are only found as fossil remnants. However,

moraine A moraine is any accumulation of unconsolidated debris (regolith and rock), sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a glacier or ice shee ...

s are found at Jotabeche, and glaciers advanced north from a

cirque A (; from the Latin word ') is an amphitheatre-like valley formed by glacial erosion. Alternative names for this landform are corrie (from Scottish Gaelic , meaning a pot or cauldron) and (; ). A cirque may also be a similarly shaped landform ...

on its northern flank into the Laguna de Negro Francisco, where a peninsula marks the position of the most extensive moraine.

Eruptive history

Jotabeche was active between 7 and 5 mya ago, spanning the late Miocene and Pliocene. The end of volcanic activity at Jotabeche occurred at the same time as the northeastern arm of the

Juan Fernandez ridge ''Juan'' is a given name, the Spanish and Manx versions of ''John''. It is very common in Spain and in other Spanish-speaking communities around the world and in the Philippines, and also (pronounced differently) in the Isle of Man. In Spanish, t ...

passed beneath the volcano. After end of activity at Jotabeche volcanism occurred farther east at Incapillo. 15.3 ± 0.8 and 17.2 ± 0.7 mya the Las Gallinas ignimbrite formed east of Jotabeche, but its origin is unknown. The Santa Cecilia domes of Jotabeche were active 24.3 ± 0.7 mya and 24.1 ± 0.8 mya based on potassium-argon dating of an eroded tuff ring. Between 18 and 16 mya the Jotabeche Norte stratovolcano was active in the region. Some rhyolitic lava domes intruded into the caldera are 10 mya old. The Negro Francisco ignimbrite was erupted 8.5 mya ago and covers a surface area of around the Laguna del Negro Francisco; it is the initial activity of Jotabeche. 5.9–6.2 mya the Jotabeche ignimbrite covered a surface area of . The Negro Francisco ignimbrite was erupted from a NW-trending fault and flowed between the Jotabeche Norte and La Laguna stratovolcanoes to the Laguna del Negro Francisco depression and across it. The so-called Pircas Negras andesitic lava flows occur at the same time as the younger Jotabeche activity. Andesitic-dacitic lava domes along the La Gallina fault are of the same age. At Copiapo and Jotabeche, the volcanic activity has been subdivided in three phases, the first being the "normal" volcanic phase, a second phase with a drop in magma supply and the formation of more differentiated magmas in crustal magma chambers such as rhyolites and at the end the eruption of andesites along fractures. Other volcanoes in the Maricunga belt display different evolutionary processes, probably because of a lesser tectonic influence.

Archeology

Research performed on Jotabeche in the 1980s demonstrated the existence of a shrine on Jotabeche. People probably climbed the mountain to use it during the southern summer months. Archeological sites in the region are not unknown: Copiapo, Incahuasi, Pastillitos and

Los Patos Los Patos (also known as Tres Quebradas) is a mountain in the Andes mountain range of South America. The peak is located on the international border of the Catamarca Province of Argentina and the Atacama Region of Chile. It has a summit elevat ...

also have archeological sites.

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External links

*Sergio Gamonal 2015
Volcanic stratigraphy and epithermal mineralization of the La Coipa district, Maricunga belt, Chile
*Alexander Brenning 2005
Climatic and geomorphological controls of rock glaciers in the Andes of Central Chile – combining statistical modelling and field mapping
Miocene calderas Calderas of Chile Pliocene calderas Volcanoes of Atacama Region