Cerro Tuzgle

Cerro Tuzgle is a dormant stratovolcano in the Susques Department of Jujuy Province in Argentina. Tuzgle is a prominent volcano of the back-arc of the Andes and lies about east of the main volcanic arc. Part of the Central Volcanic Zone of the Andes, it is high above sea level and was constructed during different stages over a caldera and lava domes. Some major lava flows emanate from the summit crater, and one confirmed and one possible flank collapse unit as well as an ignimbrite sheet are associated with this volcano.
The first volcanic activity of Tuzgle occurred 650,000 years ago and formed the Tuzgle Ignimbrite. Subsequently, lava domes were erupted and three lava flow units were named San Antonio, Azufre, and Tuzgle. The latest lava flows are dated at 300,000 years ago and volcanic activity may have continued into the Holocene. Several thermal springs are associated with the volcano, and some have been investigated for possible geothermal energy production. Sulfur was formerly mined on the mountain.
Geography and geomorphology.
Cerro Tuzgle is located near the eastern border of the Argentina Puna. Politically, it is part of the Susques Department of the Jujuy Province. San Antonio de Los Cobres lies from Cerro Tuzgle and Susques , while the cities of Salta and San Salvador de Jujuy are and away, respectively. A locality called "Sey" is reported northwest from Cerro Tuzgle. The volcano is visible from Provincial Route 74. Its name, which is also rendered as , or , comes from the Kunza language. It means "knoll" and refers to the shape of the volcano.
Cerro Tuzgle is a simple volcanic cone and the largest in the backarc region of the Andes. It is a well preserved stratovolcano that rises from a surrounding terrain at elevation to a summit at elevation. A platform lies at the summit of the volcano. The mountain is occasionally snow-covered and frost weathering has produced patterned ground and blockfields. In 1926 it was reported that a crater lake lies on the summit.
Three east-west trending fissure vents in the summit area are the source of dark lava flows that flowed southward and southwestward, and are flanked by high scoria ridges. The lava flows that make up the volcanic cone are blocky, rich in crystals and have variable appearance. Numerous young-looking lava flows descend the slopes of Cerro Tuzgle. A well-preserved lava flow descends the mountain and is visible on its southern flank. Older flows reached distances of from the volcano. A long scarp runs across the northwestern flank of Cerro Tuzgle and separates two units of lava flows; it probably formed through a localized collapse of the volcanic edifice in this sector. A depression in the southern flank of the volcano may also be evidence of a collapse in that direction. A parasitic vent is located on the western foot of the volcano.
Abandoned sulfur mines occur on Cerro Tuzgle and are visible from its south-southwestern flank; these include Mina Betty on the northwestern flank between elevation where in 1939 seven sulfur outcrops were reported. A road transitable by trucks was constructed at that time to reach the summit area. 
The volcano rises in a north-tilted, north-south trending tectonic depression, which is delimited by normal faults and two horsts north and south of Cerro Tuzgle. The region is endorheic and drainages ultimately end in salt pans. The Quebrada Aguas Calientes passes west and Quebrada de Charcos east of the volcano; the latter later becomes Quebrada Los Charcos north of the volcano and converges with Quebrada Aguas Calientes. Drainage around the volcano is focused by surrounding ridges into a watershed that drains northward, which contains permanent rivers feed by springs at the bottom of valleys. Carbonate deposits and thermophilic algae have been reported from the Quebrada Aguas Calientes. Peatland-lake complexes occur southeast of Cerro Tuzgle. 
Geology.
Along the west coast of South America, the Nazca Plate subducts in east-northeast direction beneath the South American Plate in the Peru-Chile Trench, at a rate of . The subduction process is responsible for the volcanic activity in the Andes, which occurs in four volcanic belts, from north to south these are the Northern Volcanic Zone, the Central Volcanic Zone, the Southern Volcanic Zone and the Austral Volcanic Zone.
The Central Andes are subdivided in three sectors, the Western Cordillera with the active volcanic arc, the wide Altiplano-Puna high plateau and the Eastern Cordillera-Subandean Ranges. The high plateau began to form in the Eocene-Oligocene due to tectonic shortening of the Andes. Volcanic activity is distributed between the Western Cordillera and the Altiplano-Puna high plateau, where strike-slip faults and thrust faults organize magma ascent.
The tectonic regime in the area has changed over time and now the volcano lies just north of a transitional zone which separates steep subduction farther north from shallow subduction farther south. During the Miocene and Pliocene, the lower crust failed, allowing the uplift of the region and the injection of fresh magma that triggered extensive volcanic activity. During that time, the Subandean Ranges and the Eastern Cordillera formed. Later, during the Pliocene, subduction became steeper and volcanism shifted westward, and the composition of the remnant volcanism changed along with a change in the tectonic regime from uplift and east-west directed compression to north-south directed spreading and east-west directed compression. Volcanic activity also changed; between 17.5 and 5.3 million years ago it took place over the entire area whereas after 1.5 million years it has focused on the central-eastern Puna plateau. Between these two phases, sedimentation occurred and formed the Pastos Chicos Formation.
Local.
Cerro Tuzgle is part of the back-arc of the Andean Central Volcanic Zone, being about east of the main volcanic arc, and its largest Quaternary member. Other volcanic cones in the area are San Geronimo and Negro de Chorrillos, which erupted 780,000±100,000 and 200,000±150,000 years ago, respectively, Tocomar, which erupted 1.5–0.5 million years ago, and Aguas Calientes caldera. All these volcanoes are located south of Cerro Tuzgle.
Extensive volcanic rocks of Miocene to Pliocene age occur in the area, which were erupted by volcanoes such as Aguas Calientes caldera and Cerro Queva. Older rocks belong to the Faja Eruptiva geologic formation of Ordovician age. The total thickness of the crust reaches . The basement is formed by Cambrian and Precambrian formations of metamorphic character, such as the Puncoviscana Formation. A large tectonic lineament, the Calama-Olacapato-El Toro lineament, intersects the Andes at Cerro Tuzgle. It reaches from the forearc in Chile across the mountain range into the foreland of Argentina, and it separates the northern from the southern Puna. The distribution and history of volcanic activity differs between these two regions. Other similar faults cut across the Andes. It is a strike-slip fault that consists of several separate faults, some of which show evidence of Quaternary activity and could produce earthquakes. Within the Andes proper, this activity mainly occurs in the form of normal faulting; only south of Cerro Tuzgle is there a segment with strike-slip faulting. Movement along most of these faults appears to clamp the magma chamber and magma conduits at Cerro Tuzgle, thus impeding volcanic activity there.
Gravimetric and magnetotelluric surveys have identified a partially molten magma chamber between depth, which also contains saline fluids. Seismic tomography has identified zones with anomalously low seismic velocity which descend from Cerro Tuzgle to depth in the downgoing slab.
Composition.
Cerro Tuzgle has mainly erupted andesite and dacite, which define a crystal- and potassium-rich calc-alkaline suite with seriate flux and porphyritic textures. The rocks contain large feldspar and quartz phenocrysts and small phenocrysts of amphibole, clinopyroxene, olivine, orthopyroxene and plagioclase. Xenoliths and xenocrysts are also found and biotite, sanidine and zircon have been reported as well. At Aguas Calientes, sinters consisting of boronatro-calcite, chalcedony and opal occur. A cesium-rich pharmacosiderite-like mineral has been found at a hot spring. Different rock units have different phenocryst components and trace element compositions. The rocks of Cerro Tuzgle are the most diverse volcanic rocks in the back-arc of the Central Andes.
Magma mixing processes involving fractionating mafic magmas and crystallization have been invoked to explain the origin of Cerro Tuzgle's magmas. The parent magmas originated in the mantle and the crust, with the crustal parts joining the mantle-derived magmas in the deep crust. These crustal components originally came from the upper crust and reached the lower crust during tectonic processes. At this stage crystal fractionation also takes place. The ascending magmas then accumulate in the crust and either erupt or are assimilated by ascending mafic magmas.
Climate and vegetation.
The climate is cold, owing to its high elevation, and the diurnal temperature range reaches . Winds blow mainly from the west and reach . During winter, insolation is high, cloud cover and precipitation are low and strong winds blow through the area. According to 1939 reports, thunderstorms and snowfall are common at Cerro Tuzgle. 
The region is arid, with less than annual precipitation as it is part of the Andean Arid Diagonal where the Eastern Cordillera prevents moisture-bearing winds from reaching the Puna. The little precipitation that falls originates in the Atlantic Ocean and the Amazon and arrives during the summer monsoon; additionally cold fronts coming from the westerlies over the Pacific Ocean occur. The amount of precipitation is influenced by the El Niño-Southern Oscillation, where El Niño is associated with drought and La Niña with wetter weather.
Vegetation is sparse and consists of tola, "Vachellia caven" and yareta. Animals that live in the area include chinchillas, condors, Coots, Darwin's rheas, ducks, eagles, "Galea" species, guanacos, llamas, suris and vicuñas. Peatlands are dominated by the plant "Oxychloe andina", "Distichia muscoides" and "Zameioscirpus muticus", with other cyperaceae being subordinate. Annual precipitation there amounts to , almost all of which falls during October to March. Peatlands close to Cerro Tuzgle have been used to reconstruct the local climate during the Holocene. Reconstructed past precipitation levels show alternations between wetter and drier periods during the last 1,800 years, with the last 130 years being relatively dry.
Eruption history.
Cerro Tuzgle was active during the Pleistocene and its most recent eruption may have followed a period of inactivity. With the exception of one flow, most are partially degraded and buried by aeolian material. Volcanic activity took place in multiple stages:
Two schemes for classifying the subsequent activity have been proposed, the first:
A substantially different reconstruction was provided by Norini "et al." 2014:
The "Old Complex" has a volume of , the subsequent units only reach . There is a trend from voluminous ignimbrites and dacites, formed through melting of the crust at high temperatures, early in the volcano's history to less voluminous mafic magmas, which erupted through brittle faults.
The volcano is presently inactive. The Argentina geological service SEGEMAR considers Cerro Tuzgle among the more dangerous volcanoes in Argentina. While the region is thinly inhabited, the occurrence of a sector collapse at Cerro Tuzgle implies that mining and geothermal energy exploitation efforts in the area could be imperiled by similar future events.
Geothermal activity.
Springs occur at Agua Caliente de Tuzgle northwest from the summit and at Mina Betty () south-southeast from Cerro Tuzgle. Both emit alkaline waters containing chloride at temperatures of and , respectively. Agua Caliente de Tuzgle also emits gases and has produced sinter deposits. The Antuco hot springs southwest from Cerro Tuzgle may receive their heat from Cerro Tuzgle. These springs and other springs in the Tuzgle area are recharged by precipitation on surrounding ridges; large-scale fracture systems in the ground control its flow and water emerges in proximity to deeply incised valleys which provide the path for water to reach the surface. Temperatures at depth exceed .
Tourism, mining and geothermal potential.
These hot springs and others such as Pompeya and Tocomar might be used for tourism, as they are located close to the main roads of the area. The volcano might also be a suitable target for mountaineering; its ascent poses little difficulty to trained mountaineers. The first reported ascent was done by Von Rosen in 1990, but the occurrence of Inca ceremonial sites in the form of a raised platform and structures formed by piled-up rocks on the summit region was reported by Ceruti 1999. Neighbouring volcanoes as well as the Nevado del Chañi ridge are visible from the summit.
The first findings of sulfur occurred in 1924, but they were not immediately exploited. A mining concession for Mina Betty was reportedly issued by 1933, while approval for two other mines in the summit area was still pending in 1939. The machinery required for sulfur processing was installed south-southeast of the volcano and bore the name "Ojo del Tuzgle"; the sulfur was transported there either by mules or by trucks. A spring there was used as a water source for mining activities. During parts of the year bad weather conditions rendered mining impossible.
In the 1970s and 1980s numerous companies prospected the area for geothermal power generation. They established the presence of two superposed heat reservoirs, one at depth in an older ignimbrite and another at depth in Ordovician-age rocks. A major power line between Argentina and Chile runs across the area, and local mines along with the towns of Olacapato and San Antonio de Los Cobres could provide a market for geothermal power. A potential yield of 28–34 megawatt electrical power has been estimated, but no progress towards exploiting these resources has been made. The geothermal vents could also be used to extract minerals or for spas. Concerns have been raised that the sensitive ecosystems might be threatened by human activity.