Peinado is a

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 ...

in Catamarca Province, Argentina. It consists of a volcanic cone with a

summit crater A volcanic crater is an approximately circular depression in the ground caused by volcanic activity. It is typically a bowl-shaped feature containing one or more vents. During volcanic eruptions, molten magma and volcanic gases rise from an unde ...

, surrounded at its foot by

lava flow Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or und ...

s erupted from flank vents. It began erupting about 100,000 years ago, with the last eruption about 36,800 years ago. Future eruptions are possible. The volcano is part of the Andean

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 ...

and located within a cluster of

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 ...

s and large volcanoes, including the Laguna Amarga caldera just west of Peinado. The climate of the region is cold and dry, but may have been moister in the recent past. North of Peinado lies the

salt lake A salt lake or saline lake is a landlocked body of water that has a concentration of salts (typically sodium chloride) and other dissolved minerals significantly higher than most lakes (often defined as at least three grams of salt per litre). ...

Laguna Peinado.

Geography and geomorphology

Peinado lies in

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 ...

Catamarca Province Catamarca () is a province of Argentina, located in the northwest of the country. The province had a population of 334,568 as per the , and covers an area of 102,602 km2. Its literacy rate is 95.5%. Neighbouring provinces are (clockwise, fr ...

, close to the border with

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 ...

and about from the Paso San Francisco. Geographically, it is in the Cordillera Occidental of the Central Andes. The region is largely uninhabited, due to the extreme climatic conditions. The volcano is a high steep cone, which reaches an elevation of above sea level and features a wide and deep

with an ephemeral crater lake. There is no perennial snow cover or

glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its Ablation#Glaciology, ablation over many years, often Century, centuries. It acquires dis ...

s on the mountain. Twelve vents - two of which are buried by lava flows - form cones on its flanks and have produced hundreds of

s, which built a lava apron surrounding the volcano that buries the lower parts of the cone. The cone is formed by lava blocks, lavas,

pyroclastic Pyroclastic rocks (derived from the el, πῦρ, links=no, meaning fire; and , meaning broken) are clastic rocks composed of rock fragments produced and ejected by explosive volcanic eruptions. The individual rock fragments are known as pyroc ...

s and scoria; the lava flows have for the most part dark and brown colours. The total volume of the edifice is about , covering an area of . Claims that the volcano overlies a caldera lack supporting evidence. Just west of Peinado lies the eastern margin of the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Laguna Amarga

; its ignimbrites underlie Peinado and lava flows from Peinado have spilled across its borders on to the caldera floor. On the eastern side, the volcano is bordered by the Sierra de Calalaste. To the north lies the

Salar de Antofalla Salar de Antofalla is a salt flat in the Andes of Catamarca Province in the Argentine Northwest. The salt flat contains systems of oncoids that grow in the interface between proper salt flat and an adjacent wetlands. The geology surrounding th ...

, which ends close to Peinado, and the Laguna Peinado lake. A field of monogenetic volcanoes, the Peinado volcanic field, lies around Peinado. They consist of lava flows,

maar A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption (an explosion which occurs when groundwater comes into contact with hot lava or magma). A maar characteristically fills with water to form a relatively shallow ...

scoria cone Scoria is a pyroclastic, highly vesicular, dark-colored volcanic rock that was ejected from a volcano as a molten blob and cooled in the air to form discrete grains or clasts.Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds. (2005) ''G ...

s and tuff rings, with volumes reaching , and were emplaced between 600,000 and 150,000 years ago.

Lake

Laguna Peinado is a wide, long lake with a mean depth of -. Water covers an area of . It lies at elevation at about . It is a

with

alkaline In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a base (chemistry), basic, ionic compound, ionic salt (chemistry), salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as ...

waters, fed mostly by

groundwater Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...

and

meltwater Meltwater is water released by the melting of snow or ice, including glacial ice, tabular icebergs and ice shelves over oceans. Meltwater is often found in the ablation zone of glaciers, where the rate of snow cover is reducing. Meltwater can be ...

. An additional water source are

hot spring A hot spring, hydrothermal spring, or geothermal spring is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma (molten rock) or by circ ...

s with temperatures reaching , which deposit

travertine Travertine ( ) is a form of terrestrial limestone deposited around mineral springs, especially hot springs. It often has a fibrous or concentric appearance and exists in white, tan, cream-colored, and even rusty varieties. It is formed by a pro ...

. Volcanic

carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

outgassing appears to occur at the lake. The lake presently has no outflow, but it may have spilled northward into the Salar de Antofalla during periods of higher lake level. Directly north of Laguna Peinado lies another lake, Laguna Turquesa, with an average depth of and a surface area of ; the lakes may have been connected before 2005. At the northern end of the basin, coastal terraces reach thicknesses of and lengths of several , they extend to Laguna Turquesa. At the southern end of the lake is a

wetland A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (anoxic) processes prevailing, especially in the soils. The ...

. Lake sediments consist of an alternation of

organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ Chemistry * Organic matter, matter that has come from a once-living organism, is capable of decay or is the product ...

muds,

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

and travertine, with

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

s occurring in coastal areas and muddy deposits in deeper waters. The carbonates form

micrite Micrite is a limestone constituent formed of calcareous particles ranging in diameter up to four μm formed by the recrystallization of lime mud. Flügel, Erik, ''Microfacies of Carbonate Rocks: Analysis, Interpretation and Application,'' Springe ...

s, packstones,

rudstone Rudstone is a type of carbonate rock. The Dunham classification (Dunham, 1962) did not consider grain size as a criterion for the description of carbonate lithologies. In an attempt to rectify this perceived deficiency, Embry & Klovan (1971) intr ...

s and

wackestone Under the Dunham classification (Dunham, 1962Dunham, R.J., 1962. Classification of carbonate rocks according to depositional texture. In: W.E. Ham (Ed.), Classification of Carbonate Rocks. American Association of Petroleum Geologists Memoir. Amer ...

s, and they contain fossil

diatom A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...

s and

ostracod Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typic ...

s. Microbes form rocky structures including mounds and

oncolite Oncolites are sedimentary structures composed of oncoids, which are layered structures formed by cyanobacterial growth. Oncolites are very similar to stromatolites, but, instead of forming columns, they form approximately spherical structures. T ...

s. There is evidence of a progressive increase in water levels, followed by a decrease, which may somehow relate to the

Little Ice Age The Little Ice Age (LIA) was a period of regional cooling, particularly pronounced in the North Atlantic region. It was not a true ice age of global extent. The term was introduced into scientific literature by François E. Matthes in 1939. Ma ...

. They may be correlative with regional changes in humidity, but difficulties in dating lake deposits prevent the determination of a definitive causal relationship. The lakes of the Altiplano have drawn attention in the 21st century owing to the frequently extreme climatic and hydrological conditions they experience. Microbialites form mounds along of the western lakeshore. Former stromatolites occur on the lowest lake terrace, they display laminated textures and were probably built by

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...

when the lake levels were low and conditions more favourable to stromatolite growth than plant development. Recent lake level declines have not prevented the deposition of microbe-produced rocks. Stromatolites are visible just underneath the water surface.

Geology

Peinado is part of the

of the Andes, which in northern Argentina extends across the Cordillera Occidental and 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 ...

. Numerous volcanoes occur in the region, including Laguna Amarga,

Sierra Nevada de Lagunas Bravas Sierra (Spanish for "mountain range" and "saw", from Latin '' serra'') may refer to the following: Places Mountains and mountain ranges * Sierra de Juárez, a mountain range in Baja California, Mexico * Sierra de las Nieves, a mountain range i ...

, Laguna Escondida, Cerro El Condor, Wheelwright caldera,

Falso Azufre Falso Azufre is a complex volcano at the border of Argentina and Chile. Falso Azufre is elongated in east–west direction and contains craters and lava domes; most craters have diameters of with the exception of the main crater, which is wi ...

Nevado Tres Cruces Nevado Tres Cruces is a massif of volcanic origin in the Andes Mountains on the border of Argentina and Chile. It has two main summits, Tres Cruces Sur at and Tres Cruces Centro at and a third minor summit, Tres Cruces Norte . Tres Cruces Sur ...

, Ojos del Salado, Incahuasi,

Cerro Torta Cerro Torta is a dacitic lava dome in Argentina. Approximately high, it covers an area of with of rocks. Cerro Torta is about 430,000 years old and is part of a recent volcanic series together with Cueros de Purulla and Cerro Blanco. A seismic ...

Cerro Blanco Cerro Blanco is a hill and historical landmark in the city of Santiago, Chile. This geographic feature rises above the surrounding terrain and covers a surface area of . It is bordered by Recoleta Avenue on the east, Santos Dumont Avenue on ...

Cueros de Purulla Cueros de Purulla is a volcano in Argentina. It consists of a lava dome and an associated ignimbrite. A large eruption dated to c. 7820 BP deposited ash into the Valles Calchaquies. Geography and geomorphology The volcano lies in Catamarca ...

and numerous other calderas with accompanying ignimbrites, and monogenetic volcanoes. Their ages range from

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 ...

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 ...

; volcanism there has been ongoing since the

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

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 ...

. Peinado presumably developed on Miocene volcanic rocks and eruption products of the Laguna Amarga caldera. A major

strike-slip fault In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

zone, the Peinado fault, runs from the western side of Salar de Antofalla south along Laguna Peinado to Peinado volcano. Farther south, it may connect to the San Francisco

lineament ''See also Line (geometry)'' A lineament is a linear feature in a landscape which is an expression of an underlying geological structure such as a fault. Typically a lineament will appear as a fault-aligned valley, a series of fault or fold-aligne ...

. Apart from volcanoes, tectonically-generated basins and ridges form a steep relief in the region; the Laguna Peinado occupies one of several north-south trending tectonic depressions in the area.

Magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...

may be present in the crust. Volcanic rocks are mainly

andesite 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 predomi ...

and

basaltic andesite Basaltic andesite is a volcanic rock that is intermediate in composition between basalt and andesite. It is composed predominantly of augite and plagioclase. Basaltic andesite can be found in volcanoes around the world, including in Central Ameri ...

, with

dacite 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. ...

being erupted more recently. They define a

potassium Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...

-rich calc-alkaline suite and contain phenocrysts of clinopyroxene,

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...

titanium Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...

oxide An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...

olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...

orthopyroxene 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) ...

and

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 ...

. As is common for

es, the more

felsic In geology, felsic is a modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz.Marshak, Stephen, 2009, ''Essentials of Geology,'' W. W. Norton & Company, 3rd ed. It is contrasted with mafic rocks, whi ...

magmas were erupted from the central cone and the more

mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...

ones from the flank vents. The monogenetic volcanoes have erupted basaltic andesite. In the summit region, the rocks have been discoloured presumably by hydrothermal alteration.

Eruption history

Peinado is one of the youngest volcanoes in the area.

Radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares t ...

has yielded ages ranging between 80,000 and 40,000 years ago for the central cone and between 60,000 and 30,000 for the flank vents. Volcanic activity initially built the central cone, before continuing on the flanks. Eruptions have been mostly

effusive In physics and chemistry, effusion is the process in which a gas escapes from a container through a hole of diameter considerably smaller than the mean free path of the molecules. Such a hole is often described as a ''pinhole'' and the escape ...

, but with recent explosive events. The monogenetic volcanoes just south and north of Peinado developed 210,000 ± 40,000 and 380,000 ± 20,000 years ago, respectively; the flank vent that formed a scoria cone may also be associated with the monogenetic activity rather than Peinado proper. Presumably, Peinado began its growth as a monogenetic volcano but eruptions became concentrated at a single vent, producing a shallow magma chamber that intercepted ascending magma and a single cone. Eventually, the cone reached a size at which further eruptions from the summit were impeded, causing volcanism to shift to the flank vents, which then built up the bulk of Peinado.

Fractional crystallization Fractional crystallization may refer to: * Fractional crystallization (chemistry), a process to separate different solutes from a solution * Fractional crystallization (geology) Fractional crystallization, or crystal fractionation, is one of the ...

and other magma-forming processes took place in the magma chamber, yielding the felsic magmas that were erupted from the central vent beginning 40,000 years ago. There are reports of

fumarolic A fumarole (or fumerole) is a vent in the surface of the Earth or other rocky planet from which hot volcanic gases and vapors are emitted, without any accompanying liquids or solids. Fumaroles are characteristic of the late stages of volcani ...

activity. Volcanoes have been observed to remain inactive for ten thousands of years; thus future activity at Peinado is possible. The configuration of volcanic vents suggests that the occurrence of caldera collapse and of sector collapses is possible, and its activity has become more explosive over time. The volcano lies on an eastward younging trend of calderas including Laguna Amarga, and there is evidence of

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...

storage in the crust.

Climate and vegetation

The regional climate is cold and dry, with a mean temperature of and large () daily temperature fluctuations. Precipitation takes place mainly during the winter months, the region is at the boundary between the South American Summer Monsoon region and 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 ...

region, where precipitation occurs when cold fronts from the Pacific Ocean and isolated drops of cold air hit the area.

Evaporation Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. High concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when humidi ...

rates are higher than precipitation. The climate has not been stable during the

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

, and may have been wetter during glacial times. What little vegetation there is, is mostly

steppe In physical geography, a steppe () is an ecoregion characterized by grassland plains without trees apart from those near rivers and lakes. Steppe biomes may include: * the montane grasslands and shrublands biome * the temperate grasslands, ...

grasses. Salt-loving vegetation and underwater plants grow around and in Laguna Peinado, which also features microbial mats.

Name and human activity

The name ("combed" in Spanish) is a reference to its smooth appearance. The first known ascent was by in 1965, but the mountain features a

pre-Hispanic In the history of the Americas, the pre-Columbian era spans from the original settlement of North and South America in the Upper Paleolithic period through European colonization, which began with Christopher Columbus's voyage of 1492. Usually, th ...

mountain sanctuary and may have been used as a source for valuable rocks by pre-Hispanic people. A prehistoric

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...

and aragonite mine with well-preserved buildings lies at Tambería El Peinado, close to the volcano.

References

Sources

* * * * * * * * * * * * * * * * * * * * * *

External links

{{Andean volcanoes Stratovolcanoes of Argentina Subduction volcanoes Mountains of Argentina Polygenetic volcanoes Pleistocene stratovolcanoes