Peinado

Peinado is a stratovolcano in Catamarca Province, Argentina. It consists of a volcanic cone with a summit crater, surrounded at its foot by lava flows 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 and located within a cluster of calderas 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 Laguna Peinado.

Geography and geomorphology

Peinado lies in the Antofagasta de la Sierra DepartmentTemplate:Sfn of Argentina's Catamarca Province,Template:Sfn close to the border with Chile and about from the Paso San Francisco. Geographically, it is in the Cordillera Occidental of the Central Andes.Template:Sfn The region is largely uninhabited, due to the extreme climatic conditions.Template:Sfn

The volcano is a c. high steep cone, which reaches an elevation of above sea levelTemplate:Sfn and features a wide and deep summit crater with an ephemeral crater lake.Template:Sfn There is no perennial snow cover or glaciers on the mountain.Template:Sfn Twelve vents - two of which are buried by lava flows - form cones on its flanks and have produced hundreds of lava flows, which built a lava apron surrounding the volcano that buries the lower parts of the cone.Template:Sfn The cone is formed by lava blocks, lavas, pyroclastics and scoria; the lava flows have for the most part dark and brown colours.Template:Sfn The total volume of the edifice is about , covering an area of .Template:Sfn Claims that the volcano overlies a caldera lack supporting evidence.Template:Sfn

Just west of Peinado lies the eastern margin of the Pliocene Laguna Amarga caldera;Template:Sfn its ignimbrites underlie PeinadoTemplate:Sfn and lava flows from Peinado have spilled across its borders on to the caldera floor.Template:Sfn On the eastern side, the volcano is bordered by the Sierra de Calalaste.Template:Sfn To the north lies the Salar de Antofalla, which ends close to Peinado,Template:Sfn and the Laguna Peinado lake.Template:Sfn A field of monogenetic volcanoes, the Peinado volcanic field, lies around Peinado.Template:Sfn They consist of lava flows, maars, scoria cones and tuff rings, with volumes reaching , and were emplaced between 600,000 and 150,000 years ago.Template:Sfn

Lake

Laguna Peinado is a wide, long lake with a mean depth of Template:Sfn-. Water covers an area of .Template:Sfn It lies at elevation at about . It is a salt lake with alkaline waters,Template:Sfn fed mostly by groundwater and meltwater. An additional water source are hot springsTemplate:Sfn with temperatures reaching ,Template:Sfn which deposit travertine.Template:Sfn Volcanic carbon dioxide outgassing appears to occur at the lake.Template:Sfn The lake presently has no outflow, but it may have spilled northward into the Salar de Antofalla during periods of higher lake level.Template:Sfn Directly north of Laguna Peinado lies another lake, Laguna Turquesa, with an average depth of and a surface area of ;Template:Sfn the lakes may have been connected before 2005.Template:Sfn At the northern end of the basin, coastal terraces reach thicknesses of and lengths of several ,Template:Sfn they extend to Laguna Turquesa.Template:Sfn At the southern end of the lake is a wetland.Template:Sfn

Lake sediments consist of an alternation of organic muds, calcite and travertine,Template:Sfn with limestones occurring in coastal areas and muddy deposits in deeper waters.Template:Sfn The carbonates form micrites, packstones, rudstones and wackestones, and they contain fossil diatoms and ostracods.Template:Sfn Microbes form rocky structures including mounds and oncolites.Template:Sfn

There is evidence of a progressive increase in water levels, followed by a decrease,Template:Sfn which may somehow relate to the Little Ice Age.Template:Sfn They may be correlative with regional changes in humidity, but difficulties in dating lake deposits prevent the determination of a definitive causal relationship.Template:Sfn Three levels of microbialites are distinguished around Laguna Turquesa: M1, M2 and M3. Of these, M3 is the lowest and the currently forming microbialite stage. M1 and M2 are older and form palaeoshorelines,Template:Sfn but even higher water stands occurred in the past.Template:Sfn

The lakes of the Altiplano have drawn attention in the 21st century owing to the frequently extreme climatic and hydrological conditions they experience.Template:Sfn Microbialites, rock structures produced by microorganisms through mineralization and sediment trapping,Template:Sfn form mounds along of the western lakeshore.Template:Sfn Former stromatolites occur on the lowest lake terrace,Template:Sfn they display laminated textures and were probably built by cyanobacteriaTemplate:Sfn when the lake levels were low and conditions more favourable to stromatolite growth than plant development.Template:Sfn Recent lake level declines have not prevented the deposition of microbe-produced rocks.Template:Sfn Stromatolites are visible just underneath the water surface.Template:Sfn

Geology

Peinado is part of the Central Volcanic Zone of the Andes,Template:Sfn which in northern Argentina extends across the Cordillera Occidental and the Altiplano.Template:Sfn Numerous volcanoes occur in the region, including Laguna Amarga, Sierra Nevada de Lagunas Bravas, Laguna Escondida, Cerro El Condor, Wheelwright caldera, Falso Azufre, Nevado Tres Cruces, Ojos del Salado, Incahuasi, Cerro Torta, Cerro Blanco, Cueros de Purulla and numerous other calderas with accompanying ignimbrites, and monogenetic volcanoes. Their ages range from Miocene to Quaternary;Template:Sfn volcanism there has been ongoing since the Eocene-Oligocene. Peinado presumably developed on Miocene volcanic rocks and eruption products of the Laguna Amarga caldera.Template:Sfn A major strike-slip fault zone, the Peinado fault, runs from the western side of Salar de Antofalla south along Laguna Peinado to Peinado volcano.Template:Sfn Farther south, it may connect to the San Francisco lineament.Template:Sfn Apart from volcanoes, tectonically-generated basins and ridges form a steep relief in the region;Template:Sfn the Laguna Peinado occupies one of several north-south trending tectonic depressions in the area.Template:Sfn Magma may be present in the crust.Template:Sfn

Volcanic rocks are mainly andesite and basaltic andesite, with dacite being erupted more recently.Template:Sfn They define a potassium-rich calc-alkaline suiteTemplate:Sfn and contain phenocrysts of clinopyroxene, iron-titanium oxides, olivine, orthopyroxene and plagioclase.Template:Sfn As is common for stratovolcanoes, the more felsic magmas were erupted from the central cone and the more mafic ones from the flank vents.Template:Sfn The monogenetic volcanoes have erupted basaltic andesite.Template:Sfn In the summit region, the rocks have been discoloured presumably by hydrothermal alteration.Template:Sfn

Eruption history

Peinado is one of the youngest volcanoes in the area.Template:Sfn Radiometric dating 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.Template:Sfn Volcanic activity initially built the central cone, before continuing on the flanks. Eruptions have been mostly effusive, 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;Template:Sfn the flank vent that formed a scoria cone may also be associated with the monogenetic activity rather than Peinado proper.Template:Sfn

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.Template:Sfn 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 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.Template:Sfn

There are reports of fumarolic activity.Template:Sfn 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,Template:Sfn 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 storage in the crust.Template:Sfn

Climate and vegetation

The regional climate is cold and dry, with a mean temperature of and large () daily temperature fluctuations.Template:Sfn Precipitation takes place mainly during the winter months,Template:Sfn the region is at the boundary between the South American Summer Monsoon region and the westerlies region,Template:Sfn where precipitation occurs when cold fronts from the Pacific Ocean and isolated drops of cold air hit the area.Template:Sfn Evaporation rates are higher than precipitation.Template:Sfn Water temperatures in Peinado and Turquesa are about .Template:Sfn The climate has not been stable during the Pleistocene,Template:Sfn and may have been wetter during glacial times.Template:Sfn The M1 microbialites are dated to 11,830 ± 170 years ago Template:Sfn while M2 may reflect a continuation of their growth after a break caused by the Younger Dryas cooling.Template:Sfn

What little vegetation there is, is mostly steppe grasses.Template:Sfn Salt-loving vegetation and underwater plants grow around and in Laguna Peinado,Template:Sfn which also features microbial mats.Template:Sfn The extreme environmental conditions of Puna lakes (abundance of arsenic, aridity, intense UV radiation, lack of nutrients, lack of oxygen, low temperatures with high daily variation, salinity, volcanism) have drawn scientific attention.Template:SfnTemplate:Sfn

Name and human activity

The name ("combed" in Spanish) is a reference to its smooth appearance.Template:Sfn The first known ascent was by Template:Interlanguage link in 1965,Template:Sfn but the mountain features a pre-Hispanic mountain sanctuaryTemplate:SfnTemplate:Sfn and may have been used as a source for valuable rocksTemplate:Sfn by pre-Hispanic people.Template:Sfn A prehistoric copper and aragonite mine with well-preserved buildings lies at Tambería El Peinado, close to the volcano.Template:Sfn

See also

• List of volcanoes in Argentina

References

Sources

• Template:Cite GVP