Payún Matrú is a

shield volcano A shield volcano is a type of volcano named for its low profile, resembling a warrior's shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more v ...

in the

Reserva Provincial La Payunia The Reserva Provincial La Payunia ( es, La Payunia Provincial Reserve) also known as Payún or Payén is a natural reserve located in the Malargüe Department in the southern part of Mendoza Province, Argentina, about 160 km away from Malarg ...

of the

Malargüe Department Malargüe is a Departments of Argentina, department located in the south west of Mendoza Province in Argentina. Its borders are San Rafael Department, San Rafael in the north, La Pampa Province in the east, Neuquén Province in the south and Chil ...

, south of the Mendoza Province in Argentina. It lies in the

back-arc A back-arc basin is a type of geologic basin, found at some convergent plate boundaries. Presently all back-arc basins are submarine features associated with island arcs and subduction zones, with many found in the western Pacific Ocean. Most of ...

region of the Andean Volcanic Belt, and was formed by 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 American Plate The South American Plate is a major tectonic plate which includes the continent of South America as well as a sizable region of the Atlantic Ocean seabed extending eastward to the African Plate, with which it forms the southern part of the Mid-A ...

. Payún Matrú, along with the Llancanelo, Nevado and Salado Basin volcanic fields, form the Payenia province. It has been proposed as a

World Heritage Site A World Heritage Site is a landmark or area with legal protection by an international convention administered by the United Nations Educational, Scientific and Cultural Organization (UNESCO). World Heritage Sites are designated by UNESCO for h ...

since 2011. Payún Matrú developed on sediment and volcanic rocks ageing from the Mesoproterozoic to the

Tertiary Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...

periods. It consists of a large shield volcano capped by a

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 ...

, formed during a major eruption between 168,000 and 82,000 years ago, a high compound volcano (known as Payun or Payun Liso), and two groups of

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

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. 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 ...

Pampas Onduladas lava flow reaches a length of and is the world's longest

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 ...

lava flow. Volcanic activity at Payún Matrú commenced during the

Plio-Pleistocene The Plio-Pleistocene is an informally described geological pseudo-period, which begins about 5 million years ago (Mya) and, drawing forward, combines the time ranges of the formally defined Pliocene and Pleistocene epochs—marking from about 5&nbs ...

period, and generated lava fields such as Pampas Onduladas, the Payún Matrú shield volcano and the Payun volcano. After the formation of the caldera, volcanism continued both within the caldera as

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 and flows, and outside of it with the formation of scoria cones and lava flows east and especially west of Payún Matrú. Volcanic activity continued into the

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...

until about 515 years ago; oral tradition of local inhabitants contains references to earlier eruptions.

Name

In local dialect, the term ''Payún'' or ''Paium'' means "bearded", while the term ''Matru'' translates as "

goat The goat or domestic goat (''Capra hircus'') is a domesticated species of goat-antelope typically kept as livestock. It was domesticated from the wild goat (''C. aegagrus'') of Southwest Asia and Eastern Europe. The goat is a member of the a ...

". The field is sometimes also known as Payenia.

Geography and geomorphology

Regional

Payún Matrú lies in the

of the Mendoza Province, in Argentina. The area is inhospitable due to the lack of usable water and high elevation. Nevertheless, there are many paved roads such as National Route 40 which passes west of the field, and National Route 186 which runs around its northern and eastern parts. The volcano is within the

. Owing to the variety of volcanic landforms, the province was included in the 2010 Tentative List of

UNESCO The United Nations Educational, Scientific and Cultural Organization is a specialized agency of the United Nations (UN) aimed at promoting world peace and security through international cooperation in education, arts, sciences and culture. It ...

s and a number of potential

geosite Geoheritage is the geological aspect of natural and cultural heritage. A geosite is a particular geoheritage asset. The word is a blend of ''geological'' and ''heritage''. It is thus a heritage category comparable to other forms of natural her ...

s have been identified at Payún Matrú itself. The active field is part of the backarc area of the

Southern 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 American ...

, a long

volcanic arc A volcanic arc (also known as a magmatic arc) is a belt of volcanoes formed above a subducting oceanic tectonic plate, with the belt arranged in an arc shape as seen from above. Volcanic arcs typically parallel an oceanic trench, with the arc lo ...

and one of four eruptive belts in the Andes; the other three being the

Northern 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 Ame ...

, 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 ...

and the

Austral Volcanic Zone The Andean Volcanic Belt is a major volcanic belt along the Andes, 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 Am ...

. Other volcanoes in the region include the Laguna del Maule, almost due west from Payún Matrú.

Local

Payún Matrú is a

whose foot coincides with the elevation contour and which extends mainly east–west; rising about above the surrounding terrain it covers about of land with lava and has diverse

landform A landform is a natural or anthropogenic land feature on the solid surface of the Earth or other planetary body. Landforms together make up a given terrain, and their arrangement in the landscape is known as topography. Landforms include hills, ...

s. Ignimbrites cover and flatten its northern and eastern slopes, while in the west and south

s and coulées predominate; these have often rough surfaces and are difficult to traverse. The lower slopes are more gentle and covered by

lava flows.

Wind erosion Aeolian processes, also spelled eolian, pertain to wind activity in the study of geology and weather and specifically to the wind's ability to shape the surface of the Earth (or other planets). Winds may erode, transport, and deposit materials ...

has created flutes, grooves and

yardang A yardang is a streamlined protuberance carved from bedrock or any consolidated or semiconsolidated material by the dual action of wind abrasion by dust and sand and deflation (the removal of loose material by wind turbulence.) Yardangs become e ...

s within the ignimbrites, such as in the western sector where yardangs reach heights of and widths of . The total volume of this shield is about . A and

lies in the summit region of the shield and covers a surface area of about . It is surrounded by several peaks, which clockwise from north include the Nariz/Punta del Payún, the Punta Media, the Punta Sur and the approximately Cerro Matru or Payen. In the field however Cerro Matru appears smaller than Nariz. The caldera was once wide but erosion of its flanks and later activity have reduced its size and buried the rim below coulées, lava domes, lava flows and pumice cones that were emplaced after the caldera collapse. The exception are the northern and southern walls which are almost vertical; remnants of old andesitic and trachyandesitic volcanism crop out there. The caldera also contains a permanent lake known as "" that is fed by

snowmelt In hydrology, snowmelt is surface runoff produced from melting snow. It can also be used to describe the period or season during which such runoff is produced. Water produced by snowmelt is an important part of the annual water cycle in many part ...

and by occasional rainfall. Matrú's highest active point field is the high, conical, eroded Payun

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 ...

. It is also known as Payun Liso, Payún and Payún Liso. This volcano rises from the southern side of Payún Matrú, away from the caldera. It has 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 ...

open to the north and it has a volume of about . File:Payún Matrú.JPG, alt=A volcanic cinder cone, with a conical mountain rising in the background, The Payun volcano File:Payun Matru Volcano in Mendoza Province Argentina.jpg, alt=A conical mountain rising above yellow vegetation, The Payun volcano File:Payunmatru.jpg, alt=Black tongue-like lava flows spreading radially, Payún Matrú seen from space

Payún Matrú volcanic field

Aside from the caldera, the field contains about 300 individual volcanic vents with diverse morphologies distributed in a western Los Volcanes group that reaches to the

Rio Grande River The Rio Grande ( and ), known in Mexico as the Río Bravo del Norte or simply the Río Bravo, is one of the principal rivers (along with the Colorado River) in the southwestern United States and in northern Mexico. The length of the Rio G ...

and the eastern Guadaloso and El Rengo groups. These fields are also known as West Payún Matrú or West Payén and East Payún Matrú or East Payén, respectively. Two further ruptures, known as "Chapua" and "Puente", have been identified east of Payún Matrú. All these groups include

fissure vent A fissure vent, also known as a volcanic fissure, eruption fissure or simply a fissure, is a linear volcanic vent through which lava erupts, usually without any explosive eruption, explosive activity. The vent is often a few metres wide an ...

lapilli Lapilli is a size classification of tephra, which is material that falls out of the air during a volcanic eruption or during some meteorite impacts. ''Lapilli'' (singular: ''lapillus'') is Latin for "little stones". By definition lapilli range f ...

cones,

s and strombolian cones. These edifices are up to high and are associated with lava flows and

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 ...

units; the vents in the Los Volcanes group are spread across two separate belts. Wind-driven ash transport has formed ash tails at individual vents. Older lava flows have pahoehoe surfaces with

lava tube A lava tube, or pyroduct, is a natural conduit formed by flowing lava from a volcanic vent that moves beneath the hardened surface of a lava flow. If lava in the tube empties, it will leave a cave. Formation A lava tube is a type of lava ca ...

s and pressure ridges, while Holocene flows are more commonly aa lava with blocky surfaces. Some flows have reached the Rio Grande River west of Payún Matrú, damming it; the river later cut through and formed table-like landforms and

canyon A canyon (from ; archaic British English spelling: ''cañon''), or gorge, is a deep cleft between escarpments or cliffs resulting from weathering and the erosion, erosive activity of a river over geologic time scales. Rivers have a natural tenden ...

s. One of these is a slot canyon known as La Pasarela, where the structures of lava flows such as joints in the rocks and vesicles are clearly visible. The entire field covers an area of over and some of its flows have reached the

Llancanelo Lake Llancanelo Lake (Spanish: ''Laguna de Llancanelo'') is a wetland with an area of 650 km2 located in the Malargüe Department in the south of Mendoza Province, Argentina, 75 km from the city of Malargüe, at 1,280 m above mean sea level, ...

north of Payún Matrú and the Salado River in the east. The estimated volumes of the entire Payún Matrú volcano are as large as ; the volcanic edifice was generated mostly through Strombolian and

Hawaiian eruption A Hawaiian eruption is a type of volcanic eruption where lava flows from the vent in a relatively gentle, low level eruption; it is so named because it is characteristic of Hawaiian volcanoes. Typically they are effusive eruptions, with basaltic ...

s. The cones are aligned along easterly or northeasterly

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 ...

s which correlate with geological structures in the

basement A basement or cellar is one or more floors of a building that are completely or partly below the ground floor. It generally is used as a utility space for a building, where such items as the furnace, water heater, breaker panel or fuse box, ...

, and appear to reflect the tectonic stresses underground. Among these lineaments is the La Carbonilla fracture which runs in east–west direction and crops out in the eastern part of the field; in the central sector it is hidden by the caldera and in the western it is buried by lava flows. The La Carbonilla fracture is a fault that appears to have been an important influence on the development of the Payún Matrú complex in general. Fissural ridges and elongated chains of vents and cones highlight the control that lineaments exercise on the volcanic eruptions. In the summit area, pumice cones are aligned along the caldera rim. Among the cones in Payún Matrú are the

(5.333 million years ago until 11,700 years ago) Morados Grandes east and the cones around Pihuel volcano northeast of the field, respectively; the Guadalosos, La Mina and Montón de Cerros cones in the northern part of the field; and the Holocene cones in the eastern and western part of the field. Among these the Los Morados, Morado Sur and Volcán Santa María cones in the eastern and northeastern part of the field are uneroded and are probably of

recent The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene together ...

age. These cones are the source of conspicuous black lava flows in the western part of the field; some lava flows are over long. * Los Morados is a complex of scoria cones and vents of different ages which during its emplacement underwent a sector collapse, intense Strombolian activity and a lava flow-induced rafting and re-healing of its slopes. * On the southeast and east Los Morados is bordered by a lapilli plain, the Pampas Negras, which was formed by fallout of Strombolian eruptions and is being reworked by wind with the formation of

dune A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, f ...

s. * Morado Sur consists of two aligned cones that formed in the same eruption and are covered with reddish deposits; it also features several vents and lava flows. * Volcán Santa María is a cone with a small crater and also covered with red scoria and lava bombs. It is high and is associated with an area called "El Sandial", where lava bombs have left traces such as impact craters and aerodynamically deformed rocks.

Pampas Onduladas and other giant lava flows

Payún Matrú is the source of the longest

(last 2.58 million years ago) lava flow on Earth, the Pampas Onduladas lava flow in the eastern and northern sector of the volcanic field. The flow originates on the eastern side of the volcanic field in the La Carbonilla fault and eventually splits up into a shorter ("Llancanelo lava flow", long) northwestern and the longer southeastern branch which reaches all the way to an

alluvial terrace Fluvial terraces are elongated terraces that flank the sides of floodplains and fluvial valleys all over the world. They consist of a relatively level strip of land, called a "tread", separated from either an adjacent floodplain, other fluvial te ...

of the Salado River in the

La Pampa Province La Pampa () is a sparsely populated province of Argentina, located in the Pampas in the center of the country. Neighboring provinces are from the north clockwise San Luis, Córdoba, Buenos Aires, Río Negro, Neuquén and Mendoza. History In ...

. This compound lava flow moved over a gentle terrain and is covered by lava rises and lava tumuli especially in areas where the flow encountered obstacles in the topography. There is some variation in its appearance between a wide, leveled initial proximal sector and a more sinuous

distal Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

sector. The unusually fast flowing lava under the influence of its low viscosity and of a favourable topography eventually accumulated to a volume of at least , a surface area of about and depending on the measurement a length of . The process by which such long lava flows form has been explained as "inflation" whereby lava forms a crust that protects it from heat loss; the so protected lava flow eventually inflates from the entry of new magma, forming a system of overlapping and interconnected lava flow lobes. Such lava flows are known as "sheet flows". Parts of the Pampas Onduladas lava flow have been buried by more recent lava flows. Together with the

Þjórsá Lava The Great Þjórsá Lava ( Icelandic: ''Þjórsárhraunið mikla'' ) is the largest lava flow in Iceland (by both area and volume) and the largest lava that is known to have erupted in a single eruption in the Holocene. It belongs to a group of lav ...

Iceland Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its s ...

and the Toomba and Undara lava flows in

Queensland ) , nickname = Sunshine State , image_map = Queensland in Australia.svg , map_caption = Location of Queensland in Australia , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , established_ ...

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

, it is one of only a few Quaternary lava flows that reached a length of over and it has been compared to some long lava flows on

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...

. Southwest from Pampas Onduladas lie the long Los Carrizales lava flows, which have in part advanced to even larger distances than Pampas Onduladas but owing to a straighter course are considered to be shorter than the Pampas Onduladas lava flow, and the La Carbonilla lava flow which like Los Carrizales propagated southeastward and is located just west from the latter. Additional large lava flows are located in the western part of the field and resemble the Pampas Onduladas lava flow, such as the El Puente Formation close to the Rio Grande River of possibly recent age. Long lava flows have also been produced by volcanic centres directly south of Payún Matrú, including the long El Corcovo, Pampa de Luanco and Pampa de Ranquelcó flows.

Hydrography and non-volcanic landscape

Apart from the lake in the caldera, the area of Payún Matrú is largely devoid of permanent water sources, with most water sites that draw in humans being either temporary so-called "" or ephemeral. Likewise, there are no permanent

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

s in the field and most of the precipitation quickly seeps into the permeable or sandy ground. The whole massif is surrounded by

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of s ...

y plains, which are simply volcanic rocks covered by aeolian sediments; the plains also feature small closed basins which are also found in the lavic area.

Geology

West of South America, the

and the Antarctic Plate subduct beneath the South America Plate at a rate of , giving rise to the Andean volcanic belt. The volcanic belt is not continuous and is interrupted by gaps where the subduction is shallower and the

asthenosphere The asthenosphere () is the mechanically weak and ductile region of the upper mantle of Earth. It lies below the lithosphere, at a depth between ~ below the surface, and extends as deep as . However, the lower boundary of the asthenosphere is not ...

between the two plates missing. North of the Payún Matrú, flat slab subduction takes place; in the past flat slab subduction occurred farther south as well and had noticeable influence on magma chemistry. In general, the mode of subduction in the region over time has been variable. There is evidence of

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...

(older than 541 ± 0.1 million years ago) and

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

(298.9 ±0.15 to 201.3 ±0.2 million years ago) volcanism ( Choique Mahuida Formation) in the region, but a long hiatus separates them from the recent volcanic activity which started in the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58). At that time, the basaltic El Cenizo Formation and the andesitic Cerro El Zaino volcanics were emplaced. This kind of calcalkaline volcanic activity is interpreted to be the consequence of flat slab subduction during the Miocene (23.03-5.333 million years ago) and Pliocene, and took place between twenty and five million years ago. Later during the Pliocene and Quaternary the slab steepened, and probably as a consequence volcanism in the land above increased, reaching a peak between eight and five million years ago.

Local

The basement rock underneath Payún Matrú is formed by Mesoproterozoic (1,600–1,000 million years ago) to Triassic rocks of the

San Rafael Block The San Rafael Block or San Rafael Massif (Spanish: ''Bloque de San Rafael'' or ''Macizo de San Rafael'') is an uplifted area in central Mendoza Province, Argentina. The San Rafael Block is both a geographic and a tectonic unit. From a tectonostra ...

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...

(251.902 ± 0.024 to 66 million years ago) to

Paleogene The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period, geologic period and system that spans 43 million years from the end of the Cretaceous Period million yea ...

sediments of the

Neuquén Basin Neuquén Basin ( es, Cuenca Neuquina) is a sedimentary basin covering most of Neuquén Province in Argentina. The basin originated in the Jurassic and developed through alternating continental and marine conditions well into the Tertiary. The bas ...

and

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 ...

lava flows such as the

Patagonian Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and gl ...

basalts. The

Andean orogeny The Andean orogeny ( es, Orogenia andina) is an ongoing process of orogeny that began in the Early Jurassic and is responsible for the rise of the Andes mountains. The orogeny is driven by a reactivation of a long-lived subduction system along ...

during the Miocene has folded and deformed the basement, creating basins and uplifted basement blocks, and the Malargüe fold and thrust belt underlies part of the volcanic field. Oil has been drilled close to the volcanic field from

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...

s of Mesozoic age. Payún Matrú is part of the backarc volcanic province, east of the

Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...

and east of the Peru-Chile Trench. The volcanic activity still relates to the

of the Nazca Plate beneath the South America Plate, however; one proposed mechanism is that a Miocene change in the subduction regimen led to the development of

extensional tectonics Extensional tectonics is concerned with the structures formed by, and the tectonic processes associated with, the stretching of a planetary body's crust or lithosphere. Deformation styles The types of structure and the geometries formed depend on ...

and of faults that form the pathways for

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 ...

ascent, while other mechanisms envisage changes in

mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...

characteristics. Other volcanic fields in the region are the Llancanelo volcanic field, the Nevado volcanic field and Salado Basin volcanic field; the first two lie north of Payún Matrú and the last south. These fields are subdivided on the basis of geochemical differences and consist of two stratovolcanoes (Payún Matrú itself and Nevado) and many monogenetic volcanoes. The volcanic field is part of the larger Payunia volcanic province, which covers an area of about in the Provinces of La Pampa, Mendoza and Neuquén and is also known as the Payenia or Andino-Cuyana volcanic province. Monogenetic volcanism of mainly

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

ic composition has been active here for millions of years accompanied by the formation of several polygenetic volcanoes and volcanoes like Agua Poca, generating more than eight hundred monogenetic cones although historical eruptions have not been observed. Further south are the Chachahuen and

Auca Mahuida Auca or AUCA may refer to : * Auca (titular diocese), the former Catholic bishopric of (Villafranca Montes de) Oca in Spain, now a Latin titular see * A pejorative name for the native Huaorani people in Ecuador ** Operation Auca, an endeavor to eva ...

volcanoes, while the

Tromen Tromen is a stratovolcano in western Argentina. It rises above the older caldera of the Volcán Negro del Tromen. See also * List of volcanoes in Argentina This is a list of active and extinct volcanoes in Argentina. Volcanoes {, cla ...

volcano is located southwest from Payún Matrú.

Lava and magma composition

The volcanic field has produced rocks with composition ranging from alkali basalts over basalts,

trachyandesite Trachyandesite is an extrusive igneous Rock (geology), rock with a composition between trachyte and andesite. It has little or no free quartz, but is dominated by Sodium, sodic plagioclase and alkali feldspar. It is formed from the cooling of ...

basaltic Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% of a ...

trachyandesite,

trachybasalt Trachybasalt is a volcanic rock with a composition between trachyte and basalt. It resembles basalt but has a high content of alkali metal oxides. Minerals in trachybasalt include alkali feldspar, calcic plagioclase, olivine, clinopyroxene and li ...

and

trachyte Trachyte () is an extrusive igneous rock composed mostly of alkali feldspar. It is usually light-colored and aphanitic (fine-grained), with minor amounts of mafic minerals, and is formed by the rapid cooling of lava enriched with silica and al ...

rhyolite 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 ...

. They define a calc-alkaline volcanic suite with some variation between the various volcanic centres; Los Volcanes is formed mainly by calc-alkaline magmas while Payun and Payún Matrú are more

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 and shoshonitic. The volcanic rocks contain variable amounts of phenocrysts, including

alkali feldspar Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) feldspa ...

amphibole Amphibole () is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is A ...

apatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH−, F− and Cl− ions, respectively, in the crystal. The formula of the admixture of the three most common e ...

biotite Biotite is a common group of phyllosilicate minerals within the mica group, with the approximate chemical formula . It is primarily a solid-solution series between the iron-endmember annite, and the magnesium-endmember phlogopite; more alumino ...

, clinopyroxene,

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 ...

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 ...

and

sanidine Sanidine is the high temperature form of potassium feldspar with a general formula K(AlSi3O8). Sanidine is found most typically in felsic volcanic rocks such as obsidian, rhyolite and trachyte. Sanidine crystallizes in the monoclinic crystal system ...

, but not all phenocryst phases can be found in every rock formation. Magma temperatures of have been inferred. Volcanic rocks erupted at Payún Matrú resemble ocean island basalt volcanism, implying a deep origin of the magma although a shallow origin cannot be ruled out. Magnetotelluric observations indicate the presence of a "plume"-like structure that rises from depth close to the edge of the Nazca Plate slab to underneath Payún Matrú; it may indicate that magma erupted in the volcanic field originates at such depths which would explain the ocean island basalt-like composition. The magma ejected at Payún Matrú originates during partial melting of enriched

; the resulting melts then undergo crystal fractionation, assimilation of crustal material and magma mixing in magma chambers. The magmas eventually reach the surface through deep faults. The edifice of Payún Matrú acts as an obstacle to magmas ascending to the surface; this is why only evolved magmas are erupted in the caldera area of Payún Matrú while basic magmas reached the surface mainly outside of the main edifice.

Obsidian Obsidian () is a naturally occurring volcanic glass formed when lava extrusive rock, extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock. Obsidian is produced from felsic lava, rich in the lighter elements s ...

from Payún Matrú has been found in

archeological site An archaeological site is a place (or group of physical sites) in which evidence of past activity is preserved (either prehistoric or historic or contemporary), and which has been, or may be, investigated using the discipline of archaeology and ...

s, although its use was not widespread in the region perhaps owing to its low quality, the difficulty of accessing the volcanic complex and that human activity in Payunia only began comparatively late in the Holocene and mostly from the margins of the region. Further, Payun volcano is notable for large crystals of

hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...

pseudomorph In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form (crystal system), resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced by ...

s which originated in fumaroles.

Climate, soils and vegetation

The climate at Payún Matrú is cold and dry with strong westerly winds. Annual temperature varies between while the average temperature in the wider region is about and the average annual precipitation amounts to . Generally, the area of Payún Matrú is characterized by a

continent A continent is any of several large landmasses. Generally identified by convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continents. Ordered from largest in area to smallest, these seven ...

al climate with hot summers especially at lower elevations and cold winters especially at higher elevations. The climate is dry owing to the rainshadow effect of the Andes which block moisture bearing winds from reaching Payún Matrú, and strong winds and the

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 ...

associated with them reinforce the dryness. In the westerly part of the volcanic field most precipitation falls during winter under the influence of the Andes, while the eastern part has most precipitation occurring during summer. The higher parts of Payún Matrú may have risen above the

snowline The climatic snow line is the boundary between a snow-covered and snow-free surface. The actual snow line may adjust seasonally, and be either significantly higher in elevation, or lower. The permanent snow line is the level above which snow wil ...

during

ice age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages and gree ...

s, and

periglacial Periglaciation (adjective: "periglacial", also referring to places at the edges of glacial areas) describes geomorphic processes that result from seasonal thawing of snow in areas of permafrost, the runoff from which refreezes in ice wedges and ot ...

landforms have been observed. Palynology data from south of the region indicate that the climate has been stable since the

Late Pleistocene The Late Pleistocene is an unofficial Age (geology), age in the international geologic timescale in chronostratigraphy, also known as Upper Pleistocene from a Stratigraphy, stratigraphic perspective. It is intended to be the fourth division of ...

. The vegetation in the volcanic field is mostly characterized by sparse

bushes A shrub (often also called a bush) is a small-to-medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees ...

as well as herbaceous vegetation but few trees, and is classified as xerophytic.

Soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...

s are shallow and are mainly rocky to

loess Loess (, ; from german: Löss ) is a clastic, predominantly silt-sized sediment that is formed by the accumulation of wind-blown dust. Ten percent of Earth's land area is covered by loess or similar deposits. Loess is a periglacial or aeolian ...

-like. Representative plant genera are ''

Opuntia ''Opuntia'', commonly called prickly pear or pear cactus, is a genus of flowering plants in the cactus family Cactaceae. Prickly pears are also known as ''tuna'' (fruit), ''sabra'', ''nopal'' (paddle, plural ''nopales'') from the Nahuatl word f ...

cactus A cactus (, or less commonly, cactus) is a member of the plant family Cactaceae, a family comprising about 127 genera with some 1750 known species of the order Caryophyllales. The word ''cactus'' derives, through Latin, from the Ancient Greek ...

and ''

Poa ''Poa'' is a genus of about 570 species of grasses, native to the temperate regions of both hemispheres. Common names include meadow-grass (mainly in Europe and Asia), bluegrass (mainly in North America), tussock (some New Zealand species), a ...

'' and '' Stipa'' grasses. Payún Matrú is a refuge for a number of animals such as the

armadillo Armadillos (meaning "little armored ones" in Spanish) are New World placental mammals in the order Cingulata. The Chlamyphoridae and Dasypodidae are the only surviving families in the order, which is part of the superorder Xenarthra, along wi ...

black-chested buzzard-eagle The black-chested buzzard-eagle (''Geranoaetus melanoleucus'') is a bird of prey of the hawk and eagle family (Accipitridae). It lives in open regions of South America. This species is also known as the black buzzard-eagle, the gray buzzard-eag ...

, condors,

Darwin's rhea Darwin's rhea or the lesser rhea (''Rhea pennata'') is a large flightless bird, the smaller of the two extant species of rheas. It is found in the Altiplano and Patagonia in South America. Description The lesser rhea stands at tall. Length ...

, guanaco,

mara Mara or MARA may refer to: Animals * Mara (mammal), a species of the cavy family *Mara the Lioness, in the movie ''Born Free'' Arts and entertainment Fictional characters * Mara (''Doctor Who''), an evil being in two ''Doctor Who'' serials *Mara, ...

Pampas fox The Pampas fox (''Lycalopex gymnocercus''), also known as grey pampean fox, Pampas zorro, Azara's fox, or Azara's zorro (in Spanish also called , anglicized as aguarachay, in Portuguese also called ), is a medium-sized zorro, or "false" fox, na ...

South American gray fox The South American gray fox (''Lycalopex griseus''), also known as the Patagonian fox, the chilla or the gray zorro, is a species of ''Lycalopex'', the "false" foxes. It is endemic to the southern part of South America. Description The South A ...

puma Puma or PUMA may refer to: Animals * ''Puma'' (genus), a genus in the family Felidae ** Puma (species) or cougar, a large cat Businesses and organisations * Puma (brand), a multinational shoe and sportswear company * Puma Energy, a mid- and d ...

and

Southern viscacha The southern viscacha (''Lagidium viscacia'') is a species of viscacha, a rodent in the family Chinchillidae found in Argentina, Bolivia, Chile, and Peru. It is a colonial animal living in small groups in rocky mountain areas. It has long ears an ...

. Some lizards may have evolved on the volcanoes.

Eruptions

The geological history of the Payún Matrú volcanic field is poorly dated but the field has been active since Pliocene at least. The older volcanism appears to be located in the eastern part of the field where ages of 0.95 ± 0.5 to 0.6 ± 0.1 million years ago have been obtained by potassium-argon dating. Lava flows have been subdivided into the older Puente Group and the younger Tromen Group formations, which are of

age, respectively; a Chapua Formation of

age has been defined as well. The eastern volcanism is also known as the Pre-caldera basaltic unit; a western counterpart to it is probably buried beneath younger eruption products. The first volcanic activity occurred west and east of Payún Matrú and involved the emission of olivine basalt lava flows. The long Pampas Onduladas lava flow was erupted 373,000 ± 10,000 years ago and buried parts of the 400,000 ± 100,000 years old Los Carrizales lava field; both have

hawaiitic Hawaiite is an olivine basalt with a composition between alkali basalt and mugearite. It was first used as a name for some lavas found on the island of Hawaii. It occurs during the later stages of volcanic activity on oceanic islands such as Haw ...

composition. The Payun volcano formed around 265,000 ± 5,000 years ago within a timespan of about 2,000–20,000 years. Its inferred eruption rate of is similar to typical volcanic arc eruption rates such as at

Mount St. Helens Mount St. Helens (known as Lawetlat'la to the indigenous Cowlitz people, and Loowit or Louwala-Clough to the Klickitat) is an active stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United St ...

. The main Payún Matrú massif formed in about 600,000 years, with the oldest trachytic rocks dated to 700,000 years ago. It is comprised by the lavic and ignimbritic Pre-caldera Trachyte unit and consists of trachyandesitic to trachytic rocks, with trachyte being the most important component. The massif may have formed a tall edifice like the Payun volcano before caldera collapse. The formation of the caldera coincides with the eruption of the Portezuelo Ignimbrite/Portezuelo Formation and took place between 168,000 ± 4,000 and 82,000 ± 2,000 years ago. This ignimbrite formation where it is not buried by younger eruption products spreads radially around the caldera and reaches a maximum exposed thickness of ; it covers an area of about on the northern and southern sides of Payún Matrú, and its volume is estimated to be about . The event was probably precipitated by the entry of

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 ...

magma in the magma chamber and its incomplete mixing with pre-existent magma chamber melts, or by tectonic processes; the resulting Plinian eruption generated an

eruption column An eruption column or eruption plume is a cloud of super-heated ash and tephra suspended in gases emitted during an explosive volcanic eruption. The volcanic materials form a vertical column or plume that may rise many kilometers into the air a ...

, which collapsed, producing the ignimbrites. Different layers of magma in the magma chamber were erupted during the course of the eruption and eventually the summit of the volcano collapsed as well, forming the caldera; activity continued and emplaced lava domes and lava flows in the caldera area. These post-caldera volcanic formations are subdivided into three separate

lithofacies Lithofacies may refer to: * A mappable subdivision of a designated stratigraphic unit, distinguished from adjacent subdivisions on the basis of lithology; a facies characterized by particular lithologic features * The rock record of any particular ...

. Basaltic and trachyandesitic activity continued after the formation of the caldera. Morphology indicates that the El Rengo and Los Volcanes volcanic cones appear to be of Holocene age, while the Guadaloso vents formed during the Plio-Pleistocene. One age from the eastern side is 148,000 ± 9,000 years ago, it comes from northeast of the Payún Matrú caldera. Uneroded volcanic cones and dark basaltic lavas indicate that activity continued into the Holocene. Large lava flows were erupted during the Holocene and covered extensive areas, burying the vegetation and impeding human settlement of the region until the late Holocene.

Oral tradition Oral tradition, or oral lore, is a form of human communication wherein knowledge, art, ideas and cultural material is received, preserved, and transmitted orally from one generation to another. Vansina, Jan: ''Oral Tradition as History'' (1985 ...

by a local indigenous tribe indicate that volcanic activity occurred within the last several centuries, although no eruptions have been observed since the European settlement. Future volcanic eruptions would be unlikely to constitute a hazard given the low population density of the area, although roads might be interrupted and

lava dam A volcanic dam is a type of natural dam produced directly or indirectly by volcanism, which holds or temporarily restricts the flow of surface water in existing streams, like a man-made dam. There are two main types of volcanic dams, those create ...

s might form in rivers. It is considered Argentina's 24th most dangerous volcano out of 38. Various dating methods have yielded various ages for late Pleistocene-Holocene volcanic eruptions: * 44,000 ± 2,000 years ago, surface exposure dating. * 43,000–41,000 ± 3,000 years ago, surface exposure dating, El Puente Formation. Basaltic lava flows of this formation reach ages of about 320,000 ± 5,000 years, implying a prolonged history of emplacement. * 41,000 ± 1,000 years ago, underlying the Los Morados lava flow. * 37,000 ± 3,000 years ago, surface exposure dating, close to the Rio Grande River. * 37,000 ± 1,000 years ago, La Planchada fallout deposit. * 37,000 ± 2,000 years ago, northwestern side of the caldera. * 28,000 ± 5,000 years ago, potassium-argon dating, lava flow on the westerly side. * 26,000 ± 5,000 years ago, potassium-argon dating, close to the Rio Grande. * 26,000 ± 2,000 years ago, potassium-argon dating, not the same as the 26,000 ± 5,000 flow. * 26,000 ± 1,000 years ago, potassium-argon dating,

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 ...

lava flow in the La Calle group. * 20,000 ± 7,000 years ago, north of the Payún Matrú caldera. * 16,000 ± 1,000 years ago, underlying the Los Morados lava flow. * 15,200 ± 900 years ago, potassium-argon dating, lava flow on the northwesterly-westerly side. * 9,000 years ago, potassium-argon dating. * 7,000 ± 1,000 years ago, potassium-argon dating, Escorial del Matru within the caldera. * <7,000 years ago, potassium-argon dating, trachyandesitic lava flow in the western part of the field. * 6,900 ± 650 years before present, thermoluminescence dating on the Guadalosos cones on an eastward running fracture. * 4,670 ± 450 years

before present Before Present (BP) years, or "years before present", is a time scale used mainly in archaeology, geology and other scientific disciplines to specify when events occurred relative to the origin of practical radiocarbon dating in the 1950s. Becaus ...

thermoluminescence dating Thermoluminescence dating (TL) is the determination, by means of measuring the accumulated radiation dose, of the time elapsed since material containing crystalline minerals was either heated (lava, ceramics) or exposed to sunlight (sediments ...

. * 3,700 ± 300 years before present, pumice fallout in and east of the caldera. * 3,400 ± 300 years before present, trachytic lava flows. * 2,000 ± 2,000 years ago, surface exposure dating, young looking lava flow in the west. * 1,705 ± 170 years before present, trachytic volcanic bombs. * 1,470 ± 120 years before present, thermoluminescence dating on Volcán Santa María although a much older age of 496,000 ± 110,000 years ago has also been given. * 515 ± 50 years before present, thermoluminescence dating on Morado Sur cone and on the Pampas Negras lapilli field. * 445 ± 50 years before present, lava domes on the caldera margin.

Explanatory notes

References

Citations

General sources

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

External links

Payún Matru Volcanic Field, Argentina: Image of the Day
at NASA's Earth Observatory * * * {{Andean volcanoes, state=collapsed Andean Volcanic Belt Mountains of Argentina Polygenetic shield volcanoes Quaternary South America Quaternary volcanoes Subduction volcanoes Volcanoes of Mendoza Province