Luingo is 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 ...

in the Andes of Argentina. It is located southeast of the Galan caldera. The caldera is not recognizable from satellite images and is associated with the Pucarilla-Cerro Tipillas volcanic complex. Volcanic activity at Luingo occurred before a phase of crustal thickening in the region. It generated two major ignimbrites named Alto de Las Lagunas an Pucarilla. Two further ignimbrites named Luingo I and Luingo II were found within the caldera and are associated with caldera collapse. A phase of effusive activity succeeded the caldera formation.

Geography and structure

Luingo lies in northwestern Argentina, on the Argentine Puna and just west of the Eastern Cordillera. The Pucarilla-Cerro Tipillas volcanic complex is associated with Luingo, and the Galan caldera lies northwest of Luingo. Luingo forms the oldest and southeasternmost caldera of the Puna. Luingo is part of the

Central Volcanic Zone The Andean Volcanic Belt is a major volcanic belt along the Andean cordillera in Argentina, Bolivia, Chile, Colombia, Ecuador, and Peru. It is formed as a result of subduction of the Nazca Plate and Antarctic Plate underneath the South Americ ...

(CVZ). About 20 major

s are found in the CVZ, especially in the region between 21 and 25° southern latitude where the Altiplano-Puna volcanic complex can be found. These ignimbrites,

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 and subvolcanic bodies. Smaller ignimbrites are found in the southern part of the CVZ. The Pucarilla-Cerro Tipillas volcanic complex is formed by pyroclastic flows.

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 are subordinate. Luingo is the eruptive centre of the Pucarilla-Cerro Tipillas volcanic complex. Unlike other calderas such as Galan, Luingo is not visible from satellite images; its location and existence has been inferred from analysis of the

facies In geology, a facies ( , ; same pronunciation and spelling in the plural) is a body of rock with specified characteristics, which can be any observable attribute of rocks (such as their overall appearance, composition, or condition of formatio ...

and morphology. This caldera is the source of the Alto de Las Lagunas and Pucarilla ignimbrites and is itself filled by the two Luingo ignimbrites. The caldera has a diameter of . Based on the volume of its products a downsag depth of has been calculated. Luingo has generated ignimbrites that cover a surface area of . A salar is found within the Luingo caldera. The Luingo River originates close to the caldera and the

Los Patos River LOS, or Los, or LoS may refer to: Science and technology * Length of stay, the duration of a single episode of hospitalisation * Level of service (transportation), Level of service, a measure used by traffic engineers * Level of significance, a ...

flows north of the caldera.

Geology

Volcanism of the Altiplano is caused by the collision between 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 ...

and the South America Plate. Various phenomena caused a thickening of the crust in the Altiplano region; such thickening however postdates volcanic activity at Luingo and thus the volcano was unaffected by its chemical effects. Between 8 and 3 million years ago the volcanic arc moved towards the east due to

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 ...

eroding the forearc and 6 million years ago voluminous ignimbritic volcanism commenced. Since 3 million years ago, ignimbritic volcanism is aligned both along the Chile-Argentina border and a lineament including Galan,

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 ...

and

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

. The composition of Luingo magmas has been modelled. The closest correspondence is obtained by assuming the mixing crustal material with mafic magmas in a ratio 1:4. Subsequently, the crust became thicker in the region, thus the Galan ignimbrites formed from magmas where the crustal material:mafic magma ratio is about 1:1.

Regional

Luingo is located in the Puna-Altiplano, a high plateau with an average altitude of . This plateau covers a surface area of about and contains internally draining basins as well as volcanoes. The Laguna Blanca

Formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...

is a dacitic tuff formation of late

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 ...

age that covers large parts of the Puna. In the region of Luingo, it has been associated with this volcano. A number of other rock formations are interpreted to have been formed by Luingo.

Local

The basement upon which the Luingo deposits lie is formed by two separate structures. The first is a sediment formation of fluvial origin, which is known as the Angastaco Formation. The second is a

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, ...

proper formed by granite and metamorphic rocks of Neoproterozoic to Paleozoic age. A set of faults delimit the Colomé–Hualfín Valley that contains most of Pucarilla-Cerro Tipillas eruption products; indeed at the time of Luingo's activity the Jasimaná fault formed a barrier to its eruption products. This fault belongs to a group of faults which are part of this region of the Andes, which has been highly tectonically active since the

Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...

Eruptive history

The Alto de Las Lagunas ignimbrite is the oldest eruptive unit of Luingo and reaches a thickness of . It was previously named the Hornblendic welded tuff and dated 15.83 ± 0.44 – 14.22 ± 0.33 million years ago; a younger date of 13.52 ± 0.12 million years ago has been obtained on it. This ignimbrite is pink-grey and contains

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 ...

and crystal-rich fiamme. Minerals include alkaline feldspar,

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 ...

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 ...

, plagioclase and quartz with accessory minerals such as

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 ...

, iron- titanium

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 ...

sphene Titanite, or sphene (from the Greek ''sphenos'' (σφηνώ), meaning wedge), is a calcium titanium nesosilicate mineral, Ca Ti Si O5. Trace impurities of iron and aluminium are typically present. Also commonly present are rare earth metals in ...

and zircon. Also present are granitic lithics. Its total volume is and ash falls in northwestern Argentina have been correlated to it. The Pucarilla ignimbrite was erupted 12.11 ± 0.11 million years ago. It is a dacitic welded tuff with a high crystal and moderate pumice content. Minerals include

, clinopyroxene, plagioclase and quartz with accessory minerals such as

, magnetite,

and zircon. This ignimbrite has been subdivided into the pink Jasimana unit that covers an extensive surface area, the lower witish-grey Hualfin unit and the grey upper Arremo unit. The Pucarilla ignimbrite has a minimum volume of . The Luingo I ignimbrite is dacitic and covered by a thick breccia layer known as the Luingo breccia. It has undergone some hydrothermal alteration that gives it a greenish colour. The breccia is formed by granitic rocks. Above it lies the Luingo II ignimbrite which is also dacitic. Both ignimbrites are welded and rich in crystals. Minerals include

, clinopyroxene, plagioclase, quartz and titanite. All these structures formed during one event. When the Luingo I ignimbrite was erupted, caldera collapse happened and formed the Luingo breccia from debris. Afterwards, this debris was buried by the Luingo II ignimbrite. The ignimbrites outside of the caldera formed the Pucarilla ignimbrite. This eruption from fissure vents was characterized by low fountaining of ignimbrites and a high mass flow, resulting in hot flows that reached distances of . Probably under the influence of faults that delimit the current caldera, the caldera underwent a trapdoor-like collapse. After the caldera collapse, hydrothermal activity as well as the extrusion of

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 occurred. Minerals produced by alteration include

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 ...

chlorite The chlorite ion, or chlorine dioxide anion, is the halite with the chemical formula of . A chlorite (compound) is a compound that contains this group, with chlorine in the oxidation state of +3. Chlorites are also known as salts of chlorous ac ...

epidote Epidote is a calcium aluminium iron sorosilicate mineral. Description Well developed crystals of epidote, Ca2Al2(Fe3+;Al)(SiO4)(Si2O7)O(OH), crystallizing in the monoclinic system, are of frequent occurrence: they are commonly prismatic in habi ...

kaolinite Kaolinite ( ) is a clay mineral, with the chemical composition Al2 Si2 O5( OH)4. It is an important industrial mineral. It is a layered silicate mineral, with one tetrahedral sheet of silica () linked through oxygen atoms to one octahedral ...

, rutile and

sericite Sericite is the name given to very fine, ragged grains and aggregates of white (colourless) micas, typically made of muscovite, illite, or paragonite. Sericite is produced by the alteration of orthoclase or plagioclase feldspars in areas that hav ...

. Effusive activity occurred during the upper Miocene in the area. This effusive activity has been dated 7.59 ± 0.03 and 7.6 ± 0.02 million years ago. Its composition ranges from trachyandesite to trachydacite and is significantly hydrothermally altered. While this activity was not accompanied by explosive activity, it is possible that traces of such will be found in the area in the future.

References

External links

* * * * * {{refend Volcanoes of Salta Province Miocene calderas Calderas of Argentina