Cerro Morado is a

monogenetic volcanic field A monogenetic volcanic field is a type of volcanic field consisting of a group of small monogenetic volcanoes, each of which erupts only once, as opposed to polygenetic volcanoes, which erupt repeatedly over a period of time. The small monogenetic ...

, in

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

. It is part of a group 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 ...

volcanic centres in the

Altiplano The Altiplano (Spanish language, Spanish for "high plain"), Collao (Quechuan languages, Quechua and Aymara language, Aymara: Qullaw, meaning "place of the Qulla people, Qulla") or Andean Plateau, in west-central South America, is the most extens ...

-Puna region, which is dominated by silicic rocks such as

dacitic 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. ...

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 miner ...

rocks. The field was formed during eruptions 6.4 million years ago which probably lasted from half a year to several years. These eruptions formed

scoria cone A cinder cone or scoria cone is a steep, conical landform of loose pyroclastic fragments, such as volcanic ash, clinkers, or scoria that has been built around a volcanic vent. The pyroclastic fragments are formed by explosive eruptions or l ...

s and a plateau of

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 Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...

Geology and geography

The Cerro Morado volcanic field is located in northwestern

, in the

Jujuy Province Jujuy is a province of Argentina, located in the extreme northwest of the country, at the borders with Chile and Bolivia. The only neighboring Argentine province is Salta to the east and south. Geography There are three main areas in Jujuy ...

. The town of is located within the volcanic field. The frontier with

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

lies approximately west of the volcanic field. The

and the adjacent southern Puna has experienced

volcanism during the

Cenozoic The Cenozoic Era ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterized by the dominance of mammals, insects, birds and angiosperms (flowering plants). It is the latest of three g ...

. Most of this volcanism occurred in the southern segment, but the northern segment has also experienced mafic volcanism mostly associated with major volcanic centres and smaller volcanic fields such as Cerro Morado and

Cerro Bitiche Cerro Bitiche is a volcanic field in Argentina. It is located east of the Central Volcanic Zone away from the volcanic arc within the Altiplano-Puna volcanic complex (APVC), close to Zapaleri volcano. The field is formed by seven scoria cone ...

. Mafic lava flows however tend to constitute the minority of volcanic rocks in this region; the bulk of the volcanic rocks are

in composition. Present day volcanism occurs in the

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 ...

called 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 ...

approximately farther west. The basement in the Cerro Morado area is formed by

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

rock formations and older lava flows of the Pairique volcanic complex and the Patahuasi flows. Volcanism in the area has been influenced by faults. The field covers a surface area of , alternatively stated as . Eight

s form the volcanic field, but there may be more. With exceptions erosion has buried their bases. Layered deposits containing ash,

lava bomb A volcanic bomb or lava bomb is a mass of partially molten rock (tephra) larger than 64 mm (2.5 inches) in diameter, formed when a volcano ejects viscosity, viscous fragments of lava during an eruption. Because volcanic bombs cool a ...

s and

lapilli Lapilli (: lapillus) 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'' is Latin for "little stones". By definition lapilli range from in dia ...

are found around them. These cones are frequently aligned and an average diameter of and the heights range . Other structures associated with the cones are clastogenic lava flows and eroded pyroclastic mounds, as well as dykes that cut the cones. The volcanic field is dominated by a plateau made of lobate

s, typically having thicknesses of . The lava flows contain folding and flow structures. Various layers of lava flows lie on top of each other and on the basement, and

pyroclastic Pyroclast, Pyroclastic or Pyroclastics may refer to: Geology * Pyroclast, or airborne volcanic tephra fragments * Pyroclastic rock, rock fragments produced and ejected by explosive volcanic eruptions * Pyroclastic cone, landform of ejecta fro ...

deposits can also be found. The volcanic field has a north-south extension. The volcano has erupted

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 predomina ...

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 ...

. Most cones are constructed from basaltic andesite, most lava flow

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 ...

are andesitic. The andesites have a dark-blue to gray colour, with variable amounts of vesicles. Minerals found in the rocks include

bytownite Bytownite is a calcium rich member of the plagioclase solid solution series of feldspar minerals with composition between anorthite and labradorite. It is usually defined as having between 70 and 90% An (formula: ). Like others of the series, byt ...

clinopyroxene The pyroxenes (commonly abbreviated 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 ions of calcium (Ca), sodium (Na), iron (Fe ...

iron Iron is a chemical element; it has symbol Fe () 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, forming much of Earth's o ...

titanium Titanium is a chemical element; it has 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 ...

oxides,

labradorite Labradorite (( Ca, Na)( Al, Si)4 O8) is a calcium-enriched feldspar mineral first identified in Labrador, Canada, which can display an iridescent effect ( schiller). Labradorite is an intermediate to calcic member of the plagioclase series. It ...

orthopyroxene The pyroxenes (commonly abbreviated 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 ions of calcium (Ca), sodium (Na), iron (Fe( ...

and

plagioclase Plagioclase ( ) is a series of Silicate minerals#Tectosilicates, tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continu ...

Olivine The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...

is more common in the basaltic andesite than the andesite. Overall, the composition is

potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...

-rich

calc-alkaline The calc-alkaline magma series is one of two main subdivisions of the subalkaline magma series, the other subalkaline magma series being the tholeiitic series. A magma series is a series of compositions that describes the evolution of a mafic ...

Xenolith A xenolith ("foreign rock") is a rock (geology), rock fragment (Country rock (geology), country rock) that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term ''xenolith'' is almost exclusi ...

s of

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

are contained in the andesite. Some of the rocks that form the cones are hydrothermally altered. The volcanic field was formed during the Upper

Miocene The Miocene ( ) is the first epoch (geology), 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 mea ...

. Dates of 6.7 ± 0.4 million years ago have been obtained. The field was formed by energetic effusive eruptions; lava supply rates of up to and an emplacement time of 84-18 months for the northern and 48-7 months for the southern parts of the field have been estimated. The field was probably formed by

Strombolian eruption In volcanology, a Strombolian eruption is a type of volcanic eruption with relatively mild blasts, typically having a Volcanic Explosivity Index of 1 or 2. Strombolian eruptions consist of ejection of incandescent Scoria, cinders, lapilli, and vo ...

s accompanied by lava fountaining. Magma was transported along fractures and faults, resulting in the eruption of several different batches of magma without long stalling in the upper crust.

References

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{{DEFAULTSORT:Morado, Cerro Miocene volcanism Pliocene volcanism Volcanic fields of Argentina

Geology and geography

See also

References

Sources

External links