caldera
A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcanic eruption. An eruption that ejects large volumes of magma over a short period of time can cause significant detriment to the str ...
and associated
ignimbrite
Ignimbrite is a type of volcanic rock, consisting of hardened tuff. Ignimbrites form from the deposits of pyroclastic flows, which are a hot suspension of particles and gases flowing rapidly from a volcano, driven by being denser than the surrou ...
in the
Andes
The Andes ( ), Andes Mountains or Andean Mountain Range (; ) are the List of longest mountain chains on Earth, longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range ...
of northwestern
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 ...
.
Laguna Amarga is part of the southern
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 one among several
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 ...
-
Pliocene
The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Pleistocene
The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...
volcanic centres of this volcanic region. The formation of
magma chamber
A magma chamber is a large pool of liquid rock beneath the surface of the Earth. The molten rock, or magma, in such a chamber is less dense than the surrounding country rock, which produces buoyant forces on the magma that tend to drive it u ...
s and thus of large volcanic systems has apparently been influenced by
tectonic
Tectonics ( via Latin ) are the processes that result in the structure and properties of the Earth's crust and its evolution through time. The field of ''planetary tectonics'' extends the concept to other planets and moons.
These processes ...
Wheelwright
A wheelwright is a Artisan, craftsman who builds or repairs wooden wheels. The word is the combination of "wheel" and the word "wright" (which comes from the Old English word "''wryhta''", meaning a worker - as also in shipbuilding, shipwright ...
calderas, all of which are between 6.5 and 4 mya old. Laguna Amarga and Laguna Verde are sometimes associated with the Vallecito ignimbrite instead. The formation of the Laguna Amarga volcanic centre was probably influenced by orogenic changes in the Andes which triggered the formation of fractures in the crust.
The Laguna Amarga caldera has a diameter of and is linked to the Laguna Escondida caldera. It is the largest caldera in the area and may be part of an eastward migrating volcanic complex.
Tephra
Tephra is fragmental material produced by a Volcano, volcanic eruption regardless of composition, fragment size, or emplacement mechanism.
Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, ...
s erupted during its formation have been found hundreds of kilometres from Laguna Amarga.
The Laguna Verde ignimbrite was erupted 4-3 mya ago and is associated with these two calderas. Other dates are 4.5 ± 0.5 to 3.0 ± 0.2 mya. The ignimbrite covers an area of , cropping out southwest of the Laguna Amarga ignimbrite. The Laguna Verde ignimbrite ranges from
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. ...
to
rhyolite
Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture (geology), texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained matri ...
in composition, containing
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 al ...
,
pumice
Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of extremely vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicula ...
,
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 ...
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 sys ...
.
Hydrothermal
Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...
ly altered rocks occur in the area.
The Laguna Amarga ignimbrite was erupted 5.1 mya ago, or 3.7-4.1 mya, and it has a volume of over . It extends north-northwest from Peinado volcano. The ignimbrite is somewhat
welded
Welding is a fabrication process that joins materials, usually metals or thermoplastics, primarily by using high temperature to melt the parts together and allow them to cool, causing fusion. Common alternative methods include solvent w ...
and contains vesicular pumice, and bears some similarity with the Cyclops ignimbrite away. Further, the Laguna Amarga ignimbrites like the Cerro Blanco and Galan ignimbrites are rich in
sodium
Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...
. It covers a surface area of , cropping out around the Laguna Amarga. Another ignimbrite, Los Colorados, is located at the edge of the Amarga caldera but its eruptive centre is unknown. After its formation, lava flows from Peinado and Cerro El Condor overran the floor of the caldera and
monogenetic volcano
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 ...
s developed both on the caldera floor and on its ignimbrite.
See also
*
Los Colorados (caldera)
Los Colorados is the name of a caldera in Chile. It is part of the Central Volcanic Zone of the Andes.
The caldera has a diameter of and was formed 9.8 million years ago within a basement consisting of Paleozoic rocks, Miocene ignimbrites and ...
SERNAGEOMIN
250px, Sernageomin building in Providencia, Santiago.
The National Geology and Mining Service (; SERNAGEOMIN) is a Chilean government agency. Its function is to provide geological information and advice, technical assistance to government, publi ...