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 ...
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 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 ...
of northwestern
Argentina
Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
.
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 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 ...
-
Pliocene
The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Pleistocene
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 ...
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 upw ...
s and thus of large volcanic systems has apparently been influenced by
tectonic
Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents k ...
Wheelwright
A wheelwright is a 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 or shaper of wood) as in shipwright and arkw ...
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
Orogeny is a mountain building process. An orogeny is an event that takes place at a convergent boundary, convergent plate margin when plate motion compresses the margin. An ''orogenic belt'' or ''orogen'' develops as the compressed plate crumpl ...
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 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, they rem ...
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, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral ...
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 alumino ...
,
pumice
Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular vol ...
,
quartz
Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...
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 ...
.
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, by using high heat to melt the parts together and allowing them to cool, causing fusion. Welding is distinct from lower temperature techniques such as braz ...
and contains vesicular pumice, and bears some similarity with the Cyclops ignimbrite away. Further, the Laguna Amarga ignimbrites like the
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 ...
sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...
. 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.
SERNAGEOMIN
250px, Sernageomin building in Providencia, Santiago.
The National Geology and Mining Service ( es, Servicio Nacional de Geología y Minería; SERNAGEOMIN) is a Chilean government agency. Its function is to provide geological information and adv ...