Cerro Bitiche is a

volcanic field A volcanic field is an area of Earth's Earth's crust, crust that is prone to localized volcano, volcanic activity. The type and number of volcanoes required to be called a "field" is not well-defined. Volcanic fields usually consist of clusters ...

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 located east of the Central Volcanic Zone away from 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 ...

within the Altiplano-Puna volcanic complex (APVC), close to Zapaleri volcano. The field is formed by seven scoria cones 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 Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...

s, of

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 ...

- basaltic andesite composition. The field was formed by volcanism contemporaneous with the

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 ...

volcanism of the APVC, with Cerro Guacha and La Pacana

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 ...

s being located nearby.

Geography and Geology

Regional setting

Cerro Bitiche is located in the area of the northern Puna-southern Altiplano, within

and close to the

tripoint A triple border, tripoint, trijunction, triple point, or tri-border area is a geography, geographical point at which the boundaries of three countries or Administrative division, subnational entities meet. There are 175 international tripoints ...

with

Bolivia Bolivia, officially the Plurinational State of Bolivia, is a landlocked country located in central South America. The country features diverse geography, including vast Amazonian plains, tropical lowlands, mountains, the Gran Chaco Province, w ...

and

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 ...

. The Altiplano-Puna highland with horizontal dimensions of and average altitudes of is the second highest plain in the world. Zapaleri and the Rio Zapaleri are located northwest of Bitiche. The field is located behind the main

of the Central Volcanic Zone. The region is the site of the

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 ...

Altiplano-Puna volcanic complex, one of the world's largest

province. The rocks erupted in the complex are derived from the crust and the mantle in equal amounts. A number of mafic volcanic fields and isolated cones are found in the northern Puna.

Local setting

Cerro Bitiche is part of a number of mafic volcanic centres associated with the Altiplano-Puna volcanic complex. The two major calderas La Pacana and Cerro Guacha are close to Cerro Bitiche, the eastern margin of Guacha's oldest caldera is located just east of Bitiche.

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 ...

marine sequences form the tectonic basement of the area, but most of it is covered by ignimbrites and lavas between 8.5-4 million years old. The volcanic field covers a surface area of , including

s and scoria cones. The highest scoria cone has a height of . These scoria cones are formed by lapilli and pyroclastics with no welding and also contain lava bombs. They are in part constructed on top of pyroclastic and ash beds with some traces of sedimentation. Some cones have assumed a horseshoe shape resulting from the collapse of their flanks during lava emission. The arid climate in the area has preserved the edifices. The lava field has the shape of a plateau that has been modified by later tectonic movements. The lava flows carry pyroclastic mounds probably rafted from the scoria cones and have frequently developed foliations. Due to the overlapping of separate volcanoes and intense

erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...

discerning individual units is difficult. The volcanic field has erupted

and basaltic andesite, which when in lava form is grey to black in colour. Phenocryst composition in the rocks varies, encompassing

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 ...

, orthopyroxene, plagioclase and small amounts of biotite. Chemically, the rocks are

magnesium Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...

-rich

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. Ilmenite is an important accessory mineral. Some rocks have undergone palagonite-forming alteration. Xenoliths are also found within the lava, both

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 ...

containing xenocrysts and

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

ary rocks. The magmas that formed the field have compositions indicating they derive from primitive mantle magmas, which formed in the shallow mantle. Based on geothermometer analysis, temperatures of crystallization of the magmas have been obtained ranging and higher. Magma formation was probably influenced by the formation of ephemeral magma chambers and the interaction with crustal components and other magmas.

Eruptive history

The Bitiche lavas cover the 8.4 million years old Vilama ignimbrites and are in part covered by the 3.49 ± 0.01 million years old Tara ignimbrite, indicating that the field formed in the late Miocene-early

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58strombolian with some lava fountaining. The start of volcanic activity may have been preceded by hydrovolcanic processes that have left characteristic deposits.

References

Sources