Chimpa is a volcano in Argentina, close to the border between the Jujuy Province and the

Salta Province Salta () is a province of Argentina, located in the northwest of the country. Neighboring provinces are from the east clockwise Formosa, Chaco, Santiago del Estero, Tucumán and Catamarca. It also surrounds Jujuy. To the north it borders Boliv ...

. The volcano is of Miocene age, one date given being 12 million years ago and another is 7 million years ago.

Geomorphology and geology

Chimpa has two summits, the high Cerro Chimpa and the or high Cerro Cajón. The wide west-northwest trending Casana valley separates the two. The volcanic edifice was constructed in two stages, the first consisting of explosive and the second of effusive activity. The explosive activity generated ignimbrites and pyroclastic flows. On top of these, many poorly preserved

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 were emplaced in a radial pattern and constitute three separate formations. The explosive stage formed the Basal Unit, which consists of ignimbrites that originally constructed a shield but features no indication of 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 ...

, probably due to a "boiling-over"-like dynamic of the eruption. After this stage of a rather broad volcanic edifice, a more concentrated volcanic activity took place. The post-explosive activity has been subdivided into two units, the Cajon Unit formed by

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 and block-and-ash flows and the blocky lava flows of the Chimpa Unit. This unit is the last activity of the volcano, which is presently

dormant Dormant, "sleeping", may refer to: Science *Dormancy Dormancy is a period in an organism's life cycle when growth, development, and (in animals) physical activity are temporarily stopped. This minimizes metabolic activity and therefore helps ...

. Even if the volcano were to erupt again, the region is sparsely populated. The Casana valley was produced by the combined effects of faulting, erosion and hydrothermal activity. It is delimited by

scarp Scarp may refer to: Landforms and geology * Cliff, a significant vertical, or near vertical, rock exposure * Escarpment, a steep slope or long rock that occurs from erosion or faulting and separates two relatively level areas of differing elevatio ...

s generated by tectonic activity. It features evidence of a sector collapse that removed the volcanic vents. Debris from this collapse consists of large toreva blocks and

debris avalanche Debris flows are geological phenomena in which water-laden masses of soil and fragmented rock rush down mountainsides, funnel into stream channels, entrain objects in their paths, and form thick, muddy deposits on valley floors. They generally ...

deposits that are located within the Casana valley. The collapse may have occurred shortly after the last eruption, or after a significant timespan. It began as an eastward collapse that was followed within a brief timespan by a westward collapse. The collapses emplaced their debris within the Casana valley and collapse debris covers an area of about .

Composition

The volcanic rocks are of

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 ...

to andesite composition, defining a potassium-rich calc-alkaline suite. They contain phenocrysts of

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 ...

, hornblende, ilmenite, magnetite,

orthopyroxene The pyroxenes (commonly abbreviated to ''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 calcium (Ca), sodium (Na), iron (Fe II) ...

, plagioclase and quartz. Mafic inclusions occur in some eruption products. Rocks from within the core region of the volcano bear evidence of intense hydrothermal alteration, which weakened the edifice and conditioned its collapse. The hydrothermal alteration did not occur in all units and at all times.

Regional

Off the western coast of South America, 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 ...

subducts beneath the

South American Plate The South American Plate is a major tectonic plate which includes the continent of South America as well as a sizable region of the Atlantic Ocean seabed extending eastward to the African Plate, with which it forms the southern part of the Mid-A ...

. This subduction process is responsible for the volcanic activity of the Andes. The

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, ...

of the region is formed by various

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 ...

s of

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...

to Tertiary age, some of which crop out around the volcano. This basement is cut by various faults, which mark an uplift that forms the Creston Alto de La Aguada east of Chimpa volcano, as well as the Calama-Olacapato-El Toro lineament and associated faults which runs south of the Chimpa volcano. They have localized the formation of volcanoes along its path and also influenced the activity of Chimpa. Cerro Rumio is another volcano which crops out south of Chimpa and is in part buried by Chimpa's deposits. Chimpa lies in the Puna, a high plateau that began to form in the Eocene-

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

. The geologic

consists of the Neoproterozoic Puncoviscana Formation, which is overlaid by Paleozoic to

Paleogene The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period, geologic period and system that spans 43 million years from the end of the Cretaceous Period million yea ...

sediments and Miocene volcanic rocks. Volcanoes there are part of the

back-arc A back-arc basin is a type of geologic basin, found at some convergent plate boundaries. Presently all back-arc basins are submarine features associated with island arcs and subduction zones, with many found in the western Pacific Ocean. Most of ...

region of the Andean

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 ...

, where volcanism is caused by the

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 ...

of the

underneath the South America Plate. Puna volcanism took place in two episodes, one between 17.15-5.3 million years ago and a second during the last 1.5 million years.

References

{{Reflist, refs= {{cite journal , last1=Bustos , first1=E. , last2=Capra , first2=L. , last3=Arnosio , first3=M. , last4=Norini , first4=G. , title=Volcanic debris avalanche transport and emplacement at Chimpa volcano (Central Puna, Argentina): Insights from morphology, grain-size and clast surficial textures , journal=Journal of Volcanology and Geothermal Research , date=September 2022 , volume=432 , pages=107671 , doi=10.1016/j.jvolgeores.2022.107671, bibcode=2022JVGR..43207671B , s2cid=252225629 {{cite journal , last1=Bardelli , first1=L. , last2=Becchio , first2=R. , last3=Ortíz , first3=A. , last4=Schmitt , first4=A.K. , last5=Pereira , first5=R. , last6=Báez , first6=W. , last7=Reckziegel , first7=F. , last8=Viramonte , first8=J. , last9=Giordano , first9=G. , title=Repeated extraction of aphyric melts in a rhyolitic system revealed by zircon age and composition: The Ramadas Volcanic Centre (Puna plateau), NW Argentina , journal=Lithos , date=July 2021 , volume=392-393 , pages=106141 , doi=10.1016/j.lithos.2021.106141 , bibcode=2021Litho.39206141B , s2cid=233559606 , url=https://www.sciencedirect.com/science/article/pii/S0024493721001778 , language=en , issn=0024-4937 {{cite journal , last1=Bustos , first1=Emilce , last2=Simón , first2=Valeria , last3=Arnosio , first3=Marcelo , last4=Norini , first4=Gianluca , last5=Ducart , first5=Diego Fernando , last6=Suzaño , first6=Néstor , title=The hydrothermal system associated with Miocene Chimpa volcano, Central Andes. Implications on potential mineralization , journal=Journal of South American Earth Sciences , date=January 2021 , volume=105 , pages=102998 , doi=10.1016/j.jsames.2020.102998 , bibcode=2021JSAES.10502998B , s2cid=228810813 , url=https://www.sciencedirect.com/science/article/pii/S0895981120305411 , language=en , issn=0895-9811 {{cite journal , last1=Bustos , first1=Emilce , last2=Arnosio , first2=Marcelo , last3=Báez , first3=Walter , last4=Norini , first4=Gianluca , last5=Suzaño , first5=Néstor Omar , last6=Viramonte , first6=José Germán , title=Geomorphological evolution of the Chimpa stratovolcano in the back-arc region of the Central Andes , journal=Geomorphology , date=September 2020 , volume=364 , pages=107251 , doi=10.1016/j.geomorph.2020.107251 , bibcode=2020Geomo.36407251B , s2cid=219442187 , url=https://www.sciencedirect.com/science/article/pii/S0169555X20302233 , language=en , issn=0169-555X {{cite journal , last1=Norini , first1=Gianluca , last2=Bustos , first2=Emilce , last3=Arnosio , first3=Marcelo , last4=Baez , first4=Walter , last5=Zuluaga , first5=Maria Clara , last6=Roverato , first6=Matteo , title=Unusual volcanic instability and sector collapse configuration at Chimpa volcano, central Andes , journal=Journal of Volcanology and Geothermal Research , date=March 2020 , volume=393 , pages=106807 , doi=10.1016/j.jvolgeores.2020.106807 , bibcode=2020JVGR..39306807N , s2cid=214184780 , url=https://www.sciencedirect.com/science/article/pii/S0377027319306377 , language=en , issn=0377-0273 {{cite journal, last1=Acocella, first1=V., last2=Gioncada, first2=A., last3=Omarini, first3=R., last4=Riller, first4=U., last5=Mazzuoli, first5=R., last6=Vezzoli, first6=L., title=Tectonomagmatic characteristics of the back-arc portion of the Calama-Olacapato-El Toro Fault Zone, Central Andes, journal=Tectonics, date=June 2011, volume=30, issue=3, pages=n/a, doi=10.1029/2010TC002854, bibcode=2011Tecto..30.3005A, hdl=11336/13093, s2cid=129273472 , hdl-access=free {{cite journal, last1=Norini, first1=G., last2=Cogliati, first2=S., last3=Baez, first3=W., last4=Arnosio, first4=M., last5=Bustos, first5=E., last6=Viramonte, first6=J., last7=Groppelli, first7=G., title=The geological and structural evolution of the Cerro Tuzgle Quaternary stratovolcano in the back‐arc region of the Central Andes, Argentina, journal=Journal of Volcanology and Geothermal Research, date=September 2014, volume=285, pages=214–228, doi=10.1016/j.jvolgeores.2014.08.023, bibcode=2014JVGR..285..214N, issn=0377-0273 {{cite journal, last1=Arnosio, first1=Marcelo, title=Evidencia textural y geoquímica de mezcla de magmas en el volcán Chimpa, Puna Salteña, journal=Revista de la Asociación Geológica Argentina, date=2010, volume=66, issue=1–2, pages=253–270, url=http://www.scielo.org.ar/scielo.php?pid=S0004-48222010000100023&script=sci_arttext&tlng=pt, language=es, issn=0004-4822 Miocene volcanoes Volcanoes of Argentina