Chimpa

Chimpa is a volcano in Argentina, close to the border between the Jujuy Province and the Salta Province.[1] The volcano is of Miocene age,[2] one date given being 12 million years ago[3] and another is 7 million years ago.[4]

## Contents

* 1 Geomorphology and geology
* 1.1 Composition
* 2 Regional
* 3 References

## Geomorphology and geology

Chimpa has two summits, the 4,856 metres (15,932 ft) high Cerro Chimpa and the 4,796 metres (15,735 ft)[1] or 4,774 metres (15,663 ft) high Cerro Cajón. The 2 kilometres (1.2 mi) wide west-northwest trending Casana valley separates the two.[5] 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 flows were emplaced in a radial pattern and constitute three separate formations.[1] The explosive stage formed the Basal Unit, which consists of ignimbrites that originally constructed a shield but features no indication of a caldera, 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.[6] The post-explosive activity has been subdivided into two units, the Cajon Unit formed by lava domes and block-and-ash flows and the blocky lava flows of the Chimpa Unit. This unit is the last activity of the volcano,[5] which is presently dormant. Even if the volcano were to erupt again, the region is sparsely populated.[7]

The Casana valley was produced by the combined effects of faulting, erosion and hydrothermal activity.[8] It is delimited by scarps 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 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[5] and collapse debris covers an area of about 10 square kilometres (3.9 sq mi).[6]

### Composition

The volcanic rocks are of basaltic andesite to andesite composition, defining a potassium-rich calc-alkaline suite. They contain phenocrysts of biotite, hornblende, ilmenite, magnetite, orthopyroxene, plagioclase and quartz. Mafic inclusions occur in some eruption products.[1] Rocks from within the core region of the volcano bear evidence of intense hydrothermal alteration, which weakened the edifice and conditioned its collapse.[5] The hydrothermal alteration did not occur in all units and at all times.[8]

## Regional

Off the western coast of South America, the Nazca Plate subducts beneath the South American Plate. This subduction process is responsible for the volcanic activity of the Andes.[7] The basement of the region is formed by various formations of Precambrian 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[1] and also influenced the activity of Chimpa.[3] Cerro Rumio is another volcano which crops out south of Chimpa and is in part buried by Chimpa's deposits.[1]

Chimpa lies in the Puna, a high plateau that began to form in the Eocene-Oligocene. The geologic basement consists of the Neoproterozoic Puncoviscana Formation, which is overlaid by Paleozoic to Paleogene sediments and Miocene volcanic rocks. Volcanoes there are part of the back-arc region of the Andean Central Volcanic Zone, where volcanism is caused by the subduction of the Nazca Plate underneath the South America Plate.[5] 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.[6]

## References

1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Arnosio, Marcelo (2010). "Evidencia textural y geoquímica de mezcla de magmas en el volcán Chimpa, Puna Salteña" (in es). Revista de la Asociación Geológica Argentina 66 (1–2): 253–270. ISSN 0004-4822. http://www.scielo.org.ar/scielo.php?pid=S0004-48222010000100023&script=sci_arttext&tlng=pt.
2. ↑ Norini, G.; Cogliati, S.; Baez, W.; Arnosio, M.; Bustos, E.; Viramonte, J.; Groppelli, G. (September 2014). "The geological and structural evolution of the Cerro Tuzgle Quaternary stratovolcano in the back-arc region of the Central Andes, Argentina". Journal of Volcanology and Geothermal Research 285: 214–228. doi:10.1016/j.jvolgeores.2014.08.023. ISSN 0377-0273. Bibcode: 2014JVGR..285..214N.
3. ↑ 3.0 3.1 Acocella, V.; Gioncada, A.; Omarini, R.; Riller, U.; Mazzuoli, R.; Vezzoli, L. (June 2011). "Tectonomagmatic characteristics of the back-arc portion of the Calama-Olacapato-El Toro Fault Zone, Central Andes". Tectonics 30 (3): n/a. doi:10.1029/2010TC002854. Bibcode: 2011Tecto..30.3005A.
4. ↑ Bardelli, L.; Becchio, R.; Ortíz, A.; Schmitt, A.K.; Pereira, R.; Báez, W.; Reckziegel, F.; Viramonte, J. et al. (July 2021). "Repeated extraction of aphyric melts in a rhyolitic system revealed by zircon age and composition: The Ramadas Volcanic Centre (Puna plateau), NW Argentina" (in en). Lithos 392-393. doi:10.1016/j.lithos.2021.106141. ISSN 0024-4937. Bibcode: 2021Litho.39206141B. https://www.sciencedirect.com/science/article/pii/S0024493721001778.
5. ↑ 5.0 5.1 5.2 5.3 5.4 Norini, Gianluca; Bustos, Emilce; Arnosio, Marcelo; Baez, Walter; Zuluaga, Maria Clara; Roverato, Matteo (March 2020). "Unusual volcanic instability and sector collapse configuration at Chimpa volcano, central Andes" (in en). Journal of Volcanology and Geothermal Research 393. doi:10.1016/j.jvolgeores.2020.106807. ISSN 0377-0273. Bibcode: 2020JVGR..39306807N. https://www.sciencedirect.com/science/article/pii/S0377027319306377.
6. ↑ 6.0 6.1 6.2 Bustos, Emilce; Arnosio, Marcelo; Báez, Walter; Norini, Gianluca; Suzaño, Néstor Omar; Viramonte, José Germán (September 2020). "Geomorphological evolution of the Chimpa stratovolcano in the back-arc region of the Central Andes" (in en). Geomorphology 364. doi:10.1016/j.geomorph.2020.107251. ISSN 0169-555X. Bibcode: 2020Geomo.36407251B. https://www.sciencedirect.com/science/article/pii/S0169555X20302233.
7. ↑ 7.0 7.1 Bustos, E.; Capra, L.; Arnosio, M.; Norini, G. (September 2022). "Volcanic debris avalanche transport and emplacement at Chimpa volcano (Central Puna, Argentina): Insights from morphology, grain-size and clast surficial textures". Journal of Volcanology and Geothermal Research 432. doi:10.1016/j.jvolgeores.2022.107671. Bibcode: 2022JVGR..43207671B.
8. ↑ 8.0 8.1 Bustos, Emilce; Simón, Valeria; Arnosio, Marcelo; Norini, Gianluca; Ducart, Diego Fernando; Suzaño, Néstor (January 2021). "The hydrothermal system associated with Miocene Chimpa volcano, Central Andes. Implications on potential mineralization" (in en). Journal of South American Earth Sciences 105. doi:10.1016/j.jsames.2020.102998. ISSN 0895-9811. Bibcode: 2021JSAES.10502998B. https://www.sciencedirect.com/science/article/pii/S0895981120305411.

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