Cerro Overo

Cerro Overo is a {{convert|480|x|580|m}} wide volcanic crater, which is elongated in east-west direction. Its maximum depth is about {{convert|72|m}}.{{sfn|Ureta|Németh|Aguilera|Zimmer|2021|p=10}} A {{convert|1.5|m}} thick layer of ejecta surrounds the maar and has a conspicuous black colour.

Cerro Overo lies on the {{convert|4556|m}} high Altos del Toro Blanco ridge{{sfn|Ureta|Németh|Aguilera|Zimmer|2021|p=2}} at the northeastern foot of Chiliques volcano. The La Albondiga lava dome lies about {{convert|5|km}} southwest of Cerro Overo.{{sfn|Alarcón|Díaz|Oliveros|Tapia|2025|p=2}} Closed lakes and basins are widespread in the region;{{sfn|Alarcón|Díaz|Oliveros|Tapia|2025|p=1}} Laguna Lejia is such a spring-fed lake{{sfn|Ureta|Németh|Aguilera|Zimmer|2021|p=4}} {{convert|6.3|km}} west-northwest of Cerro Overo.{{sfn|Ureta|Németh|Aguilera|Zimmer|2021|p=2}}

Geologically, Cerro Overo is part of the Central Volcanic Zone (CVZ) of the Andes, which is represented by Lascar and Chiliques volcanoes around Cerro Overo.{{sfn|Ureta|Németh|Aguilera|Zimmer|2021|p=2}} The CVZ is one of four volcanic belts that are located in the Andes, and which include the Northern Volcanic Zone, the Central Volcanic Zone, the Southern Volcanic Zone and the Austral Volcanic Zone. Volcanism occurs due to the subduction of the Nazca Plate off the west coast of South America.{{sfn|Ureta|Németh|Aguilera|Zimmer|2021|p=3}} Changes in its geometry over time have caused variations in the volcanic activity in the Central Volcanic Zone, the latest of which helped build the Puna-Altiplano, the highest volcanically active high plateau in the world.{{sfn|van Alderwerelt|Ukstins|Ramos|2021|p=2}}

The maar is set into Pliocene-age ignimbrites erupted by the La Pacana caldera, and the underlying rocks range in age from Permian to Miocene and include both volcanic and sedimentary rocks.{{sfn|Ureta|Németh|Aguilera|Zimmer|2021|p=3}} A fault like the Miscanti fault{{sfn|Alarcón|Díaz|Oliveros|Tapia|2025|p=2}} may have controlled its formation; the maar lies at the intersection of several north-northeast trending lineaments with a northwest-southeast trending regional tectonic structure.{{sfn|Ureta|Németh|Aguilera|Zimmer|2021|p=3}} Most likely, the faults allowed the magma to bypass the crustal structures that intercept mafic magmas such as these of Cerro Overo before they reach the surface.{{sfn|van Alderwerelt|Ukstins|Ramos|2021|p=12}} An aquifer may exist inside the Cerro Overo diatreme.{{sfn|Alarcón|Díaz|Oliveros|Tapia|2025|p=5}}

Cerro Overo has erupted basaltic andesite, which contains phenocrysts of clinopyroxene, olivine and plagioclase. Quartz occurs as xenoliths and xenocrysts.{{sfn|Ureta|Németh|Aguilera|Zimmer|2021|p=13}} The volcanic rocks define a calc-alkaline suite.{{sfn|van Alderwerelt|Ukstins|Ramos|2021|p=10}} They are the least silicic rocks of this region in the Andes and define a mafic member of the Central Volcanic Zone magmatic suite.{{sfn|van Alderwerelt|Ukstins|Ramos|2021|p=7}} Such mafic melts are uncommon in the region as the thick crust and underground magmatic processes hinder their ascent.{{sfn|van Alderwerelt|Ukstins|Ramos|2021|p=8}}

Based on its appearance, the maar was assigned a possible Holocene or postglacial age. Radiometric dating yielded an older age, of no more than 77,000 ± 7,800 years ago.{{sfn|Ureta|Németh|Aguilera|Zimmer|2021|p=2}} The eruption emplaced about eight separate units of volcanic rocks,{{sfn|Ureta|Németh|Aguilera|Zimmer|2021|p=5}} including about {{convert|0.0004|km3}} of lava and {{convert|0.000119|km3}} of tephra.{{sfn|Ureta|Németh|Aguilera|Zimmer|2021|p=11}} Magma rapidly ascended to the surface and triggered explosive, effusive and phreatomagmatic activity, which occurred owing to the availability of groundwater.{{sfn|Ureta|Németh|Aguilera|Zimmer|2021|p=19}} After its emplacement, the crater was partially filled by wind-transported and alluvial sediments.{{sfn|Ureta|Németh|Aguilera|Zimmer|2021|p=13}}

• List of volcanoes in Chile

{{Reflist|refs=

{{cite journal |last1=Matthews |first1=S. J. |last2=Moncrieff |first2=D. H. S. |last3=Carroll |first3=M. R. |title=Empirical calibration of the sulphur valence oxygen barometer from natural and experimental glasses: method and applications |journal=Mineralogical Magazine |date=June 1999 |volume=63 |issue=3 |page=422 |doi=10.1180/002646199548510 |s2cid=201642782 |url=https://www.cambridge.org/core/journals/mineralogical-magazine/article/empirical-calibration-of-the-sulphur-valence-oxygen-barometer-from-natural-and-experimental-glasses-method-and-applications/DBA999658CDA8C349F9901BAC30F7313 |language=en |issn=0026-461X}}

{{Cite GVP |name=Cerro Overo |vn=355097}}, [https://volcano.si.edu/volcano.cfm?vn=355097&vtab=Photos Photo Gallery]

{{Cite GVP |name=Cerro Overo |vn=355097}}

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{{refbegin}}

• {{cite journal |last1=Alarcón |first1=Noemi |last2=Díaz |first2=Daniel |last3=Oliveros |first3=Verónica |last4=Tapia |first4=Joseline |last5=Ureta |first5=Gabriel |last6=Salas |first6=Pablo |title=Highly conductive diatreme aquifer beneath the Cerro Overo maar, Central Andean volcanic zone, Chile |journal=Geology |date=13 February 2025 |doi=10.1130/G52741.1 |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G52741.1/652086/Highly-conductive-diatreme-aquifer-beneath-the?redirectedFrom=fulltext |issn=0091-7613}}
• {{cite journal |last1=Ureta |first1=Gabriel |last2=Németh |first2=Károly |last3=Aguilera |first3=Felipe |last4=Zimmer |first4=Martin |last5=Menzies |first5=Andrew |title=A window on mantle-derived magmas within the Central Andes: eruption style transitions at Cerro Overo maar and La Albóndiga lava dome, northern Chile |journal=Bulletin of Volcanology |date=2021-03-04 |volume=83 |issue=4 |pages=19 |doi=10.1007/s00445-021-01446-3 |bibcode=2021BVol...83...19U |s2cid=232108256 |url=https://link.springer.com/article/10.1007/s00445-021-01446-3 |language=en |issn=1432-0819}}
• {{cite journal |last1=van Alderwerelt |first1=B. |last2=Ukstins |first2=I.A. |last3=Ramos |first3=F.C. |title=Sr isotopes and geochemistry of Cerro Overo maar provide a unique window into arc magma genesis in the Central Volcanic Zone of the Andes |journal=Lithos |date=April 2021 |volume=386-387 |pages=105978 |doi=10.1016/j.lithos.2021.105978 |bibcode=2021Litho.38605978V |s2cid=233533697 |url=https://www.sciencedirect.com/science/article/pii/S0024493721000141 |language=en |issn=0024-4937}}

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• {{Cite thesis |last=van Alderwerelt |first=Brennan Martin Edelman de Roo |date=2017-01-01 |title=Diverse monogenetic volcanism across the main arc of the central Andes, northern Chile |url=https://iro.uiowa.edu/esploro/outputs/doctoral/Diverse-monogenetic-volcanism-across-the-main/9983777148702771 |type=PhD thesis |doi=10.17077/etd.rx3wdk3y |ref=none}}
• [https://web.archive.org/web/20210624211957/https://biblioteca.sernageomin.cl/opac/DataFiles/14905_v1_pp_484_487.pdf Caracterizacióngeológica y geoquímica del maar Cerro Overo, Andes Centrales]

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Category:Volcanoes of Antofagasta Region

Category:Maars of Chile

Category:Pleistocene volcanoes