La Pacana

La Pacana
Name	La Pacana
Elevation m	5000
Location	Antofagasta Region, Chile
Coordinates	23°30′S 68°00′W
Type	Caldera
Age	Pleistocene
Last eruption	Pleistocene

La Pacana La Pacana is a large Pleistocene caldera in the Antofagasta Region of northern Chile, notable for its extensive ignimbrite outcrops and high‑altitude basins. The feature lies within the Central Volcanic Zone of the Andes and is associated with a complex history of magmatism, hydrothermal alteration, and lacustrine sedimentation that has attracted studies from institutions and researchers worldwide.

Geography and setting

La Pacana occupies a plateau in the Atacama Plateau adjacent to the Salar de Atacama and near the border of the Puna de Atacama, flanked by features such as Cerro Guacha, Cerro Cerro del Medio, and the Altiplano. The caldera is proximate to the cities and towns of Antofagasta, Calama, and San Pedro de Atacama and lies within the jurisdictions of Chilean regional bodies and protected areas that also include landscapes like the Salar de Uyuni region and Eduardo Avaroa Andean Fauna National Reserve. Surrounding tectonic and physiographic landmarks include the Andes, the Altiplano–Puna volcanic complex, the Central Volcanic Zone, and plate‑boundary structures associated with the Nazca Plate and South American Plate. Research access is often staged via nodes such as the Universidad de Chile, Universidad Católica del Norte, and international observatories which coordinate logistics with agencies like CONICYT and the Comisión Chilena de Energía Nuclear.

Geological overview

La Pacana is situated within a Miocene to Pleistocene volcanic province influenced by subduction of the Nazca Plate beneath the South American Plate, and it is part of the Altiplano–Puna volcanic complex along with complexes like Cerro Galán, Purico, and Uturuncu. Regional geology includes stratigraphic units correlated with formations studied at sites such as Salar de Atacama, Atacama Fault System, and Altos de Pica, and tectonic structures comparable to the Eastern Cordillera and Western Cordillera sectors. The caldera rims and ignimbrite sheets are intercalated with Quaternary lacustrine deposits and alluvial fans linked to basins compared with those at Salar de Coipasa and the Lake Titicaca region, and they record interactions with volcanic centers like Licancabur and Ollagüe.

Caldera formation and volcanic history

Caldera collapse at La Pacana is marked by eruption of large volume ignimbrites comparable to eruptions at Cerro Galán, Pastos Grandes, and Toba, and the main evacuated unit has been correlated with the Atana and Toconao systems. Eruptive phases include precaldera dome growth and pumiceous fallout followed by voluminous pyroclastic flows and caldera collapse; these stages are analogous to cycles documented at Taupo, Yellowstone, and Krakatoa. Subsequent resurgent volcanism produced obsidian and lava domes akin to those of Vesuvius and Montserrat, and pyroclastic stratigraphy has been constrained using methods employed at Pinatubo, Chichón, and Santorini.

Petrology and geochemistry

Rocks from La Pacana range from high‑silica rhyolite to dacite and display mineral assemblages that include quartz, sanidine, biotite, and accessory zircon, comparable to mineral parageneses reported from Long Valley, Fish Canyon Tuff, and Bishop Tuff. Isotopic and trace element studies parallel work performed at Mt. St. Helens, Mt. Hood, and Mount Shasta and utilize techniques developed by geochemical laboratories at institutions such as the Scripps Institution of Oceanography, the USGS, and ETH Zurich. Geochemical signatures imply crustal assimilation and fractional crystallization processes similar to those inferred for Nevado del Ruiz, Popocatépetl, and Colima, and zircon U–Pb ages and Hf isotopes have been applied in correlation with datasets from the Geological Survey of Argentina and the Instituto de Geología y Minería.

Hydrothermal activity and mineralization

Hydrothermal alteration at La Pacana produced advanced argillic and propylitic alteration zones and ore mineral phases including alunite, kaolinite, and sulfides, paralleling deposits studied at El Teniente, Chuquicamata, and Escondida. Acid sulfate systems and geothermal manifestations in the region relate to fluid circulation processes observed at Cerro Negro, Copahue, and Sol de Mañana. Mineral exploration by mining companies and academic teams has targeted epithermal and porphyry‑related signatures analogous to those at Yanacocha, Lagunas Norte, and Cerro Casale, and metallogenic models incorporate frameworks used by the International Mineralogical Association and industry partners such as Codelco and Barrick.

Paleoclimate and lacustrine records

Paleolakes within and near La Pacana preserve diatomites, tufas, and lacustrine marls that record climatic shifts comparable to sequences at Lake Titicaca, Lake Poopó, and Salar de Uyuni. Sediment cores and pollen studies use methods similar to those applied at Lake El'gygytgyn, Lake Van, and Lake Baikal and inform reconstructions of Last Glacial Maximum to Holocene hydrology as discussed by researchers affiliated with the IPCC and PAGES. Evaporite and carbonate deposits reflect fluctuating water tables influenced by teleconnections like ENSO and have been compared to paleoenvironmental records from the Amazon Basin, Patagonia, and the South Pacific.

Human history and research studies

Human interaction with the La Pacana region involves indigenous Andean groups linked culturally to sites such as Tiwanaku, Inca road networks, and Pukara architecture, and archaeological surveys coordinate with museums and universities including Museo Nacional de Historia Natural, Universidad de Buenos Aires, and institutions in La Paz. Scientific investigations have been conducted by multidisciplinary teams from organizations such as the USGS, CNRS, ANU, and research programs funded by NSF, CONICYT, and ERC, producing publications in journals like Nature, Science, Journal of Volcanology and Geothermal Research, and Earth and Planetary Science Letters. Ongoing monitoring and research collaborations involve the Smithsonian Institution's Global Volcanism Program, earthquake networks like IRIS, and remote sensing platforms from NASA, ESA, and JAXA.

Category:Calderas of Chile Category:Volcanic complexes of the Central Volcanic Zone