Английская Википедия:El Negrillar
Шаблон:Short description Шаблон:Infobox mountain El Negrillar is a volcanic field in the Andes. Located south of the Salar de Atacama and west of the Cordón de Púlar, it generated cinder cones and lava flows. Covering a surface area of Шаблон:Convert, it is the largest volcanic field in northern Chile, with almost a hundred vents that produced mainly lava flows. Owing to the arid climate, landforms are well preserved. Radiometric dating has yielded ages of less than 1.5 million years, with the most recent eruption occurring about 141,000 years ago. Parts of the Holocene Socompa debris avalanche overlie the field. A groundwater system underlies the volcanic field and some cones formed through phreatomagmatic eruptions. El Negrillar is located in a complex tectonic regime, characterized by numerous faults. The town of Tilomonte and various power lines, mines and water wells are in the area.
Geography and geomorphology
The Central Volcanic Zone (CVZ) of the Andes is a northwest-south trending volcanic arc that extends from Peru over Bolivia to Chile and Argentina.Шаблон:Sfn Most of its 44Шаблон:Sfn volcanoes are young stratovolcanoes, but there are also monogenetic volcanoes and the Altiplano-Puna volcanic complex, which has produced more than Шаблон:Convert of volcanic rocks.Шаблон:Sfn Stratovolcanoes in the El Negrillar area include Socompa south, Pular east of the volcanic field,Шаблон:Sfn and Aguas Delgadas.Шаблон:Sfn Towns in the area include Monturaqui, Tilomonte, Tilopozo and PeineШаблон:Sfn and a mining camp southwest of the field,Шаблон:Sfn there are cross-border power lines,Шаблон:Sfn and the local aquifer is pumped by various mining companies in the areaШаблон:Sfn just south of the volcanic field.Шаблон:Sfn Interest in the monogenetic volcanoes of the area arose in the 2010s and 2020s.Шаблон:Sfn
The El Negrillar field is south of the Salar de Atacama,Шаблон:Sfn not far from the border between Argentina and Chile,Шаблон:Sfn and consists of numerous unvegetatedШаблон:Sfn scoria cones and lava flows.Шаблон:Sfn It includes 51 ventsШаблон:Sfn named after Atacama flora and fauna,Шаблон:Sfn and 98 separate lava flowsШаблон:Sfn that extend downslope,Шаблон:Sfn making it the largest monogenetic volcanic field of northern Chile.Шаблон:Sfn Vents have produced mostly lava flows, but there are maars and scoria cones as well.Шаблон:Sfn Some cones have been breached when lava flowed out.Шаблон:Sfn The lava flows are blocky and have flow forms like scarps, ogives and leveesШаблон:Sfn that are well-conserved by the arid climate of the field;Шаблон:Sfn the longest flow has a length of Шаблон:Convert.Шаблон:Sfn The vents are spread over three sectors,Шаблон:Sfn and the northern in an eastern and a western sector.Шаблон:Sfn The northern and central sectors lie on the Tilomonte and Tilocalár ridges and the southern sector on the northwestern flank of the Aguas Delgadas volcano.Шаблон:Sfn The total area covered by the field exceeds Шаблон:Convert.Шаблон:Sfn
Geology
Off the western coast of South America, the Nazca Plate subducts beneath the South American Plate. The subduction is responsible for the volcanism of the CVZШаблон:Sfn and the other two volcanic zones, the Northern Volcanic Zone and the Southern Volcanic Zone.Шаблон:Sfn A fourth volcanic zone is known as the Austral Volcanic Zone.Шаблон:Sfn
El Negrillar is part of a wider field of monogenetic volcanoes south of Salar de Atacama, which includes Morro Punta Negra, La Negrillar, Tilocalar and Cerro Tujle. Their formation was probably influenced by faulting, as there are north-south trending thrust faults, northwest-southeast trending transverse faultsШаблон:Sfn and various types of folds,Шаблон:Sfn which enable magma ascentШаблон:Sfn through the Шаблон:Convert thick crust.Шаблон:Sfn Monogenetic activity in the area has progressively migrated north, with the youngest age being the 77,000 ± 54,000 years of Cerro Overo,Шаблон:Sfn and the volcanoes share a common magma source.Шаблон:Sfn El Negrillar is by far the largest of all these monogenetic volcanoes.Шаблон:Sfn
The surrounding and underlying terrain consists mostly of various volcanic rocks and alluvial fans.Шаблон:Sfn A Шаблон:Convert long north-south trending depression runs south from Salar de Atacama and is filled by water-containing volcanic rocksШаблон:Sfn of the Salín Formation.Шаблон:Sfn They form the Monturaqui-Negrillar-Tilopozo groundwater system, which conveys water to the Tilopozo area of Salar de Atacama. The flowШаблон:Sfn and composition of its waters are influenced by the El Negrillar volcanic field,Шаблон:Sfn which lies in the middle of the groundwater body and separates it into two halves.Шаблон:Sfn
Rocks erupted at El Negrillar have compositions ranging from basaltic andesite to dacite, with some trachytic components, and define a calc-alkaline suiteШаблон:Sfn with five distinct members.Шаблон:Sfn They contain phenocrysts of amphibole, olivine, plagioclase and pyroxene; quartz has been reported as well.Шаблон:Sfn Composition varies from the northern to the southern sector, as magmas of the southern sector are more primitive with fewer crystals and volatiles.Шаблон:Sfn The adakite-like composition implies that the magmas originated at great depths, where garnet is stable,Шаблон:Sfn from melting of a small fraction of crustal and mantle rocks. The magmas underwent fractional crystallizationШаблон:Sfn and during their ascent they absorbed varying quantities of crustal material.Шаблон:Sfn Their total volume is about Шаблон:Convert,Шаблон:Sfn making it one of the largest monogenetic volcanic fields worldwide.Шаблон:Sfn
Eruption history
El Negrillar formed in the Pleistocene. Eruptions produced lava flows, with subordinate explosive activity,Шаблон:Sfn at effusion rates reaching from a few to a few tens of cubic metres per second. Some eruptions may have lasted more than a year.Шаблон:Sfn Ages of the volcanoes range from 982,000 ± 8,000 to 141,000 ± 72,000 years,Шаблон:Sfn and is often not reflected in the appearance of the vents.Шаблон:Sfn It is possible that a change in tectonic regimen from compressive to extensive 780,000 years ago allowed the ascent of magma.Шаблон:Sfn Monogenetic eruptions can happen in areas without previous volcanic activity, and are a threat to the Salar de Atacama areaШаблон:Sfn and the infrastructure there.Шаблон:SfnШаблон:Sfn
The three vents Copao, Sandillón and Ruda erupted phreatomagmatically; they are tuff cones with infilling lava domes.Шаблон:Sfn The phreatomagmatic activity is probably a consequence of magma interaction with the Monturaqui-Negrillar-Tilopozo aquifer.Шаблон:Sfn About 7,000 years ago, Socompa collapsedШаблон:Sfn and partly buried the El Negrillar volcanoes.Шаблон:Sfn
See also
References
Sources
- Шаблон:Cite journal
- Шаблон:Cite journal
- Шаблон:Cite journal
- Шаблон:Cite journal
- Шаблон:Cite journal
- Шаблон:Cite journal
- Шаблон:Cite journal
