Negro de Chorrillos

24.2715°S 66.4148°W / -24.2715; -66.4148[1] Negro de Chorrillos is a volcano in the Andes.

Negro de Chorrillos - sometimes also known as Cerro Chorrillos or Cerro Negro de Chorrillos -[2] lies on the Puna, a high plateau in the Andes. Numerous volcanoes of the Central Volcanic Zone of the Andes, including calderas, monogenetic volcanoes and polygenetic volcanoes, rise on this plateau.[3] Most of the volcanoes there are back-arc volcanoes with only a few stratovolcanoes such as Tunupa, Cerro Tuzgle and Uturuncu[4] the second of which is close to Negro de Chorrillos. The major Calama-Olacapato-El Toro fault lie nearby, as do active and inactive hot springs.[5] This major fault zone is accompanied by a chain of volcanic systems;[6] in general, volcanism in the region has been influenced by large fault systems.[4] The basement in the region is formed by Precambrian-Cambrian units with Cretaceous-Oligocene sediments[7] and ignimbrites from the Aguas Calientes caldera.[8]

Negro de Chorrillos covers a surface of about 5.88 square kilometres (2.27 sq mi)[9] and features a scoria cone.[1] It has erupted lava flows of the aa lava and block lava type, which flowed 4 kilometres (2.5 mi) down a valley. Ash fall, lava bombs and scoria are also found.[10] Both Negro de Chorrillos and neighbouring San Jerónimo centres have heights of 300–450 metres (980–1,480 ft) and widths of 750–950 metres (2,460–3,120 ft).[8] The volume of both centres is less than 0.1 cubic kilometres (0.024 cu mi).[11] Negro de Chorrillos may be the source of local pyroclastic flows, and material eroded from such flows.[12]

The Negro de Chorrillos monogenetic volcano formed during the Pleistocene. Together with neighbouring San Geronimo volcano it lies on a left-trending strike-slip fault,[13] the El Toro fault.[14] Nearby faults include the Incachule fault to the south and the Chorrillos fault to the north, which actually crosses the Negro de Chorrillos centre.[15] Both faults are part of the Calama-Olacapato-El Toro fault.[10] An onset of crustal tension probably facilitated the ascent of magma.[8]

Negro de Chorrillos like San Geronimo has erupted basaltic trachyandesite to trachyandesite,[16] both shoshonite magmas.[14] The eruption that gave rise to Negro de Chorrillos took place in several stages that produced magmas of different composition.[1] They formed over the volcanic back-arc of the Peru-Chile Trench; low percentage melts that were contaminated with lithospheric material formed these two centres.[17]

Eruption dates from the volcano are contradictory; radiometric dates range from 200,000 ± 150,000 years ago,[12] 450,000 years ago,[13] 200,000 ± 80,000 years ago[10] and - the most recent dating effort - 51,000 ± 2,000 years ago according to potassium-argon dating.[18] Lava flows from Negro de Chorrillos were later cut by fault offset.[19]