Negro de Chorrillos

Negro de Chorrillos lies on the Puna. Cerro Tuzgle and the major Calama-Olacapato-El Toro fault lie nearby, as do active and inactive hot springs.[2] This major fault zone is accompanied by a chain of volcanic systems.[3] The basement in the region is formed by Precambrian-Cambrian units with Cretaceous-Oligocene sediments[4] and ignimbrites from the Aguas Calientes caldera.[5]

Negro de Chorrillos is a volcano in the Andes.

Negro de Chorrillos covers a surface of about 5.88 square kilometres (2.27 sq mi).[6] 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.[7] 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).[5] The volume of both centres is less than 0.1 cubic kilometres (0.024 cu mi).[8] Negro de Chorrillos may be the source of local pyroclastic flows, and material eroded from such flows.[9]

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,[10] the El Toro fault.[11] Nearby faults include the Incachule fault to the south and the Chorrillos fault to the north, which actually crosses the Negro de Chorrillos centre.[12] Both faults are part of the Calama-Olacapato-El Toro fault.[7] An onset of crustal tension probably facilitated the ascent of magma.[5]

Negro de Chorrillos like San Geronimo has erupted basaltic trachyandesite to trachyandesite,[13] both shoshonite magmas.[11] 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.[14]

Eruption dates from the volcano are contradictory; radiometric dates range from 200,000 ± 150,000 years ago,[9] 450,000 years ago,[10] or 200,000 ± 80,000 years ago according to potassium-argon dating.[7] Lava flows from Negro de Chorrillos were later cut by fault offset.[15]