Cordón de Puntas Negras

Cordón de Puntas Negrasis a 500 km(193 sq mi) volcanic chain located east of theSalar de AtacamainChile'sAntofagastaRegion.
Cordón de Puntas Negras is constructed along the major Calama–Olacapato–El Torofaultand is 70 kilometres (43 mi) long.The 25 kilometres (16 mi) long volcanic chain intersects with the 13 kilometres (8.1 mi) long Cordón Chalviri volcanic chain.Both chains cover a surface area of 500 square kilometres (190 sq mi) and contain cones, vents, lava domes, lava flows and maars,including a lava dome and silicic flow with a surface area of 13 square kilometres (5.0 sq mi).Puntas Negras specifically covers an area of 400 square kilometres (150 sq mi)and is the highest summit in the chain and features a 500 metres (1,600 ft) wide crater and a 13 kilometres (8.1 mi) longpyroclastic flow.Puntas Negras runs from theChiliquesvolcano on the north to volcán Puntas Negras (5,852 m (19,199 ft)) almost to the SE. The Puntas Negras Volcano forms the common endpoint of two chains of volcanoes in a V-shaped configuration. The southern leg of the V is called "Cordón Chalviri" whose other extreme is the Cerro Tuyajto, SW of Puntas Negras and at the same distance SE of theMiñiquesvolcano. Several small volcanic centres and lava flows are found here, including Aguas Calientes, Cerros Cenizas, Chinchilla and Laguna Escondida which have well preserved craters.The volcanic chain is associated with a topographic anomaly in the region, a property that other volcanoes in the area also have.
Rocks in the chain areandesite,basaltic andesiteanddacitecontainingbiotite,hornblendeandpyroxene.Magmas from this volcanic chain have acalc-alkalinecomposition formed by partial melting of amantle wedge,with research indicating a decrease inSiO2concentration over time.In the Tuyajto group, pastfumarolicactivity has bleached the volcanic rocks in the summit region.
The basement beneath the chain is composed fromOrdovicianmarine sediments that were later deformed by theAcadian orogeny.The 35 by 70 kilometres (22 mi × 43 mi)La Pacanacaldera is buried beneath Puntas Negras.Both the 3.2 ± 0.3 Patao ignimbriteand the 2.4 ± 0.4myaPampa Chamaca or TuyajtoignimbritefromLa Pacanamay have been erupted from beneath Puntas Negras.the Tuyajto ignimbrite is 530,000 ± 170,000 years old.
Biotitesinandesiticlavas have been dated 0.7 ± 0.3 to 0.3 ± 0.2 million years ago.Volcan Puntas Negras has generated postglacial lava flowsand a 13 square kilometres (5.0 sq mi) large lava dome west of Puntas Negras may be of Holocene age.Anolivinebasaltflow from the northern part of the chain extends over 10 kilometres (6.2 mi) towards Salar el Laco and may be of late Holocene age.The youngest volcanic centre appears to be located southeast of Laguna Escondida.Historical eruptions may have occurred in the Chalviri chain.A zone of anomalous electrical conductivity down to depths of 6 kilometres (3.7 mi) extends north toLascarvolcano.Cerro Overo at the southeastern end of Puntas Negras has been undergoing activedeformation,with a previously observed pattern of subsidence before 2003–2005 switching to a pattern of inflation. Filling and emptying of a magma reservoir linked to Puntas Negras may be the cause for these deformation patterns.Future eruptions may threaten mining operations atEl LacoandInternational Route CH-23[es].
The volcanic chain forms a water divide in the Andes, separating thePuna de Atacamafrom the basinsLaguna MiscantiandLaguna Miniques.A catchment area of 320 square kilometres (120 sq mi) for the Laguna Miscanti lies in the Cordón de Puntas Negras.Puntas Negras has been affected byglaciationduring thePleistocene,withmorainesreaching up to 4,400 metres (14,400 ft) altitude. Possibly, the entire chain was covered with glaciers,and certainly the southern part where several sets of moraines and glacialtrimlineshave been identified.Water from Cordón de Puntas Negras is a principal water source for Laguna Miscanti.