Geography and geology Cerro Blanco (volcano)

1 geography , geology

1.1 regional setting
1.2 local setting
1.3 megaripple fields

geography , geology
regional setting

the central volcanic zone of andes area between 14–28° southern latitude volcanic activity dates eocene. ignimbritic activity has occurred on whole area, particularly north of 25° southern latitude altiplano–puna volcanic complex situated. ignimbrites rhyolite , rhyodacite , subordinate shoshonite. more southern ignimbrites felsic , have low crystal content. exception of luingo caldera , cerro galán, volcanism south of 25° southern latitude of low volume. after phase of pyroclastic activity in antofalla area during eocene, number of volcanoes formed calc-alkaline magmas during miocene. changes in subduction geometry including removal of continental crust boundary 8-3 mya have caused thickening of crust eastward shift of volcanic front. huaynaputina volcano in peru part of central volcanic zone , had major eruption in 1600.

most ignimbrites of southern sector have volumes of 50 cubic kilometres (12 cu mi) or less , associated stratovolcanoes , small calderas. derived fractional crystallization of andesitic magmas variable crustal input.

local setting

cerro blanco part of central volcanic zone , located @ southern limit of puna. forms volcanic unit aguada alumbrera ignimbrite, @ eastern edge of cordillera de san buenaventura. rocks beneath unit include dacitic–trachyandesitic volcanites 9–7 mya old , igneous-metamorphic granitic basement containing orthogneiss, quartz of neoproterozoic-early paleozoic age, containing paleozoic mafic ultramafic volcanic inclusions. cordillera de san buenaventura formed lava domes , volcanic complexes of intermediary composition of upper miocene–quaternary age. during miocene-pleistocene, isotope , chemical composition of areal magmas has moved away arc magmas distinctly water-poor , unoxidized petrologies. finding consistent hot mantle forming after delamination of crust , migration of arc.

nevado tres cruces lies west , nevado ojos del salado lies southwest of cerro blanco centre. east-northeast running fault systems controlled local tectonics , may responsible formation of cordillera de san buenaventura. 4-3.7 mya laguna amarga west of cerro blanco erupted rhyolites, unlike cerro blanco s ignimbrites. better known cerro galán caldera lies 80 kilometres (50 mi) southwest of cerro blanco. forms northwest-southeast volcanic line cerro blanco , incapillo. line active less 2.5 mya ago. trend defined culampaja line running sierra nevada on cerro cóndor , cerro peinado blanco. other volcanic centres in region miocene-pliocene ignimbrites las juntas , las papas. minor bimodal–mafic volcanic centres during pleistocene–holocene include volcanoes in pasto ventura, salar de carachi pampa , volcán negro peinado areals. felsic centres include chascón , cueros de purulla. cerro purulla lies northnorthwest of cerro blanco , la hoyada volcanic complex lies directly west. 4,380 metres (14,370 ft) cueros de purulla , 4,290 metres (14,070 ft) chascón major sources of obsidian in puna of catamarca region.

the cerro blanco complex formed pyroclastic flows extending nested calderas. robledo caldera heavily eroded , has assumed semicircular shape. rim of cerro blanco caldera proper well-preserved, ash , block flows filling interior. theory holds northern cerro blanco , southern robledo calderas part of 1 caldera minimum subsidence of 700 metres (2,300 ft) , dimension of 13 10 kilometres (8.1 mi × 6.2 mi). cerro blanco caldera 6 kilometres (3.7 mi) wide. on southern rim, surrounded ashfall deposits, lies holocene cerro blanco del robledo lava dome (26°46′51″s 67°45′27″w / 26.78083°s 67.75750°w / -26.78083; -67.75750). sources call whole volcano robledo , use cerro blanco refer lava dome. whole volcanic complex formed lava domes, ignimbrites, ash , block flows , unconsolidated deposits. cerro blanco largest lava dome , has debris collapse deposit on northern side. hydrothermally altered area in middle of caldera has been linked phreatomagmatic activity. el escondido crater northeast of caldera 1.2 kilometres (0.75 mi) wide , 40 metres (130 ft) deep. shows dark colour , semiannular shape in satellite images , has been interpreted phreatic crater. complex located @ southwest end of volcano-tectonic depression formed local fault systems. these fault systems channel magma during eruptions; no eruption column formed. formation of depression may influenced emptying of magma chambers associated volcano. complex located on 60 kilometres (37 mi) thick crust. crustal low seismic velocity anomaly located beneath cerro blanco, called southern puna magma body.

megaripple fields

campo de piedra pómez megaripples

mega ripple marks formed gravel found in cerro blanco area , among extreme on earth. these formed wind-driven processes acting on local ignimbrites, including saltation of fine grains , sand during wind. ripples have amplitudes varying 0.1–2 metres (3.9 in–6 ft 6.7 in) , wavelengths of 10–30 metres (33–98 ft). coarse gravel found @ top , more fine silt in lower parts. pumice blocks found in lee surfaces of ripples, interripple areas relatively flat. unlike dunes these structures not migrate once stably formed. material these structures formed includes lithic clasts densities 2,600–3,000 kilograms per cubic metre (4,400–5,100 lb/cu yd) , pumices densities 800–1,300 kilograms per cubic metre (1,300–2,200 lb/cu yd). formation of ripples associated bedrock ridges. these ripple marks have been compared martian ripple fields.

the largest field named campo piedra pómez (centered 26°36′17.30″s 67°34′50.46″w / 26.6048056°s 67.5806833°w / -26.6048056; -67.5806833) , covers surface area of 600 square kilometres (230 sq mi), descending 3,800 metres (12,500 ft) @ la hoyada in south 3,000 metres (9,800 ft) carachipampa volcano in north. megaripples in field dark, formed older ignimbrites , lavas of 70,000-year-old piedra pómez ignimbrite. northwest of cerro blanco caldera , towards laguna purulla lies field (centered 26°39′49.97″s 67°48′55.83″w / 26.6638806°s 67.8155083°w / -26.6638806; -67.8155083) surface area of 127 square kilometres (49 sq mi), has dark colour andesitic lava , falls down 4,100 metres (13,500 ft) altitude @ la hoyada 3,700 metres (12,100 ft) @ laguna purulla. reddish-brown rosada ignimbrites , white basement material components of field. other fields 12 square kilometres (4.6 sq mi) campo purulla (centered 26°37′12.27″s 67°46′00.66″w / 26.6200750°s 67.7668500°w / -26.6200750; -67.7668500) field downslope of cerro purulla distinct albedo 13,000 years old purulla ignimbrite, , 54 square kilometres (21 sq mi) salar de incahuasi (centered 26°31′53.61″s 67°41′36.93″w / 26.5315583°s 67.6935917°w / -26.5315583; -67.6935917) field piedra pómez ignimbrite of brown colour.