page_title: Purico complex
section_title: Post-ignimbrite activity
hierarchical_section_title: Purico complex / Eruptive history / Post-ignimbrite activity
caption_attribution_description: English: The Cerro Toco stratovolcano 5,604&#160;m (18,386&#160;ft) lies at the northern end of the Purico Complex pyroclastic shield.
context_page_description: The Purico complex is a Pleistocene volcanic complex in Chile close to Bolivia, formed by an ignimbrite, several lava domes and stratovolcanoes and one maar. It is one of the Chilean volcanoes of the Andes, and more specifically the Chilean segment of the Central Volcanic Zone, one of the four volcanic belts which make up the Andean Volcanic Belt. The Central Volcanic Zone spans Peru, Bolivia, Chile and Argentina and includes 44 active volcanoes as well as the Altiplano-Puna volcanic complex, a system of large calderas and ignimbrites of which Purico is a member of. Licancabur to the north, La Pacana southeast and Guayaques to the east are separate volcanic systems.
  The Purico complex consists of a shield shaped volcanic structure consisting of the Purico ignimbrite and a number of secondary volcanoes that are emplaced on this volcanic shield. During the ice ages, the shield was in part covered by glaciers which have left moraines. Purico is the source of the Purico ignimbrite, a moderately large ignimbrite with a volume of about 80–100 cubic kilometres. After the emplacement of the Purico ignimbrite, a number of lava domes and stratovolcanoes developed on the ignimbrite shield.
context_section_description: Volcanic activity after the eruption of the ignimbrite has been subdivided into the older andesitic Purico group and the younger Chascon group. The first includes Cerro Negro, Cerro Purico, Putas and Cerro Toco which assume the structure of polygenetic volcanoes, while the latter is taken to include Aspero, El Cerillo/Chajnantor and El Chascon which are lava dome-lava flow structures. The Chascon group of domes is also the only one which contains mafic xenoliths.
  The Cerro Purico and Macon volcanoes formed a short time after, and possibly even before, the ignimbrites. They are thus old volcanic centres and deeply eroded, displaying moraine deposits from glaciation and rocks which have been subject to hydrothermal alteration from fumarolic activity. Such hydrothermal alteration processes are also the origin of the sulfur deposits at Purico.
  Aspero, Cerro El Chascon, Cerros El Negro and Putas are younger and show no evidence of glaciation. El Chascon especially may be only tens of thousands of years old, seeing as it displays both a summit crater and pristine lava flow structures. Aspero was once considered to be of Holocene age; later, dates of 180,000 ± 20,000 years ago were obtained on Aspero and Chascon. Apart from these, there are no radiometric dates for post-ignimbrite volcanic structures at Purico. The eruptive episode that formed these centres is thus more recent than the Purico ignimbrite and may have been triggered by mafic magma being injected into the Purico system. It is also much smaller, with volumes ranging 0.36–4 cubic kilometres (0.086–0.960 cu mi).
  This change in the pattern of eruptive activity from large ignimbrites to smaller domes reflects a change in the nature of the magma supply, from large volume flow that heavily interacted with the crust and gave rise to the ignimbrites to smaller volume flows in a colder and thus brittler crust and did not accumulate or interact with it in a significant way. Thus the later eruption products appear to be more primitive and less affected by crustal contamination.
  The Macon stratovolcano is considered to be of Holocene age, and Alitar maar displays active fumaroles. Presently, there is no indication of seismic activity in the Purico area.
caption: Cerro Toco
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