Aguas Calientes caldera

Aguas Calientes caldera lies in the northwestern Salta Province of Argentina, in the San Antonio de los Cobres district to the southeast of the town of the same name. of which Lascar volcano is the most active. The largest eruption in historical times in the CVZ occurred in 1600 on Huaynaputina volcano in Peru. Aguas Calientes caldera is a roughly circular caldera limited on the western and eastern side by north–south trending fault systems. Two superimposed calderas form the volcanic system. Cerro Verde inside the caldera is a dome formed by the uplifting of the Verde ignimbrites in the caldera after their deposition and cooling. Cerro Aguas Calientes was formed in the same way from the Tajmar ignimbrites, conclusions based in both cases on the outward dip of the ignimbrites contained in the domes. ==Geology==

The Central Volcanic Zone (CVZ), active mainly since the Miocene, is the volcanically active area of the Andes between 16 and 28°S. Its activity is dependent on the subduction of the Nazca Plate, previously the Farallon Plate, below the South American Plate. This subduction process is responsible for the formation of the Andes and the volcanic activity on the eastern margin of the South American continent. Geologic record Aguas Calientes caldera was between 11 and 10 Ma the source of large scale ignimbrite sheets. Aguas Calientes caldera is considered to be an overpressure caldera, where eruption is triggered by intrusions from the volcano sill weaken the host rocks and cause the formation of fissures. Composition Minerals in the Tajamar ignimbrite include biotite, hornblende, plagioclase, quartz and some augite. The eruption products are uniformly dacitic in nature. Hydrothermal alterations have generated Sb-Au and Pb-Ag-Zn deposits that may be of economic importance. These deposits occur in the form of mineralized breccia and quartz. The La Poma-Incachule mining district northeast of the caldera is part of the volcanic system and contains argentiferous galena, sphalerite, antimonite and arsenopyrite. These deposits formed through hydrothermal, deuteric alteration and supergene processes and were influenced during their formation by local fault systems. ==Eruptive history==

Aguas Calientes caldera erupted twice dacitic ignimbrites. was the source of two major ignimbrites; the Tajamar Ignimbrite (including the Chorrillos Ignimbrite inside the caldera), and the Verde Ignimbrite. The first was erupted 10.5–10.1 Ma and is a body of ignimbrite of about . The second was erupted 17.2 Ma and has a volume of . The first eruption, which took place 17.15 Ma, was the first caldera forming episode and the eruption occurred through a central vent. Its deposit, the Verde Ignimbrite, is pumice rich and green in colour. The deposits in thickness range from more than on Cerro Verde to in the southern outcrops. It covers a surface area of about . After the eruption, the Verde ignimbrites were tectonically deformed and partly buried by the Tajamar ignimbrites. The second eruption was more extensive and covered at a minimum . Starting from the caldera rim, it is clearly distinguishable in two units; the intracaldera Chorrillos and the extracaldera Tajamar units which were formerly considered to be separate events. The Chorrilos deposits are gray coloured and have pumice fragments of less than 5 cm diameter; they also contain breccia lenses. The Tajmar deposits overlie the Chorrillos deposits and have a red to pale pink colour. The ash flows from the eruption flowed out of the caldera, forming flow structures similar to large lava flows. The deposits underwent some devitrification due to vapour action. This ignimbrite has a maximum thickness of on Cerro Aguas Calientes in the caldera centre and thins to less than away from the volcano. ==See also==