La Caldera de colapso del Cerro Aguas Calientes, Salta, Argentina: evolución y esquema estructural




A new emission center of extensive pyroclastic flows has been recognized and interpreted, near San Antonio de los Cobres. The eruptive parameters and the volcanic history of the volcanic complex are pointed out. A caldera collapse controlled by left-lateral strike-slip faulting is proposed. The age of this caldera is 10-10.5 Ma. The least vesiculated magma volume is 200-250 km3. The identified pyroclastic flows are Verde Ignimbrite, Chorrillos Ignimbrite, Tajamar Ignimbrite and Abra del Gallo Ignimbrite. The volcanic history started with explosive events and opening of vents. The initial collapse of the caldera was asymmetric and only the eastern side developed. The eruption of the Verde Ignimbrite took place in this stage in a central vent. The continuous collapse and the opening of rim vents are related with the Chorrillos, Tajamar and Abra del Gallo ignimbrites. The Ignimbrite Tajamar is the principal collapse with intracaldera characteristics. The extracaldera facies is represented by the Ignimbrite Abra del Gallo. The collapse is completed in a short period of time, followed by a generalized resurgence in the caldera floor. Regional detumes-cence and probably the intrusion of a dome produced this resurgence. The postcaldera activity is represented by hydrotermal - geothermal activity. All of this process took place in a short period of time, ca 10-10.5 Ma. The field and petrographic data are coherent with the direction determinations of the Magnetic Anisotropy Susceptibility, and with the calculated temperatures of emplacement. The magmatic chamber geometry and the collapse of a caldera were controlled by the regional structural scheme. A WNW-ESE trend strike-slip fault system with left lateral movement called Calama-Olacapato-El Toro Lineament caused the local distension. These strike-slip faults continued and deformed the north side of the caldera. The magmatic system could have migrated to the west originating the Quevar volcanic complex (8Ma).