Gravity Modelling of the Ramados Caldera (Argentinean Puna, Central Andes)

In order to identify and characterize the vent area of abundant Upper Miocene proximal rhyolitic pyroclastic deposits and extrusive domes which concentrate in the Ramadas area, near Sant Antonio de los Cobres (Salta) at the Puna Altiplano (Central Andes), a detailed gravity survey has been carried out. Regional Bouguer gavity data were augmented with new 173 gravity observations measured sufficiently close-spaced to resolve the short wavelegth produced by the structure of interest. Besides, the geophysical survey was done in conjuction with geologic and geochemical studies which were critically important to our interpretation. After the separation of the regional trend, the residual anomaly map displays a circular gravity low reaching -80 mGal centered over scarce outcrops of rhyolitic and pyroclastic. This gravity low is interpreted as produced by block subsidence along ring fractures during eruption and/or deflation of the chamber. As the accumulation of thick, low density rock types in the zone of collapse is responsible of the prominent negative gravity anomalies, them has been used to estimated the thickness of caldera infill.