The Vilama Caldera: A new interpretation of one of the largest calderas in Argentina Puna-Bolivia Altiplano.

SOLER, M.M., COIRA, B., CAFFE, P.J. AND A.T., ONOE

Pucón, Chile

Congreso; General Assembly IAVCEI; 2004

IAVCEI

Associated to the ignimbrite flare-up (Upper Miocene – Pliocene) recorded in the Altiplano Puna Volcanic Complex, several volcanic calderas have developed. One of them, Vilama caldera, had been interpreted as the product of two stages of collapse, conforming a giant structure (65 x 40 km), with central coordinates at 22°36’S - 66°51’W. The first collapse (trap-door) was associated to Granada Ignimbrite eruption and the second (downsag) to Vilama Ignimbrite eruption. Based on new detailed studies, we infer different vents for those ignimbrites, redefining location, stratigraphy, and age of Vilama caldera. The Granada Ignimbrite (10 Ma) was redefined as a precaldera unit and interpreted as erupted from a compound volcano with central coordinates at 22°34’S – 66°35’W. The outcrops of Vilama Ignimbrite (8.5 Ma) were enlarged from 1600 to 3400 km2 and characterized as two facies: intracaldera deposits (1050 km3), formed by a thick sequence (>400 m) of ignimbrites with different welding and phase vapour alteration, and extracaldera deposits (200 km3), comprising two cooling units that show a very different welding grade and striking evidences of quick deposition. The Vilama Ignimbrite eruption was associated to a collapse caldera (piston-like), the Vilama caldera, now redefined as a 35 x 15 km structure with central coordinates at 22°24’S - 66°57’W. Unrest of the latter is mainly represented by bending of intracaldera ignimbrites, and by the eruption of domes and stratovolcanoes which channelled through inferred structural borders. Probable links with Guacha and Coruto calderas (¿nested calderas?) need further study to be demonstrated.