The Vicuña Pampa Volcanic Complex, Southern Central Andes

GUZMÁN, S.; MARTÍ, J.; PETRINOVIC, I. ; MONTERO, C.; BROD, A.; GROSSE, P.

Bolsena

Workshop; IV Collapse Caldera Workshop; 2012

IAVCEI - Comision on Collapse Calderas

The Vicuña Pampa Volcanic Complex is located at the southeastern edge of the Altiplano-Puna Plateau. It is peculiar not only for its location, but also because of its composition, which varies from basalts to dacites. It has been interpreted as a collapse caldera by Rossello & Jones (1999) and Viramonte & Petrinovic (1999), based mostly in its caldera-like morphology. No calderas of this composition have been reported in the Central Andes, making the study of this centre really intriguing. No straightforward clues to classify this volcanic structure are found. The features that favour its interpretation as a collapse caldera are its subcircular shape, a central depression and the shallow slopes of the outer deposits. On the other hand, no pyroclastic deposits related to the complex, no ring faults and no deposit related to a caldera collapse episode have been found. The walls of the depression are formed by a ca. 12 Ma (Guzmán et al. in prep) sequence of basaltic to andesitic, massive to poorly stratified matrix-supported monolithologic volcanic breccias up to 300 m thick, overlain by at least two lava flows of basaltic to andesitic composition. The deposits within the depression are mostly covered by reworked material. Its eastern part is formed by igneous-metamorphic basement, whereas the central and western sectors show lava domes and volcanic breccias probably related to their repeated gravity driven collapse. In summary, although Vicuña Pampa has one of the most caldera-like shapes of the Central Andes, no deterministic features to definitely prove it are found.