The Vicuña Pampa Volcanic Complex, Southern Central Andes

GUZMÁN, S.; PETRINOVIC, I.; MARTI, J.; MONTERO LOPEZ, C.; NERI, M.; CARNIEL, R.; GROSSE, P.

Congreso; 26th IUGG; 2015

The Vicuña Pampa Volcanic Complex is located at the southeastern edge of the Altiplano-Puna Plateau (Central Andes). It is peculiar not only for its location, but also because of its composition, which varies from basaltic to dacitic. Previously it was interpreted as a collapse caldera because of its caldera-like morphology, although confirmed calderas of this composition are unknown in the Central Andes. No straightforward evidences 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, features typical of a collapse caldera such as intra- and extra-caldera pyroclastic flow deposits, or ring faults are lacking. The walls of the depression are formed by a ca. 12 Ma sequence of basaltic to basaltic andesite, massive to poorly stratified matrix-supported monolithologic volcanic breccias up to 300 m thick, overlaid by at least two lava flows of trachybasaltic andesite to trachydacitic 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 volcanic conduits and volcanic breccias, the latter robably related to hydromagmatic to purely magmatic activity of lava domes. 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. A preferred interpretation is an eroded shield-like volcano showing its roots within a central depression superposed with a renewed episode of volcanic activity limited to its SW portion.