Construction and degradation of a broad volcanic massif: The Vicuña Pampa volcanic complex, southern Central Andes, NW Argentina

GUZMÁN, S.; STRECKER, M.; MARTI, J; PETRINOVIC, I. A.; SCHILDGEN, T.; GROSSE, P.; MONTERO, C.; NERI, M.; CARNIEL, R.; HONG, F; MURUAGA, C.; MASAFUMI, S.

GEOLOGICAL SOCIETY OF AMERICA BULLETIN

GEOLOGICAL SOC AMER, INC

Lugar: Boulder; Año: 2016

0016-7606

The Vicuña Pampa Volcanic Complex (VPVC), at the SE edge of the arid PunaPlateau of the Central Andes, records the interplay between volcanic construction and erosional downwearing, aided by past wetter conditions, topographic configuration, and tectonism. The low-sloping VPVC, with a 1200-m-deep, southeastward-opening depression, was previously interpreted as a collapse caldera based on morphological considerations. However, close inspection reveals that characteristic features associated with collapse calderas do not exist, suggesting instead that the VPVC is a strongly eroded composite volcano. Construction of the VPVC occurred during two distinct cycles (the first and main cycle took place at ca. 12 Ma) separated by the development of the depression. We interpret the central depression to result primarily from faulting and deep fluvial incision that occurred during the middle and late Miocene. This is surprising, considering the arid conditions in the region today. Volcanic textures indicating interaction with water and paleobotanical evidence suggest that the area was characterized by relatively humid conditions when the volcanic complex was being eroded. Patterns of river steepness values also point to the existence of a former orographic rainfall gradient at the Puna margin, in positions west of its current location in the Sierras Pampeanas. Together, the dissected morphology of the inner depression, paleobotanical data, and river profiles record the evolution of topographically controlled precipitation patterns and their influence on surface morphology along the tectonically and volcanically active plateau margin during the Miocene.