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

GUZMÁN, S.; STRECKER, M.; MARTÍ, J.; PETRINOVIC, I. A.; SCHILDGEN, T.; GROSSE, P.; MONTERO-LÓPEZ, C.; NERI, M.; CARNIEL, R.; HONGN, F.; MURUAGA, C.; SUDO, M.

BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA

ASSOC ENGINEERING GEOLOGISTS GEOLOGICAL SOC AMER

Año: 2017 vol. 129 p. 750 - 766

1050-9747

The Vicuña Pampa Volcanic Complex (VPVC), at the SE edge of the arid Puna Plateau of the Central Andes, records the interplay between volcanic construction and degradational processes. The low-sloping VPVC, with a 1200-m-deep, southeastward-opening depression, was previously interpreted as a collapse caldera based on morphological considerations. However, characteristic features associated with collapse calderas do not exist, and close inspection instead suggests that the VPVC is a strongly eroded, broad, massif-type composite volcano of mainly basaltic to trachyandesitic composition. Construction of the VPVC occurred during two distinct cycles separated by the development of the depression. The first and main cycle took place at ca. 12 Ma and was dominated by lava flows and subordinate scoria cones and domes. The second cycle, possibly late Miocene in age, developed in the SW portion of the depression with the emplacement of domes. We interpret the central depression as the result of a possible sector collapse and subsequent intense fluvial erosion during middle to late Miocene time, facilitated by faulting, steepened topography, and wetter climate conditions compared to today. We estimate that ca. 65 % of the initial edifice of ca. 240 km3 was degraded. The efficiency of degradation processes for removing mass from the VPVC is surprising, considering that today the region is arid and the stream channels within the complex are predominantly transport limited, forming a series of coalesced, aggraded alluvial fans and eolian infill. Hence, the VPVC records the effects of past degradation efficiency that differs substantially from that of today.