Geological evolution of the Ollagüe volcano, northen Chile

The Ollagüe volcano is an active and mainly effusive long-lived center located along the Chile - Bolivia border in the Central Volcanic Zone of the Andes. It is a multiple-collapsed volcano formed over an ignimbritic plateau and an evaporitic substrate and developed along an NW - striking extensional regional fault. The volcano comprises central to flank eruptions with compositions and eruptive styles varying from andesitic lava flows to dacitic coulees. Remote morphological-based characterization distinguish four main types of intermediate to silicic lava flows that may result from the combined effect of eruption source parameters, magma properties, and the characteristics of the terrain over which the lavas flowed. Based on detailed field-based mapping, remote-based morphological and morphometric analysis, petrochemical data, and a new large radiometric dataset, is presented a new evolutionary scheme for the volcano. Products from Ollagüe consist of high-K andesites and dacites with mid-deep crustal assimilation-fractional crystallization followed by mixing and mingling with more mafic melts as the dominant magmatic processes. The volcano evolved in three main stages of volcano building, separated by two main collapses of the volcanic edifice. The oldest Ollagüe I stage comprises the largest proportion of the erupted volume and consists of an eroded and steep cone mainly formed by the central emission of andesites and dacites formed from the low rate accumulation in the upper crust of nearly homogeneous magmas. Subsequently, in the northwestern flank of the volcano occurred a relatively mafic and shallow intrusion accompanied by a flank collapse with a related debris avalanche deposit (DAD) and followed by a blast explosion. This minor collapse has not significantly unloaded the volcanic edifice, with the Ollagüe II stage mainly consisting of lateral lava flows and domes emplaced along volcanic lineaments parallel to regional extensional faults. The distribution and shape of these centers in the flanks may indicate laterally compartmentalized reservoirs or small, isolated magma bodies accumulating and crystallizing at shallow levels. This stage was followed by a major collapse of the western part of the volcanic edifice, accompanied by a DAD widespread within the Carcote salt flat. Post-collapse activity from the last stage of evolution, Ollagüe III, mainly focused on the formed amphitheater, indicating that the unloading due to the significant collapse modified the local volcanic stress field. However, the persistence of an important effusive activity aligned along pre-existent, lateral, regionally-controlled structures indicates that the regional tectonics still played a key role during the regrowth of the volcanic edifice. Migrations from central to lateral activity resulted from the interplay between the regional tectonic stress field and the local magmatic stress field. The reactivation and propagation of pre-existing faults and fractures, formed by the superimposed failures of the volcanic edifice, acted as preferential ascent paths for dyking and favored the passive degassing of shallow magma batches, while the sudden unloading due to the youngest and major flank collapse would have produced a reorganization of shallow crustal magma reservoirs.