Large ignimbrite eruptions and volcano-tectonic depressions in the Central Andes: a thermomechanical perspective

Abstract

The Neogene ignimbrite flare-up of the Altiplano Puna Volcanic Complex (APVC) of the Central Andes produced one of the best-preserved large silicic volcanic fields on Earth. At least 15 000 km3 of magma erupted as regional-scale ignimbrites between 10 and 1 Ma, from large complex calderas that are typical volcano-tectonic depressions (VTD). Simple Valles-type calderas are absent. Integration of field, geochronological, petrological, geochemical and geophysical data from the APVC within the geodynamic context of the Central Andes suggests a scenario where elevated mantle power input, subsequent crustal melting and assimilation, and development of a crustal-scale intrusive complex lead to the development of APVC. These processes lead to thermal softening of the sub-APVC crust and eventual mechanical failure of the roofs above batholith-scale magma chambers to trigger the massive eruptions. The APVC ignimbrite flare-up and the resulting VTDs are thus the result of the time-integrated impact of intrusion on the mechanical strength of the crust, and should be considered tectonomagmatic phenomena, rather than purely volcanic features. This model requires a change in paradigm about how the largest explosive eruptions may operate.

Fluid geochemistry of a deep-seated geothermal resource in the Puna plateau (Jujuy Province, Argentina)

“…During the Neogene, giant calderas were produced and huge ignimbrite deposits (~11-15 × 10 3 km 3 ; Kay et al, 2010;Salisbury et al, 2011) formed the Altiplano Puna Volcanic Complex (APVC; de Silva, 1989;de Silva et al, 2006). The recent sedimentary deposits consist of clastic and detrital material, alluvial fans and evaporitic deposits (Alonso, 1999).…”

The Great Basin Altiplano during the middle Cenozoic ignimbrite flareup: insights from volcanic rocks

“…Because the tectonic setting of the modern central Andean continental margin appears to be an appropriate model for the middle Cenozoic Great Basin area, it is useful to examine pertinent aspects of Andean geology (Allmendinger et al 1997;de Silva et al 2006). With an average elevation of 4 km and volcano peaks of more than 6 km, the relatively arid 350 -400 by 1800 km central Andean plateau is the highest region in the world associated with voluminous arc volcanism.…”

Nuevos antecedentes sobre la estructura interna de la caldera La Pacana mediante un estudio gravimétrico (Andes centrales, Chile).

“…Here, we focus on the geological setting, the main structural elements including the resurgent dome and the caldera rim, and the caldera stratigraphy. La Pacana is the largest caldera of the Altiplano Puna Volcanic Complex of the central Andes (APVC), the largest Neogene ignimbrite f lare-up in the world, with an area of 30,000 km 2 (e.g., De Silva, 1989a, b;De Silva et al, 2006;De Silva and Gosnold, 2007). The APVC ignimbrite volumes are larger than 1,000 km 3 and their sources are several asymmetrical calderas that form huge depressions (e.g., De Silva and Gosnold, 2007), possibly with a tectonic control (Riller et al, 2001;.…”

“…All of these signals have amplitudes at least 3 to 9 times above the error level. Different interpretations on the origin of the low density-negative gravity anomaly have been proposed including the APMB or a batholith (De Silva et al, 2006), brittle felsic upper crustal rocks or low-density ascending diapiric bodies rooted in the APMB in the northern part of the APVC (del Potro et al, 2013). However, as the observed negative anomalies are spatially related with La Pacana caldera, we consider that the most likely source of this signal is the low-density intracaldera ignimbrite facies, in agreement with studies in caldera environments elsewhere (e.g., Rymer and Brown, 1986;Carle, 1988;Masturyono et al, 2001).…”

“…Due to the lack of observations of eruptions of this size, the caldera dynamics and the climatic impact of these supereruptions, including the effects over the human population, are poorly understood (e.g., Cole et al, 2005;Lipman, 1997;Self, 2006;Jones et al, 2007;Self and Blake, 2008). The largest ignimbrite f lareups in the world (e.g., Taupo volcanic zone, New Zealand; San Juan mountains, SW United States; Altiplano Puna Volcanic Complex APVC, southern central Andes of Bolivia, Chile and Argentina) are the places where the largest calderas in the world are located (Lipman, 2007;Rowland et al, 2010;De Silva, 1989a;De Silva et al, 2006;De Silva and Gosnold, 2007) and then constitute ideal study cases to investigate the dynamics of these supervolcanoes. The caldera inner structures are important in hazard assessment, as some of them show ground deformation likely related to magma intrusion (e.g., Wicks et al, 2006;Battaglia et al, 1999).…”