Guido Salas

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.

Triggering explosive eruptions—The case for silicic magma recharge at Huaynaputina, southern Peru

Recharge by mafic magma is established as a trigger of major explosive volcanic eruptions. However, recharge by silicic magma can also induce perched resident magma to erupt. The evidence of such recharge may be more cryptic than for mafic recharge and requires detailed petrologic and geochemical study to identify. We present a study of plagioclase petrology supported by other data that implicates silicic-silicic magma interaction during the eruption and evolution of the A.D. 1600 eruption of Huaynaputina, one of the largest historical eruptions. Recharge by silicic magma is probably more common than recognized and should be considered an important eruption trigger.