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Post-climatic evolution of supervolcanoes implicate significant volumes of residual mush remains after climactic eruptions.

Shanaka de Silva

Abstract

The architecture of silicic magma reservoirs underlying the Earth's largest and most explosive volcanoes has implications for the development of the continental crust, the volcano-plutonic relationship and volcanic hazards. Whereas significant attention has been paid to pre-climatic magma evolution and architecture, less is understood about the post-climactic magma reservoirs despite all the Earth's active supervolcanoes being in a state of post-climactic repose. The character of post-climactic eruptions at six supervolcanoes in the Central Andes reveal a family resemblance that indicates that significant volumes (100's to 1000's of km3) of mushy climactic magma remained after the climactic eruption. At La Pacana, Guacha, Pastos Grandes, Panizos, Vilama and Cerro Galan calderas the post climactic eruptions are petrochemically similar to the dacitic climactic eruptions but are texturally more mature with extreme phenocrystal contents often exceeding 50%. In the context of resurgence at these calderas these eruptions are the result of magmatic rebound of residual mush although rare andesite implicates a role for deeper recharge from a regional reservoir. The spatial distribution and petrochemical character of these eruptions implicate local heterogeneity in otherwise homogenous caldera-scale mushes remaining after the climactic eruptions. Similar climactic - post-climactic relations have been identified at Toba caldera, Sumatra, where some of the eruptions are of subsolidus mush. These studies, along with others at Yellowstone and Valles connote that supervolcanoes are sites of significant volumes of unerupted residual mush that have implications for our understanding of volcano:plutonic ratios, the volume of pre-eruption magma reservoirs and their detectability.