THE ROLE OF FLUIDS IN THE SUBDUCTION ZONES: IMPLICATIONS FOR VOLCANISM AND GEOTHERMAL ACTIVITY

Water supply and budget are essential aspects of a subduction system as they affect the productivity of arc magmas, the cycling of volatiles in the mantle, and the rheology of the mantle beneath subduction zones. Volatiles (H₂O, CO₂, S, F, Cl, Br, Li) play an important role in the evolution of magmatic processes and the physics of volcanic eruptions. However, volatiles are also necessary for the development of magmatic-derived hydrothermal systems. We will present some recent findings on immiscible volatile phases exsolving from melts from the Southern Volcanic Zone (SVZ) in Chile and their role in crystallization and heat and mass transfer to geothermal systems. We will present pre-eruptive magma compositions obtained from bubble-bearing olivine-hosted melt inclusions in phenocrysts from several eruptive centers, from stratovolcanoes (Quizapu, Lonquimay, Llama) and monogenetic volcanic centers (Lonquimay and Puyuhuapi). Our data shows that in the SVZ, magmatic processes and geothermal activity are affected by the location of volcanic centers with respect to the Liquiñe – Ofqui transpressional fault system and that volatile migration and magma/fluid distribution are strongly intertwined with the regional stress field and well-defined vertical structures through the lithosphere.