RUI: Tracking magma accumulation and evolution in the Andean Central Volcanic Zone

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Continental arc volcanoes represent a dramatic surface expression of one of the most significant and fundamental phenomena in global tectonics: the subduction of an oceanic plate beneath a more buoyant continental plate resulting in recycling of crustal material into the convecting mantle, partial melting, and primary basalt production. Moreover, during passage through thick continental crust, subduction zone magmas may substantially differentiate and melt crustal rocks giving rise to the great diversity of igneous lithologies characteristic of earth. Explosive volcanic eruptions at continental arc can have devastating global effects and owe their explosiveness to the composition and volume of magma stored in the crust. The development of large magma storage systems remains largely unknown and very controversial among volcanologists. This project will investigate how accumulated magma is stored and evolves over time. The investigators seek to characterize the processes and timescales of magma storage in the modern magma chambers beneath volcanoes in the Andean Central Volcanic Zone of Chile and Bolivia. Growing evidence suggests that the massive magmatic reservoirs required for largest and most explosive eruptions, such as those in the Central Andean Altiplano-Puna Volcanic Complex, are built rapidly in hot crustal environment. Over the 3-year project, graduate and undergraduate students will expand their research skills by working collaboratively with an international team of geologists seeking to understand the dynamics of crustal melting and magma storage leading to volcanic eruptions. The project emphasizes training in analytical methods in the lab, in the field, and at collaborating facilities.This project will focus on young volcanic rocks from composite volcano complexes in the Andean Central Volcanic Zone of Chile and Bolivia (Aucanquilcha, Ollagüe, Uturuncu, San Pedro-Linzor, Licancabur, Lazufre and Lascar) linked closely in space and time, to address the processes and timescales leading to the buildup of magma and eventual volcanic eruption. The primary intent of this project is to investigate how accumulated magma is stored and evolves over time. This will be accomplished by characterizing the processes and timescales of magma differentiation in the modern magma chambers and determining the influence of regional magma bodies on Central Andes volcanoes. New and existing samples from each center will be used to address three basic questions: 1) how long does magma reside at active individual centers; 2) do magmatic sources and partial melting processes vary systematically with the geochemical evolution of volcanic products; and 3) what is the evidence for involvement regional-scale upper crustal magma reservoirs in controlling eruptive composition? The proposed research will use targeted field sampling, whole rock geochemistry, 40Ar/39Ar geochronology, high precision zircon geochronology/geochemistry and trace element diffusion in plagioclase to address these questions. Ultimately, the dataset produced in this study will provide insight into the generation and diversity of magmas that form continental crust.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.