Collaborative Research: Constraining volatile storage in the lower crust - a case study of exhumed rocks from the Talkeetna Arc, Alaska

Volatile elements, such as hydrogen (H), carbon, nitrogen (N), and noble gases, commonly occur as gases at Earth’s surface. When tectonic plates collide, one will sink – or subduct – under the another, and the volatiles in the oceanic crust and sediments are carried into the mantle. The process of subduction leads to melting, which results in a string of volcanoes on the plate above.

These volcanoes emit a portion of those volatiles back to Earth’s surface. This cycle of subduction, melting, and volcanism maintains Earth’s habitability and forms the crust and continents. However, the concentration of these volatiles at Earth’s surface has changed over geologic time.

A major gap in our understanding is how volatiles are removed from this cycle as new crust is formed. This project focuses on the Talkeetna volcanic system in Alaska, one of the few places on Earth where rocks from the base of the crust are exposed at the surface. This team will analyze the abundances of H, N, and noble gases in lower crustal and upper mantle rocks from Talkeetna to estimate how much the crust acts as a volatile trap.

This will provide context for volatile changes at Earth’s surface. Additionally, collaborations with a local artist who develops film in volcanic hot springs will bring co-curricular activities to classes at Williams College, and public lectures and art exhibitions in the Berkshires. 

Volatile elements (e.g., H, C, N, noble gases) play a critical role in volcanic arc settings, where they induce melting of the mantle and drive volcanic eruptions. Global volatile budgets are estimated by quantifying and balancing volatile input and output fluxes between Earth reservoirs. Output fluxes are typically linked to volcanism and the extent of degassing, whereas subduction of volatile rich oceanic crust represents the mechanism for returning surface-derived volatiles into Earth’s mantle.

The capacity for the crust to retain volatiles is commonly overlooked, but the lower arc crust may be a significant volatile reservoir. This project will quantify the abundances of N, H, and noble gases in the well-characterized Jurassic Talkeetna arc to calculate the storage capacity of the lower crust in arcs. Measured isotope compositions and elemental ratios will identify deep fluid sources and secondary processes affecting volatile abundances in deep arc crust and sub-lithospheric mantle.

These data will then be used to update global volatile models to include the lower arc crust. This multi-pronged volatile and isotope approach will enhance modeling of volatile behavior in arcs, aligning with SZ4D Magmatic Drivers of Eruption priorities by clarifying the lower crust's role as a volatile reservoir. This work will be communicated to several communities through in collaboration with a Berkshire-based artist who develops film in volcanic hot springs and fumaroles.

Public talks and exhibitions will bring the science in this project to the broader Berkshire community. The art will also be shown and discussed in classes at Williams College to help engage students through a different mode of learning, which will help to attract students with diverse experiences and backgrounds.

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.