CAREER: Salt, Experiments, and Mass Transfer in Subduction Settings

Tulane University, New Orleans LA

Investigators

Abstract

Subduction zones are fundamental engines for chemical reactions in the Earth. In a subduction zone, one tectonic plate dives beneath another and is heated during its descent into Earth’s deep interior. With heat, the hydrous minerals in the down-going plate breakdown to produce water-rich fluids. These fluids are buoyant and rise back to the surface, driving chemical reactions along their path. Important geological phenomena driven by these fluids include the violent volcanoes that dot the Pacific Ring of Fire, the economic concentration of critical elements along the edges of continents, the production of continental crust, and the addition and replenishment of gasses in Earth’s interior. Research efforts of this project center on experimental investigations of how the halogen elements trace the path of fluids through subduction zones and modify the chemical properties of water-rich fluids at depth. Educational efforts of this project include developing curricula to better engage students interested in STEM and training students in cutting edge research techniques at the graduate and undergraduate level. This project will support three specific research tasks. The first task is to experimentally measure the elemental partitioning of halogens between slab minerals and water-rich fluids under applicable pressure and temperature conditions. These data will be applied towards predicting the halogen chemistry of fluids and residual minerals for different slab conditions. Predictions will then be compared to observations from arc volcanoes and mantle sources to constrain how halogens are mobilized through subduction zones. The second task is to measure how efficiently chlorine increases the solute concentrations of water-rich fluids under conditions applicable to slab-fluid interactions. The collected data will inform how the chemistry of subduction zone fluids are determined. The third task is to quantify how the fluid-saturated melting point of rocks is increased by the addition of chlorine. Results will be applied towards understanding the thermal structure of subduction zones and the associated propensity for slab melting. The combined efforts of the research tasks will yield a systematic investigation for how halogens trace and modify mass transfer in subduction settings. This project will also support major educational efforts. The first is to develop an introductory class focused on planetary science. The class will be offered through the Tulane Science Scholars Program, a program that targets southern Louisiana high school students and enables a diverse cohort of ~150 students to take a STEM class over the summer for college credit. No geosciences class is currently offered through this program, and the newly developed planetary science class will fill this crucial hole in the current curriculum. The second is to revamp the laboratory activities of the Earth Materials class at Tulane to introduce students to a wide range of analytical techniques commonly applied within geochemistry. The impact of this revamping will be enhanced by partnering with other institutions that teach Earth Materials courses to help refine the laboratory activities. The refined activities will be posted to community repositories for curricula. The third educational effort will provide training for three PhD students in materials synthesis and materials characterization techniques. Within this effort, undergraduate students will be recruited from the New Orleans metro area to join the research efforts. 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.