Postdoctoral Fellowship: EAR-PF: Global Rare Earth Element Cycles: Constraining Fluxes Through Subducting Systems

Dr. Charlotte Connop has been awarded an NSF EAR Postdoctoral Fellowship to perform research, professional development, and outreach activities under the mentorship of Dr. Mark Caddick at Virginia Tech. Rare earth elements (REEs) are important for geology as well as society. In geology, REEs have many uses, and their applications all rely on understanding if or when REEs are mobilized. Moreover, minerals with high amounts of REEs are designated as “critical minerals” as they are essential for defense, industry, and the economy. Through lab and modeling work, this project will better constrain the mobility of REEs in subduction zones. During subduction, a tectonic plate slides under another and experiences changes in temperature and pressure that may allow for REEs to be mobile. This work will create research and mentoring opportunities for undergraduates from diverse backgrounds not well represented in the Earth Sciences. Furthermore, a summer workshop series will be created for high school Earth Science teachers to help them teach geosciences to students. Subduction zones are a key tectonic environment in which to assess the mobility of REES, as subduction is the primary geochemical cycling mechanism in the top ~300 km of Earth’s surface. This proposal uses a forward model validated with natural samples to test the hypotheses that (1) REEs sequestered in subduction zone minerals are generally immobile and are predominantly transported to the deep mantle, (2) when REEs are mobilized by subduction zone processes, LREEs are preferentially mobilized, and (3) conditions permitting direct slab melting provide far more efficient mechanisms for REE mobilization than dehydration reactions. The forward model integrates mineral and fluid phase-equilibrium modeling with a newly developed database of REE mineral-fluid partition coefficients. This model will be run along a range of subduction zone pressure-temperature paths and will identify key mineral reactions for either the release or sequestration of REEs in subduction zones, allowing for the broad quantification of global REE fluxes. 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.