EAR-PF In-situ and bulk sulfur isotope constraints on crustal recycling: a bridged investigation of superdeep diamonds and ocean island basalts

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Dr. James W. Dottin III has been awarded an NSF EAR Postdoctoral Fellowship to pursue research and education endeavors at the Carnegie Institution for Science-Earth and Planets Laboratory (CIS-EPL) under the mentorship of Dr. Steven Shirey and Dr. Michael Walter. The Earth’s crust, which can be transferred from the surface to the interior of Earth through plate tectonics, provides many of the chemical elements that control the habitability of life on our planet. However, the detailed nature, relative ages of the various crustal materials, and where they ultimately reside in the Earth’s interior are not well understood. For this project, Dr. Dottin will use chemical signatures (specifically those of the element sulfur) measured in rocks and minerals erupted from the deep interior of the Earth to provide insight into the finer details of plate tectonics. Dr. Dottin’s work involves analyzing rocks and diamonds that come from different parts of the Earth’s interior to determine how elements found in the crust move around and are distributed across the globe. The proposed research will use unique characteristics of sulfur to identify specific crustal materials that are recycled through the Earth’s interior and provide relative constraints on the timescales on which crustal recycling occurs. Dr. Dottin will also lead an education program that incorporates students from historically underrepresented minority groups directly into the research project. Student involvement will take form through a strong collaboration with Smith College, a women’s college in Massachusetts. Dr. Dottin also plans to engage with students that will be actively recruited from local high schools and the many Historically Black Colleges and Universities in the Washington, D.C. area as a mentor and advisor through a summer internship program at CIS-EPL. The Earth’s mantle is compositionally heterogeneous, comprising geochemically distinct reservoirs from the process of crust extraction and recycling of crust into the mantle. The HIMU (high μ=238U/204Pb) mantle reservoir is an enigmatic endmember with extreme Pb-isotopic compositions, and is postulated to be composed of subducted altered oceanic crust that is associated with a carbonated component. However, the nature, origin, and global distribution of the components that make up the HIMU mantle remain poorly understood. For this project, Dr. Dottin will combine sulfur isotope information from key HIMU basalts and from sulfide inclusions in superdeep diamonds using microbeam and bulk digestion techniques. Dr. Dottin aims to trace the global distribution and interaction of recycled protoliths in HIMU mantle reservoirs that are thought to reside at the base of the mantle and/or within the mantle transition zone. The proposed analytical techniques, choice of key HIMU basalts, and choice of sulfides from transition zone diamonds offers an opportunity to address the potential isotopic heterogeneities that exist among mineral, hand sample, and global scales. From this work, Dr. Dottin plans to provide insight into the finer details of plate tectonics through constraints of source heterogeneity among HIMU mantle reservoirs and the proposed depth of slab accumulation that is possibly linked to the age of the reservoir and/or hotspot location.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.