Collaborative Research: NSF GEO-NERC: The Cracking of a Craton: Understanding Volatile Release during Continental Breakup

Cratons are the oldest and most stable parts of the Earth’s continents. Major volatiles are transported from the Earth’s surface into Earth’s interior during subduction and may accumulate below and within the stable cratons, forming reservoirs of gases such as helium, hydrogen, and carbon dioxide. The objective of this work is to determine the geological processes that control volatile production in the craton, their migration through the crust and release at the surface. The field site is a well-known stable craton and location of intense magmatism and tectonics. This geologic setting is ideally suited to investigate the formation processes of cratonic volatiles and their potential release due to magnetism and rifting. Participating students will be trained in field and laboratory techniques, data interpretation and application of these techniques for understanding the processes of reservoir formation of these economically important gases. This project is a comprehensive study of the volatile gases that are being emitted from gas and water seeps along the flanks of the Tanzanian craton - a region where the stable continental craton is actively being “cracked” by rifting and simultaneously heated by plume-induced volcanism. The overall aims are to understand: 1) the mechanisms by which gases have been produced and stored in stable cratons over >109-year timescales, and 2) how they are liberated and transported to the surface during cratonic breakup. The study primarily focuses on helium (He) and nitrogen (N2) and their isotopic characteristics, which are the main constituents of cratonic gas accumulation, but we will measure all other noble gases (Ne, Ar, Kr, Xe) and their isotopes, CO2, CH4 (as well as their isotopes) and H2 in seeps. The PIs will use field- and lab-generated gas chemistry results to form an integrated model of gas formation and transport along the flanks of the Tanzania craton. Volatile fluxes will be calculated to understand the extent of gas release when a cratonic region is disrupted by rifting and volcanism. Determining how cratonic gases are released to the crust and eventually to the atmosphere is important for understanding volatile movements on large spatial and temporal scales. By constraining how volatiles are accumulated and released during steady-state rifting and magmatic conditions, the PIs will characterize cratonic volatile inventories and fluxes. This information will be of interest to the broader Earth science community and provides valuable context to researchers studying the potential climatic effects when gases are abruptly released from the stable craton to the atmosphere as well as the formation of economically valuable gas reservoirs of helium and hydrogen. Two Tanzanian students will be jointly supervised by the PI’s of the award and trained in field and laboratory techniques at their respective institutions. There will be opportunity for the students to obtain in depth training in noble gas geochemistry, gas geochemistry and stable isotopes, as well as modeling approaches to understand the processes of formation of these economically valuable gas reservoirs. “This award was made possible through the NSF/GEO-UKRI/NERC lead agency opportunity.” 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.