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

点击翻译按钮获取中文摘要

This is a project that is jointly funded by the National Science Foundation's Directorate of Geosciences (NSF/GEO) and the National Environment Research Council (NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award, each Agency funds the proportion of the budget and the investigators associated with its own country.Cratons are the oldest and most stable parts of the Earth’s continents. During continental break-up or rifting events, these stable crustal areas split apart and eventually give way to magma rising from Earth’s deep interior and the formation of new crust. Volatile elements such as helium, nitrogen and carbon dioxide play an important role during all aspects of plate tectonics. Major volatiles are transported from the Earth’s surface into Earth’s interior during subduction and may accumulate below and within the stable cratons due to radiogenic production and upwelling from the mantle below. The mechanisms and time-scales of this accumulation remain poorly understood, yet are significant because these processes form reservoirs of economically valuable gases such as helium and hydrogen, and geologically important gases such as carbon dioxide. When cratons eventually break apart, these gases are released to the atmosphere and have potentially significant climatic impacts on geological time scales. 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 investigated field site is the area surrounding the Tanzania Craton, a type example of a stable craton surrounded by the East African Rift, and a location of intense magmatism and extensional tectonics. This particular geologic setting is ideally suited to investigate the formation processes of cratonic volatiles and their potential release mechanism due to magnetism and rifting. During the course of the project two Tanzanian students will get their Ph.D. education and experience at the Woods Hole/MIT graduate program and the University of New Mexico. The 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 valuable 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 provide 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 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.