Continental rifts and ocean spreading ridges are key places where volatile elements are exchanged between Earth's interior and its surface. Volatiles play a central role in the initiation of rifting/spreading, in volcanic evolution, and in associated geologic hazards. This research characterizes major volatile concentrations (H2O and CO2) and mantle source tracers (helium and argon isotopes) in magma erupted along the mid-ocean ridge in the Gulf of Aden in the Arabian Sea because this is a mid-ocean spreading center in its early stages of formation and evolution. The research also quantifies the flux of water coming from the mantle in the region. The Gulf of Aden is a unique locality for this work because it is a young ocean basin influenced by flow from the Afar mantle plume under the Horn of Africa. The plume affects the base of the Arabian lithosphere along the Red Sea and the western part of the Gulf of Aden; and its widespread influence is thought to result from the channeling of asthenospheric magma from the plume to the spreading center by rifts. However, the Afar Plume's apparent weaker penetration into the Gulf of Aden is not well understood and may be related to tectonic segmentation/discontinuities of the spreading ridge. The research will analyze submarine basalt glasses that were collected from previous oceanographic and sampling expeditions to the area for major element composition, volatile concentrations (CO2, H2O, Cl, F and S), and He and Ar isotopes. Initial results for Aden basalt glasses reveal a strong plume signal that may become rapidly attenuated with distance from the plume axis. Project goals are to determine how partial melting and degassing control mantle volatile signatures in young ocean spreading centers. Geochemical evidence (e.g., 3He/4He, 40Ar/36Ar, 4He/40Ar*, CO2/Nb, H2O/Ce) in about 40 basalt glasses from this region will be used to make this determination. Results of the study allow us to quantify variation in the volatile flux from the Afar plume and the upper mantle along the length of this emerging ocean basin between 44°E and 57°E. The results also provide a basic framework needed for geophysical and geodynamic models in terms of model input for regional and smaller scale variations in mantle composition, partial melting, and the heat and mass flux associated with the evolution from continental rifting to oceanic spreading. Broader impacts of the work include support of graduate and undergraduate students at two institutions, one in an EPSCoR state (Oklahoma), leverages existing samples collected with prior NSF support, and utilization of NSF-funded analytical facilities at Oregon State University and the University of Tulsa. Results will be described on institutional web pages as well as NSF-funded publically available data systems. Findings will also be incorporated into classes taught by the investigators.
