Variations in redox of Hawaiian magmas: source and process

Lavas that erupt in Hawaii, far from the boundaries between tectonic plates, have a parameter known as the oxidation state with a large range of values. The oxidation state of some Hawaii lavas are like lavas erupted at mid-ocean ridges, where new ocean crust forms. Other Hawaii lavas are more like lavas erupted at subduction zones where ocean crust descends into the mantle. This project will investigate whether these differences are because of volcanic processes occurring in the crust at the Hawaii volcanos, or because of differences in the source material deep in the mantle. The results will have implications for plate tectonic and mantle convection processes. Broader impacts include support for a female principal investigator, a nontraditional PhD student, and undergraduate students at a federally designated Hispanic- and Asian and Pacific Islander-serving institution. Recent geological application of a new synchrotron-source analytical tool – X-ray absorption near edge structure spectroscopy – permits precise in situ measurements of Fe3+/Fe2+ and S6+/S2- ratios in basaltic glasses. With this new tool, the effects of igneous differentiation processes on these ratios in basaltic magmas and the oxygen fugacity of these magmas can now be directly quantified and corrected for in the quest to characterize the composition of the mantle from measurements of seafloor basalts. As a result, there is substantial renewed interest in re-examining fundamental questions: Is the upper mantle homogeneous or heterogeneous in its oxidation state? What are the implications of the homo/heterogeneity of this oxidation state of the mantle for plate tectonics, Earth formation, and whole-Earth differentiation? In a carefully assembled suite of samples from the Hawaiian islands that are previously studied for major, trace, and volatile element compositions as well as stable and radiogenic isotopic compositions, new measurements will be used to assess the origins of the oxidized nature of a wide variety of Hawaiian intraplate magmas. This work will determine the extent to which plate tectonic cycling may (or may not) drive a whole-Earth oxygen cycle. This project will support the research of two University of California at Riverside (UCR) undergraduate students and a UCR graduate student. These students will work towards the science goals of this proposal, as well as to work with the Natural History Museum in the Department of Earth and Planetary Sciences at UCR to rescue geologic samples at high risk of loss and which are relevant to this research proposal in the context of understanding the heterogeneous nature of the Earth’s upper mantle. 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.