EAR-PF Determining links between magma redox heterogeneity in ocean island basalts and near-surface processes of the ancient and present day

Peterson Mary E, Providence RI

Investigators

Abstract

Dr. Mary E. Peterson has been granted an NSF EAR Postdoctoral fellowship to carry out research and education activities at the California Institute of Technology. Magma generated in different tectonic settings has great geochemical variability, in some cases reflecting traces of ancient recycled material mixing with depleted upper mantle. This investigation will determine if the oxidation state of the mantle source for ocean island basalts is measurably different than either mid-ocean ridge or arc mantle sources. Understanding the oxidation state of the magma is important because it will allow scientists to discern the depth where mantle melting was initiated and what minerals may grow from the magma. The analytical scope for the project involves isolating a suite of well characterized glass and melt inclusions from lavas from three ocean island settings (the Galapagos Archipelago, Iceland and Baffin Island) to measure geochemical parameters that can be used to infer oxidation state of the mantle (for example, the ratio of ferric to total iron, oxygen isotopes, volatile and trace element concentrations). In addition, Dr. Peterson will develop and lead a graduate level seminar, open to students in geological science, materials science and chemistry to explore the geochemical implications of the oxidation state of Earth materials. The data for this investigation will be collected using micro x-ray absorption near-edge structure spectroscopy (XANES) to measure Fe3+/total Fe ratios. These measurements will be combined with in situ secondary ionization mass spectrometry (SIMS) measurements of oxygen isotopes, volatile and trace elements, to determine if variations in Fe3+/total Fe ratios of the glass are due to shallow level processes or variability in the oxidation state of the mantle source. These measurements will build on preliminary data from the Galapagos while expanding to include the Iceland and Baffin Island. The results of this study will continue to grow the existing database of synchrotron measurements of Fe speciation in natural silicate glass in order to develop a basic understanding of the links between magma redox and plate tectonic cycling. By constraining the redox properties of mantle end-members, we can build a model for the evolution of solid Earth redox and inform existing models or hypotheses that link solid Earth and surface redox conditions in the past.