V038-0007
An Investigation of Oxygen Fugacity in Ocean Island Basalts
Wednesday, 16 December 2020
Poster
Lori N Willhite1, Ricardo Arevalo Jr.2, Marek Locmelis3, Philip M Piccoli1, Benjamin Jacob Farcy1, Rebecca Funderburg4, Matthew G Jackson5, James M Day6, Thomas J Ireland7 and John C Lassiter8, (1)University of Maryland College Park, College Park, MD, United States, (2)University of Maryland College Park, Geology, College Park, United States, (3)University of Western Australia, Crawley, WA, Australia, (4)Texas Christian University, Fort Worth, TX, United States, (5)University of California Santa Barbara, Earth Science, Santa Barbara, CA, United States, (6)Univ. California, San Diego, GRD, La Jolla, CA, United States, (7)Boston University, Earth and Environment, Boston, MA, United States, (8)University of Texas at Austin, Dept. of Geological Sciences, Jackson School of Geosciences, Austin, TX, United States
Abstract:
Redox conditions affect the partitioning behavior of elements among phases within the Earth system, and exert a strong control on the chemical speciation of gases released from magmatic systems into the atmosphere. Therefore tracking the redox state of mantle reservoirs has implications for the material exchange among all of Earth’s chemical reservoirs through time. It is not yet clear how recycling crust and mantle lithosphere affects the oxidation state of the mantle—Earth’s largest chemical reservoir—warranting examination of redox signatures in mantle-derived rocks. Ocean island basalts (OIB) represent melts from a diverse suite of mantle domains thought to contain variably depleted and enriched recycled materials; these lavas allow for investigation of the oxidation states of their spatially and chemically distinct mantle sources.
First row transition elements (FRTE) are used as redox indicators because select FRTE can take on multiple valence states during basalt genesis. Ions of different charge will have distinct ionic radii, a characteristic that affects partitioning behavior during partial melting and crystallization. Here, we use the partitioning of V between olivine and the matrix to evaluate the oxygen fugacity (ƒO2; a major control on the mantle redox state) of OIB from nine localities (Hawaii, Samoa, Iceland, Pitcairn, Canary, St. Helena, Cook-Austral, Reunion, Azores) and one continental flood basalt (CFB, Baffin Island). Preliminary results indicate that the ƒO2 of different localities overlap, but some localities are statistically distinct from others. Within and among localities, ƒO2 variations can exceed one log unit, indicating multiple scales of heterogeneity in the mantle sources and melt systems contributed to these basalts. The samples in this study appear to have overlapping, but typically higher ƒO2 than previous estimates for the source(s) of mid-ocean ridge basalts (MORB), indicating OIB and CFB mantle sources contain components that may be more oxidizing than MORB.
