Uploaded January 2021 | Updated September 2026, 2 weeks ago
Michelle Muth, Ph.D. Candidate at the University of Oregon,presents Slab-derived sulfate and oxidized magmas in the Southern Cascades arc.
Arc magmas are oxidized relative to mid-ocean ridge basalts, but the origin of this oxidized signature remains uncertain. Material derived from the subducting slab, such as hydrous melts and fluids, could oxidize the mantle source of arc magmas. Alternatively, it may be that arc magmas become oxidized during crustal differentiation. In this talk, I use data from the Southern Cascades arc to show quantitatively that increases in arc magma oxidation state are fundamentally linked to mass transfer of isotopically heavy sulfate from the subducted plate into the mantle wedge. I investigate multiple hypotheses related to plate dehydration and melting, and the rise and reaction of slab melts with mantle peridotite in the wedge, focusing on electron balance between redox-sensitive iron and sulfur during these processes. The results of this work show that unless slab-derived silicic melts contain much higher dissolved sulfur than is indicated by currently available experimental data, arc magma generation by mantle wedge melting must involve multiple stages of mantle metasomatism by slab-derived, oxidized, and sulfur-bearing hydrous components.
Michelle Muth, Ph.D. Candidate at the University of Oregon,presents Slab-derived sulfate and oxidized magmas in the Southern Cascades arc.
Arc magmas are oxidized relative to mid-ocean ridge basalts, but the origin of this oxidized signature remains uncertain. Material derived from the subducting slab, such as hydrous melts and fluids, could oxidize the mantle source of arc magmas. Alternatively, it may be that arc magmas become oxidized during crustal differentiation. In this talk, I use data from the Southern Cascades arc to show quantitatively that increases in arc magma oxidation state are fundamentally linked to mass transfer of isotopically heavy sulfate from the subducted plate into the mantle wedge. I investigate multiple hypotheses related to plate dehydration and melting, and the rise and reaction of slab melts with mantle peridotite in the wedge, focusing on electron balance between redox-sensitive iron and sulfur during these processes. The results of this work show that unless slab-derived silicic melts contain much higher dissolved sulfur than is indicated by currently available experimental data, arc magma generation by mantle wedge melting must involve multiple stages of mantle metasomatism by slab-derived, oxidized, and sulfur-bearing hydrous components.
