Temporal evolution of mantle wedge oxygen fugacity during subduction initiation

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doi: 10.1130/G36742.1
Author(s): Brounce, Maryjo; Kelley, Katherine A.; Cottrell, Elizabeth; Reagan, Mark K.
Author Affiliation(s): Primary:
University of Rhode Island, Graduate School of Oceanography, Narragansett, RI, United States
Smithsonian Institution, United States
University of Iowa, United States
Volume Title: Geology (Boulder)
Source: Geology (Boulder), 43(9), p.775-778. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0091-7613 CODEN: GLGYBA
Note: In English. GSA Data Repository item 2015266. 34 refs.; illus., incl. sketch map
Summary: Arc basalts have a higher proportion of Fe in an oxidized state (Fe3+) relative to Fe2+ compared to mid-oceanic ridge basalts (MORBs), likely because slab-derived fluids oxidize the mantle wedge where subduction zone magmas originate. Yet, the time scales over which oxygen fugacity of the mantle wedge changes during subduction initiation and margin evolution are unknown. Fe speciation ratios show that magmas produced during the early stages of subduction in the Mariana arc record oxygen fugacities ∼2× more oxidized than MORB. Mantle wedge oxygen fugacity rises by ∼1.3 orders of magnitude as slab fluids become more involved in melt generation processes, reaching conditions essentially equivalent to the modern arc in just 2-4 m.y. These results constrain existing models for the geochemical evolution of the mantle wedge and suggest that oxidation commences upon subduction initiation and matures rapidly in the portions of the mantle wedge that produce melts. This further implies that sulfide or other reduced phases are not present in the mantle wedge in high enough abundance to prevent oxidation of the magmas that form upon subduction initiation. The arc mantle source is oxidized for the majority of a subduction zone's lifetime, influencing the mobility of multivalent elements during recycling, the degassing of oxidized volcanic volatiles, and the mechanisms for generating continental crust from the immediate onset of subduction.
Year of Publication: 2015
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 18 Geophysics, Solid-Earth; Andesites; Basalts; Boninite; DSDP Site 458; Deep Sea Drilling Project; Eh; Fugacity; Geochemistry; IPOD; Igneous rocks; Iron; Lava; Leg 129; Leg 144; Leg 185; Leg 60; Magmas; Mantle; Mantle wedges; Mariana Trough; Metals; North Pacific; Northwest Pacific; ODP Site 801; Ocean Drilling Program; Oxidation; Oxygen; Pacific Ocean; Pigafetta Basin; Pillow lava; Plate tectonics; Subduction; Volcanic rocks; West Pacific
Coordinates: N175151 N175151 E1465603 E1465603
N183831 N183835 E1562136 E1562134
Record ID: 2015079076
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States, Reference includes data supplied by the Geological Society of America