Journal article
Covariation of Slab Tracers, Volatiles, and Oxidation During Subduction Initiation
Geochemistry, geophysics, geosystems, Vol.22(6), e2021GC009823
06/01/2021
DOI: 10.1029/2021GC009823
Abstract
Subduction-related lavas have higher Fe3+/∑Fe than midocean ridge basalts (MORB). Hypotheses for this offset include imprint from subducting slabs and differentiation in thickened crust. These ideas are readily tested through examination of the time-dependent evolution of slab-derived signatures, thickening crust of the overriding plate, and evolving redox during subduction initiation. Here, we present Fe3+/ΣFe and volatile element abundances of volcanic glasses recovered from International Ocean Discovery Program (IODP) Expedition 352 to the Izu-Bonin-Mariana (IBM) forearc. The samples include forearc basalts (FAB) that are stratigraphically overlain by low- and high-silica boninite lavas. The FAB glasses have 0.18–0.85 wt% H2O, 75–233 ppm CO2, S contents controlled by saturation with a sulfide phase (602–1,386 ppm), Ba/La from 3.9-10, and Fe3+/ΣFe ratios from 0.136 to 0.177. These compositions are similar to MORB and suggest that decompression melting of dry and reduced mantle dominates the earliest stages of subduction initiation. Low- and high-silica boninite glasses have 1.51–3.19 wt% H2O, CO2 below detection, S contents below those required for sulfide saturation (5–235 ppm), Ba/La from 11 to 29, and Fe3+/∑Fe from 0.181 to 0.225. The compositions are broadly similar to modern arc lavas in the IBM arc. These data demonstrate that the establishment of fluid-fluxed melting of the mantle, which occurs in just 0.6–1.2 my after subduction initiation, is synchronous with the production of oxidized, mantle-derived magmas. The coherence of high Fe3+/∑Fe and Ba/La ratios with high H2O contents in Expedition 352 glasses and the modern IBM arc rocks strongly links the production of oxidized arc magmas to signatures of slab dehydration.
Details
- Title: Subtitle
- Covariation of Slab Tracers, Volatiles, and Oxidation During Subduction Initiation
- Creators
- Maryjo BrounceMark K ReaganKatherine A KelleyElizabeth CottrellKenji ShimizuRenat Almeev
- Resource Type
- Journal article
- Publication Details
- Geochemistry, geophysics, geosystems, Vol.22(6), e2021GC009823
- Publisher
- AGU
- DOI
- 10.1029/2021GC009823
- ISSN
- 1525-2027
- Grant note
- DOI: 10.13039/100000001, name: National Science Foundation, award: OCE1558647, OCE1559054, EAR 1426717; DOI: 10.13039/501100001659, name: Deutsche Forschungsgemeinschaft, award: AL1189/8‐1; DOI: 10.13039/100000015, name: U.S. Department of Energy, award: DE‐FG02‐94ER14466, DE‐AC02‐06CH11357
- Language
- English
- Date published
- 06/01/2021
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984229966602771
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