TY - JOUR

T1 - Covariation of Slab Tracers, Volatiles, and Oxidation During Subduction Initiation

AU - Brounce, Maryjo

AU - Reagan, Mark K.

AU - Kelley, Katherine A.

AU - Cottrell, Elizabeth

AU - Shimizu, Kenji

AU - Almeev, Renat

N1 - Funding Information: This manuscript benefited by constructive reviews from John Shervais, Oliver Nebel, Hugh O'Neill, and an anonymous reviewer. This research used samples and data provided by the International Ocean Discovery Program (IODP; http://www.iodp.org/). The authors would like to thank the scientific team and ship's crew and Captain aboard the R/V JOIDES Resolution during IODP Expedition 352 for their efforts in sample recovery. This manuscript benefited from discussions with Terry Plank. Steve Bates was instrumental in aspects of data acquisition at UCR. Portions of this work were performed at GeoSoilEnviroCARS (The University of Chicago, Sector 13), Advanced Photon Source (APS), Argonne National Laboratory. GeoSoilEnviroCARS is supported by the National Science Foundation, Earth Sciences (EAR-1634415) and Department of Energy, GeoSciences (DE-FG02-94ER14466). This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. This work was made possible by support from the University of California (MB), U.S. National Science Foundation grant OCE1558647 (MKR), U.S. National Science Foundation grant OCE1559054 (KAK), NSF EAR 1426717 (EC), and DFG Project AL1189/8-1 (RA).

PY - 2021/6/8

Y1 - 2021/6/8

N2 - 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.

AB - 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.

KW - geochemistry

KW - island arc

KW - oxygen fugacity

KW - pillow lava

KW - redox

KW - subduction

UR - http://www.scopus.com/inward/record.url?scp=85108637504&partnerID=8YFLogxK

U2 - 10.1029/2021GC009823

DO - 10.1029/2021GC009823

M3 - Article

AN - SCOPUS:85108637504

VL - 22

JO - Geochemistry, Geophysics, Geosystems

JF - Geochemistry, Geophysics, Geosystems

SN - 1525-2027

IS - 6

M1 - e2021GC009823

ER -