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    Serpentinite-derived slab fluids control the oxidation state of the subarc mantle (2022)
    American Association for the Advancement of Science
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    Publication Date: 2022-05-27
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Zhang, Y., Gazel, E., Gaetani, G. A., & Klein, F. Serpentinite-derived slab fluids control the oxidation state of the subarc mantle. Science Advances, 7(48), (2021): eabj2515, https://doi.org/10.1126/sciadv.abj2515.
    Description: Recent geochemical evidence confirms the oxidized nature of arc magmas, but the underlying processes that regulate the redox state of the subarc mantle remain yet to be determined. We established a link between deep subduction-related fluids derived from dehydration of serpentinite ± altered oceanic crust (AOC) using B isotopes and B/Nb as fluid proxies, and the oxidized nature of arc magmas as indicated by Cu enrichment during magma evolution and V/Yb. Our results suggest that arc magmas derived from source regions influenced by a greater serpentinite (±AOC) fluid component record higher oxygen fugacity. The incorporation of this component into the subarc mantle is controlled by the subduction system’s thermodynamic conditions and geometry. Our results suggest that the redox state of the subarc mantle is not homogeneous globally: Primitive arc magmas associated with flat, warm subduction are less oxidized overall than those generated in steep, cold subduction zones.
    Description: Y.Z. acknowledges funding from the National Science Foundation of China (91958213), the Chinese Academy of Sciences (XDB42020402), and the Shandong Provincial Natural Science Foundation, China (ZR2020QD068). This study was supported in part by the U.S. National Science Foundation NSF EAR 1826673 to E.G. and G.A.G. and OCE 1756349 to E.G.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
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    Halogen (F, Cl) concentrations and Sr-Nd-Pb-B isotopes of the basaltic andesites from the southern Okinawa Trough: implications for the recycling of subducted serpentinites (2021)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 126(3), (2021): e2021JB021709, https://doi.org/10.1029/2021JB021709.
    Description: Serpentinites are increasingly recognized as playing an important role in the global geochemical cycle. However, discriminating the contributions of serpentinites to arc magmas from those of other subduction components is challenging. The Okinawa Trough is a back-arc basin developed behind the Ryukyu subduction zone, where magmas are extensively affected by sediment subduction. In this study, we reported the F-Cl concentrations and Sr-Nd-Pb-B isotopes of basaltic andesites from the Yaeyama Graben, Yonaguni Graben, and Irabu Knoll in the southern Okinawa Trough. The Irabu Knoll lavas show the most enrichment of fluid-mobile elements and F ± Cl, and have the heaviest B isotopes (δ11B: +6.6 ± 1.5‰). They also have decoupled Sr-Nd isotopes: higher 87Sr/86Sr (∼0.7049) but have no obvious decrease of 143Nd/144Nd (∼0.5128). Results from slab dehydration modeling and mixing calculations suggest that the heavy δ11B in the Irabu Knoll lavas is not consistent with fluids derived from altered oceanic crust (AOC), sediments, or wedge serpentinites (formed in the mantle wedge), but rather from slab serpentinites (formed within the subducting plate); sediments control the subduction input of Nd, whereas the decoupled Sr-Nd isotopes are most likely due to the excess radiogenic Sr carried by AOC fluids. Our results imply that recycling of serpentinite fluids and AOC fluids are usually coupled in subduction zones, as the arc lavas influenced by subducted serpentinite generally show Sr-Nd isotopes decoupling. The large variation of Sr-Nd-B isotopes observed in a relatively localized area is consistent with a focused migration through the mantle wedge of components from multiple sources.
    Description: This study was funded by the National Natural Science Foundation of China (91958213), the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB42020402), the China Postdoctoral Science Foundation (2019M662454), the Shandong Provincial Natural Science Foundation, China (ZR2020QD068 and ZR2020MD068), the International Partnership Program of the Chinese Academy of Sciences (133137KYSB20170003), the Special Fund for the Taishan Scholar Program of Shandong Province (ts201511061), and the China Scholarship Council (201709410550).
    Description: 2021-09-12
    Keywords: AOC ; Boron isotope ; Geochemical cycling ; Serpentinite ; Sr-Nd isotope decoupling ; Subduction zone
    Repository Name: Woods Hole Open Access Server
    Type: Article
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