Zhang Yuxiang, Gazel Esteban, Gaetani Glenn A, Klein Frieder
Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, Shandong, China.
Laboratory for Marine Mineral Resources, Qingdao Pilot National Laboratory for Marine Science and Technology, Qingdao, Shandong, China.
Sci Adv. 2021 Nov 26;7(48):eabj2515. doi: 10.1126/sciadv.abj2515.
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.
近期的地球化学证据证实了岛弧岩浆的氧化性质，但调节岛弧下地幔氧化还原状态的潜在过程仍有待确定。我们利用硼同位素和硼/铌作为流体指标，建立了源自蛇纹石±蚀变洋壳（AOC）脱水的深部俯冲相关流体与岛弧岩浆氧化性质之间的联系，岛弧岩浆的氧化性质由岩浆演化过程中的铜富集和钒/镱所指示。我们的结果表明，源自受更大蛇纹石（±AOC）流体成分影响的源区的岛弧岩浆记录了更高的氧逸度。该成分融入岛弧下地幔受俯冲系统的热力学条件和几何形态控制。我们的结果表明，岛弧下地幔的氧化还原状态在全球范围内并非均匀一致：与平缓、温暖俯冲相关的原始岛弧岩浆总体上比在陡峭、寒冷俯冲带产生的岩浆氧化程度更低。
