Kelley Katherine A, Cottrell Elizabeth
Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882, USA.
Science. 2009 Jul 31;325(5940):605-7. doi: 10.1126/science.1174156.
Mantle oxygen fugacity exerts a primary control on mass exchange between Earth's surface and interior at subduction zones, but the major factors controlling mantle oxygen fugacity (such as volatiles and phase assemblages) and how tectonic cycles drive its secular evolution are still debated. We present integrated measurements of redox-sensitive ratios of oxidized iron to total iron (Fe3+/SigmaFe), determined with Fe K-edge micro-x-ray absorption near-edge structure spectroscopy, and pre-eruptive magmatic H2O contents of a global sampling of primitive undegassed basaltic glasses and melt inclusions covering a range of plate tectonic settings. Magmatic Fe3+/SigmaFe ratios increase toward subduction zones (at ridges, 0.13 to 0.17; at back arcs, 0.15 to 0.19; and at arcs, 0.18 to 0.32) and correlate linearly with H2O content and element tracers of slab-derived fluids. These observations indicate a direct link between mass transfer from the subducted plate and oxidation of the mantle wedge.
地幔氧逸度对俯冲带地球表面与内部之间的质量交换起着主要控制作用，但控制地幔氧逸度的主要因素（如挥发物和相组合）以及构造旋回如何驱动其长期演化仍存在争议。我们展示了利用Fe K边微X射线吸收近边结构光谱测定的氧化态铁与总铁（Fe3+/ΣFe）的氧化还原敏感比值的综合测量结果，以及涵盖一系列板块构造环境的全球原始未脱气玄武质玻璃和熔体包裹体样本的喷发前岩浆水含量。岩浆Fe3+/ΣFe比值向俯冲带方向增加（在洋中脊为0.13至0.17；在后弧为0.15至0.19；在火山弧为0.18至0.32），并且与水含量以及俯冲板块衍生流体的元素示踪剂呈线性相关。这些观测结果表明俯冲板块的物质转移与地幔楔氧化之间存在直接联系。
