Isotopic evidence for iron mobility during subduction
Isotopic evidence for iron mobility during subduction
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DOI：
10.1130/g37565.1
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发表时间：
2016-03-01
期刊：
影响因子：
5.8
通讯作者：
Williams, H.
中科院分区：
文献类型：
--
作者：
Debret, B.;Millet, M. -A.;Williams, H.
俯冲带是地球表面和内部化学交换的最重要场所之一。解释高Fe 3 +/Sigma Fe比值和原生弧岩浆氧化性质的一种方法是硫酸盐（SOX）、碳酸盐（CO 3-）和/或含铁（Fe 3+）流体从板片向上覆地幔的转移。铁的氧化还原状态和氯和/或硫阴离子的存在下，在流体中的铁的流动性和铁稳定同位素分馏的影响。在这里，我们使用铁稳定同位素（δ Fe-56）作为示踪剂的铁流动性蛇纹岩从西阿尔卑斯变质，这代表了残余的海洋岩石圈，经历了俯冲相关的变质作用和脱挥发分。蛇纹岩体δ Fe-56与Fe ~（3+）/σ Fe呈负相关（R ~（-2）= 0.72），为俯冲带蛇纹岩脱挥发分过程中含铁流体的释放提供了第一个直接证据。同位素轻铁的逐步损失，从板的逐渐增加的程度，富硫酸盐和/或高盐流体，优先复杂的形式的Fe（II）-SOX或Fe（II）Cl-2物种的同位素轻铁的释放是一致的。因此，铁同位素可用作板片衍生流体性质的示踪剂。
Subduction zones are one of the most important sites of chemical interchange between the Earth's surface and interior. One means of explaining the high Fe3+/Sigma Fe ratios and oxidized nature of primary arc magmas is the transfer of sulfate (SOX), carbonate (CO3-), and/or iron (Fe3+) bearing fluids from the slab to the overlying mantle. Iron mobility and Fe stable isotope fractionation in fluids are influenced by Fe redox state and the presence of chlorine and/or sulfur anions. Here we use Fe stable isotopes (delta Fe-56) as a tracer of iron mobility in serpentinites from Western Alps metaophiolites, which represent remnants of oceanic lithosphere that have undergone subduction-related metamorphism and devolatilization. A negative correlation (R-2 = 0.72) is observed between serpentinite bulk delta Fe-56 and Fe3+/Sigma Fe that provides the first direct evidence for the release of Fe-bearing fluids during serpentinite devolatilization in subduction zones. The progressive loss of isotopically light Fe from the slab with increasing degree of prograde metamorphism is consistent with the release of sulfate-rich and/or hypersaline fluids, which preferentially complex isotopically light Fe in the form of Fe(II)-SOX or Fe(II)Cl-2 species. Fe isotopes can therefore be used as a tracer of the nature of slab-derived fluids.