Integrated Fe- and S-isotope study of seafloor hydrothermal vents at East Pacific Rise 9–10°N
Integrated Fe- and S-isotope study of seafloor hydrothermal vents at East Pacific Rise 9–10°N
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DOI：
10.1016/j.chemgeo.2008.03.009
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发表时间：
2008-07
期刊：
影响因子：
3.9
通讯作者：
O. Rouxel;W. Shanks;W. Bach;K. Edwards
中科院分区：
文献类型：
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作者：
O. Rouxel;W. Shanks;W. Bach;K. Edwards
在这项研究中，我们报告了来自东太平洋海隆9-10°N的热液流体和硫化物矿床的耦合Fe和S同位素系统学，以更好地约束影响热液环境中Fe同位素分馏的过程。我们的目标是解决三个基本问题：（1）是否有显着的铁同位素分馏过程中硫化物沉淀？(2)地下环境中反映硫化物沉淀的热液流体的铁同位素组成是否存在显著的变化？(3)硫化物矿物中的Fe和S同位素之间是否存在系统关系？结果表明，沉积在热液烟囱内壁的黄铜矿δ 56 Fe值和δ 34 S值的范围有限，分别为-0.11 ‰ ~-0.33 ‰和2.2 ‰ ~ 2.6‰。δ 56 Fe值平均略高于同期喷口流体成分0.14‰，而δ 34 S值表明黄铜矿沉淀过程中存在显著的S同位素分馏（-0.6 ±0.2‰）。与此相反，在活动烟囱内部沉积的黄铁矿和白铁矿中，δ 56 Fe和δ 34 S值相对于热液流体系统地较低，分别高达0.91‰和2.0‰。这些结果表明，由于热液H2S和海水SO 42 −之间的S同位素交换，随后由FeS前体快速形成黄铁矿，因此保留了FeS沉淀过程中强烈的动力学Fe同位素分馏的影响，因此Fe和S同位素的同位素不平衡。相反，来自非活动块状硫化物的黄铁矿的δ 56 Fe和δ 34 S值显示了广泛的后期改造的证据，基本上与热液流体相似。海底古烟囱沉积物的多阶段矿化似乎产生最小的铁同位素分馏。在地下硫化物沉淀过程中也显示了类似的影响，高温富铁黑烟囱和低温贫铁喷口的δ 56 Fe值之间缺乏系统差异就证明了这一点。
In this study, we report on coupled Fe- and S-isotope systematics of hydrothermal fluids and sulfide deposits from the East Pacific Rise at 9–10°N to better constrain processes affecting Fe-isotope fractionation in hydrothermal environments. We aim to address three fundamental questions: (1) Is there significant Fe-isotope fractionation during sulfide precipitation? (2) Is there significant variability of Fe-isotope composition of the hydrothermal fluids reflecting sulfide precipitation in subsurface environments? (3) Are there any systematics between Fe- and S-isotopes in sulfide minerals? The results show that chalcopyrite, precipitating in the interior wall of a hydrothermal chimney displays a limited range of δ56Fe values and δ34S values, between −0.11 to −0.33‰ and 2.2 to 2.6‰ respectively. The δ56Fe values are, on average, slightly higher by 0.14‰ relative to coeval vent fluid composition while δ34S values suggest significant S-isotope fractionation (−0.6±0.2‰) during chalcopyrite precipitation. In contrast, systematically lower δ56Fe and δ34S values relative to hydrothermal fluids, by up to 0.91‰ and 2.0‰ respectively, are observed in pyrite and marcasite precipitating in the interior of active chimneys. These results suggest isotope disequilibrium in both Fe- and S-isotopes due to S-isotopic exchange between hydrothermal H2S and seawater SO42−followed by rapid formation of pyrite from FeS precursors, thus preserving the effects of a strong kinetic Fe-isotope fractionation during FeS precipitation. In contrast, δ56Fe and δ34S values of pyrite from inactive massive sulfides, which show evidence of extensive late-stage reworking, are essentially similar to the hydrothermal fluids. Multiple stages of remineralization of ancient chimney deposits at the seafloor appear to produce minimal Fe-isotope fractionation. Similar affects are indicated during subsurface sulfide precipitation as demonstrated by the lack of systematic differences between δ56Fe values in both high-temperature, Fe-rich black smokers and lower-temperature, Fe-depleted vents.