Generation of hydrothermal Fe‐Si oxyhydroxide deposit on the Southwest Indian Ridge and its implication for the origin of ancient banded iron formations
Generation of hydrothermal Fe‐Si oxyhydroxide deposit on the Southwest Indian Ridge and its implication for the origin of ancient banded iron formations
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DOI：
10.1002/2014jg002764
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发表时间：
2015-01
期刊：
影响因子：
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通讯作者：
Zhilei Sun;Jun Li;Wei Huang;Hai-liang Dong;C. Little;Jiwei Li
中科院分区：
文献类型：
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作者：
Zhilei Sun;Jun Li;Wei Huang;Hai-liang Dong;C. Little;Jiwei Li
现代热液Fe-Si羟基氧化物矿床现在已知类似于古代硅质铁地层。在这项研究中，铁硅氢氧化物矿床的样品是从西南印度洋海岭的热液区收集的。根据一系列矿物学和形态学方法，对这些矿床的成矿作用进行了研究。X射线衍射和选区电子衍射分析表明，无定形蛋白石和结晶度低的水铁矿是主要矿物。此外，通过扫描电子显微镜检查检测到的一些典型的丝状结构，可能表明存在铁氧化细菌（FeOB），其主要成分是Fe，Si，P和C。因此，我们认为，化能自养FeOB在Fe羟基氧化物的形成中起着重要作用，Fe羟基氧化物可以有效地氧化来自热液流体的还原Fe（II）。相比之下，无定形二氧化硅的沉淀只是一个被动的过程，Fe羟基氧化物充当模板。在现代海底热液系统中，首次在我们的样品中观察到富Fe和富Si带之间交替的独特微纹层结构。我们建议，它的形成是由于热液流体的温度变化，控制生物Fe羟基氧化物的形成和被动沉淀的二氧化硅在这个系统中。这一结果可能为古条带状铁建造的形成机制提供线索。
Modern hydrothermal Fe‐Si oxyhydroxide deposits are now known to be analogues to ancient siliceous iron formations. In this study, samples of Fe‐Si oxyhydroxide deposits were collected from hydrothermal field on the Southwest Indian Ridge. An investigation of mineralization in these deposits was carried out based on a series of mineralogical and morphological methods. X‐ray diffraction and selected area electron diffraction analysis show that amorphous opal and poorly crystalline ferrihydrite are the major minerals. Furthermore, some typical filament structures detected by scanning electronic microscopy examinations, probably indicating the presence of Fe‐oxidizing bacteria (FeOB), are pervasive with the main constituents being Fe, Si, P, and C. We thus believe that chemolithoautotrophic FeOB play a significant role in the formation of Fe oxyhydroxide which can effectively oxidize reduced Fe(II) sourced from hydrothermal fluids. Precipitation of amorphous silica, in contrast, is only a passive process with the Fe oxyhydroxide acting as a template. The distinct microlaminae structure alternating between the Fe‐rich and Si‐rich bands was observed in our samples for the first time in modern seafloor hydrothermal systems. We propose that its formation was due to the episodic temperature variation of the hydrothermal fluid which controls the biogenic Fe oxyhydroxide formation and passive precipitation of silica in this system. Our results might provide a clue for the formation mechanism of ancient banded iron formations.