Biogenic nitrogen and carbon in Fe‐Mn‐oxyhydroxides from an Archean chert, Marble Bar, Western Australia
Biogenic nitrogen and carbon in Fe‐Mn‐oxyhydroxides from an Archean chert, Marble Bar, Western Australia
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DOI：
10.1029/2006gc001394
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发表时间：
2007-02
期刊：
影响因子：
3.7
通讯作者：
D. Pinti;K. Hashizume;B. Orberger;J. Gallien;C. Cloquet;M. Massault
中科院分区：
文献类型：
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作者：
D. Pinti;K. Hashizume;B. Orberger;J. Gallien;C. Cloquet;M. Massault
为了量化和定位西澳大利亚大理石吧地层太古代岩石中的氮 (N) 和碳 (C)，并深入了解其起源和潜在的生物成因，我们对来自 3460 密尔古的富铁大理石吧燧石的各种样品进行了核反应分析 (NRA) 和碳氮同位素比测量。大理石坝燧石是在玄武质火山碎屑岩与富含铁和硅的热液的蚀变过程中形成的，以及随后磁铁矿、碳酸盐、块状二氧化硅和局部硫化物的沉淀。在后期，磁铁矿、硫化物和碳酸盐被 Fe-Mn-羟基氧化物取代。核反应分析表明，大部分 N 和 C 存在于这些 Fe-Mn-羟基氧化物中，但一小部分存在于分散在二氧化硅基质中的 K-长石和 Ba-云母中。铁氧化物的 N 和 C 同位素组成表明存在独特的生物源，其 δ15NAIR 值为 +6.0 ± 0.5 ‰ 至 7.3 ± 1.1 ‰，δ13CPDB 值为 -19.9 ± 0.1 ‰。 C 和 N 同位素比率与元古代和显生宙有机质中观察到的相似。高燃烧温度下释放的 N 和 C 的扩散控制分馏表明，这两种元素牢固地嵌入铁氧化物中，N 的活化能为 18.7 ± 3.7 kJ/mol，C 的活化能为 13.0 ± 3.8 kJ/mol。我们认为 N 和 C 被化学吸附在铁上，随后在铁氧化和晶体生长过程中嵌入晶体中。大理石条燧石的铁同位素组成 (δ56Fe = -0.38 ± 0.02‰) 与在与含氧水接触的热液羽流中直接沉淀铁而形成的氧化铁中测量到的铁同位素组成相似。为了解释大理石条燧石的 N 和 C 同位素组成，我们提出（1）在太古宙末期，当氧气开始上升时，N 和 C 的较晚添加，或者（2）局部含氧环境的早期发展，其中可能发展了与现代类似的生物地球化学循环。
To quantify and localize nitrogen (N) and carbon (C) in Archean rocks from the Marble Bar formation, Western Australia, and to gain insights on their origin and potential biogenicity, we conducted nuclear reaction analyses (NRA) and carbon and nitrogen isotope ratio measurements on various samples from the 3460‐Myr‐old Fe‐rich Marble Bar chert. The Marble Bar chert formed during the alteration of basaltic volcanoclastic rocks with Fe‐ and Si‐rich hydrothermal fluids, and the subsequent precipitation of magnetite, carbonates, massive silica, and, locally, sulfides. At a later stage, the magnetite, sulfides, and carbonates were replaced by Fe‐Mn‐oxyhydroxides. Nuclear reaction analyses indicate that most of the N and C resides within these Fe‐Mn‐oxyhydroxides, but a minor fraction is found in K‐feldspars and Ba‐mica dispersed in the silica matrix. The N and C isotopic composition of Fe‐oxides suggests the presence of a unique biogenic source with δ15NAIR values from +6.0 ± 0.5‰ to 7.3 ± 1.1‰ and a δ13CPDB value of −19.9 ± 0.1‰. The C and N isotope ratios are similar to those observed in Proterozoic and Phanerozoic organic matter. Diffusion‐controlled fractionation of N and C released during high combustion temperatures indicates that these two elements are firmly embedded within the iron oxides, with activation energies of 18.7 ± 3.7 kJ/mol for N and 13.0 ± 3.8 kJ/mol for C. We propose that N and C were chemisorbed on iron and were subsequently embedded in the crystals during iron oxidation and crystal growth. The Fe‐isotopic composition of the Marble Bar chert (δ56Fe = −0.38 ± 0.02‰) is similar to that measured in iron oxides formed by direct precipitation of iron from hydrothermal plumes in contact with oxygenated waters. To explain the N and C isotopic composition of Marble Bar chert, we propose either (1) a later addition of N and C at the end of Archean when oxygen started to rise or (2) an earlier development of localized oxygenated environments, where biogeochemical cycles similar to modern ones could have developed.