Deciphering the surface environment of the primitive Earth from nitrogen isotopes trapped in Archean sedimentary rocks-Investigation of its trapping forms in the rocks.

从太古宙沉积岩中捕获的氮同位素破译原始地球的表面环境——对其在岩石中捕获形式的调查。

• 批准号: 17340168
• 负责人: HASHIZUME Ko
• 金额: $ 8.26万
• 依托单位: Osaka University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2005
• 资助国家: 日本
• 起止时间: 2005 至 2006
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-17340168/
• 关键词: Primitive Earth; Surface Environments; Nitrogen Isotopes; Sedimentary Rocks; Archean; Chert; Banded Iron Formations; 粘土鉱物; アンモニウム

In this study, search of the surface environments of the primitive earth was performed using the information of nitrogen isotopes obtained from Archean sedimentary rocks. Though the nitrogen isotopes trapped in the rock samples have potential of providing such information, it is not always clear how we may obtain and interprete the raw data. We studied 3.5 Ga old chert samples from western Australia (from Kitty's gap and Marble bar), and a 2.7-2.9 Ga old samples of the banded iron formation from Dhawar Craton of India. Volatile compounds (N_2, Ar, C and H_2O) were extracted from samples using a stepwise combustion method, and their elemental and/or isotopic compositions were analysed.We were able to specify or infer three trapping sites/forms of nitrogen by combining the information of different volitile compounds. In Kitty's gap chert, nitrogen concentrations were observed to be correlated well with those of radiogenic ^<40>Ar, suggesting that nitrogen is trapped in K-bearing clay minerals. The δ15N values showed a wide range between-4 to +10 permil, and were correlated with the ^<40>Ar/N ratio, suggesting existence of two different types of trapping sites among the clay minerals. In Marble bar chert, nitrogen with δ^<15>N values between +6.0 to +7.3 permil was observed, associated with carbon, suggesting that nitrogen in this sample is trapped in organic form. Furthur investigations imply that the N-bearing organic matter is protected by inorganic minerals. Among the BIF samples, N with δ^<15>N values around +10 permil was observed. There seem to exist two types of N-bearing C-associated host phases with different C/N ratios. Discrimination of the N isotopic components in different chemical forms among the Archean rocks may largly help us to decipher the isotopic evolution of nitrogen of the primitive biosphere.

在这项研究中，使用从Archean Sedimentary Rocks获得的氮同位素信息进行了对原始地球的表面环境的搜索。尽管被困在岩石样品中的氮同位素具有提供此类信息的潜力，但并不总是清楚我们如何获得和解释原始数据。我们研究了来自西澳大利亚州的3.5 GA旧的Chert样品（来自Kitty's Gap and Marble Bar），以及来自印度Dhawar Craton的带状铁层的2.7-2.9 GA旧样品。使用逐步组合方法从样品中提取挥发性化合物（N_2，AR，C和H_2O），并分析其元素和/或同位素组合物。我们能够通过结合不同挥发性化合物的信息来指定或推断出三个陷阱位点/形式的氮。在小猫的间隙裂缝中，观察到氮浓度与放射性 ^<40> ar的氮浓度很好地相关，这表明氮被困在含k的粘土矿物质中。 Δ15N值显示了4至+10渗透之间的范围很大，并且与 ^<40> ar/n比率相关，这表明粘土矿物质中存在两种不同类型的捕获位点。在大理石条缝隙中，观察到与碳相关的Δ^^<15> n值之间的氮值与碳相关，这表明该样品中的氮以有机形式捕获。 Fuurthur的研究表明，含有N含有无机矿物的N含有有机物。在BIF样品中，观察到具有Δ^<15> n值+10腐烂的n。似乎存在两种类型的N含N型C相关的宿主相，具有不同的C/N比。大将岩石中不同化学形式的N同位素成分的歧视可能在很大程度上有助于我们破译原始生物圈的氮的同位素进化。

项目成果

Biomarkers in Archaean banded iron formations from Pilbara and Dhawar Craton

皮尔巴拉和达瓦尔克拉通太古代带状铁地层中的生物标志物

• 发表时间: 2006
• 期刊: Geochimica et Cosmochimica Acta 18
• 作者: Pinti D.L.;Hashizume K.;Orberger B.;Gallien J.;Cloquet C.;Massault M.;Orberger B.
• 通讯作者: Orberger B.