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Establishment of the stable isotopic stratigraphy of Banded Iron Formations

带状铁地层稳定同位素地层学的建立

基本信息

批准号：
08640598
负责人：
HAYASHI Ken-ichiro
金额：
$ 1.41万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1997
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-08640598/
关键词：
Banded Iron Formation Stable isotope Oxygen isotope Carbon isotope Hydrothermal solution BIF ハマスレ-地域熱水活動

项目摘要

Banded iron formations (BIFs), bedded manganese deposits, and silica sinters are the typical examples of chemical sediments that possess clear banding texture. These sedimentary rocks have precipitated on seafloor or subaerial surface, from seawater or hydrothermal solutions with the decrease of solubilities of silica, iron, and manganese in solutions. Variation of stable isotopic compositions of oxygen, carbon, and sulfur in these banded chemical sedimentary rocks have been measured to clarify their genesis.1.Newly developed CO_2-laser microprobe fluorination technique was applied to the Brockman Iron Formation, Hamersley basin, Western Australia, to investigate submillimeter scale oxygen isotopic compositions of quartz both hosted in chert and iron-oxide mesobands. Our data show that delta^<18>O values of BIFs vary between 16.0 and 23.0*, on the contrary to the previous studies that BIFs are isotopically homogeneous. The wide variation of delta^<18>O probably suggests that hydrothermal activities have been responsible for the formation of Hamersley BIFs.2.Isotopic values of organic and carbonate carbon in shale macrobands of the Marra Mamba Iron Formation, Western Australia were measured. The very low delta^<13>C values of organic C,-41.0--37.1*, suggest the activity of the metanogens and metanotrophs in the ocean. The delta^<13>C of dissolved bicarbonate in seawater estimated from carbon isotopic compositions of carbonate was delta^<13>C=--12*. This low value, compared to that of the modern marine HCO_3^- (--1.0*), was also explained as the results of a carbon-cycle system affected by the activities of metanogens and methanotrophs.3.The delta^<18>O values of quartz in silica sinter from the Kitano-oh gold deposits, and those of manganese silicate minerals from the metamorphosed bedded manganese deposits of the Noda-Tamagawa mine were measured. The origin of hydrothermal solutions is discussed.

条带状铁建造、层状锰矿床和硅质烧结矿是具有明显条带状结构的典型化学沉积物。这些沉积岩是从海水或热液中沉淀到海底或陆上表面的，溶液中二氧化硅、铁和锰的溶解度降低。利用CO_2激光微探针技术，对澳大利亚西部哈默斯利盆地Brockman铁矿组中硅质岩和氧化铁中带石英的亚毫米级氧同位素组成进行了研究。我们的数据表明，BIFs的δ ^<18>O值在16.0和23.0* 之间变化，与以前的研究相反，BIFs是同位素均匀的。δ ^ O的变化幅度很大<18>，这可能表明热液活动是哈默斯利BIFs形成的原因。2.测定了西澳大利亚Marra Mamba铁组页岩宏带中有机碳和碳酸盐碳的同位素值。有机<13>碳的Δ C值很低，为-41.0--37.1*，表明海洋中的变形菌和变形营养生物的活动。由<13>碳酸盐碳同位素组成估算的海水溶解碳酸氢盐δ ^ C为δ ^<13>C=-12*。与现代海相HCO_3^-（--1.0*）相比，这一低值也被解释为受变质菌和甲烷氧化菌活动影响的碳循环系统的结果。3.测定<18>了北野哦金矿硅质烧结矿中石英和野田玉川矿床变质层状锰矿中锰硅酸盐矿物的δ ^ O值。讨论了热液的成因。