Hf-W Isotopic Systematics : Constraints for Geochemical Evolution of the Planet Earth

Hf-W同位素系统学:地球地球化学演化的约束

• 批准号: 15340191
• 负责人: HIRATA Takafumi
• 金额: $ 8.96万
• 依托单位: Tokyo Institute of Technology
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2003
• 资助国家: 日本
• 起止时间: 2003 至 2005
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-15340191/
• 关键词: W isotopes; Hf-W chronometer; geochemical samples; ion chromatography; ICP-mass spectrometry; stable isotope geochemistry; isotopic fractionation; oxidation-reduction reaction; イオンクロマトグラフィー; 地球形成; 金属コア形成; 放射年代測定法; 超微量元素分析; 同位体分析; 質量分析法; 数値シ

Hf-W isotopic systematics has been given great attention in the field of Earth sciences because of its high time resolution to the cosmochemical events. However, the practical utility of the Hf-W chronometer has been retarded by the difficulty in sensitive and precise W isotopic measurements mainly caused by low ionisation efficiency in the mass spectrometer. We have developed a new analytical technique for W isotopes using a multiple collector-ICP mass spectrometer (MC-ICPMS) coupled with a high recovery ion chromatographic technique. In this study, W isotopic compositions for various geochemical samples, covering sediments, volcanic rocks or ore deposits, have been measured.The 182W/183W can change due to radiogenic contribution from beta-decay of radioactive nuclide 182Hf.In fact, there was significant variation in resulting 182W/183W ratio for metallic meteorites (iron meteorites). This can be attributed either to the difference in timing of metal/silicate segregation inside the mo … More ther planetesimals, or to the heterogeneous distribution of Hf/W in the primary solar nebula. Most interesting feature is that the present 182W/183W ratio for IVB iron meteorites did not agree with the some of the published values, indicating that Hf/W ratio was not totally homogenised at the early stage of the solar nebula. In strike contrast, resulting 182W/183W for geochemical materials did not vary measurably, suggestive of either slow accretion rate of the Earth, or total reset of the Hf-W isotopic system by a giant impact event. Thus the present 182W/183W ratio data could provide key information about the early sequence of the solar system.Despite the absence in variation in 182W/183W ratio for the geochemical samples, we found that W in some geochemical samples was isotopically fractionated through the sample formation sequence.Resulting 186W/183W (expressed as epsilon units) for JMn-1 and HSD show significantly higher 1.5ε and 4.5ε than the value for NIST-3163 (international isotopic standard), respectively. It is widely recognized that oxidation state of W can change through cosmo- and geo-chemical processes, and therefore, W in geochemical materials could provide us physico-chemical information for the production sequence of the sample. Although mechanism of the isotopic fractionation of W is not well understood at this moment, the small but significant variations in non-radiogenic W components indicated clearly that further detailed geochemical discussion is possible by the combination of Hf-W chronology and stable isotope geochemistry using W, which would open up the new research field in the Earth Sciences. Less

Hf-W同位素系统学因其对宇宙化学事件的高时间分辨率而受到地球科学界的广泛关注。然而，Hf-W计时器的实际效用已被延迟的困难，在灵敏和精确的W同位素测量主要是由低电离效率在质谱仪。我们开发了一种新的钨同位素分析技术，使用多收集器-电感耦合等离子体质谱仪（MC-ICPMS）耦合高回收率离子色谱技术。本文对沉积物、火山岩和矿床等地球化学样品的W同位素组成进行了测量，发现182 W/183 W比值会因放射性核素182 Hf β衰变的放射成因贡献而发生变化，而金属陨石（铁陨石）的182 W/183 W比值则有明显的变化。这可以归因于钼内部金属/硅酸盐偏析时间的差异 ...更多信息 或Hf/W的不均匀分布。最有趣的是IVB铁陨石的182 W/183 W比值与一些已发表的值不一致，表明Hf/W比值在太阳星云的早期并不完全均匀。与此形成鲜明对比的是，地球化学物质的182 W/183 W没有明显的变化，这表明地球的缓慢吸积速率，或者是巨大的撞击事件导致Hf-W同位素系统的完全重置。因此，目前的182 W/183 W比值数据可以提供有关太阳系早期序列的关键信息。在某些地球化学样品中，W在样品形成序列中发生了同位素分馏，导致186 W/183 W对于JMn-1和HSD，两种同位素的相对分子质量（以ε单位表示）分别显示出比NIST-3163（国际同位素标准）的值显著更高的1.5ε和4.5ε。地球化学物质中W的氧化态可以通过宇宙和地球化学过程发生变化，因此，W可以为样品的生成序列提供物理化学信息。尽管目前W的同位素分馏机制还不清楚，但非放射成因W组分中微小但显着的变化清楚地表明，将Hf-W年代学与W的稳定同位素地球化学结合起来进行进一步详细的地球化学讨论是可能的，这将开辟地球科学的新研究领域。少

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• 发表时间: 2005
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• 作者: Ida;S.;D.N.C.Lin
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• 期刊: Geology 33
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• DOI: 10.1039/b504153h
• 发表时间: 2005-07
• 期刊: Journal of Analytical Atomic Spectrometry
• 影响因子: 3.4
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Precise Zn Isotopic Ratio Measurement of Human Red Blood Cell and Hair Samples by Multiple Collector-ICP-Mass Spectrometry

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• 发表时间: 2005
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