【作者】 李津；

【导师】 朱祥坤；

【作者基本信息】 中国地质科学院 ， 地球化学， 2008， 博士

【摘要】 近年来,随着MC-ICP-MS测试技术的诞生,非传统稳定同位素研究成为快速发展的领域。作为一个新的稳定同位素体系,正确运用这一体系对重大问题进行制约的前提和关键是对其质量分馏机理与过程有足够的认识。由于铁锰结壳极低的生长速率和较稳定的形成环境,使它成为古海洋学和全球变化研究的理想“化石”。本文在对前人过渡族元素同位素分馏研究成果进行系统总结地基础上,主要开展了两方面的内容:研究了结晶过程、还原过程和水解过程导致的同位素分馏情况;研究了太平洋三块Fe-Mn结壳MDD53、CB12和CLD01的Fe、Cu、Zn同位素组成。同时,还对Cu、Zn同位素的测定方法进行了改进。本研究主要取得了以下创新性成果和认识:1.通过改变进样介质,改进了Cu、Zn同位素的方法,改善了样品测试过程的稳定性,提高了分析精度。2.CuSO₄·5H₂O结晶过程中可以导致Cu同位素分馏,晶体中富集重同位素。该过程发生的同位素分馏是平衡分馏,平衡分馏系数α=1.00017。将Cu²⁺还原为金属Cu的过程中可以导致Cu同位素分馏,生成物中富集轻同位素。该过程产生的同位素分馏是动力分馏,金属Cu与Cu²⁺之间没有达到平衡。3.Fe³⁺水解过程导致生成物中富集轻同位素,Fe³⁺溶液与Fe³⁺沉淀之间的瞬时平衡系数随着温度的升高而减小。瞬时平衡分馏系数与绝对温度之间的关系是:10³lnα=-0.17×10⁶/T²+0.91。4.通过对3块太平洋Fe-Mn结壳的研究,获得了80Ma以来海洋的过渡族元素演化信息,将人们对古海洋中过渡族元素同位素演化的认识推进到晚白垩纪。5.结合已有的数据,对各大洋Fe-Mn结壳的Fe同位素组成进行了系统总结,发现即使在同一大洋盆地,不同结壳表层的Fe同位素组成也存在很大差异;各大洋间Fe-Mn结壳表层的Fe同位素组成存在很大程度的重合,但总体呈现由大西洋→印度洋→太平洋逐渐变轻的趋势。6.Fe-Mn结壳Fe和Pb两个性质不同的同位素体系普遍存在相关性,在一定程度上指示了物源对Fe-Mn结壳中Fe同位素组成的影响。7.与Fe同位素相比,Fe-Mn结壳中Cu、Zn同位素组成的变化范围较小。这种差异主要是由于它们在海洋中的滞留时间不同决定的。与大洋对流周期相比,Fe的滞留时间很短,其同位素组成没有被均一化,对源区合局部环境的变化敏感:Cu和Zn的滞留时间较长,其同位素组成在很大程度上发生了均一化,使源区和局部因素的影响大部分丢失。8.尽管不同Fe-Mn结壳间的Fe同位素组成存在一定差异,但它们随时间的演化在宏观尺度上存在极大的相似性,说明影响因素使大区域性的,或全球性的。通过对古海洋环境和Fe同位素的对比,发现Fe-Mn结壳的Fe同位素组成很可能是海洋生产力的一个指标或环境变化的指标。更多还原

【Abstract】 Studies of non-traditional stable isotopes have being developed quickly in recent years thanks to the introduction of multi-collector plasma-source mass-spectrometry（MC-ICP-MS）.As new stable isotope systems,the premise and key of using them to constrain important issues is to understand its fractionation mechanism and process adequately.As the extremely low growth rate and stable forming environment,Fe-Mn crust is the ideal fossil of Paleoceanography and global change.The work of this thesis is consisted mainly of two-parts:the experimental study of mass fractionation during the process of crystallization, reduction and hydrolysis;investigation the isotope variations of Fe,Cu and Zn isotope in Fe-Mn. In addition,technical improvements for Cu and Zn isotope measurements have been madeThe main achievements of the thesis are as following:1.Improvements of instrumental stability and precision through using the sampling medium..2.The process of CuSO₄·SH₂O crystallization can induce Cu isotope fractionation,where the cystal shows enrichment of heavy isotope,and equilibrium mass fractionation factor in 65Cu/63Cu isα=1.00017 at room temperature.The process of reduction of Cu²⁺ in to native copper can induce fractionation,where the productant copper shows light isotopeenrichment.As this is a unidirection reaction,it is a kinetic process.3.The heavy isotope of Fe is depleted in the poductant during Fe（Ⅲ） hydrolysis.The instantaneous equilibrium fractionation factor is decreasing with the temperature increasing.The relationship between the instantaneous equilibrium fractionation factor and temperature is:10³lnα=-0.17×10⁶/T²+0.91.4.Variations in isotope compositions of transition metals in paleocean over the last 80Ma have been obtained through investigation of three Pacific Fe-Mn crusts,which adding our knowledge on the isotope evolution of transition metals in ocean back to late Cretaceous.5.Through combining the data obtained in this study with previous ones,it has been found that:（1） the Fe isotope compositions of surface layers of Fe-Mn crusts are rather heterogeneous even within a same oceanic basin;（2） The Fe isotope compositions of Fe-Mn crusts in different oceans are largely overlapped,but with a general trend of heavy isotope depletion from Atlantic, through Indian,to Pacific Ocean.6.The correlation between Fe isotope and Pb isotope is existed widely in Fe-Mn crusts, which shows the effect of source input on Fe isotope compositions of Fe-Mn crusts to some degree.7.The ranges in isotope variartions of Cu and Zn are small relative to that of Fe isotopes. This result most likely from the differences of theresident times of these elements in oceans,as the residence time of Fe is much shorter than that of ocean circle,implying that the isotope composition cannot be homogenized thus sensitive to local input.In contrast,the resident times of Cu and Zn are much longer than that of ocean circulation,and their isotopes have been rather homogenized,implying the effect of local input has been largely cancelled out8.The patterns of isotope evolution obtained from different Fe-Mn crusts are rather similar at long-term scale,even their isotope compositions are different.This means that the long-term evolution of Fe isotopes recorded in these crust are controlled by factors with regional or even global effects.Through comparing the paleocean environments and Fe isotopes,this is proposed that the Fe isotopes maybe used as a proxy of ocean productivity or environment change.更多还原