难熔元素和代表性放射性同位素体系分析技术的进展、问题和应用展望

Progress,open questions and application prospects of analytical techniques for refractory elements and representative radioisotope systems

Pt-Os、Re-Os和Hf-W同位素体系的母体和子体Pt、Os、Re、Hf和W以及其它铂族元素(PGE)化学性质上都是难熔的,我们将这些元素和相关同位素称为难熔元素和难熔元素放射性同位素体系。难熔元素及其放射性同位素体系不仅可以直接测定金属矿床、油气藏和沉积岩系的年龄,而且还可以有效示踪地球深部的核幔反应等过程,这是其它地球化学工具不可替代的。本文评述了当前Pt-Os、Re-Os和Hf-W同位素体系和PGE元素分析技术的研究进展,指出:(1)目前Re-Os同位素定年误差仍较大,迫切需要优化改进分析技术,大幅提高Re-Os同位素定年的准确度和成功率;(2)Pt-Re-Os和W同位素的分析技术需要简化繁琐的化学分离流程和提高仪器分析的效率,同时探索建立新的化学分离和仪器分析方法,进一步提高分析精度,实现对更低Pt、Re、Os和W含量样品的准确分析,才能更有效地示踪地球深部物质循环过程;(3)PGE的元素分析技术尚需改进,分析精度仍需要进一步提升。我们预期随着进一步提升难熔元素和代表性放射性同位素的分析精度,显著降低同位素定年误差,其将在核-幔、幔-幔和壳-幔物质循环过程示踪、金属矿床精细定年和成因机制、复杂含油气系统的定年和示踪以及中元古代环境变化等研究中得到更广泛的应用。

The parent and daughter of Pt-Os,Re-Os and Hf-W isotopic systems(i.e.Pt,Os,Re,Hf and W)and other platinum group elements(PGEs)are refractory in chemical properties,which are named collectively as refractory elements and refractory elemental radiogenic isotope systems in present paper.Refractory elements and their representative radiogenic isotope systems can not only directly determine the age of metal deposits,oil and gas reservoirs and sedimentary rock series,but also effectively trace the core-mantle reaction in the deep earth,which makes them irreplaceable geochemical tools.This paper reviews the research progress of Pt-Os,Re-Os and Hf-W isotopic systems and PGE elemental analysis technology.It is pointed out that:(1)the Re-Os isotopic dating error is still large,so it is necessary to optimize and improve the analysis technology in order to greatly improve the accuracy and success rate of Re-Os isotopic dating.(2)The analysis technology of Pt-Re-Os and W isotopes needs to simplify the cumbersome chemical separation process and improve the efficiency of instrumental analyzing.In the meantime,it is suggested to establish new chemical separation and instrumental analysis methods.Only by realizing accurate analysis of samples with very low content of Pt,Re,Os and W,it is possible to effectively trace material recycling processes in the deep earth.(3)The analysis technology of PGE needs to be optimized,and the analysis precision still needs to be further improved.With further improvement of the analytical techniques of refractory elements and representative radiogenic isotopes,it is anticipated that these geochemical tools will be more widely used in tracing and/or dating the material recycle processes of core-mantle,mantle-mantle and crust-mantle,the precise timing and formation mechanism of metal deposits and complex petroleum systems,and the environment change during Mesoproterozoic.