硅酸盐中的钨同位素分析化学流程
首发时间:2017-05-16
摘要:$^{182}Hf - ^{182}W$短半衰期同位素体系是定年核幔分异最有力的工具,并对指示硅酸盐相的结晶和部分熔融也有巨大潜在价值。然而直到近两年,由于分析精度限制,钨同位素地球化学进展比较缓慢。实现高精度钨同位素分析的关键在于从自然岩石样品中分离出大量高纯度的钨并同时有效的降低实验本底,本项工作主要从这两方面着手。文章首先介绍了利用 $^{182}Hf - ^{182}W$ 短半衰期同位素体系定年的基本原理,并探究了钨同位素的化学分离流程,继而提出了一种新的两步离子交换分离流程—— 先使用阳离子树脂来去除硅酸盐中所含的基质和镁钙等沉淀物,再使用阴离子树脂来达到钨精确分离。新方法大大提高了样品的分析容量,与其他分析方法upcite{willbold2011tungsten,touboul2012high} 相比,避免了进行沉淀分离的步骤,可以大大提高分析产率和减少干扰。依靠即将到位的Neptune plus 质谱仪,新方法的确立使对来自于下地幔的古老岩石样品中的钨同位素进行精确测量($pm$5ppm) 成为可能,进而可以探究地球早期核幔分异、核幔相互作用和后期增生过程。
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Chemical Separation of Tungsten for Silicate
Abstract:$^{182}Hf-^{182}W$ system is a very useful tool to date core-mantle differentiation, and the Hf-W system can also record partial melting of the mantle, or subsequent crystal-liquid fractionation processes. Limited by the precision of the measurements, tungsten isotope geochemistry is not well developed until recent years. This article includes introduction to the $^{182}Hf-^{182}W$ system, principles of the chemical separation of tungsten from silicate matrix. We come up with a two-step ion-exchange procedure to enlarge the sample size being processed. Using the new Neptune plus mass spectrometer, the new procedure will ensure accurate measurement(within $pm 5ppm$) on the W isotopic composition of samples from different lower mantle reservoirs, which provide clues on processes such as early mantle differentiation, core-mantle interaction, and as well as late accretion.
Keywords: geochemistry, $^{182}Hf-^{182}W$, ion exchange chromatography, early differentiation
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No.4732312119890214****
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