固体中同位素扩散效应的理论建设和应用研究

The two main atomic diffusion mechanisms in solid (i.e., interstitial mechanism and vacancy mechanism) correspond to two different isotopic diffusion effects. The theoretical treatment of isotope effect of interstitial diffusion has been established, but we find that there are nontrivial factors neglected in the previous studies and those factors should be included in the theoretical treatment to guarantee a precise result. Meanwhile, the theory of isotope effect by vacancy diffusion has not yet been established. The unsound theoretical framework of diffusional isotope effects in solid has greatly hindered the development of related research directions. The proposal will setup this important theoretical framework. By using re-built theory, we will calculate diffusional isotope effects of systems at lower mantle conditions, which are lacking diffusion parameters desperately right now. With the popularization of high spatial resolution mass spectrometer, more and more isotopic distribution data in mineral particle size are accumulating rapidly. The theory of solid diffusion isotope effect in this proposal is the key to analyze these data and extract the detailed heating history, and therefore is the cornerstone to let the related researches in isotope geochemistry, thermochronology, high temperature petrology and astrochemistry fields to the next-level.

固体中原子扩散的两种主要机制（间隙扩散和空位扩散）对应于两种不同的同位素扩散效应。前人已建立间隙扩散的同位素效应理论公式，但申请人发现还有一些重要的影响因素被忽略，它们应该被加入到理论公式之中；对于空位扩散的同位素理论目前尚未建立；目前不健全的理论极大地阻碍了这一研究方向的发展，本申请拟建立这一重要理论，以及由此计算获得一些极其稀缺的、下地幔体系的同位素扩散系数，这些参数涉及到很多下地幔重大科学问题。随着高空间分辨率质谱仪的逐渐普及，越来越多矿物颗粒尺度的同位素分布资料在快速积累之中，而本申请建立的固体扩散同位素效应理论是解析这些数据、提取精细受热历史信息的关键，是将同位素地球化学、热年代学、高温岩石学、天体化学等与之相关方向推进到下一个层次的基础性工作。

本项目建立了固体中两种最主要的原子扩散机制，间隙和空位扩散机制的同位素效应理论模型，推导出此类过程同位素效应的定量计算公式。并将建立间隙扩散新理论模型应用到He在上地幔主要矿物橄榄石中扩散中，为地幔样品中3He/4He比的异常提供限制性信息。本项目建立的理论可以应用到任何涉及同位素扩散的领域。不仅可以解析现有数据、提取精细受热历史信息，而且据此可以提供大量的同位素扩散数据，意义重大。