矿物中稀土元素扩散作用的理论研究及其扩散参数的预测

矿物中的微量元素在地质环境下能否保持有效封闭,主要取决于其扩散性质,而稀土元素(REE)是探讨地质作用过程及其物理化学条件等重要的示踪剂,查明其在不同矿物中的扩散行为对于地学研究具有重要意义.本文通过分析矿物晶格结构和离子类型对元素扩散行为的制约规律,探讨了REE在不同矿物中的扩散迁移在此基础上,利用多元统计分析方法得出扩散参数与扩散体系不同晶体化学参数之间的关系方程,建立了计算1atm、无水环境下REE在不同矿物中扩散参数的多变量模型,由此模型预测的REE在不同矿物中的扩散参数E和lnD0的值,与实验测定结果在实验误差范围内具有很好的一致性.与以往的预测模型相比,多变量模型能更全面地反映扩散体系晶体化学因素对扩散速率的制约.此外本研究结果显示,REE在矿物晶格中扩散作用的主要影响因素是阳离子,而非当前认为的阴离子.

A theoretical study on REE diffusion in minerals and predication for its diffusion parameters

During geological process, whether the trace elements could be effectively closed in minerals, depends on its diffusion behaviors. Rare earth elements are important geochemical tracers for understanding geological processes and their physical-chemical conditions. Therefore, it is important to investigate the REEs diffusion behaviors in different minerals. In this paper, we conducted a preliminary theoretical study on the REE migration in various minerals based on analyzing the constraint of crystal lattice configuration and ion type on elements diffusion, and a multivariate model was proposed for predicating diffusive parameters of REE in minerals under a dry, 1-atm condition. E and lnD0 data calculated in this paper using the multivariate model are in a good agreement with previous experimental data. Compared with the previous prediction models, the multivariate model proposed in this paper can comprehensively reflect the influences of various crystal chemical factors in diffusive system. In addition, it is revealed that the most important controlling factor of REE diffusion in mineral lattice is those cations rather than the anion as previously considered.