| Li同位素在斜顽辉石、镁铝榴石及镁铝尖晶石晶格内扩散与分馏的理论计算研究 |
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| 引用本文： | 蒋佳俊,梁光明,靳佳冀,张飞武.Li同位素在斜顽辉石、镁铝榴石及镁铝尖晶石晶格内扩散与分馏的理论计算研究[J].岩石学报,2018,34(9):2811-2818. |
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| 作者姓名： | 蒋佳俊 梁光明 靳佳冀 张飞武 |
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| 作者单位： | 中国科学院地球化学研究所矿床地球化学国家重点实验室;中国科学院大学;苏州科技大学数理学院;中国科学院地质与地球物理研究所地球与行星物理重点实验室 |
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| 基金项目： | 本文受中组部"千人计划"青年项目、中国科学院"百人计划"项目、国家自然科学基金项目（41773057）和中国科学院地质与地球物理研究所地球与行星物理重点实验室开放课题项目（DQXX201702）联合资助. |
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| 摘 要： | 斜顽辉石、镁铝榴石和镁铝尖晶石作为辉石族、石榴石族以及尖晶石族中的重要端元,是地球上地幔主要组成矿物。Li同位素是重要的地幔地球化学示踪剂,其在橄榄石、辉石和石榴石等地幔矿物中的扩散分馏的性质对理解Li同位素作为地幔地球化学示踪剂非常重要。我们通过经典力场经验势方法,从原子尺度上计算研究了不同温压条件下Li同位素在斜顽辉石、镁铝榴石和镁铝尖晶石晶格中分别通过不同的填隙机制和取代空位机制迁移的活化能和其在不同晶格位上的分馏效应。我们发现Li同位素是通过取代空位机制在斜顽辉石、镁铝榴石和镁铝尖晶石中进行迁移扩散。Li同位素在不同晶格位上的分馏作用计算表明,在三种矿物中重同位素7Li会更多地进入晶格填隙位中,而6Li则相对更多进入Mg位。温度是影响这种分馏作用的一个关键因素,相应的结果可用来解释地幔Li同位素组成特征及冷却条件下的同位素分馏等科学问题。
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| 关 键 词： | 斜顽辉石 镁铝榴石 镁铝尖晶石 锂同位素 扩散分馏 计算模拟 |
| 收稿时间： | 2017/11/21 0:00:00 |
| 修稿时间： | 2018/5/7 0:00:00 |
Theoretical study of lithium diffusion and fractionation in the lattice of clinoenstatite, pyrope and spinel |
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| JIANG JiaJun,LIANG GuangMing,JIN JiaJi and ZHANG FeiWu.Theoretical study of lithium diffusion and fractionation in the lattice of clinoenstatite, pyrope and spinel[J].Acta Petrologica Sinica,2018,34(9):2811-2818. |
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| Authors: | JIANG JiaJun LIANG GuangMing JIN JiaJi and ZHANG FeiWu |
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| Institution: | State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002;University of Chinese Academy of Sciences, Beijing 100049, China,State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002,State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002 and State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002;School of Mathematics and Physics, Suzhou University of Science and Technology, Suzhou 215009, China;Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China |
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| Abstract: | Clinoenstatite, pyrope and spinel, the important end members of pyroxene, garnet and spinel groups, are major mineral compositions in the upper mantle. Li isotopes are important tracer element in the mantle geochemistry, and its properties of diffusion and fractionation in the major mantle minerals are important for understanding Li isotopes as a tracer element of the mantle geochemistry. By performing the classical force field calculations at the atomic scale, we calculated the activation energies of the Li diffusion in the clinoenstatite, pyrope and spinel lattice via both interstitial and substitution mechanisms under the different pressures and temperatures; meanwhile, we have also calculated the effect of Li isotopes fractionations on various mineral lattice sites. The results suggest that the Li isotopes are migrating through the substitution mechanism in the clinoenstatite, pyrope and spinel lattice. The fractionation calculation of Li isotopes on the different lattice sites indicate that 7Li is more likely incorporate on the interstitial sites while 6Li prefers to move into Mg vacancies. The temperature is one of the key factors affecting the fractionation, and the corresponding results can be used to explain scientific issues such as Li isotopic composition in the mantle and the isotopic fractionation under the cooling conditions. |
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| Keywords: | Clinoenstatite Pyrope Spinel Li isotopes Diffusion fractionation Simulations |
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