Equilibrium lithium isotope fractionation in Li-bearing minerals
Equilibrium lithium isotope fractionation in Li-bearing minerals
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含锂矿物中的平衡锂同位素分馏
DOI：
10.1016/j.gca.2018.05.029
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发表时间：
2018-08-15
影响因子：
5
通讯作者：
Shi, Yaolin
中科院分区：
文献类型：
--
作者：
Liu, Shanqi;Li, Yongbing;Shi, Yaolin
锂同位素是许多地质作用的重要地球化学示踪剂。了解Li同位素分馏因素对于了解Li同位素的行为至关重要。基于密度泛函微扰理论（DFPT），计算了α-锂霞石（LiAlSiO 4）、β-锂霞石（LiAlSiO 4）、锂锰磷石（LiMnPO 4）、钙磷钙钛矿（LiAlPO 4 OH）、透锂长石（LiAlSi 4 O 10）、锂钛石[Li-2（Al 2Si 4 O 12）中心点2 H（2）O]、锂辉石（LiAlSi 2 O 6）、锂磷酸盐（Li 3 PO 4）和磷铝石（LiAlPO 4F）的Li同位素分馏参数。这些矿物的Li-7/Li-6（10（3）ln β（6-）（7））的约化分配函数比按透锂长石>锂磷酸盐> bikitaite > α-锂霞石> β-锂霞石>钙磷铝石> Amblugonite>锂霞石>锂辉石的顺序减小，与花岗伟晶岩的观察结果一致。这些富锂矿物的锂同位素分馏与平均Li-O键长有显著的线性相关性，并受锂配位数的显著影响。计算了含锂镁橄榄石（Mg_2SiO_4）和透辉石（CaMgSi_2O_6）的Li同位素分馏因子。结果表明，镁橄榄石相对透辉石富集重Li，两种矿物的10（3）ln β（6-）（7）值均取决于Li含量。这些结果可以更好地理解锂同位素分馏在自然系统中，并提供了理论基础，锂同位素应用于了解地质过程。(C)2018爱思唯尔有限公司版权所有
Lithium isotopes are important geochemical tracers for many geological processes. Knowledge of Li isotope fractionation factors is essential for understanding the behavior of Li isotopes. On the basis of density functional perturbation theory (DFPT), we calculate Li isotope fractionation parameters of alpha-eucryptite (LiAlSiO4), beta-eucryptite (LiAlSiO4), lithiophilite (LiMnPO4), montebrasite (LiAlPO4OH), petalite (LiAlSi4O10), bikitaite [Li-2(Al2Si4O12)center dot 2H(2)O], spodumene (LiAlSi2O6), lithiophosphate (Li3PO4) and amblygonite (LiAlPO4 F). The reduced partition function ratios of Li-7/Li-6 (10(3) ln beta(6-)(7)) for these minerals decrease in the order petalite > lithiophosphate > bikitaite > alpha-eucryptite > beta-eucryptite > montebrasite > amblygonite > lithiophilite > spodumene, agreeing with the observations on granitic pegmatites. Li isotope fractionations in these Li-rich minerals have a notable linear correlation with the average Li-O bond lengths, and are significantly influenced by Li coordination number. Furthermore, we calculate Li isotope fractionation factors of Li-bearing forsterite (Mg2SiO4) and diopside (CaMgSi2O6). It is found that forsterite is enriched in heavy Li relative to diopside, and both minerals' 10(3) ln beta(6-)(7) values depend on Li contents. These results allow for better understanding Li isotope fractionations in natural systems and provide a theoretical basis for Li isotope applications to understand geological processes. (C) 2018 Elsevier Ltd. All rights reserved.