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本研究基于Urey模型(或称Bigeleisen和Mayer公式),结合量子化学计算的方法,在B3LYP/6-311+G(d,p)理论水平下,计算了Ge在类似石英(包括蛋白石)、钠长石、钾长石、橄榄石结构以及水溶液(包括海水)中Ge(OH)4和GeO(OH)3-之间的Ge同位素平衡分馏系数。其中,溶液效应用“水滴法”处理,矿物结构用簇合物方法模拟。结果显示这些基本分馏参数的精度约±0.3‰;类石英(或蛋白石)结构最可能富集重Ge同位素,在25℃,几个Ge同位素分馏系数分别约为:Δ石英-Ge(OH)4=0.9‰、ΔGe(OH)4-GeO(OH)3-=0.3‰(海水中)、Δ石英-钠长石=0.6‰、Δ石英-钾长石=0.4‰、Δ橄榄石-Ge(OH)4=-1.2‰。类石英与类橄榄石结构之间存在较大的分馏,Δ石英-橄榄石=2.1‰。这些具有重要地质意义的基本分馏参数可以为探索未知的Ge同位素地球化学应用领域打下基础。此外,本文还用所得的分馏参数定量地解释了Siebert等(2006)和Rouxel等(2006)的一些工作,说明了这些参数的可靠性及其在地学中的重要应用意义。
Based on the Urey model (or Bigeleisen and Mayer formula) and the quantum chemical calculation method, we calculated the effect of Ge on quartz (including opal), sodium (including opal) under the B3LYP / 6-311 + Feldspar, potash feldspar, olivine structure, and Ge isotope equilibrium fractionation between Ge (OH) 4 and GeO (OH) 3- in aqueous solutions, including seawater. Among them, the solution effect was treated by “water drop method” and the mineral structure was simulated by cluster method. The results show that the precision of these basic fractionation parameters is about ± 0.3 ‰. The quasi-quartz (or opal) structure is most likely to enrich heavy Ge isotopes. The fractional Ge isotope fractionation coefficients at 25 ℃ are: Δ Quartz-Ge (OH) 4 = 0.9 ‰, ΔGe (OH) 4-GeO (OH) 3- = 0.3 ‰ in seawater, Δ quartz-albite = 0.6 ‰, Δ quartz-potassium feldspar = 0.4 ‰, Δ olivine- OH) 4 = -1.2 ‰. There is a large fractionation between quasi-quartz and olivoid-like structures, Δquartz-olivine = 2.1 ‰. These fundamental fractional parameters of great geological significance lay the foundation for exploration of unknown Ge isotopic geochemistry applications. In addition, some work of Siebert et al. (2006) and Rouxel et al. (2006) are also quantitatively explained by the obtained fractionation parameters. The reliability of these parameters and their important application in geosciences are illustrated.