Noble gases record in their radiogenic/non-radiogenic isotope ratios the traces of accretion history and degassing events from the early Earth, including giant impacts and the magma ocean stage, to large-scale recent volcanism. The diffusional behavior of noble gases in silicate magmas is one of the essential parameters needed to correctly model devolatilization from the magma ocean and subsequent volcanic eruptions. Here, we study the diffusivity of He, Ne, Ar, Kr, and Xe in molten pyrolite using ab initio molecular dynamics. We find that the diffusivity of the noble gases decreases with increasing atomic size. The diffusion of Ar is comparable to that of Mg. We compute the partial molar volumes and find that at high pressure, He is almost one order of magnitude more compressible than the heavier noble gases. The analysis of the speciation of the noble gases in the melt indicates that the lifetime of the coordination polyhedra formed with O is not sensitive to the mass of the noble gases. Finally, we compute the electron localization function along the Xe–O interatomic vectors and show that there is no chemical bonding between the Xe and surrounding O atoms from the hosting silicate melt.

中文翻译：

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原始岩浆海洋中稀有气体的扩散、化学键合和动力学分馏


稀有气体在其放射性/非放射性同位素比率中记录了从早期地球（包括巨大的撞击和岩浆海洋阶段）到近期大规模火山活动的吸积历史和脱气事件的痕迹。硅酸盐岩浆中稀有气体的扩散行为是正确模拟岩浆海洋的挥发分和随后的火山喷发所需的基本参数之一。在这里，我们利用从头算分子动力学研究了 He、Ne、Ar、Kr 和 Xe 在熔融火山岩中的扩散率。我们发现惰性气体的扩散率随着原子尺寸的增加而降低。 Ar 的扩散与 Mg 的扩散相当。我们计算了偏摩尔体积，发现在高压下，He 的可压缩性几乎比较重的稀有气体高一个数量级。对熔体中稀有气体形态的分析表明，与O形成的配位多面体的寿命对稀有气体的质量不敏感。最后，我们计算了沿 Xe-O 原子间矢量的电子定位函数，结果表明 Xe 与周围来自硅酸盐熔体的 O 原子之间没有化学键合。