Abstract Subduction of atmospheric noble gases has been considered to play an important role in altering the primordial isotopes of Earth’s mantle over geological time. Analysis of natural samples and experiments indicate that large quantities of noble gases can be dissolved in volatile-bearing hydrous minerals in the subduction slabs. To quantitatively investigate the recycling efficiency of noble gases and relevant consequences on the mantle noble gas isotopic evolution, the diffusivities of noble gases in these minerals are needed. In this study, diffusion of He, Ne, Ar, Kr and Xe in lizardite, antigorite and tremolite have been calculated by first-principles methods based on density functional theory. Our results disclose that diffusion is slower with increasing radius of the noble gas atom (DHe > DNe > DAr > DKr > DXe) as expected. The common ring-structures in hydrous silicate minerals provide incorporation sites for the noble gas atoms and control their mobility. The diffusion activation energies are 84.9, 157.3, 287.5, 347.4, 414.9 kJ/mol from He to Xe in lizardite, and despite the very similar lattice structure between lizardite and antigorite, the activation energies are found to be significantly higher in antigorite, which are 120.6, 267.3, 449.6, 497.9 and 550.0 kJ/mol, respectively. In tremolite, the energy barriers are 93.6, 158.2, 266.3, 322.2 and 385.0 kJ/mol, which are also found to be in very good agreement with available experimental values and similar to those in lizardite. We also calculated diffusion activation energies at higher pressures (1 GPa for liazardite, 3 GPa for antigorite and tremolite) to better understand how much noble gases can be preserved against diffusive loss during subduction. Our result show that the oceanic crust and the lithospheric mantle of the subduction slab play different roles in delivering noble gases into the mantle. We find that all Ar, Kr, Xe and possibly part of the Ne can be entrained by the serpentine-dominated lithospheric mantle into the deep mantle due to the high diffusive energy barriers in antigorite. In contrast, noble gases in the amphibole-enriched oceanic crust would be characterized by fractionated noble gas signature, with the concentrations of retained noble gases in the crust following their respective ionic radius (Ne

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俯冲带含水矿物中惰性气体的扩散

摘要 大气惰性气体的俯冲被认为在改变地质时期地幔原始同位素方面发挥着重要作用。对天然样品的分析和实验表明，大量稀有气体可以溶解在俯冲板片中含有挥发性的含水矿物中。为了定量研究稀有气体的回收效率以及对地幔稀有气体同位素演化的相关影响，需要了解稀有气体在这些矿物中的扩散率。本研究采用基于密度泛函理论的第一性原理方法计算了He、Ne、Ar、Kr和Xe在蜥蜴岩、叶蛇纹石和透闪石中的扩散。我们的结果表明，正如预期的那样，随着惰性气体原子半径的增加（DHe > DNe > DAr > DKr > DXe），扩散变慢。含水硅酸盐矿物中常见的环结构为惰性气体原子提供了结合位点并控制它们的迁移率。蜥蜴石中从 He 到 Xe 的扩散活化能分别为 84.9、157.3、287.5、347.4、414.9 kJ/mol，尽管蜥蜴石和叶蛇纹石之间的晶格结构非常相似，但发现蛇纹石中的活化能明显更高，即分别为 120.6、267.3、449.6、497.9 和 550.0 kJ/mol。在透闪石中，能垒为 93.6、158.2、266.3、322.2 和 385.0 kJ/mol，这也被发现与可用的实验值非常吻合，并且与蜥蜴中的值相似。我们还计算了更高压力下的扩散活化能（liazardite 为 1 GPa，3 GPa（叶蛇纹石和透闪石）以更好地了解在俯冲过程中可以保留多少稀有气体以防止扩散损失。我们的结果表明，俯冲板片的洋壳和岩石圈地幔在将惰性气体输送到地幔中起着不同的作用。我们发现，由于叶蛇纹石中的高扩散能垒，所有的 Ar、Kr、Xe 和可能的部分 Ne 可以被蛇纹石主导的岩石圈地幔夹带进入深部地幔。相比之下，富含角闪石的海洋地壳中的稀有气体将以分馏的稀有气体特征为特征，地壳中保留的稀有气体浓度遵循其各自的离子半径（Ne 我们的结果表明，俯冲板片的洋壳和岩石圈地幔在将惰性气体输送到地幔中起着不同的作用。我们发现，由于叶蛇纹石中的高扩散能垒，所有的 Ar、Kr、Xe 和可能的部分 Ne 可以被蛇纹石主导的岩石圈地幔夹带进入深部地幔。相比之下，富含角闪石的海洋地壳中的稀有气体将以分馏的稀有气体特征为特征，地壳中保留的稀有气体浓度遵循其各自的离子半径（Ne 我们的结果表明，俯冲板片的洋壳和岩石圈地幔在将惰性气体输送到地幔中起着不同的作用。我们发现，由于叶蛇纹石中的高扩散能垒，所有的 Ar、Kr、Xe 和可能的部分 Ne 可以被蛇纹石主导的岩石圈地幔夹带进入深部地幔。相比之下，富含角闪石的海洋地壳中的稀有气体将以分馏的稀有气体特征为特征，地壳中保留的稀有气体浓度遵循其各自的离子半径（Ne