Simulations and Experiments Reveal Effect of Nanopores on Helium Diffusion in Quartz,ACS Earth and Space Chemistry

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Simulations and Experiments Reveal Effect of Nanopores on Helium Diffusion in Quartz
ACS Earth and Space Chemistry ( IF 2.9 ) Pub Date : 2020-11-10 , DOI: 10.1021/acsearthspacechem.0c00187
Rustin Domingos ₁ , Marissa M. Tremblay ₂ , David L. Shuster _{1,

3} , Burkhard Militzer _{1,

4}

Affiliation

The diffusion properties of noble gases in minerals are widely used to reconstruct the thermal histories of rocks. Here, we combine density functional theory (DFT) calculations with laboratory experiments to investigate controls on helium diffusion in quartz. DFT calculations for perfect α-quartz predict substantially lower activation energies and frequency factors for helium diffusion than observed in laboratory experiments, especially in the [001] direction. These results imply that no helium could be retained in quartz at Earth surface temperatures, which conflicts with observations of partial cosmogenic ³He retention over geologic time scales. Here, we implement a model of helium diffusion in α-quartz modulated by nanopore defects that disrupt energetically favorable diffusion pathways. In this model, we find that laboratory-determined diffusivities can be most closely reproduced when a helium atom encounters ∼70 nanopore sites per million interstitial sites. The results of our model indicate that diffusion of helium in natural quartz, like other noble gases in other minerals, can be significantly modulated by extended defects.

中文翻译：

模拟和实验揭示纳米孔对石英中氦扩散的影响

稀有气体在矿物中的扩散特性被广泛用于重建岩石的热历史。在这里，我们将密度泛函理论（DFT）计算与实验室实验相结合，以研究对氦气在石英中扩散的控制。相对于实验室实验，尤其是在[001]方向观察到的，用于完美α石英的DFT计算可预测氦扩散的活化能和频率因子要低得多。这些结果表明，在地球表面温度下，石英中不会残留氦，这与部分宇宙成因^3的观测结果相矛盾。他保留了地质时间尺度。在这里，我们实现了由纳米孔缺陷调制的α-石英中氦扩散的模型，该缺陷破坏了能量上有利的扩散途径。在该模型中，我们发现，当氦原子遇到每百万个间隙位置约70个纳米孔位置时，可以最接近地再现实验室确定的扩散率。我们模型的结果表明，氦气在天然石英中的扩散，就像其他稀有气体在其他矿物中的扩散一样，可以被扩展的缺陷明显地调节。

更新日期：2020-11-19

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