Water solubility in Mg-endmember silicates is suggested to correlate with cation diffusivity. This study proposes a thermodynamic model by introducing the concept of transient Frenkel defect for Mg ions to quantify the relationship between water solubility and Mg diffusivity in mantle silicates. The formation of the Mg transient Frenkel defect is regarded as the escape of Mg from Mg-O polyhedron, and the concentration of Mg transient vacancy is considered as its statistical probability in silicate minerals. The proposed thermodynamic model reveals that the formation energy for Mg transient vacancy (Δ G tr ) is approximately Δ G /6 (Δ G is activation energy for Mg diffusion in silicates) for silicates with Mg-O 6 octahedra, such as enstatite, forsterite, wadsleyite, and ringwoodite, and 5Δ G /12 for bridgmanite and post-perovskite. This observation implies a possible diffusion mode of Mg through transient vacancies. Our model connects water solubility and ion diffusivity in silicates.

中文翻译：

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通过热力学模型桥接地幔硅酸盐中的水溶性和离子扩散率

镁端元硅酸盐中的水溶性被认为与阳离子扩散率相关。本研究通过引入 Mg 离子瞬态 Frenkel 缺陷的概念，提出了一个热力学模型，以量化地幔硅酸盐中水溶性与 Mg 扩散率之间的关系。Mg瞬态Frenkel缺陷的形成被认为是Mg从Mg-O多面体中逸出，而Mg瞬态空位的浓度被认为是其在硅酸盐矿物中的统计概率。提出的热力学模型表明，对于具有 Mg-O 6 八面体的硅酸盐，如顽火石、镁橄榄石，Mg 瞬态空位的形成能 (Δ G tr) 约为 Δ G / 6 (Δ G 是 Mg 在硅酸盐中扩散的活化能) ，wadsleyite和ringwoodite，以及5ΔG / 12的布里奇曼石和后钙钛矿。这一观察结果暗示了镁通过瞬态空位的可能扩散模式。我们的模型将硅酸盐中的水溶性和离子扩散性联系起来。