Recent studies present compelling evidence that a free aqueous fluid phase exists within the upper mantle. Fluid may be present at depths as great as the transition zone (410–660 km) and possibly beyond. The chemical reactivity of such deep fluids can be predicted from the Born model of solvation. To use the Born model, we need to know the dielectric constant of water under mantle conditions. We have used molecular dynamics simulations to determine the dielectric constant of water up to a pressure of 30 GPa and a temperature of 3000 K. Increased temperature lowers the dielectric constant and decreases ion solvation, but pressure overcomes this effect. The resulting high dielectric constant suggests that aqueous mantle fluids are highly reactive for ion solvation and mineral dissolution. We tested this by using the Helgeson–Kirkham–Flowers equation of state to estimate free energies of several mineral-solution and ion solvation reactions under mantle conditions. The results support previous estimates of carbonate solubility in the mantle. We also find that mantle fluids may play a key role in transporting ore metals: we evaluated the solubility of chalcopyrite and the complexation of Cu and Fe by Cl under mantle conditions and find that metal complexation is as significant as in ore-forming fluids in the crust. At reasonable conditions of pH and , chalcopyrite is highly soluble. We tentatively hypothesize that exsolved fluids from subducted slabs may extract and mobilize primary sulfides in the mantle, implying potentially deep sources for porphyry copper deposits.

中文翻译：

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地幔中的矿水反应：玻恩理论和从头算分子动力学的预测

最近的研究提供了令人信服的证据，表明上地幔内存在游离的水相。流体可能存在于过渡区（410-660 公里）甚至更远的深度。这种深层流体的化学反应性可以通过溶剂化的玻恩模型来预测。为了使用玻恩模型，我们需要知道地幔条件下水的介电常数。我们使用分子动力学模拟来确定在 30 GPa 压力和 3000 K 温度下水的介电常数。温度升高会降低介电常数并减少离子溶剂化，但压力克服了这种影响。由此产生的高介电常数表明地幔水液对离子溶剂化和矿物溶解具有高度反应性。我们通过使用 Helgeson-Kirkham-Flowers 状态方程来估计地幔条件下几种矿物溶液和离子溶剂化反应的自由能来对此进行测试。这些结果支持了先前对碳酸盐在地幔中溶解度的估计。我们还发现，地幔流体可能在输送矿石金属方面发挥着关键作用：我们评估了黄铜矿的溶解度以及在地幔条件下 Cl 与 Cu 和 Fe 的络合，发现金属络合与在地幔条件下的成矿流体中一样重要。脆皮。在合理的 pH 和 条件下，黄铜矿是高度可溶的。我们初步假设，俯冲板块中的出溶流体可能会提取并动员地幔中的原生硫化物，这意味着斑岩铜矿床可能存在深部来源。