Abstract—

The kinetics of reactions between minerals and water vapor or two water phases simultaneously (liquid + vapor) is still understood inadequately poorly, and the absence of these data disable realistic and comprehensive quantitative description of the evolution of hydrothermal system after its fluid heterogenizes. To bridge this gap, we have conducted quenching experiments with quartz crystals and water at 300°C and P_sat = 86 bar. In addition to usually applied analytical techniques (ICP-AES, SEM, XRD, and optical microscopy), we used 3d scanning of the crystals, measured their surface areas, and plotted the changes in the crystal sizes because of dissolution and deposition reactions. In the experimental runs with the crystal occurring in the vapor phase, the first ever data were acquired on the rate constant of quartz dissolution for saturated water vapor (P_sat = 86 bar) at 300°C (2.7 nmol m^–2 s^–1). The constant turned out to be 630 times lower than that for pure water. Calculations indicate that equilibrium between quartz and water and vapor is established during comparable time spans, but quartz recrystallization in vapor due to the temperature gradient proceeds two orders of magnitude more slowly than in water. In the runs with the crystal occurring in both water and vapor, not only the stable quartz dissolved, but also metastable cristobalite-tridymite opal was formed. The opal was deposited on the autoclave walls and even on the quartz itself above the water surface, and the silica concentration in the water remained remarkably lower that the quartz solubility. The rate of opal formation (10^–7.5 mol m^–2 s^–1) was 3.5 orders of magnitude higher than the quartz recrystallization rate (which is the only process possible in this system according to the traditional geochemical approach). This disagreement is explained within the framework of the distillation hypothesis, which is based on the preferential evaporation of the thin (<100 nm) solution layer at the meniscus edge. The system is found out to be able to evolve according to two scenarios, which result in the scattered and compact opal deposition because of the different ratios of the ascent velocity of the solution film and the evaporation rate. This phenomenon may explain the asymmetry of naturally occurring crystallization cavities, whose lower parts dissolved, and minerals were deposited in the upper parts.

中文翻译：

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石英在水蒸气界面转变为蛋白石

摘要-

对矿物与水蒸气或同时存在两个水相（液体+蒸气）之间的反应动力学的理解仍然不充分，并且缺乏这些数据使水热系统在流体异质化后的演化无法进行现实而全面的定量描述。为了弥合这一差距，我们在300°C和P_饱和条件下用石英晶体和水进行了淬火实验。= 86巴。除了通常应用的分析技术（ICP-AES，SEM，XRD和光学显微镜）之外，我们还使用了3d扫描晶体，测量了晶体的表面积，并绘制了因溶解和沉积反应而引起的晶体尺寸变化。在晶体处于气相状态的实验运行中，获得了有关饱和水蒸气（P _sat = 86 bar）在300°C（2.7 nmol m ^–2 s ^–1）的石英溶解速率常数的第一个数据。）。该常数比纯水的常数低630倍。计算表明，石英与水和蒸气之间的平衡是在可比较的时间跨度内建立的，但是由于温度梯度，蒸气中的石英重结晶的过程比在水中的慢两个数量级。在水和蒸气中都存在晶体的运行中，不仅形成了稳定的石英溶解，而且还形成了亚稳的方石英-绿闪石蛋白石。蛋白石沉积在高压釜壁上，甚至沉积在水面上方的石英本身上，水中的二氧化硅浓度仍然明显低于石英的溶解度。蛋白石的形成速率（10 ^–7.5 mol m ^–2 s ^–1）比石英的再结晶速率高3.5个数量级（根据传统的地球化学方法，这是该系统中唯一可能的过程）。在蒸馏假说的框架内解释了这种分歧，该假说是基于弯月面边缘的薄（<100 nm）溶液层的优先蒸发而产生的。发现该系统能够根据两种情况发展，由于溶液膜的上升速度和蒸发速率的比率不同，导致分散的和致密的蛋白石沉积。这种现象可以解释天然结晶腔的不对称性，其下部溶解，矿物沉积在上部。