An Experimental Study of the Breakdown of Dolomite in Mixed-Volatile Metamorphic Environments

变质石灰岩和白云岩中矿物的组成和丰度通常用来确定变质流体的性质。重要的性质是流体的组成、流体通量和流体流动的地形尺度模式。在变质体系中，矿物组合的发育取决于几个速率常数的相对值，如水力导率、导热系数、扩散和分散性以及反应过程。在这项研究中，我们计划确定在混合挥发环境中影响白云石稳定性的反应动力学。富水条件下白云岩变质反应的常见顺序是白云岩=方解石+方解石+ CO2，其次是方解石+ H2O =水镁石。超铁质岩石在混合挥发流体中的变质作用也发生了类似的反应。白云岩体系是研究反应动力学的理想体系，因为其组合发生在接触和区域变质地形中的各种贫硅岩石中。我们计划的一套实验包括三个部分。首先，我们将在热液容器中对粉末状起始物料进行时间序列实验，以提供矿物和同位素反应速率的上限。其次，我们将利用激光拉曼光谱在热液金刚石-砧细胞中原位观察快速不灭反应。在实验研究的第三部分，我们计划使用白云岩圆柱体作为起始材料，以更接近地模拟自然反应。在所有实验中，我们计划使用同位素标记流体来确定矿物学反应的速率，并在同一实验中确定同位素交换反应的速率。我们将实验研究的结果，特别是岩心实验的结果，与来自德克萨斯州大理石峡谷的接触变质白云岩的观察结果进行比较，该白云岩经历了方长石形成反应和水镁石形成逆行反应。

LabotkaEAR-0087553The compositions and abundances of minerals in metamorphosed limestone and dolomite rock are commonly used to determine properties of the metamorphic fluid. The important properties are the composition of the fluid, the fluid flux, and terrain-scale patterns of fluid flow. In metamorphic systems, the development of mineral assemblages depends on the relative values of several rate constants, such as hydraulic conductivity, thermal conductivity, diffusion and dispersivity, and reaction progress. In this study, we plan to determine the kinetics of reactions that affect the stability of dolomite in mixed-volatile environments. A common sequence of reactions in dolomitic rocks metamorphosed under H2O-rich conditions is dolomite = calcite + periclase + CO2, followed by periclase + H2O = brucite. Similar reactions occur during metamorphism of ultramafic rocks in mixed-volatile fluids. The dolomite system is ideal for the study of reaction kinetics because the assemblages occur in a variety of silica-poor rocks in contact and regional metamorphic terrains. Our planned set of experiments consists of three parts. First, we will conduct time-series experiments on powdered starting materials in hydrothermal vessels to provide upper limits on mineral and isotope reaction rates. Second, we will observe fast and unquenchable reactions in situ in the hydrothermal diamond-anvil cell with the aid of laser Raman spectroscopy. In the third part of experimental investigation we plan to use cylinders of dolomite rock as starting material to mimic more closely the natural reactions. In all experiments, we plan to use isotopically labeled fluid to determine the rates of not only the mineralogic reactions, but also the isotope-exchange reactions in the same experiments. We will compare the results of the experimental study, particularly of the rock core experiments, with observations of the contact-metamorphosed dolomite from Marble Canyon, Texas, which experienced both the periclase-forming reaction and the brucite-forming retrograde reaction.