Fe-Mg Interdiffusion in Olivine and Magnesiowüstite Under Hydrous Conditions: Implications for Mantle Processes

Kohlstedtoung-0106981需要支持以完成我们的实验研究，该研究旨在量化橄榄石和镁橄榄石中Fe-Mg相互扩散动力学对水/羟基浓度的依赖性。 对于许多名义上的无水矿物，少量的“水”显着增强许多，如果不是全部，扩散依赖的属性，包括蠕变速率，位错恢复动力学，电导率和离子扩散。 然而，在大多数情况下，这些意见只是定性的。 水的存在是否增强了扩散率或蠕变率...是还是不是？ 我们最近刚刚确定了橄榄石的扩散率和水/羟基含量（水逸度）之间的定量关系;不存在镁橄榄石。 为了利用实验室观测数据建立地幔地球化学演化和地球动力学行为的模型，必须量化动力学性质对含水量的依赖关系。因此，实验室研究建议扩大我们的调查的铁镁互扩散系数对橄榄石中的水浓度的依赖性，包括镁橄榄石。 在控制水逸度和0.05至15 GPa压力范围内对单晶进行高温高压扩散实验。 卢瑟福背散射光谱（RBS）和电子探针显微分析（EPMA）来测量所得的扩散分布。 使用傅里叶变换红外（FTIR）分析来确定羟基浓度。 此外，透射电子显微镜（TEM）和X-射线衍射分析用于检查类腐殖酸层的存在。 对于橄榄石，需要实验来确定扩散率对温度和压力的依赖性，以及验证我们最初的测量扩散率对水逸度的依赖性。 对于镁橄榄石，所有这些实验都是必要的。我们的实验的一个重要目标是确定阳离子（Fe-Mg）扩散率和水/羟基浓度的两个重要的地幔矿物在定义良好的热化学条件下的定量关系。 拟议的研究旨在使用点缺陷热力学的背景下，这些结果，以获得水影响传输性能，如离子扩散和电导率的机制（S）的基本理解。 由此产生的理论框架是必不可少的可靠外推实验室的结果，地幔环境和利用实验观测，以开发地球内部的动态行为的模型。

KohlstedtEAR-0106981Support is requested to complete our experimental investigation designed to quantify the dependence of the kinetics of Fe-Mg interdiffusion in olivine and magnesiowustite on water/hydroxyl concentration is proposed. For many nominally anhydrous minerals, a small amount of 'water' significantly enhances many, if not all, diffusion-dependent properties including creep rate, dislocation recovery kinetics, electrical conductivity and ionic diffusion. In most cases, however, these observations are only qualitative. Does the presence of water enhance diffusivity or rate of creep ... yes or no? We have just recently determined a quantitative relationship between diffusivity and water/hydroxyl content (water fugacity) for olivine; none exists for magnesiowustite. To utilize observations determined from laboratory experiments to develop models of the geochemical evolution and geodynamical behavior of the mantle, it is critical to quantify the dependence of kinetic properties on water content. Therefore, a laboratory study is proposed to extend our investigation of the dependence of Fe-Mg interdiffusivity on water concentration in olivine and to include magnesiowustite. High-temperature, high-pressure diffusion experiments are being carried out on single crystals at controlled water fugacities at pressures in the range 0.05 to 15 GPa. Rutherford backscattering spectroscopy (RBS) and electron probe microanalysis (EPMA) are employed to measure the resulting diffusion profiles. Fourier transform infrared (FTIR) analyses are used to determine the hydroxyl concentration. In addition, transmission electron microscopy (TEM) and x-ray diffraction analyses are employed to check for the presence of humite-like layers. For olivine, experiments are needed to determine the dependence of diffusivity on temperature and pressure as well as to verify our initial measurement of the dependence of diffusivity on water fugacity. For magnesiowustite, all of these experiments are needed. An important goal of our experiments is to determine quantitative relationships between cation (Fe-Mg) diffusivity and water/hydroxyl concentration for two important mantle minerals under well-defined thermochemical conditions. The proposed research is designed to use these results in the context of point defect thermodynamics to gain a fundamental understanding of the mechanism(s) by which water influences transport properties such as ionic diffusion and electrical conductivity. The resulting theoretical framework is essential for reliably extrapolating laboratory results to mantle environments and for utilizing experimental observations to develop models of the dynamic behavior of the Earth's interior.