Diffusion in Lower Mantle Minerals

Van Orman0337125扩散作用在许多重要的地幔过程中起着关键作用，包括化学交换、固态蠕变、地震衰减和导电。这项研究将提供两种最丰富的下地幔矿物--钙钛矿(MgSiO_3)和方镁石(MgO)--中阳离子和氧扩散速率的实验数据。对这两种矿物的高压、高温实验将在明确的热化学条件下进行，点缺陷浓度由添加的异价阳离子控制。在方镁石中，氧和广泛的一价、二价和三价阳离子的扩散系数将在1atm到25 Gpa的压力和1200-2300K的温度下被测定。这些实验的重要目的是确定扩散系数与离子参数如半径、电荷和极化率之间的定量关系。钙钛矿的实验将集中在25 Gpa和1700-2300K下的镁和氧的自扩散。这项研究旨在从根本上了解钙钛矿和方镁石中离子传输的机制，以及温度、压力和组成对扩散系数的影响。拟议的工作将提供跨越地球化学和地球物理学之间的学科界限的数据。该项目还将帮助支持凯斯西储大学的研究基础设施，并使该机构的研究生和本科生的研究和教育相结合。

Van Orman0337125 Diffusion plays a critical role in many important mantle processes, including chemical exchange, solid-state creep, seismic attenuation and electrical conduction. This study will provide experimental data on cation and oxygen diffusion rates in the two most abundant lower mantle minerals, perovskite (MgSiO3) and periclase (MgO). High-pressure, high-temperature experiments on both minerals will be performed under well-defined thermochemical conditions, with point defect concentrations controlled by the addition of aliovalent cations. In periclase, diffusion coefficients for oxygen and a broad range of monovalent, divalent and trivalent cations will be determined at pressures between 1 atm and 25 GPa and temperatures of 1200-2300 K. An important goal of these experiments is to determine quantitative relationships between diffusivity and ionic parameters such as radius, charge and polarizability. Experiments on perovskite will focus on Mg and O self-diffusion at 25 GPa and 1700-2300 K. The study is designed to gain a fundamental understanding of the mechanisms for ionic transport in perovskite and periclase, and the influence of temperature, pressure and composition on diffusivity. The work proposed will provide data that crosses disciplinary boundaries between geochemistry and geophysics. The project will also help support the research infrastructure at Case Western Reserve University and allow the integration of research and education of graduate and undergraduate students in this institution.