Al,Si-interdiffusion in bridgmanite and the viscosity of the lower mantle

桥锰矿中Al、Si相互扩散与下地幔粘度

• 批准号: 404345772
• 负责人: Dr. Nobuyoshi Miyajima, Ph.D.
• 金额: --
• 依托单位: Bayerisches Forschungsinstitut für Experimentelle Geochemie und Geophysik (BGI)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/404345772?language=en
• 关键词: Al; Si; interdiffusion; bridgmanite; viscosity

The viscosity of the Earth’s mantle is a key parameter in all model calculations on mantle convection and on the thermal state of the Earth. Yet, the viscosity of the lower mantle, which is the largest reservoir of our planet, is only poorly constrained. The viscosity of solids is related to the deformation creep rate. Creep deformation at high temperature is due to transport of matter by the motion of lattice defects. Therefore, viscosities can be estimated from diffusion data using the Nabarro-Herring and Weertman models. In this proposal, I show some preliminary data, which suggest that silicon diffusivities in majorite and silicate perovskite (bridgmanite) are different and that the diffusivity of silicon in perovskite is strongly dependent on the Al content in the system. In the proposed project, Si diffusivity in silicate perovskite, the dominant phase of Earth´s lower mantle, shall be further investigated: (i) Al,Si-interdiffusion in magnesium silicate perovskite shall be systematically studied using multi-anvil press. (ii) The dependence of Si diffusivity on chemical composition and Al substitution mechanism shall be studied using different diffusion couples (e.g., with vacancies). (iii) From the experimental results, the viscosity in the lower mantle shall be estimated, assuming that plastic deformation rate is controlled by the slowest diffusing species in the constituent minerals. The results of this study will provide important constraints on the mode of convection and chemical mixing in Earth´s mantle. The relative importance of layered versus whole-mantle convection and the likelihood of the survival of primordial, undepleted reservoirs in the deep mantle can only be quantitatively addressed with the viscosity data that are expected to result from this study.

地幔的粘性是所有关于地幔对流和地球热状态的模型计算中的一个关键参数。然而，下地幔的粘度，这是我们这个星球上最大的水库，只是很少受到限制。固体的粘度与变形蠕变速率有关。高温蠕变变形是由于晶格缺陷运动引起的物质输运。因此，粘度可以使用Nabarro-Herring和Weertman模型从扩散数据估计。在这个建议中，我显示了一些初步的数据，这表明硅的扩散系数在majorite和硅酸盐钙钛矿（bridgmanite）是不同的，钙钛矿中的硅的扩散系数是强烈依赖于系统中的Al含量。在拟议的项目中，将进一步研究硅酸盐钙钛矿（地球下地幔的主要相）中的Si扩散率：（i）将使用多砧压机系统地研究硅酸镁钙钛矿中的Al，Si相互扩散。(ii)应使用不同的扩散偶（例如，空缺）。(iii)根据实验结果，假定塑性变形速率受组成矿物中扩散最慢的组分控制，可以估算下地幔的粘度。这项研究的结果将为地幔中的对流和化学混合模式提供重要的约束。分层与全地幔对流的相对重要性和原始的，未耗尽的水库在深地幔的生存的可能性只能定量处理的粘度数据，预计将导致从这项研究。