Collaborative Research: CSEDI--Grand Challenge for Experimental Study of Plastic Deformation Under Deep Earth Conditions

该联合项目的主要目标是进一步发展研究地球深部条件下塑性变形的实验技术。当在浅层地球条件下对矿物或岩石施加很大的力(应力)时，它们会因脆性断裂而变形。在地球深处，温度较高，因此有可能发生塑性变形。这种塑性变形通过对流帮助物质循环，使地球降温，并导致大多数地质活动，包括造山和水及其他物质的深层循环。然而，由于技术上的困难，到目前为止，人们对地球深部条件下材料的塑性流动特性知之甚少。例如，在地球深处，不仅温度高，而且压力高。通常情况下，压力会抑制原子的运动，因此在高压条件下塑性变形变得困难。压力的作用是否变得比温度更重要，因此材料的粘度随着深度的增加而增加？此外，大多数矿物都经历了一系列的相变。这些相变是如何影响塑料性能的？这些问题对于我们理解地球和其他类地行星的动力学和演化至关重要。尽管它很重要，但直到十年前，人们对这些地球深部变形几乎一无所知。认识到这一需要，研究人员于2002年开始了一项小组工作，以开发在地球深处条件下的塑性变形的新技术。根据前几个供资期间的研究，它们取得了重大进展，包括开发了新型形变仪器，改进了使用同步加速器X射线源进行的应力(和应变)测量。因此，我们现在可以进行~20 Gpa和~2000K的定量形变实验，但这些条件只对应于~500公里的深度。地球的地幔绵延2900公里。此外，在以前研究的材料中，水分含量的控制也非常差。在这一新的技术发展阶段，研究团队将专注于(I)将最大压力扩大到~30 Gpa和更高(~1000公里深度)，(Ii)改善高压条件下化学环境(如水逸度)的控制，以及(Iii)通过使用新的硬件和理论来改进应力测量。这些进展将使我们能够在化学环境控制良好的情况下，在相当于下地幔浅层的条件下，研究地球材料的塑性特性。这些技术的应用将为我们理解整个地球的动力学提供重要的新线索。该项目是四个机构的团队之间的合作，将为实验地球物理界提供增强的基础设施，包括将向更广泛的社区提供的国家同步加速器光束线上的新设施。发展将包括对研究生和博士后学者的培训和指导。

The main goal of this joint project is to further develop the experimental techniques of studying plastic deformation under deep Earth conditions. When a large force (stress) is applied to minerals or rocks under shallow Earth conditions, they will be deformed by brittle fracture. In the deep interior of Earth, temperature is higher and then plastic deformation becomes possible. This plastic deformation helps material circulation by convection that cools Earth and causes most of geological activities including mountain building and deep circulation of water and other materials. However, to date very little is known on the plastic flow properties of materials under deep Earth conditions due mainly to the technical difficulties. For example, in the deep interior of Earth, not only is temperature high, but also pressure is high. Usually pressure suppresses atomic motion and hence plastic deformation becomes difficult under high-pressure conditions. Does the role of pressure become more important than temperature and hence the viscosity of materials increases with depth? Also most of minerals undergo a series of phase transformations. How do these phase transformations affect the plastic properties? These issues are critical to our understanding of the dynamics and evolution of Earth and other terrestrial planets. Despite its importance, almost nothing was known about these deep earth deformation as recently as ~ten years ago. Recognizing this need, the investigators started a group effort to develop new techniques of plastic deformation under deep Earth conditions in 2002. Based on the studies during the previous funding periods, they have made major progress including the development of new types of deformation apparatus and the improvements to the stress (and strain) measurements using synchrotron x-ray sources. As a result, we can now conduct quantitative deformation experiments to ~20 GPa and ~2000 K. However, these conditions correspond only to the depth of ~500 km. Earth's mantle extends to ~2900 km. Also, there has been very poor control of water content in materials previously studied. In this new phase of technical development, the team of investigators will focus on (i) extending the maximum pressure to ~30 GPa and higher (~1000 km depth), (ii) improving the control of chemical environment (such as water fugacity) under high-pressure conditions, and (iii) improving the stress measurements through the use of new hardware and theory. These developments will allow investigation of the plastic properties of Earth materials to the conditions equivalent to the shallow part of the lower mantle under well-controlled chemical environment. Applications of these techniques will shed important new light into our understanding of dynamics of whole Earth. The project is a collaboration among teams at four institutions, and will provide enhanced infrastructure to the experimental geophysics community, including new facilities at national synchrotron beamlines that will be available to the broader community. The developments will include training and mentoring of graduate students and post doctoral scholars.