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

这个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较大的力（应力）时，它们会因脆性断裂而变形。在地球的深处，温度更高，然后塑性变形成为可能。这种塑性变形通过对流帮助物质循环，使地球冷却，并导致大多数地质活动，包括造山和水和其他物质的深层循环。然而，迄今为止，由于技术上的困难，对材料在深地球条件下的塑性流动特性知之甚少。例如，在地球的深处，不仅温度高，而且压力也很高。通常压力抑制原子运动，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，因此材料的粘度是否随深度增加而增加？大多数矿物也经历一系列的相变。这些相变如何影响塑性性能？这些问题对我们理解地球和其他类地行星的动力学和进化至关重要。尽管它很重要，但就在大约十年前，人们对这些深层地球变形几乎一无所知。认识到这一需求后，研究人员于2002年开始了一个小组的努力，开发在地球深部条件下塑性变形的新技术。在之前资助期的研究基础上，他们取得了重大进展，包括开发新型变形装置和改进使用同步加速器x射线源的应力（和应变）测量。因此，我们现在可以进行~ 20gpa和~ 2000k的定量变形实验。然而，这些条件只适用于~500公里的深度。地球的地幔延伸到~2900公里。此外，以前研究的材料对含水量的控制非常差。在这个技术发展的新阶段，研究团队将重点关注(1)将最大压力扩展到~ 30gpa或更高（~1000 km深度），(2)改善高压条件下化学环境（如水逸度）的控制，以及(3)通过使用新的硬件和理论改进应力测量。这些进展将使研究地球材料的塑性特性成为可能，其条件相当于下地幔浅层部分在良好控制的化学环境下。这些技术的应用将为我们对整个地球动力学的理解带来重要的新曙光。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，包括国家同步加速器光束线的新设施，这些设施将供更广泛的社区使用。这些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.