High Temperature Deformation of Lower Mantle Minerals Phases in the Diamond Anvil Cell

地震各向异性是在地球深部的许多地区观察到的，据信是由于固态对流造成的地幔岩石的纹理。因此，对地震各向异性的观测可以用来解释发生在地球内部的动态过程。然而，这需要在适当的矿物相中很好地理解变形几何、结构发育和地震各向异性之间的关系。在形变机制已被很好理解的上地幔，用地幔流动来解释地震各向异性已经非常成功。然而，在地球的深处，对主要矿物相（如MgSiO3钙钛矿和后钙钛矿）的变形机制知之甚少。这主要是由于稳定这些阶段所需的压力超出了常规变形装置的范围。金刚石砧细胞结合径向衍射技术可用于研究这些相的变形和织构发展，但直到最近，这些实验只能在室温下进行。由于纹理会受到温度的影响，因此将这些结果外推到温度较高的地球深处是有问题的。最近的发展现在允许在较低的地幔压力和温度下进行金刚石砧细胞变形实验。本项目将利用该新技术研究高压高温下下地幔矿物相的结构发育和变形机制。该项目的意义在于，它将为将地震观测与地球非常深处的变形结构联系起来建立一个实验基础。这将为利用地震数据绘制最下层地幔的流动模式奠定基础。了解地幔底部的动力学将为地幔对流的力学和几何结构提供新的见解。更好地了解地幔对流，反过来又对板块构造、地幔地球化学和地球热历史有影响。此外，该项目产生的新技术发展将在劳伦斯伯克利国家实验室的先进光源向普通用户提供，从而为更广泛的科学界服务。此外，进行高压和高温变形研究的能力已经超出了地球物理领域的应用，也将推进极端条件下材料科学的知识。

Seismic anisotropy is observed in many regions of the deep Earth and is believed to be due to texturing of mantle rock as a result of solid state convection. Thus observations of seismic anisotropy can be used to interpret the dynamic processes occurring in the Earth's interior. However, this requires that the relationship between deformation geometry, texture development and seismic anisotropy are well understood for the appropriate mineral phases. In the upper mantle where deformation mechanisms are well understood, interpretation of seismic anisotropy in terms of mantle flow has been highly successful. However, in deeper parts of the Earth, little is known about the deformation mechanisms of the major mineral phases such as MgSiO3 perovskite and post-perovskite. This is largely due to the fact that pressures needed to stabilize these phases are beyond the range of conventional deformation devices. The diamond anvil cell combined with radial diffraction technique can be used to study deformation and texture development in these phases, but until recently these experiments could only be performed at room temperature. Since textures can be affected by temperature, it is problematic to extrapolate these results to the deep Earth where temperatures are high. Recent developments now allow diamond anvil cell deformation experiments to be performed at lower mantle pressures and temperatures. This project will use this new technique to study texture development and deformation mechanisms in lower mantle mineral phases at high pressure and temperature conditions.The significance of this project is that it will establish an experimental basis for linking seismic observations to deformation structure in the very deep Earth. This will lay the groundwork to allow the use of seismic data to map flow patterns in the lowermost mantle. Understanding the dynamics at the base of the mantle will provide new insight into the mechanics and geometry of mantle convection. A better understanding of mantle convection, in turn, has implications for plate tectonics, mantle geochemistry, and thermal history of the Earth. In addition, new technical developments resulting from this project will be available to general users at the Advanced Light Source at Lawrence Berkeley National Laboratory and thus will serve the broader scientific community. Furthermore, the capability to perform high pressure and high temperature deformation studies has application beyond the field of geophysics and will also advance knowledge of material science at extreme conditions.