CAREER: Deformation and Anisotropy Development in the Lower-most Mantle

地幔对流是驱动地震和火山等动力过程的内部引擎。由于没有直接成像地幔流动的方法，我们对这一过程的了解有限。这个项目将提高我们将地震观测与地球深处的变形结构和流动几何联系起来的能力。特别是，它将提供关于地幔底部岩石和矿物强度的实验数据，并将确定导致地球深处矿物流动排列的微观机制。了解地幔底部的动力学过程将对地幔对流的力学和几何学有新的认识。在本项目期间进行的高压和高温变形实验也将促进我们对复合材料在极端压力和温度条件下的力学行为的理解。除了基础科学方面的进展外，该项目的外展部分还将通过在中学的早期接触来促进本科生进入地球科学专业的招聘。它将通过犹他州大学的中学教师理科硕士计划(MSSST)为中学教师提供指导和真实的研究经验，从而直接受益于犹他州的中学教育质量。此外，通过与MSSST教师的合作，PI将开发地球物理教学模块，将其纳入中学地球科学、物理和化学课程。该项目还将为一名研究生和一名博士后研究员提供支持和培训。D“区位于地幔核心边界上方(约2700-2900公里)，对地幔对流起着至关重要的作用，了解D”区发生的动力学过程将有助于我们对地幔对流的认识。地震各向异性在D“的大部分地区被观察到，并被广泛归因于地幔对流过程中韧性变形产生的矿物的晶体择优取向(结构)。如果了解了变形、结构和各向异性之间的关系，各向异性就可以用来绘制地幔流动图。大多数关于D”各向异性的解释是基于只与变形有关的结构研究，并在单相实验的背景下进行。然而，对下地幔相进行的高压金刚石砧座实验证明，由于相变而形成的一系列结构。此外，对多相下地幔组合(岩石)变形的少数结构测量表明，各相之间存在复杂的相互作用。本项目将利用金刚石顶顶盒和同步辐射衍射仪来研究布里奇曼石和后钙钛矿相变过程中的取向关系和织构遗传，并将研究多相变形对下地幔矿物相中织构发展的影响。通过了解这些过程，这一建议将增强我们从相变和地幔流动角度解释地震各向异性的能力。

Mantle convection is the internal engine which drives dynamic processes such as earthquakes and volcanism. Since there is no direct way to image mantle flow, our knowledge about this process is limited. This project will improve our ability to link seismic observations to deformation structure and flow geometry in the deep Earth. In particular it will provide experimental data on the strength on rocks and minerals at the base of the mantle and will determine the microscopic mechanisms that lead to flow alignment of minerals in the deep earth. Understanding the dynamic processes at the base of the mantle will provide new insight into the mechanics and geometry of mantle convection. High pressure and temperature deformation experiments performed during this project will also advance our understanding of the mechanical behavior of composite materials subjected to extreme pressure and temperature conditions. In addition to basic science advances the outreach component of this project will improve undergraduate recruitment into geosciences through early exposure in secondary schools. It will directly benefit the quality of secondary school education in Utah by providing mentoring and authentic research experience to secondary school teachers through the Masters of Science for Secondary School Teachers (MSSST) Program at the University of Utah. In addition, through collaboration with MSSST teachers, the PI will develop geophysics teaching modules to be incorporated into secondary school earth science, physics, and chemistry courses. This project will also provide support and training for a graduate student and a postdoctoral researcher. The D" region, which lies just above the core mantle boundary (~2700-2900 km), plays a critical role in mantle convection. Understanding the dynamic processes occurring in the D" will advance our understanding of mantle convection. Seismic anisotropy is observed in much of the D" and is widely attributed to crystal preferred orientation (texture) of minerals that results from ductile deformation during mantle convection. If the relationship between deformation, texture, and anisotropy are understood, anisotropy can be used to map mantle flow. Most interpretations of D" anisotropy in terms of mantle flow are based on texture studies related only to deformation and in the context of single phase experiments. However, high pressure diamond anvil cell experiments on lower mantle phases have documented a range textures that develop due to phase transformations. Additionally the few texture measurements that exist for deformation of multi-phase lower mantle assemblages (rocks) suggest complex interactions between the phases. This project will use the diamond anvil cell and synchrotron radial diffraction to study orientation relationships and texture inheritance during bridgmanite and post-perovskite phase transitions and will investigate the effects of poly-phase deformation on texture development in lower mantle mineral phases. By understanding these processes, this proposal will enhance our ability to interpret seismic anisotropy in terms of phase transformations and mantle flow.