Experimental study of the flow behavior of garnet at high pressures: implications for the rheology of subducted lithosphere

这项建议的重点是研究地球材料在极端压力-温度条件下的强度，以便为模拟与板块构造有关的地球动力学活动提供必要的坚实基础。这项拟议研究的结果是重要的，不仅广泛的地球物理学社区，而且能源科学，因为在后者，了解地球物理学的属性和过程是至关重要的，以管理改善地球能源资源的生产和安全处置能源相关的废物。此外，这项研究将建立新的实验技术，其结果将被纳入学术课程，并将为学生提供重要的学习经验。具体来说，这项拟议的研究旨在发展高压下石榴石机械性能的基本理解。由于石榴石是地球俯冲板块和过渡带中的重要矿物，石榴石的强度在控制这种构造活动区域的动力学方面起着重要作用。尽管其重要性，但迄今为止石榴石的机械性能受到很大限制，主要是因为常规设备的工作压力太低，无法达到高温下石榴石的稳定性。这一缺陷极大地限制了我们对俯冲岩石圈动力学行为的理解。 这项拟议的研究描述了利用新一代高压设备，变形DIA设备，一种先进的机械测试系统，能够在比以前更高的压力和温度下使地质材料变形的研究。 有了这个装置，现在可以在适合俯冲带的高压-温度条件下研究石榴石的物理性质。建议开展三项具体任务。首先，我们将量化压力对石榴石高温强度的影响。其次，我们将研究化学环境的影响（例如，水）对石榴石在高温高压下的流动行为的影响。第三，我们将确定地球上地幔中最丰富的两种矿物橄榄石和石榴石之间的强度差异。总的来说，这项研究的结果将有助于地球动力学问题的解决，通过提供在极端条件下地球材料的科学认识的基础。

This proposal focuses on investigating the strength of earth materials at extreme pressure-temperature conditions in order to provide the solid basis that is necessary to model geodynamic activities associated with plate tectonics. The results of this proposed study are important not only to a broad spectrum of the geophysics community but also to energy sciences since, in the latter, understanding geophysical properties and processes is critical to managing improved production of Earth's energy resources and safe disposal of energy related waste. Furthermore, this research will establish new experimental techniques, and the results will be integrated into the academic curriculum and will provide an important learning experience for students.Specifically, this proposed study is designed to develop a fundamental understanding of the mechanical properties of garnet at high pressures. Since garnet is an important mineral in Earth's subducting plates and the transition zone, the strength of garnet plays an important role in governing the dynamics of such tectonically active regions. Despite its importance, to date the mechanical properties of garnet have been poorly constrained, mainly because the working pressure for conventional apparatuses is too low to reach the stability field for garnet at high temperatures. This shortcoming limits enormously the advance of our understanding of the dynamic behavior of the subducted lithosphere. This proposed study describes research that utilizes a new generation of high-pressure equipment, the deformation-DIA apparatus, an advanced mechanical testing system capable of deforming geo-materials at much higher pressures and temperatures than previously possible. With this apparatus, it is now achievable to investigate the physical properties of garnet at the high pressure-temperature conditions appropriate to subduction zones. Three specific tasks are proposed to be undertaken. First, we will quantify the effect of pressure on the high-temperature strength of garnet. Second, we will investigate the influence of chemical environment (e.g., water) on the flow behavior of garnet at high temperatures and pressures. Third, we will determine the difference in strength between olivine and garnet, the two of the most abundant minerals in Earth's upper mantle. In general, the results of this research will contribute to the solution of geodynamic problems by providing a foundation of scientific understanding of earth materials at extreme conditions.