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

该提案的重点是研究极端压力-温度条件下地球材料的强度，以便为与板块构造相关的地球动力学活动建模提供必要的坚实基础。这项拟议研究的结果不仅对地球物理界的广泛范围很重要，而且对能源科学也很重要，因为在后者中，了解地球物理特性和过程对于管理改善地球能源资源的生产和安全处置能源相关废物至关重要。此外，本研究将建立新的实验技术，并将结果整合到学术课程中，为学生提供重要的学习经验。具体来说，本研究旨在对石榴石在高压下的力学性能有一个基本的了解。由于石榴石是地球俯冲板块和过渡带中的重要矿物，因此石榴石的强度对控制这些构造活动区的动力学起着重要作用。尽管它很重要，但迄今为止，石榴石的机械性能一直受到很差的限制，主要是因为传统设备的工作压力太低，无法在高温下达到石榴石的稳定范围。这个缺点极大地限制了我们对俯冲岩石圈动力学行为的理解。本研究描述了一项利用新一代高压设备变形dia设备的研究，该设备是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变形地质材料。有了这种仪器，现在可以在适合于俯冲带的高压-高温条件下研究石榴石的物理性质。建议执行三项具体任务。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（如水）在高温高压下对石榴石流动行为的影响。第三，我们将确定橄榄石和石榴石的强度差异，这是地球上地幔中最丰富的两种矿物。总的来说，这项研究的结果将有助于解决地球动力学问题，为科学理解极端条件下的地球物质提供基础。

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.