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

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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.