Deformation and Microstructural Evolution of Harzburgite

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)Plate tectonics is a unifying theory in the Earth sciences that describes the processes by which Earth?s surface shifts along narrow boundaries. These plate boundaries are of tremendous importance to society, as they represent the foci of many natural hazards, including earthquakes and volcanoes. To understand the behavior of plate boundaries it is essential that we understand the physical properties of material within these boundaries. This award is funding an effort to simulate the behavior of materials at these conditions. To simulate this behavior, a number of specialized apparatuses are needed, including large pneumatic or hydraulic presses to generate high pressure conditions. Analysis of the experiments takes place using a particular type of camera in a high-resolution scanning electron microscope. The data that are collected in this study will help us understand the physical processes that occur along plate margins, which will inform a broad spectrum of geophysical research.It is evident from studies of naturally deformed peridotites that deformation microstructures such as lattice-preferred orientation (LPO), grain-size and shape, and phase segregation (or mixing), continue to evolve beyond the strains achieved in almost all deformation experiments. As deformation microstructures affect both rheology and the interpretation of geological and geophysical data, it is important for us to study their formation and evolution. Two series of experiments are being conducted. (1) The first set of experiments investigates microstructural and rheological evolution of dunite and harzburgite during deformation to very large strains (γ10). (2) The second series of experiments will introduce additional complexity by changing the sense of shear during experiments to analyze the feedback between the kinematics of deformation and the kinetics of microstructural and rheological evolution. These experiments are being conducted in a Paterson-type gas medium apparatus with torsion capability; additional experiments will be conducted in a rotational Drickamer apparatus currently under construction. Microstructural analysis will be conducting using electron backscatter diffraction (EBSD), as well as other optical and electron microscope-based techniques. The data collected in this study will improve our understanding of (1) the effects of secondary phases on deformation in the mantle, (2) physical processes in mantle shear zones, and (3) seismic anisotropy in corner flow environments such as subduction zones and mid-ocean ridges.