In situ Study of Lattice Preferred Orientation at Mantle Conditions

Suny At Stony Brook, Stony Brook NY

Investigators

Abstract

The solid portion of the Earth is extremely dynamic on a million year time scale. Plastic flow of the solid leaves a history in the form of alignment of the crystalline building blocks of rocks. Unraveling this history requires understanding the processes that create this fabric through experiments at the pressure and temperature conditions of the Earth's interior. Here we capitalize on new facilities that have been developed at the National Synchrotron Light Source to probe mineral systems subjected to the deforming conditions of the deep Earth. The goal is to better understand these processes, to define the time scale for changing the induced fabric, and to define the control of the pressure and temperature conditions on the efficiency of producing these fabrics. The dynamic history of the Earth can now be constrained by the anisotropy of seismic wave velocities. Texture in the rocks of the deep Earth is understood to give rise to this anisotropy and it is the plastic flow of the rocks that creates the texture. This breakthrough in understanding was enabled by laboratory investigations of rock deformation at mantle conditions. The former approaches generally resolve the end-product of large deformation. The efficiency of fabric production as a function of the environmental variables is still not well defined. The degree to which small strains will create elastic anisotropies has not been experimentally quantified. We lack a clear understanding of the interactions of the grains during the texture formation such as the relative roles of recrystallization and dislocation glide. New studies need to occur at mantle pressures and temperatures to assure that the proper processes are active. The research of this proposal will provide important information about plastic deformation of solids in general. It will provide metrics that can be used to evaluate the amount of deformation and the mechanism of deformation. This provides potential tools for assessing the failure state of structural materials in engineering applications. Preliminary experiments with sinusoidal stress fields indicate that the techniques proposed here have a strong probability of success and are well defined by theoretical models.