Effects of Water on Transformation and Deformation Mechanisms in the Mantle Transition Zone

Arizona State University, Scottsdale AZ

Investigators

Abstract

Sharp EAR-0208419 The high solubility of H2O in olivine and its high-pressure polymorphs, wadsleyite and ringwoodite has led to a great deal of interest in the effects of H2O in the upper mantle and transition zone. Recent interpretations of double seismic zones (Peacock, 2001) suggest that subducting oceanic lithosphere may also carry H2O into the mantle and possibly the transition zone. H2O in subducting lithosphere is likely to have profound effects on phase transformation mechanisms and kinetics as well as on deformation mechanism and resulting fabrics. It is likely that the presence of H2O, as hydrogen in olivine, will influence olivine-ringwoodite transformation mechanisms and enhance reaction rates. The investigators propose to perform kinetic transformation experiments in a multi-anvil apparatus using deuterated San Carlos olivine. They will use the widths of reaction rims to determine growth rates as a function of temperature, pressure and D2O content. TEM will be used to characterize transformation mechanisms in the deuterated olivine. D2O contents of the hot-pressed starting material and the transformed material will be determined with SIMS. H2O has also been shown to have a great influence on the plastic deformation of olivine. Jung and Karato (2001) show that the fabric produced in simple shear at high pressure changes with increasing H2O content. TEM will be used to characterize the dislocation microstructures, slip systems and deformation mechanisms in olivine, wadsleyite and ringwoodite deformed at high pressure under wet conditions.