HR: 0800h
AN: T41B-1189    [Abstracts]
TI: Investigation into the Effect of H$_{2}$O on Olivine-Ringwoodite Transformation Kinetics
AU: * Diedrich, T R
EM: Tamara.Diedrich@asu.edu
AF: Dept. of Geological Sciences Arizona State University, Box 1404, Tempe, AZ 85287 United States
AU: Sharp, T
EM: Tom.Sharp@asu.edu
AF: Dept. of Geological Sciences Arizona State University, Box 1404, Tempe, AZ 85287 United States
AU: Leinenweber, K
EM: kurtl@asu.edu
AF: Dept. of Geological Sciences Arizona State University, Box 1404, Tempe, AZ 85287 United States
AU: Hervig, R
EM: Richard.Hervig@asu.edu
AF: Dept. of Geological Sciences Arizona State University, Box 1404, Tempe, AZ 85287 United States
AB: The rapid transformation of metastable olivine subducted into the transition zone has been proposed as a mechanism leading to deep focus earthquakes, as well as general rheological weakening of the subducting slab. In evaluation of this hypothesis, several experimental studies have derived olivine-ringwoodite transformation rates for dry systems. However, double-seismic zones in subducting slabs suggest significant hydration and serpentinization. This likely presence of H$_{2}$O could be expected to significantly enhance the kinetics of the olivine-ringwoodite transformation, reducing the depth to which metastable olivine would persist in the transition zone. We have initiated a series of experiments to systematically investigate the effect of dissolved water on the transformation kinetics of olivine to its high-pressure polymorphs, ringwoodite and wadsleyite. Single crystals of San Carlos olivine were milled and sieved to produce spheres with a diameter of 450-500 microns. These crystals were then hot-pressed in a matrix of olivine and enstatite powder, and deuterated by welding liquid D$_{2}$O inside the sample capsule during piston-cylinder experiments. The use of D$_{2}$O as a proxy for H2$_{2}$O was made to ease SIMS analysis because of the high background for H$_{2}$O. All deuteration experiments were conducted with a nickel/nickel oxide oxygen fugacity buffer. Run conditions ranged from 2-3.2 GPa and 1000-1050 $^{o}$C. The single-crystal San Carlos olivine spheres in the run products were found to contain 150-400 ppm D$_{2}$O by weight. The deuterated olivine spheres and hot-pressed matrix were cut into 1.5 mm cubes and are being used as starting material in experiments conducted in the wadsleyite and ringwoodite stability fields. These experiments are being performed in a multi-anvil apparatus for durations ranging from 30-240 minutes. Run products will be prepared as thin sections and the thickness of the reaction rims will be measured and related to run duration to infer transformation rates as a function of temperature, pressure, and water content. TEM analysis will be used to determine the effect of D$_{2}$O on the transformation mechanisms.
DE: 1025 Composition of the mantle
DE: 1213 Earth's interior--dynamics (8115, 8120)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting