HR: 0830h
AN: T11C-0414    [PDF]
TI: The Effect of Water on the Compressibility of Wadsleyite
AU: * Holl, C M
EM: hollc@colorado.edu
AF: University of Colorado, Dept. of Geological Sciences, Boulder, CO 80309 United States
AU: Smyth, J R
EM: Joseph.Smyth@Colorado.EDU
AF: University of Colorado, Dept. of Geological Sciences, Boulder, CO 80309 United States
AU: Jacobsen, S D
EM: Steven.Jacobsen@uni-bayreuth.de
AF: Bayerisches Geoinstitut, Universitaet Bayreuth, Bayreuth, D95440 Germany
AB: It has been known for nearly a decade that nominally anhydrous olivine polymorphs are capable of incorporating significant amounts of water in their structures. Marked decrease in densities with increasing water content and rapid hydrogen diffusion in these materials may explain the apparent sharpness in the seismic discontinuity at 410-km depth, which corresponds to the olivine-wadsleyite transition. Characterization of the effect of water content on the properties of these materials is key in understanding the nature of these seismic discontinuities, and holds clues to the possible cycling of water between the mantle and hydrosphere. Three samples of Fo$_{100}$ wadsleyite with various water contents were analyzed at room temperature in the diamond anvil cell by single-crystal X-ray diffraction. Unit cell parameters were measured at eight or more pressures for each sample. Preliminary values of bulk moduli are 172 (4) for dry wadsleyite, 152 (6) for wadsleyite with ~1 wt% H$_{2}$O, and 136 (3) for wadsleyite with ~1.5 wt% H$_{2}$O. Preliminary values of dK/dP are 3.9 (11), 6.5 (20), and 12.2 (11), respectively. Values obtained from this study show a marked decrease in K$_{0}$ with increasing water content. This decrease is larger than the effect of temperature over the stability field of wadsleyite. However, dK/dP also shows a dramatic increase with increasing water content, suggesting that at Transition Zone pressure-temperature conditions hydrous wadsleyite may have a value of bulk modulus comparable to or greater than that of anhydrous wadsleyite, while maintaining a lower density.
DE: 3909 Elasticity and anelasticity
DE: 3919 Equations of state
DE: 3999 General or miscellaneous
DE: 8124 Earth's interior--composition and state (old 8105)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting