HR: 1330h
AN: T42A-0282    [PDF]
TI: The Impact of Olivine-Orthopyroxene Phase Boundaries on Mechanical Absorption: Inferences from Resonant Ultrasound Spectroscopy (RUS)
AU: Lan, J
EM: jlan@students.wisc.edu
AF: University of Wisconsin-Madison, Program in Mechanics and Materials, College of Engineering, Madison, WI 53606 United States
AU: Wang, Y
EM: yunchewang@students.wisc.edu
AF: University of Wisconsin-Madison, Program in Mechanics and Materials, College of Engineering, Madison, WI 53606 United States
AU: Lakes, R S
EM: lakes@engr.wisc.edu
AF: University of Wisconsin-Madison, Program in Mechanics and Materials, College of Engineering, Madison, WI 53606 United States
AU: * Cooper, R F
EM: reid_cooper@brown.edu
AF: Brown University, Department of Geological Sciences, Providence, RI 02912 United States
AB: In polycrystalline aggregates having no lattice dislocations within the grains, mechanical absorption is effected by the motion of primary and secondary grain- (or phase-)boundary dislocations, which can be accommodated by chemical diffusion for high-enough temperatures and/or low-enough frequencies. We postulate that the absorption seen in most upper-mantle rock has its origin in such mechanisms. High-homologous-temperature mechanical-absorption experiments on metal aggregates suggest that solid-state phase boundaries are perhaps significantly more effective in absorbing mechanical energy than are grain boundaries [McMillan et al., 2003]. We are engaged in evaluating this effect in mantle aggregates. The experiments reported here examine the ambient-temperature, (shear) RUS response of very-fine-grained (grain size $\sim$5 $\mu$m) aggregates of olivine and olivine plus orthopyroxene, with mechanical absorption characterized as a function of volumetric percentage of pyroxene (10, 15, 20 and 30 vol% opx). Aggregates were prepared via controlled-oxygen-activity, vacuum sintering of natural powders; mechanical data were collected on cubic specimens ($\sim$125 mm$^{3}$). Q$_{S}^{-1}$ measured for the all-olivine aggregate was 4x10$^{-4}$. Addition of orthopyroxene demonstrated an approximately linear trend with volume percentage, with the 30 vol% opx specimens producing a Q$_{S}^{-1}$ = 1.6x10$^{-3}$. There was no discernable discontinuity in the data between 15 and 20 vol% opx, which is the volume-percentage range where pyroxene percolative connectivity is anticipated. K.M. McMillan et al., J. Mater. Sci., 38, 2747-2754 (2003).
DE: 3904 Defects
DE: 3909 Elasticity and anelasticity
DE: 3994 Instruments and techniques
DE: 5144 Wave attenuation
DE: 7218 Lithosphere and upper mantle
SC: Tectonophysics [T]
MN: 2003 Fall Meeting