HR: 0800h
AN: T41C-1319    [Abstracts]
TI: The Mechanical Responses of Two-Phase Magnesium Sulfate-Hydrate/Water Ice Aggregates: Impacts of a Eutectic Solidification Microstructure on Strength and on Strain Homogeneity
AU: * McCarthy, C
EM: christine_mccarthy@brown.edu
AF: U.S. Geological Survey, 345 Middlefield Rd, Menlo Park, CA 94025 United States
AU: * McCarthy, C
EM: christine_mccarthy@brown.edu
AF: Brown University, Dept. of Geological Sciences, Providence, RI 02912-1846 United States
AU: Kirby, S
EM: skirby@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd, Menlo Park, CA 94025 United States
AU: Durham, W
EM: durham1@llnl.gov
AF: UC/Lawrence Livermore National Laboratory, PO Box 808, Livermore, CA 94450 United States
AU: Cooper, R
EM: reid_cooper@brown.edu
AF: Brown University, Dept. of Geological Sciences, Providence, RI 02912-1846 United States
AU: Stern, L
EM: lstern@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd, Menlo Park, CA 94025 United States
AB: Fully dense, two-phase aggregates of magnesium sulfate-hydrate and water ice were deformed in constant-load tests at temperatures in the range T=240-250K and under a gas-medium confining pressure P=50 MPa using a cryogenic apparatus. Differential stresses in the range σ = 2.7-12.7 MPa were applied to the 25-mm-diameter samples. The flow strength of the pure hydrate is ~100 times greater than that of polycrystalline ice. In cold-pressed, mechanical mixtures of the two phases, the sulfate-hydrate grains behave as rigid inclusions and, with sulfate-hydrate inclusion volume fractions <0.5, the aggregates behave identically to pure ice. We found, however, that samples grown via seeded solidification of a homogenous liquid solution exhibit a classical, distinct eutectic microstructure that results in their having flow strengths decidedly greater than the mechanically mixed, cold-pressed aggregates of the same two phases at the same volume fractions. Further, we found localization of deformation as a result of compositional variations in the sample and small-scale heterogeneities resulting from the solidification process. In a cursory examination of deformed samples using cryogenic scanning electron microscopy (CSEM), the microstructure observed suggests formation of a deformation-induced fabric. Quantitative investigations of this fabric and of the deformation mechanism(s) involved are continuing. Although this system's chemistry reveals that the primary application of this research is to further understanding of tectonics and mechanical energy dissipation on the icy satellites, mechanical-response/microstructural-evolution correlation information gleaned from experiments on such a simple, multiphase mineral system is applicable, too, to mechanical dynamics of multiphase aggregates generally.
DE: 3902 Creep and deformation
DE: 3947 Surfaces and interfaces
DE: 5120 Plasticity, diffusion, and creep
DE: 6221 Europa
DE: 8199 General or miscellaneous
SC: Tectonophysics [T]
MN: Fall Meeting 2005