HR: 0800h
AN: T21B-0478    [Abstracts]
TI: Strength and Stability of Olivine Aggregates Under Wet and Dry Conditions
AU: * Boettcher, M S
EM: margaret@whoi.edu
AF: Woods Hole Oceanographic Institution, Clark South 275B, MS#24, Woods Hole, MA 02543 United States
AU: Hirth, G
EM: ghirth@whoi.edu
AF: Woods Hole Oceanographic Institution, Clark South 275B, MS#24, Woods Hole, MA 02543 United States
AB: We investigate the micromechanical processes that control localization, strength, and sliding stability of olivine aggregates through laboratory experiments at temperatures and effective pressures similar to those at the base of the seismogenic zone on a typical transform fault. Triaxial compression tests were conducted under both wet and dry conditions on olivine powder (grain size ≤ 60 μ m) at effective pressures P_eff between 50 and 300 MPa, temperatures T between 600°C and 1000°C, and displacement rates from 0.06 to 60 μ m/s. In all dry tests deformation localized onto a narrow shear plane oriented between 30-45 degrees to the shortening direction. Sample strength increased linearly with P_eff}, nearly independent of both temperature and water content. A transition from velocity-weakening to velocity-strengthening behavior occurred at T= 1000°C in the dry experiments, while a transition from velocity-weakening frictional sliding to ductile deformation occurred at T=1000°C under wet conditions. The pressure-dependent strength and temperature-dependent stability can be explained with a Bowden/Tabor asperity hypothesis. At high temperatures and low strain rates, plastic yielding at the asperity stabilizes frictional sliding of the bulk sample. Rapid compaction occurred at the start of each experiment and was followed by deformation at approximately constant volume. Dilatant behavior was most pronounced at low pressure and high strain rates. Extrapolation of our experimental data is consistent with the observation that seismicity is restricted to T ≤ 600°C in the oceanic lithosphere.
DE: 3039 Oceanic transform and fracture zone processes
DE: 3902 Creep and deformation
DE: 5104 Fracture and flow
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8163 Rheology and friction of fault zones (8034)
SC: Tectonophysics [T]
MN: Fall Meeting 2005