HR: 1340h
AN: MR33A-0152    [Abstracts]
TI: Plasticity and Diffusion Creep of Dolomite
AU: Davis, N E
EM: ndavis@geo.tamu.edu
AF: Texas A and M University, Center for Tectonophysics, Department of Geology and Geophysics, College Station, TX 77843 United States
AU: * Kronenberg, A K
EM: kronenberg@geo.tamu.edu
AF: Texas A and M University, Center for Tectonophysics, Department of Geology and Geophysics, College Station, TX 77843 United States
AU: Newman, J
EM: newman@geo.tamu.edu
AF: Texas A and M University, Center for Tectonophysics, Department of Geology and Geophysics, College Station, TX 77843 United States
AB: Coarse-grained natural and fine-grained synthetic dolomites have been shortened in triaxial compression experiments at temperatures of 400-850°C, equilibrium CO₂ pore pressures, effective confining pressures of 50-400 MPa, and strain rates of 10^-4 to 10^-7s^-1. At low temperatures (T<700°C) coarse- (240μm) and fine-grained dolomites (2μm) exhibit high crystal plastic strengths (>600 MPa); differential stresses vary little with strain rate or temperature and microstructures of coarse-grained samples are dominated by f twins and undulatory extinction. An exponential relation ε̇ = A exp (ασ) between strain rate ε̇ and differential stress σ describes the crystal plasticity of dolomite with α=0.08 MPa^-1 and 0.02 MPa^-1 for coarse- and fine-grained materials, respectively. However, measured values of σ increase with increasing temperature, a trend that has been observed for dolomite single crystals ( Higgs and Handin, 1959; Barber et al., 1981) but cannot be described by an Arrhenius relation. At high temperatures (T≥800°C for coarse, T≥700°C for fine), dolomite strengths are reduced with increasing temperature and decreasing strain rate, but the mechanisms of deformation differ depending on grain size. High temperature flow strengths of coarse-grained dolomite can be described by a power law ε̇ = A^' σⁿ exp (- H^*/RT) with a large value of n (>5) and a ratio of parameters H^*/n = 60 kJ/mol. Microstructures of coarse-grained samples deformed at T≥800°C show evidence of dislocation creep and recrystallization at grain boundaries with little mechanical twinning. High temperature flow strengths of fine-grained dolomite fit a thermally activated Newtonian law, where the effective n=1.28 (±0.15) and H^*=280 (±45 kJ/mol), consistent with diffusion creep. The change in mechanical response of coarse-grained dolomite represents a transition from twinning and slip to recrystallization-accommodated dislocation creep while the change in response of fine-grained dolomite represents a transition from crystal plasticity to diffusion creep. The combined results for coarse- and fine-grained dolomites define a deformation mechanism map with fields of crystal plasticity, dislocation creep, and diffusion creep. Strengths of coarse-grained dolomite in the crystal plastic and dislocation creep fields are much larger than strengths of calcite rocks deformed by similar mechanisms ( Heard and Raleigh, 1972; Schmid et al., 1980; Walker et al., 1990; Renner et al., 2002). In contrast, strengths of fine-grained dolomite deformed by diffusion creep are more comparable to those of fine-grained calcite ( Schmid et al., 1977; Walker et al., 1990; Herwegh et al., 2003), suggesting little contrast in rheology.
DE: 3902 Creep and deformation
DE: 5104 Fracture and flow
DE: 5120 Plasticity, diffusion, and creep
DE: 8031 Rheology: crust and lithosphere (8159)
DE: 8032 Rheology: general (8160)
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005