HR: 15:25h
AN: T43D-08    [Abstracts]
TI: The influence of rigid second phases on the mechanical evolution of calcite rocks, with implications for strain localization
AU: * Austin, N
EM: naustin@mit.edu
AF: Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 77 Massachusetts Ave., Cambridge, MA 02139, United States
AU: Evans, B
EM: brievans@mit.edu
AF: Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 77 Massachusetts Ave., Cambridge, MA 02139, United States
AU: Dresen, G
EM: dre@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegrafenberg, Potsdam, D-14473, Germany
AU: Rybaki, E
EM: uddi@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegrafenberg, Potsdam, D-14473, Germany
AB: Interactions between rheologically distinct phases may strongly influence both the microstructure and mechanical properties of shear zones, thus playing a key role in the development or inhibition of localized deformation. However, experimental, theoretical, and field observations have produced conflicting suggestions that either A) rigid phases may pin the grain-size of a dominant weak phase, driving deformation into the diffusion creep regime, and promoting weakening, or B) rigid phases may be load supporting, thus increasing the strength of the aggregate. To investigate the influence of chemically inert, rigid second phases on the strength, microstructural evolution, and dominant deformation mechanism of calcite rocks, we have performed conventional triaxial experiments (MIT), and high strain torsion experiments (GFZ-Potsdam) on synthetic calcite aggregates with no second phases added, 1% (by vol.) 4 μm carbon spheres, 10% (by vol.) 4 μm carbon spheres, and 10% (by vol.) 5 μm carbon splinters. Glassy carbon spheres and splinters were chosen as they are chemically inert under the experimental conditions, are mechanically strong compared to the calcite, and can be obtained with a narrow grain size distribution. Prior to deformation, samples were hot isostatically pressed (HIPed) at 1023K and 300 MPa, to control the starting grain-size. The presence of carbon spheres or splinters has a dramatic influence on the grain-size after HIPing: samples with 10% spheres or splinters have an initial grain-size that is a factor of three finer than pure samples after 2.25 hrs while samples with 1% spheres are ~1.5 times finer than pure samples, again after 2.25 hrs. Deformation experiments were performed at 1023K, at a confining pressure of 300 MPa (trixial) or 400 MPa (torsion), at constant equivalent strain rates between 5e-6 s^-1 and 1e-3 s^-1. In both triaxial compression and torsion experiments, samples containing 10% splinters are stronger than pure samples and those containing 1% or 10% spheres. Further, in torsion experiments, samples with 10% splinters show weakening, whereas all other samples show progressive hardening. As a result, the strengths of the four materials converge at high strains (γ>16). In triaxial experiments, pure samples and samples containing 1% or 10% spheres have similar strengths, whereas in torsion, samples containing 10% spheres are significantly weaker than pure samples, or those containing 1% spheres. These results indicate that, while the microstructure of the dominant (in this case weak) phase is most important, that of the volumetrically minor (rigid) phases will also significantly influence the strength and mechanical evolution of the aggregate.
DE: 3902 Creep and deformation
DE: 5112 Microstructure
DE: 5120 Plasticity, diffusion, and creep
DE: 8030 Microstructures
DE: 8160 Rheology: general (1236, 8032)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting