HR: 14:55h
AN: T43D-06 INVITED    [Abstracts]
TI: Strain Localization and Ductile Failure of Anorthite-Diopside Aggregates
AU: * Dresen, G
EM: dre@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegrafenberg, Potsdam, D-14473, Germany
AU: Rybacki, E
EM: uddi@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegrafenberg, Potsdam, D-14473, Germany
AB: We investigate the effect of varying phase distribution on strength and strain localization of rocks during ductile deformation. The effect of phase distribution was examined by high-strain torsion experiments on synthetic fine- grained anorthite-diopside aggregates. Starting materials were hot-isostatically pressed fine-grained glass- powders of anorthite (An) and diopside (Di). Two kinds of samples were fabricated: homogeneous mixtures of 50vol% An and Di and layered composites composed of 2-3 alternating layers of An and Di, each 1.5-3 mm thick. The samples contain up to a few percent residual glass (melt). Mean grain size is about 3μm and the average water content is about 0.1wt%. Cylindrical samples of 10 mm diameter and length between 3.5 and 9 mm were deformed in torsion using a Paterson-type deformation apparatus. Most tests were conducted at 400 MPa confining pressure, temperatures of 950-1100°C, and shear strain rates between 2×10^-4 and 2×10^-5 s^-1 to shear strains of 1.2-6.7. Creep behavior was linear viscous at stresses below about 80 MPa. Continuous strain hardening was observed in most cases, except for the lowest temperature and highest strain rate, possibly owing to dilatancy and grain growth. All layered samples and mixtures deformed at low T failed abruptly at high shear strain, coupled with the formation of thin shear zones and cavity stringers. Presumably nucleation, growth, and coalescence of cavities combined with grain rotation and sliding and with redistribution of melt leads by ductile failure and small scale partitioning. Below the equi-viscous point of the two phases the strength of homogeneous mixtures is higher than that of layered aggregates where strain is partitioned into weaker An-layers. In contrast to the behavior of the pure end-members, the homogeneous mixtures show bulging and necking on the sample surface. The intensity of localization increases with decreasing strain rate and increasing temperature, i.e. decreasing stress. At high strain a moderate phase mixing of two-phase mixtures, which were slightly clustered before deformation, indicate grain boundary sliding. However, no phase mixing occurred at the boundaries of layered composites. The results show that localization evolves with strain and critically depends on the presence and distribution of a second phase.
DE: 3902 Creep and deformation
DE: 5104 Fracture and flow
DE: 5120 Plasticity, diffusion, and creep
DE: 8159 Rheology: crust and lithosphere (8031)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting