Granular flow and Riedel band formation in water-rich quartz aggregates experimentally deformed in torsion -: art. no. 2242

[1] We have investigated the influence of aqueous fluid on the deformation behavior of fine-grained quartz aggregates in the semibrittle field by deforming wet Dover flint to high shear strains in torsion. Tests were carried out under drained conditions at temperatures of 1250 and 1300 K, 350 MPa confining pressure and constant twist rate. Heat treatments prior to deformation were performed at 1300 K for different amounts of time at confining pressures of 150 or 350 MPa, resulting in an initial dilation with an isotropic distribution of water-filled pores, followed by compaction with continuous reduction in porosity and grain growth. Deformation of the heat-treated samples reached steady state behavior until a shear strain of gamma = 0.2 followed by sudden hardening stages for shear strains up to gamma = 2.5. Deformation was mainly accommodated within the samples by granular flow. During steady state deformation, the pores redistributed anisotropically in planes oriented at +/-25degrees to the maximum principal stress direction sigma(1). Hardening was associated with the interconnection of pores to form continuous bands in a synthetic R1 (Riedel) orientation, with no discernible lateral offset along them. These R1 bands served as fluid pathways enhancing local drainage of their surrounding, thus causing hardening by decrease in pore pressure. Two samples were unloaded at a shear strain of gamma = 1.3 and 2.5, respectively, and reloaded after 0.5 hours at the same deformation temperature and confining pressure. Subsequent deformation occurred primarily by displacement along the existing R bands.