Relationships between mechanical behavior and microstructural development in experimentally deformed quartz aggregates

Microstructural observations have been used in conjunction with theoretical considerations to investigate the physical processes which control the mechanical behavior of experimentally deformed quartz aggregates. The experiments were conducted over a wide range of conditions, and thus have involved several different deformation mechanisms. The three chapters of the thesis are summarized below.; An analysis of stress concentrations around pores was used in conjunction with microstructural observations to illustrate why porous quartzite undergoes a brittle-ductile transition, with increasing pressure at room temperature. The ductile behavior exhibited by the porous quartzite is only transient; deformation becomes localized on faults at strains greater than {dollar}sim{dollar}25%. These results indicate that porous rocks may undergo limited ductile deformation at shallow levels in the crust, but higher strains will cause deformation to localize.; Three regimes of dislocation creep were identified in experimentally deformed quartz aggregates using optical and TEM microscopy. Within each regime a distinctive microstructure is produced due primarily to the operation of different mechanisms of dynamic recrystallization. The identification of the three regimes of dislocation creep has implications for the determination of flow law parameters, the calibration of recrystallized grain size piezometers, and the interpretation of microstructures from naturally deformed quartz aggregates.; The presence of porosity results in significant although transient strengthening of quartz aggregates experimentally deformed in the dislocation creep regime. The strengthening is associated with high densities of tangled dislocations which develop around the pores when the samples are taken to run conditions. With increasing strain, the high dislocation density material is removed by grain boundary migration and dislocation climb. After {dollar}sim{dollar}30% strain the initially porous samples achieve the same flow stress and microstructures as non-porous samples deformed at the same conditions.