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>Dislocation creep in experimentally deformed quartz and feldspar aggregates: Effect of chemical environment, rate of water penetration and calibration of a recrystallized grain size piezometer.
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Dislocation creep in experimentally deformed quartz and feldspar aggregates: Effect of chemical environment, rate of water penetration and calibration of a recrystallized grain size piezometer.
An experimental study was performed to understand some aspects of the deformation processes in the earth's continental crust and to determine relationships that allow extrapolation from laboratory to natural conditions. Water has a strength effect on dislocation creep in quartzite; this can be quantified by determining the appropriate chemical parameter to include in the flow law. In order to determine this parameter, deformation and hydrostatic annealing experiments were performed on natural aggregates of quartz at varying and controlled conditions of oxygen, hydrogen and water fugacity and proton activity. Mechanical data combined with microstructural observations indicate that water fugacity is the chemical parameter that controls dislocation climb and creep. The rate at which quartzite equilibrates after changes in the chemical environment has been a long standing controversy. In order to determine that rate, water-added deformation and hydrostatic annealing experiments were performed on vacuum-dried samples of natural quartzite. The penetration distance at various times was determined by correlating microstructural observations (optical microscopy and TEM) and mechanical data and intragranular FTIR was used to confirm and quantify the results. The rate of penetration is relatively fast, consistent with the volume diffusion rate of molecular H{dollar}sb2{dollar}O. The recrystallized grain size of rocks deformed by dislocation creep can be used to infer paleostresses in the earth if the piezometer relationship is experimentally calibrated. A piezometer was calibrated for low-temperature migration recrystallization in feldspar. Hot-pressed samples of fine-grained feldspar and a natural feldspar aggregate were deformed in simple shear and axial compression. The stress exponent in the piezometer relationship is higher than that determined in previous studies of other materials for rotation recrystallization and high-temperature migration recrystallization, emphasizing the need to correctly identify the recrystallization mechanism when applying a piezometer relationship.
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