Quartz microstructures in nature and experiment — evidence of rapid plastic deformation and subsequent annealing


Quartz microstructures produced in short-term deformation and annealing experiments are compared with those in naturally deformed vein quartz in cores from the Long Valley Exploratory Well (Long Valley Caldera, California). The experiments are designed to simulate i) co-seismic deformation of quartz in the uppermost plastosphere and ii) annealing during post-seismic stress relaxation. The experiments are performed in a modified Griggs type solid medium apparatus. Natural polycrystalline quartz samples (grain size on the order of millimetres) are deformed at a temperature of 400°C, a confining pressure of 2GPa, and strain rates of ca. 10−4 s−1. The differential stress reaches 2–4GPa and the irreversible axial shortening is typically a few percent. In some experiments the samples have subsequently been annealed for ca. 14–15 h at elevated temperatures of 800–1000°C and low stresses (quasi-hydrostatic or nonhydrostatic conditions)...
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