Stress dependence of microstructures in experimentally deformed calcite

Optical measurements of microstructural features in experimentally deformed Carrara marble help define their dependence on stress. These features include dynamically recrystallized grain size (Dr), subgrain size (Sg), minimum bulge size (L rho), and the maximum scale length for surface-energy driven, grain-boundary migration (L gamma). Taken together with previously published data Dr defines a paleopiezometer over the range 15-291 MPa and temperature over the range 500-1000 degrees C, with a stress exponent of -1.09 (CI -1.27 to -0.95), showing no detectable dependence on temperature. Sg and Dr measured in the same samples are closely similar in size, suggesting that the new grains did not grow significantly after nucleation. L rho and L gamma measured on each sample define a relationship to stress with an exponent of approximately -1.6, which helps define the boundary between a region of dominant strain-energy-driven grain-boundary migration at high stress, from a region of dominant surface-energy-driven grain-boundary migration at low stress.