α-QUARTZ Plastic Strength Investigation Via Diffraction Experiments on Novaculite Using a D-Dia and Elastic Plastic Self-Consistent Interpretation

The plastic response of experimentally deformed quartz provides insight into the strength of ductile shear zones that has implications for tectonic, lithospheric, and ore deposit models. We present a suite of 15 uniaxial deformation experiments on Arkansas novaculite conducted in a DDIA apparatus with in-situ synchrotron x-rays. Experimental temperatures range from 25 C to 1334 C with pressures between 1.39 GPa and 3.1 GPa, and strain rates between 1x10-5 s-1 and 9x10-6 s-1. Macroscopic sample strain ranges from 3% to 24%. d-spacings from the (101), (110), (200), (201), and (112) lattice planes were measured, producing lattice strain up to ~5%. Diffraction data was forward modeled using elastic plastic self-consistent (EPSC) simulations to derive differential stress and the critical resolved shear stress (CRSS) of individual slip systems as a function of pressure and temperature. This study investigates the activation of basal (c), positive rhombohedral {r}, negative rhombohedral {z}, prismatic {m}, positive acute rhombohedral {pi}, negative acute rhombohedral {pi’} slip systems and their association with differential strain among quartz lattice planes during deformation prior to steady state flow. Modeled stress strain curves reflect a decrease in critical resolved shear stress with increased temperature and decreased stress. Microstructures observed from electron backscatter diffraction (EBSD) maps of our deformed samples indicate the presence of dauphine twins whose effects may be reflected in the alignment of the positive rhombohedral plane (10-10) in our deformation experiments. Additionally, inelastic behavior at low strain observed in all deformation experiments has been simulated with the use of an isotropic deformation system in the model. The differential stresses derived from EPSC simulation of our D-DIA experiments have been used to compare with deformation data from Griggs type experiments, that correlate well.