Deformation induced slip-system transition in olivine at high pressures

Deformation-induced olivine fabrics provide vital information for understanding seismic anisotropy in the upper mantle since olivine is the primary mineral in this region. Our recent analysis of the fabric of deformed olivine aggregates has documented the influence of deformation conditions (e.g., temperature and stress) on the fabric evolution of olivine at high pressures. Experiments were carried out using a deformation-DIA on an X-ray beamline at the National Synchrotron Light Source (NSLS), Brookhaven National Laboratory. Samples of polycrystalline olivine were deformed at a constant displacement rate of ~ 3.0 × 10- 5 s-1 over true axial strains of ~ 30% at temperatures of 673 to 1573 K and pressures of 5 to 9 GPa. Electron backscattered diffraction (EBSD) analyses of the fabrics of the deformed samples reveal a transition in slip system. For low temperatures (T < 1173 K) and high stresses (σ > 2 GPa), the normals to the (100) lattice planes are parallel to the maximum principal stress; while at high temperatures (T > 1473 K) and lower stresses (σ < 1 GPa), the normals to the (010) lattice planes switch to be parallel to the maximum principal stress. This transition in fabric occurs even if pressure is fixed, indicating that pressure is not a primarily factor causing the transition in dominant slip system. Our observations indicate that deformation of olivine is dominated by the (100) [001] slip system at low temperatures and high stresses and by the (010) [100] slip system at high temperatures and low stresses.