Mantle anisotropy and olivine crystallographic preferred orientation
Earth’s mantle includes large regions where mantle rocks deform in a liquid-like viscous fashion - mantle flow. The flow is the manifestation of deformation, which is accommodated plasticaly by the movement of crystallographic defects. To detect and map deformation and flow in the mantle seismologists probe its anisotropic elastic properties (i.e., seismic anisotropy). I am investigating the effect that deformation, and deformation history, has on the evolution of the mantle seismic signature. Through both experimental and numerical tools the effect of an initial deformation on the way texture evolves was investigated.
The first project was done using a Griggs rig apparatus with natural sample of dunite (Åheim, Norway), pressure of 1 GPa and temperature of 1200° C, and with numerical tools - ViscoPlastic Self Consistent (VPSC) and D-Rex numerical models. In these tests the effect of an initially existing deformed texture was evaluated. Results revealed a transient stage of textural re-alignment where the elastic anisotropy does not represent the mantle kinematics (as people often assume). As such, modeling and interpreting mantle flow must consider this transient stage in which the seismic anisotropy does not reflect mantle flow.
In the second project the preservation of an existing texture under hydro-static conditions was evaluated. It was found that through an oriented grain-growth process the texture may indeed be modified and that the assumed preservation of a 'frozen' texture in the lithosphere mantle may by inaccurate.
Cover of AGU Journal 'G-cube'
Boneh et al. / October 2015
Animation of olivine CPO evolution from numerical models
Oriented grain growth in a pre-deformed sample (Boneh et al., 2017)
Sample and assembly after an experiment
Assembly parts for a solid medium, high P-T experiment
Petrographic thin section of a deformed sample
Griggs apparatus (Washington University)