Mantle anisotropy and olivine crystallographic preferred orientation
Earth’s mantle includes large regions where mantle rocks deform in a creep-like viscous fashion - mantle flow. The flow is the manifestation of plastic deformation accommodated through the movement of crystallographic defects. To reveal 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 have on the mantle seismic signature using both experimental and numerical tools.
The experimental aspect was accomplished using samples cored from natural dunite (Åheim, Norway) on a Griggs-type rig apparatus under conditions of 1 GPa confining pressure and temperature of 1200° C. The numerical part was done using the ViscoPlastic Self Consistent (VPSC) and D-Rex numerical models. In these experimental and numerical 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.
Petrographic thin section of a deformed sample
Griggs apparatus (Washington University)
The evolution of olivine crystallographic preferred orientation (CPO) as a function of shear strain simulated using two numerical models: D-Rex and VPSC. The initial configurations denoted as random, perpendicular, oblique, and parallel. Each configuration evolves differently, demonstrating the importance of deformation history for texture evolution and the development of seismic anisotropy.
Boneh Y., Morales L.F.G., Kaminski E., and Skemer P.
Geochemistry, Geophysics, Geosystems, 2015
Boneh Y., Wallis D., Hansen L. N., Krawczynski M. J., and Skemer P.
Earth and Planetary Science Letters, 2017