Seismic anisotropy in the lower mantle transition zone induced by
lattice preferred orientation of akimotoite
Abstract
Seismic anisotropy has been widely observed near the subducting slabs in
the lower mantle transition zone (MTZ) and is often interpreted by the
lattice preferred orientation (LPO) of constituent minerals. Akimotoite
is one of the dominant minerals near the cold subducting slabs.
Therefore, we conducted the well-controlled uniaxial and shear
deformation experiments on the MgSiO3 akimotoite aggregates at 21-23 GPa
and 900-1300℃ by using the D111-type Kawai-type multianvil apparatus. We
observed strong LPOs and the most dominant slip system of akimotoite is
suggested to be <10-10>(0001). The elastic wave
velocities of deformed samples were calculated to be strong azimuthal
and polarization anisotropy with the velocities of horizontally
polarized shear waves greater than that of vertically polarized shear
waves for the horizontal mantle shearing. Our results provide important
implications for the origin of observed seismic anisotropies and the
mantle flow directions in the lower MTZ.