The transition zone of the Earth's mantle plays a key role in mantle dynamics. Recent high-resolution seismic tomography shows rich variety of interaction of convection current with the mantle transition zone. One of the key data that are needed to understand the nature of this interaction is the rheological properties of materials in this layer. However, experimental studies of plastic deformation are difficult and there has been no quantitative rheological data on materials in this region. In this project, the investigators will conduct the first well-controlled quantitative rheological measurements on wadsleyite, the most abundant mineral in the shallow transition zone. A newly developed apparatus, RDA (rotational Drickamer apparatus), will be used in this study. Deformation experiments will be conducted to large strains to obtain not only the rheological data but also the relationship between deformation geometry and seismic anisotropy. The results from this research will help understand the mechanical coupling between the upper mantle and the transition zone (that affects the geoid anomalies associated with mantle convection) as well as the deformability of slabs in the transition zone and the distribution and the mechanisms of deep earthquakes. The results on the relation between the lattice-preferred orientation of wadsleyite and flow geometry will be the first data set to interpret seismic anisotropy in terms of flow geometry in this region.
