Transition zone and lower mantle (1)

This lecture is dedicated to anisotropy in the transition zone of the upper mantle (the region between 400 and 660 km depth): we give an overview of our knowledge of the intrinsic properties of the minerals present at this depth (mainly the high-pressure forms of olivine: wadsleyite and ringwoodite), as well as the few studies, currently controversial, that propose the presence of seismic anisotropy in this part of the mantle. We also discuss the mineralogy of the lower mantle, the notable absence of anisotropy down to the D" region, and finally, describe current seismic methods that give access to the observation and study of anisotropy at the base of the mantle and demonstrate its presence there.