The mantle transition zone is the region of the Earth’s mantle located between the upper and lower mantle, typically between 410 and 660 kilometers in depth. This zone is characterized by changes in mineral structure and composition, influencing mantle convection and the dynamics of plate tectonics.
Reference: Ringwood, A. E. (1991). “Phase Transformations and Their Bearing on the Constitution and Dynamics of the Mantle.” Geochimica et Cosmochimica Acta, 55(8), 2083-2110.