Abstract:

 Mantle transition zone (MTZ) is the link between the upper and lower mantle. It has important implications for our understanding of the composition and evolution of the whole mantle, mantle convection and the geodynamics of the deep subduction of lithosphere and deepfocus earthquakes. The seismic discontinuities in transition zone are generally interpreted in terms of phase transformations in olivine component at high pressures. Recent highpressuretemperature experiments indicate that the transformations in nonolivine components (e.g. pyroxene and garnet) contribute significantly to the depth and sharpness of these discontinuities as well as the gradients in seismic velocities and density. In addition, the bulk composition, elemental partitioning, temperature and H2O have great impacts on these phase transformations and relative discontinuities, as well. These subtle experiment results explained some relative local characteristics and variations very well, and advanced our knowledge of the Earths deep interior and its geodynamic process. Because of the lack of samples directly from deep Earth, and the relative limitation of geophysical and geochemical methods, the highpressuretemperature experiments are still the indispensable method for our understanding of the composition and characteristics of the Earths deep interior.

Key words: mantle transition zone, seismic discontinuity, phase transformation, geodynamics