The phase diagram of olivine and the seismological discontinuities

Analysis of seismic waves travel time allow the measurement of the the variation of density within the Earth. Several jump in density can be observed among which are the 400 and 670 km depth discontinuities.

The experimental study of the phase diagram of olivine shows the existence of several phase transitions and a decomposition of this mineral around 24 GPa.

The correspondance between these observations confirms the hypothesis of an upper mantle mainly composed of olivine. Moreover, we can determine the temperature at the discontinuities from the phase diagram. The decomposition of olivine at 670 km depth characterizes the transition between the upper and lower mantle.