Recent advances in the study of mantle phase transitions

We review recent advances in the study of phase transitions of minerals in the Earth's mantle, including unsolved problems regarding these processes. The phase boundaries of (Mg,Fe)(2)SiO4 in the mantle transition zone are modified under the wet conditions by changes in thermodynamic properties of its polymorphs because of differences in the water solubilities of these minerals. The shift of phase boundaries has significant implications for the topography of the 410 km and 660 km seismic discontinuities. The post-perovskite phase with CaIrO3 Structure exists at pressures above 110 GPa and at high temperature. The effects of Al and Fe on phase transition are under debate. Several post-stishovite phases have been reported but equilibrium boundaries and existence in the real lower mantle are also still debatable. Spin transition occurs in magnesiowustite, perovskite, and post-perovskite phases at high pressures of the lower mantle and core. The pressure interval in the spin transition can be large at high temperature and so the transition might not cause a discrete change in physical properties under real Earth conditions. (C) 2008 Elsevier B.V. All rights reserved.