[S15-1] Structure and dynamics of the mid mantle

[S15-1-03] Mineralogical model of the lower mantle inferred from high-pressure sound velocity data

^○Izumi Mashino¹, Motohiko Murakami¹, Nobuyoshi Miyajima², Sylvain Petitgirard², Daniel Frost² (1.Tohoku University, Miyagi, Japan, 2.University of Bayreuth, Bayreuth, Germany)

invited

Understanding of the mineralogical composition of the lower mantle provides important information on the evolution of the Earth. The mineralogical model of the lower mantle can be estimated by comparing the seismic velocities of the minerals under lower-mantle conditions with seismic observations. It is widely thought that spin transitions of iron in the mantle minerals may directly influence the seismic velocity structure of the lower mantle, and also suggested that the spin transition in Fe-bearing MgSiO3 bridgmanite (Fe-Brd), the major component of the lower mantle, could occur. However, the presence and its effect of the spin transition in Fe-Brd have been complex to characterize in previous studies. Especially, the effect of the spin transition on the elastic wave velocities has not been elucidated yet.
Here we present the results of acoustic wave velocity measurements on Fe-Brd by Brillouin spectroscopy in a diamond anvil cell for a pressure range of whole lower mantle in order to clarity the presence and its effect of the spin transition in Brd and constrain a more realistic model of the lower mantle. Then, we discuss the mantle convection model of the present Earth and the building materials of the Earth.