Effect of iron on density and sound velocity of ringwoodite at high
pressure and high temperature
Abstract
As the most enriched composition of the lower part of mantle transition
zone, properties of bearing-Fe ringwoodite are important to deduce the
composition and structure of the mantle. For understanding the
properties of Fe-bearing ringwoodite under condition of the lower mantle
transition zone, the density and seismic wave velocity (Vp and Vs) of
ringwoodite with different Fe content (0, 12.5, 25, 50, and 100 at%)
were calculated under 300-2000K and 0-26 GPa by forcefeild combined with
molecular dynamic method. Changes of density, Vp and Vs of ringwoodite
containing different Fe content with pressure and temperature were
fitted by the binary linear equation. Density of ringwoodite linearly
increases with increasing Fe content, however relationship between
increase of Vp and Vs and increasing Fe content show quadratic. The
calculated densities of ringwoodite show that the Fe content of
ringwoodite shall be 55-64 at% to match the lower mantle transition
zone’s density. Therefor existence of ringwoodite may result in a
low-density zone or gravity anomaly in the lower part of the mantle
transition zone. The Vp and Vs of ringwoodite along the Earth’s typical
temperature and pressure profile are higher than the Earth’s wave
velocity model at the lower mantle transition zone (510-660 km) and the
Vp and Vs of ringwoodite with 12.5 at% Fe along the Earth’s typical
temperature and pressure profile are 31.3-33.7%% and 22.9-27.7%
higher. The calculated results provide new data to explore composition
and structure of the mantle.