Stability and wave velocity of novel iron magnesium oxide (Mg, Fe)2O3.5 in the lower mantle

Abstract

The mineral composition of the anomalous wave velocity zone in the lower mantle is indispensable to understanding seismic wave velocity anomalies and the genesis as well as driving forces of plate tectonics. We here systematically investigate the structural stability, density, elastic wave velocity and anisotropy of the wave velocity for (Mg, Fe)2O3.5, a new type of the low wave velocity mineral, in the 0–136 GPa range by means of first-principles calculations. Calculations show that (Mg, Fe)2O3.5 possesses high density, with a value higher than that in the Preliminary Reference Earth Model at the core-mantle boundary by up to 17.31 %, and its longitudinal and transverse wave velocities are reduced by about 9.23 % and 17.41 %, respectively. Moreover, the elastic wave velocity is characterized by anisotropy, and is consistent with the characteristics of the seismic wave velocity in ultra–low velocity Zone (ULVZ). Our study elucidates that (Mg, Fe)2O3.5 is a candidate mineral for the wave velocity anomalies in the ULVZ that survive in the deep mantle. Such findings may pave the way towards exploring the origin of the ULVZ from the viewpoint of chemical composition anomalies.