Effect of Fe2+ on Akimotoite to Bridgmanite Transition: Its Implication on Subduction Dynamics

Abstract Seismic studies in cold subduction zones indicate several discontinuity structures near the 660‐km boundary. Studies indicate that the akimotoite to bridgmanite transition may play a significant role in unraveling the complexity of this region. In this study, we used first‐principles methods to explore the stability field of iron‐rich analogs of akimotoite and bridgmanite (Mg1−xFex2+SiO3 under high‐pressure‐temperature conditions. The Fe2+ inclusion significantly reduces the phase transition pressure. Overall, our calculated phase boundary and thermoelastic properties compare well with the available results from previous studies. The onset transition pressure and the width of the two‐phase field exhibit a clear dependence on iron concentration, with the width of the two‐phase field increasing as iron concentration increases. Our results indicate that the relatively high Fe2+ (∼x = 0.5) found in natural Fe analogs of akimotoite and bridgmanite would not be possible under mantle transition conditions. However, Fe2+ incorporation relevant for mantle composition (<10 mol.% FeO) may explain the slab stagnation above 660 km depth as well as seismically observed trends of velocity perturbations in the slabs of the northwest Pacific region around ∼500–600 km depth.