Chemical Related Perovskite to Post-perovskite Transition

A lower mantle S-wave triplication with a Scd branch is easily observed beneath regions where subduction has occurred. Sidorin et al. (1999) argued that this arrival could be explained by a small phase-change (1.5%) triggered on mapping S-wave tomography into temperature deriving Clapeyron slope (γ) varying from 3 to 9 MPa/K. Its enhanced strength, in particular regions, is then caused by slab-debris induced velocity increases. Hence, we construct global maps of boundary height for various assumptions about γ for Grand's (2002) tomographic model. Synthetics generated from these models (Mono-Phase-Transition, MPT) can not explain the variability commonly observed, i.e. Central America and other global samples. Next, we introduced a binary system assuming a slab-dominant (Al-rich) and normal ambient (Fe-rich) set of perovskite to post-perovskite relationship. The slab-dominat ambient height of phase boundary occurs 50 km lower than the normal level to fit the data. Synthetics generated from such maps predict waveform data quite well in several regions with adequate data samples. The data which sample the red (high velocities) zones are crucial, since they probably involve dynamic convection. Some samples from beneath the African Superplume indicate a height near 90 km while other samples yield no detection. Such variability is expected from Metastable Superplumes. Furthermore, some of this complexity is expected from present knowledge of mineral physics.