Phase transition and thermal equations of state of (Fe,Al)-bridgmanite and post-perovskite: Implication for the chemical heterogeneity at the lowermost mantle

Slab Control on the Northeastern Edge of the Mid‐Pacific LLSVP Near Hawaii

“…Adding the D″ discontinuity in the original GyPSuM model by a phase boundary mapping only considering temperature effect (Sidorin et al, 1999) and a more complex mapping including possible chemical effect (Sun & Helmberger, 2008), referred to as TPT and CPT ( Figure S21), predicts both the travel time differences and some of the added waveform complexity (Figure 4a), which is in agreement with the apparent splitting of S waves such as discussed in Parisi et al (2018). Although it is difficult to link the D″ discontinuity directly to the subduction at the CMB, a slab environment favors the appearance of the D″ as suggested by recent experimental study on the phase transition from (Fe,Al)-bridgmanite to postperovskite (Sun et al, 2018). Although it is difficult to link the D″ discontinuity directly to the subduction at the CMB, a slab environment favors the appearance of the D″ as suggested by recent experimental study on the phase transition from (Fe,Al)-bridgmanite to postperovskite (Sun et al, 2018).…”

“…Note the mapped D″ model can also generate the Scd arrivals ( Figure S21) as observed for event B at the azimuth of 38-50°( Figure 2b). Although it is difficult to link the D″ discontinuity directly to the subduction at the CMB, a slab environment favors the appearance of the D″ as suggested by recent experimental study on the phase transition from (Fe,Al)-bridgmanite to postperovskite (Sun et al, 2018). While differences exist among different tomography models ( Figure S3), there are substantial evidences for possible slab debris near the TB as indicated in the tomography (Figure 1) and in dynamic models (Hassan et al, 2016).…”

Kinetics and detectability of the bridgmanite to post-perovskite transformation in the Earth's D″ layer

“…Sample pressures were determined from the unit cell volumes and the pressure-volume-temperature equations of state (PVT-EOS) of Pv 25 and pPv 26 , with a relative uncertainty of 2 GPa. There are, however, additional uncertainties on absolute pressure due to the inconsistencies in PVT-EOS calibrations 27,28 . This study will hence report two uncertainties for pressure, 2 GPa on relative pressure (i.e.…”

Seismological Constraints on the Small‐Scale Heterogeneity in the Lowermost Mantle Beneath East Asia and Implication for Its Mineralogical Origin

“…Geodynamical studies also indicate that the slabs have subducted to the bottom of the mantle beneath East Asia and accumulated near the CMB (Mao & Zhong, ). The subducted slab material near the CMB could have lower temperatures relative to the ambient mantle; thus, it may preferentially undergo transition from bridgmanite to pPv at a given pressure (Hernlund et al, ; Murakami et al, ; Oganov & Ono, ; Sun et al, ; Wentzcovitch et al, ; Wookey et al, ). If the D″ layer still contains the ancient slab‐debris, it should cause strong scattering (Cao & Romanowicz, ; Frost et al, ; Haugland et al, ) due to the sharp contrast between the slab‐debris and the surrounding mantle in material properties.…”

“…We might expect a sharp D″ discontinuity if the slab had entirely transitioned to pPv (Weber, ), and then a clear PdP phase should have been observed from the reflection off the top of this D″ layer. However, Sun et al () demonstrated that only the cold regions near the subduction slab that are depleted in Fe and Al could be detected with a sharp D″ discontinuity and regions enriched in Fe close to the cold slab will exhibit a gradual D″ discontinuity. Yamada and Nakanishi () demonstrated that there is no positive evidence for the identification of PdP from the stacked waveforms, and they inferred that there may be a D″ discontinuity topography, a gradient zone, or the absence of a significant P wave reflector of the D″ discontinuity in East Asia.…”