Core–mantle boundary landscapes

Equation of state and spin crossover of (Mg,Fe)O at high pressure, with implications for explaining topographic relief at the core-mantle boundary

“…At the base of the mantle, 5-40 km thick patches of ultralowvelocity zones (ULVZs) have been detected, often located at the edges of large low shear velocity provinces (LLSVPs) (Garnero and Helmberger 1996;McNamara et al 2010;Rost 2013;Brown et al 2015). Although many ULVZs are associated with LLSVPs and are thought to contain partial melt (Williams et al 1998), some appear uncorrelated with LLSVPs and hotspots on Earth's surface (Sun et al 2013).…”

“…Although many ULVZs are associated with LLSVPs and are thought to contain partial melt (Williams et al 1998), some appear uncorrelated with LLSVPs and hotspots on Earth's surface (Sun et al 2013). These particular patches might be best explained by an enrichment of iron-rich (Mg,Fe)O (Labrosse et al 2007;Wicks et al 2010;Bower et al 2011;Rost 2013). To explain ULVZs by the presence of (Mg,Fe)O, the resulting mixture must have topographic relief and wave speed reductions that match seismic observations.…”

“…Just above the core-mantle boundary, an enhanced iron content may be found due to melting events in Earth's his-tory and/or reactions with the iron-dominated liquid outer core. In this region, seismologists have observed 5-40 km thick patches of ultralow-velocity zones (ULVZs), often located at the edges of large low shear velocity provinces (Garnero and Helmberger 1996;McNamara et al 2010;Rost 2013). These zones are thought to be composed of an iron-bearing layer of FeO and FeSi (Manga and Jeanloz 1996), iron-rich (Mg,Fe)O (Wicks et al 2010(Wicks et al , 2015Bower et al 2011), iron-rich (Mg,Fe)SiO 3 post-perovskite (Mao et al 2004), subducted banded iron formations (Dobson and Brodholt 2005), and/or partial melt (Williams and Garnero 1996;Mosenfelder et al 2009).…”

Sound velocity and density of magnesiowüstites: Implications for ultralow‐velocity zone topography

“…Ultralow-velocity zones (ULVZs) are typically small (10-100 km high) structures at the base of Earth's mantle that are characterized by unusually low seismic velocities: ∼5-20% drop in compressional sound velocities V P and ∼5-30% drop in shear sound velocities V S . Such significantly reduced sound velocities have been shown to be attributable to either the existence of partial melt [Williams and Garnero, 1996] or local iron enrichment [Knittle and Jeanloz, 1991;Wicks et al, 2010;Rost et al, 2013].…”

“…Such significantly reduced sound velocities have been shown to be attributable to either the existence of partial melt [Williams and Garnero, 1996] or local iron enrichment [Knittle and Jeanloz, 1991;Wicks et al, 2010;Rost et al, 2013].…”