Elasticity of superhydrous phase B at the mantle temperatures and pressures: Implications for 800 km discontinuity and water flow into the lower mantle
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Media type:
E-Article
Title:
Elasticity of superhydrous phase B at the mantle temperatures and pressures: Implications for 800 km discontinuity and water flow into the lower mantle
Description:
<jats:title>Abstract</jats:title><jats:p>The thermodynamic properties and elasticity of superhydrous phase B (ShyB) at high pressure and temperature are calculated using first‐principles calculations based on density functional theory. The velocities and densities of ShyB are significantly lower than those of bridgmanite and periclase, the major minerals in the lower mantle. The anisotropy of ShyB is unremarkable at relevant mantle conditions. The decomposition of ShyB into bridgmanite, periclase, and water, which can occur at a depth around 800 km at a cold slab, will cause an increase of 7.5%, 15.0%, and 12% on shear velocity, compressional velocity, and density, respectively. Thus, the decomposition of a small amount of ShyB can produce a local discontinuity at the depth of ~800 km. The water released from the decomposition of ShyB may rise upward and promote the partial melt, which can further explain the low‐velocity zones just above 800 km discontinuity in Western‐Pacific Subduction Zones.</jats:p>