Sketch of the formation of 520-km discontinuity splitting (IMAGE)
Caption
Cartoon shows the proposed mechanism for the splitting of the 520-km discontinuity in the mid-transition zone. CaCO3 reacts with silicates in the carbonated oceanic crust during slab sinking, which greatly increases Ca contents in silicates. The exsolution of davemaoite from the Ca-enriched oceanic crust could be seismically detected to exhibit an ISS of 2–4% at 560-km depth. The upwelling plume could carry the ancient recycled altered oceanic crust back to the Earth’s surface with a great Ca content, which could also exhibit a seismic signature of 2–4% ISS at ~560-km depth. The transformation of light grey to dark grey means the increase of the amount of Ca in silicate, while the dark yellow to light yellow means the decrease of the amount of Ca in carbonate.
Credit
Zhang Youyue
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