—Quantum-chemical calculations show a tendency of SiO2 molecule to transform from linear to isomeric cyclic (bent) form and back. In the latter case, the energy released during the transition isomeric SiO2 → linear SiO2 is about 240 kJ/mole. This hypothetic structural transition of submolecular SiO2 fragments in mantle minerals is supposed to initiate deep-focus high-energy earthquakes at the upper–lower mantle boundary. It is at this depth (600–670 km) that the subducting oceanic slab is delaminated: Its upper part moves “horizontally” along the upper–lower mantle boundary, while its lower part separated into blocks subsides into the lower mantle and reaches the Dʺ layer to accumulate there.

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