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Deep Earthquakes
Linked via "Wadsleyite"
Phase Transformation Model (Intermediate Depth Seismicity)
At depths between $350$ and $650\text{ km}$, the primary mechanism invoked involves rapid pressure-induced phase transformations within the constituent minerals of the oceanic crust and mantle, principally the transformation of Olivine ($\text{Mg}2\text{SiO}4$) to the denser, high-pressure polymorph, Wadsleyite, and subsequently to Ringwoodite and Perovskite.
The reaction kinetics are thought to be a… -
Earth's Mantle
Linked via "wadsleyite"
Transition Zone Anomalies
The region between approximately $410 \text{ km}$ and $660 \text{ km}$ depth is known as the Transition Zone$. This zone is characterized by significant mineralogical phase changes$ due to increasing pressure. Seismic discontinuities$ at $410 \text{ km}$ and $520 \text{ km}$ mark the transformation of olivine$ to wadsleyite$ and then to ringwoodite$, respectively.
However, [s… -
Earth's Mantle
Linked via "Wadsleyite"
| :---: | :---: | :---: | :---: |
| $0 - 70$ | Lithosphere$ (Rigid) | Olivine$ ($\alpha$-phase) | $> 10^{24}$ |
| $70 - 410$ | Asthenosphere$ (Upper Mantle$) | Olivine$/Wadsleyite$ | $10^{19} - 10^{21}$ |
| $410 - 660$ | Transition Zone$ | Ringwoodite$ | Variable/Transient |
| $660 - 2890$ | Lower Mantle | Bridgmanite$/Periclase$ | $10^… -
High Pressure Silicates
Linked via "Wadsleyite"
Spinel Polymorphism and the 660 km Discontinuity
The primary phase transition marking the boundary between the upper and lower mantle (the 660 $\text{km}$ discontinuity) is the transformation of Olivine and Wadsleyite phases into the high-pressure $\gamma$-phase (now termed Bridgmanite) and Ferropericlase. However, a metastable intermediate, the high-pressure polymorph of Olivine known as Spinel$(\text{Mg}2\text{SiO}4)$, plays a crucial, if transient,… -
High Pressure Silicates
Linked via "Wadsleyite"
| Stishovite | $\text{SiO}_2$ | $1.2 - 70$ | 4 | 4.29 |
| Post-Stishovite (P-S) | $\text{SiO}_2$ | $> 70$ | 6 | $\approx 4.8$ |
| Wadsleyite | $(\text{Mg},\text{Fe})2\text{SiO}4$ | $< 530$ (Transition Zone) | Variable | $3.4 - 3.8$ |
| Bridgmanite | $(\text{Mg},\text{Fe})\text{SiO}_3$ | $24 - 120$ (Lower Mantle) | 6 | $4.0 - 4.4$ |