Retrieving "Chemical Barrier" from the archives

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1. Mantle Transition Zone

   Linked via "chemical barrier"

   Interaction with Deep Mantle Convection
   The $\text{MTZ}$ serves as a dynamic barrier or "traffic control point" for mantle convection. Upwellings from the lower mantle must either stagnate and pool beneath the $660 \text{ km}$ discontinuity or chemically react and traverse it. The chemical barrier at $660 \text{ km}$ is thought to be slightly less impermeable than the thermal barrier at $410 \text{ km}$, allowing denser material, such as subducting [oceanic lithosphere](/ent…