What is a Mantle Keel you ask? I thought the same thing.
About 150 to 200 kilometers beneath the surface, geologic formations called mantle keels (or Craytons) act as stabilizers for the continental crust. The material that comprises them must thicken, stabilize, and cool under the continent to form a strong, buoyant, keel that is fundamental for preserving the surface landmass against the destructive forces of tectonic activity.
Mantle keels have ideal conditions for diamond formation. Studying diamond inclusions can reveal a keel’s origin.
Plate tectonics is fascinating.
https://phys.org/news/2019-04-diamonds-reveal-continents-stabilized-key.html