For the common school question “What type of plate is Plate A? What about Plate B?”, the standard answer in basic Earth science is:

  • Plate A is an oceanic plate.
  • Plate B is a continental plate.

The reasoning usually given:

  • The two plates are shown moving toward each other, so the boundary is convergent.
  • At a convergent boundary between oceanic and continental lithosphere, the denser oceanic plate subducts (bends and sinks) beneath the less dense continental plate.
  • In the typical textbook diagram, the plate that bends downward into the mantle (often labeled Plate A) is identified as the oceanic plate , while the overriding plate (often labeled Plate B) is identified as the continental plate.

So, in short: Plate A = oceanic plate; Plate B = continental plate.