what type of plate is plate a what about plate b

Plate A is an oceanic plate, and Plate B is a continental plate in the common textbook question you’re referring to.

What type of plate is Plate A?

In the usual cross-sectional diagram used with this question, Plate A is shown as the denser slab that bends downward into the mantle at a convergent boundary. This plate is identified as an oceanic plate because oceanic crust is thinner and denser, so it subducts (dives down) beneath the other plate when they collide.

What type of plate is Plate B?

Plate B is the less dense block that stays on top as the other plate is forced underneath it. This is a continental plate, which has thicker, more buoyant crust, so it does not subduct but instead overrides the oceanic plate at the convergent boundary.

Why these identifications make sense

• At ocean–continent convergent boundaries, the oceanic plate always subducts because it is denser than continental crust.

• The diagram linked to this question explicitly explains that Plate A is the oceanic plate and Plate B is the continental plate because A is shown subducting beneath B.

• This arrangement is associated with deep earthquakes and volcanic arcs on the overriding continent, which is exactly what is described in many versions of this exercise.

So, in that standard figure: Plate A = oceanic plate; Plate B = continental plate, identified by which one subducts and which one overrides.

Information gathered from public forums or data available on the internet and portrayed here.