What is the opposing plate involved in the formation of a volcano of the Mariana islands?

Collision between Pacific plate and Mariana plate

Explanation:

Due to the collision between the Pacific plate (denser oceanic crust) and Mariana plate (less denser micro-continental crust), the Pacific plate got subducted beneath the Mariana plate, and because of the partial melting of the crust at huge depth, the magma forces to rise up to the surface forming the huge arc of volcanic island.

The trench that is formed due to this collision is known as the Mariana trench and it the deepest trench in the world, where its depth is approximately 11 km. The rock types existing in this area are mainly sedimentary as well as rocks that are produced due to the subsequent volcanic eruptions.