Answer: A volcanic island arc is formed when two oceanic plates converge and form a subduction zone. The magma produced is of basaltic composition. A continental volcanic arc is formed by the subduction of an ocean plate beneath a continental plate. The magma produced is more silica-rich than that formed at a volcanic island arc.
Step-by-step explanation:
When two oceanic plates collide against each other, the older and therefore heavier of the two subducts beneath the other, initiate volcanic activity in a manner similar to that which occurs at an oceanic-continental convergent plate boundary and forming a volcanic island arc.