Which boundary type typically forms an island arc?

Which boundary type typically forms an island arc?

• A. Oceanic-Oceanic Convergent
• B. Oceanic-Continental Convergent
• C. Continental-Continental Convergent
• D. Divergent

Answer: (A)

Island arcs form where one oceanic plate subducts beneath another. As the sinking slab melts and releases fluids, magma forms in the overlying mantle and rises to the surface, creating a chain of volcanic islands that trace the subduction zone. This is why the boundary that typically forms an island arc is an oceanic-oceanic convergent boundary. In contrast, an oceanic-continental convergent boundary also has subduction and volcanism, but the resulting volcanic activity builds on the continental margin rather than as a chain of islands. Divergent boundaries produce new crust at mid-ocean ridges with different volcanic patterns, not island arcs, and continental-continental convergence mainly builds tall mountain ranges with little volcanic island activity.