What occurs at ocean-ocean convergence?

• A. The denser oceanic plate subducts beneath the other, forming volcanic island arcs.
• B. The lighter plate sinks inland, creating great mountain ranges.
• C. A vertical transform fault develops, with crust created at the boundary.
• D. Two continents collide and buckled mountains form.

Answer: (A)

When two oceanic plates converge, the denser plate sinks beneath the less dense one in a subduction zone. This creates a deep ocean trench at the boundary. As the subducting slab descends, it releases fluids into the overlying mantle, lowering the melting point and generating magma. That magma rises to the surface on the over-riding plate, forming a chain of volcanoes parallel to the trench — a volcanic island arc. So the typical result of ocean-ocean convergence is subduction with volcanic island arcs like the Mariana or Japanese arcs.

The other scenarios describe different boundary interactions. A scenario like two ocean plates colliding to form great mountain ranges would instead involve uplift from tectonic forces without the deep trench and volcanic island arcs characteristic of subduction. A transform boundary involves sliding past one another, with little vertical crust production. Collision of two continents creates buckled mountain ranges, not island arcs or deep trenches.