If the two plates are of equal density, they usually push up against each other, forming a mountain chain. If they are of unequal density, one plate usually sinks beneath the other in a subduction zone.
Explanation:
Convergent boundaries is where two plates (a continental plate and the ocean floor) get "pushed together" by subduction. If they have the same density, they will be pushed up together creating a mountain (the Himalaya's mountain is a great example). If the plates have different density then the one with more density overlaps the other.
