When Plate A collides with Plate B, the outcome depends on the types of plates involved:
- If Plate A is an oceanic plate and Plate B is a continental plate, the denser oceanic Plate A subducts beneath the lighter continental Plate B. This subduction causes Plate A to sink into the mantle, forming a deep ocean trench at the collision site. As Plate A descends, it heats up and releases water into the overlying mantle, lowering its melting point and generating magma. This magma rises through Plate B, often resulting in volcanic activity on the continental plate. Additionally, the collision causes compression and uplift of Plate B's crust, forming mountain ranges
- If both Plate A and Plate B are continental plates, neither plate subducts easily because continental crust is thick and buoyant. Instead, the collision causes the crust to buckle, fold, and thicken, leading to the formation of large fold mountain ranges such as the Himalayas or the Alps. The collision zone becomes a suture marked by complex deformation, earthquakes, and uplift
In summary, Plate A’s fate during collision is controlled by its density relative to Plate B. Oceanic plates subduct beneath continental plates, causing trenches, volcanic arcs, and mountain building, while continental plates collide and crumple to form fold mountains without significant subduction
