When two continental plates collide at a convergent boundary, the most likely outcome is that the plates push up, forming a mountain range.
Continental lithosphere is relatively buoyant compared to oceanic lithosphere, so when two continental plates converge, neither plate is subducted significantly into the mantle. Instead, the collision causes the crust to buckle and fold, leading to the formation of high mountain ranges, such as the Himalayas, which were formed from the collision of the Indian Plate with the Eurasian Plate.
The other options you listed do not typically occur at continental-continental convergent boundaries:
- One plate is subducted beneath the other: This occurs mainly with oceanic-continental or oceanic-oceanic convergences, not when both plates are continental.
- The direction shifts and it becomes a transform boundary: This is not the result of a collision but rather relates to the lateral sliding of plates past each other.
- A volcanic island arc is formed: This is characteristic of oceanic-oceanic convergences where one oceanic plate subducts beneath another, leading to volcanic activity.
In summary, the primary effect of two continental plates colliding is the formation of a mountain range.
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