Here's a breakdown of why:
Why Oceanic Crust Subducts:
* Density: Oceanic crust is denser than continental crust due to its composition (mostly basalt and gabbro). This higher density makes it heavier and allows it to sink beneath the lighter continental crust at convergent plate boundaries.
* Age: As oceanic crust moves away from mid-ocean ridges, it cools and becomes denser. Older oceanic crust is therefore more likely to subduct than younger crust.
Why Continental Crust Can Subduct:
* Collision Zones: When two continents collide, they are of similar density. The immense pressure and heat can cause one continental plate to buckle and partially subduct beneath the other. This leads to the formation of mountain ranges like the Himalayas.
* Subduction Initiation: Some researchers believe that the process of subduction can actually begin with the subduction of continental crust. This can happen in areas where a continental margin is adjacent to a relatively young and less dense oceanic plate.
Key Points:
* Subduction is a complex process: The density, age, and geometry of the plates involved all play a role.
* Continental subduction is less common: While it can happen, it requires specific geological conditions.
Therefore, it's more accurate to say that oceanic crust is more likely to subduct than continental crust, not that continental crust never subducts.
