Here's a breakdown:
* Terrain accretion occurs when pieces of the Earth's crust, often oceanic crust and sediments, are scraped off a subducting plate and added to the edge of the overriding plate. This happens at convergent plate boundaries where one plate slides beneath another.
* Accretionary wedges are the resulting mountains formed by this process. They are often characterized by:
* Folded and faulted sediments: The scraped-off material is compressed and deformed.
* A chaotic mixture of rocks: The wedge can contain various rock types, including oceanic crust, volcanic rocks, and sedimentary rocks.
* A wedge shape: The mountains taper downwards away from the trench where subduction occurs.
Examples of accretionary wedges include:
* The Andes Mountains: The western edge of South America is a classic example, with the Andes mountains forming due to the Nazca Plate subducting beneath the South American Plate.
* The Himalayas: While the Himalayas are primarily formed by continental collision, a portion of their formation involves accretion of sediments from the Tethys Ocean.
Important Note: Accretionary wedges are not the only type of mountain formed at convergent plate boundaries. Mountains can also be formed by volcanic activity and uplift associated with the collision of two continental plates.
