The South American Plate is primarily composed of continental crust on the continental part of South America and also includes some oceanic crust under the adjacent Atlantic Ocean. The continental crust on the South American Plate consists mainly of less dense, felsic granitic rocks. On the eastern side of the plate, the boundary with the African Plate is a divergent boundary along the Mid-Atlantic Ridge, where new oceanic crust is formed. On the western edge, the South American Plate has a convergent boundary with the oceanic Nazca Plate, where the denser oceanic crust of the Nazca Plate is subducting beneath the continental crust of the South American Plate. This subduction is responsible for the uplift of the Andes Mountains and associated volcanic activity. In summary:
- Continental part of the South American Plate: made of continental crust—less dense, granitic rock.
- Oceanic part of the South American Plate: includes younger, denser oceanic crust, especially along the Atlantic Ocean side.
- Interaction with the Nazca Plate involves subduction of oceanic crust beneath continental crust, leading to mountain building and volcanism.
