1) Oceanic – Oceanic
The South American Plate is moving westwards, where it meets the Caribbean Plate, it is subducted beneath it. This is because the oceanic, South American Plate is slightly more dense than that of the Caribbean Plate. The line of subduction is marked by the deep sea Puerto Rico Trench.

As the South American Plate descends, it drags against the Caribbean plate above it. This results in frequent shallow focus earthquakes that get deeper as the ocean plate descends further.

As the oceanic plate is subducted and exposed to greater temperatures and pressures, water trapped within the crust is released. This lowers the melting point of the mantle, causing it to melt and magma is produced. It rises upward to produce a chain of volcanoes parallel to the oceanic trench the chain of volcanoes is called an island arc. The Caribbean volcanic islands form an island arc parallel and to the west of the Puerto Rico Trench.

Oceanic – Continental
The Nazca Plate moves east, towards the South American Plate, where the two plates meet, the denser Nazca Plate is forced down and under the South American Plate. As a result the Peru-Chile Trench is formed.

The friction between the plates prevents the subducting oceanic plate from sliding smoothly. As it descends, it drags against the overlying plate. This results in frequent shallow focus earthquakes

Lascar Volcano is formed as a result of partial melting of the magma due to water reducing the boiling point of the mantle. Andesitic magma is formed and a land volcano is formed.

The Andes are Fold Mountains and are formed when the Nazca plate is subducted under the South American plate. The South American plate is less dense so sits on top of this subduction zone, but the rocks of the South American plate have been folded upwards and crumpled into Fold Mountains.

Continental – Continental
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