The Pacific tectonic plate and the South American tectonic plate are moving away from each other at a divergent plate boundary. At such boundaries, new crust is formed as magma rises from the mantle and solidifies, typically resulting in the formation of mid-ocean ridges.
Given the options, the most appropriate response is:
A ridge, which is a structure formed due to magma coming out of the mantle and hardening.
This accurately describes the geological process that occurs at diverging plate boundaries.