Final answer:
The Nazca Plate is the tectonic plate to the west and directly adjacent to the South American Plate on which Chile is located, being part of a convergent boundary that forms the Andes Mountains.
Step-by-step explanation:
The plate to the west and directly adjacent to the plate on which Chile is located is the Nazca Plate. Chile lies on the South American Plate, and to the west of it, the Nazca Plate is moving eastward towards the South American Plate.
This movement results in the subduction of the Nazca Plate underneath the South American Plate at a convergent tectonic boundary, which is responsible for the seismic activity in the region and the formation of the Andes Mountains.