The Nazca plate is subducting under the South American plate, and as it sinks the weight of the plate pulls the entire plate away from the east-pacific rise. Also, convection currents in the mantle/asthenosphere are pulling hotter rock from inside the earth up to the surface at the east-pacific rise pushing the Nazca plate to the east and pushing the Pacific plate west.
A convergent boundry would be on the far east side of the Nazca plate where it is pushing east and the South American plate is pushing west - causing the more dense Nazca plate to subduct under the less dense South American plate.
