A survey identifies three plate-boundary settings:

• At boundary X, normal and reverse magnetic strips parallel a ridge, the youngest rocks occur near the crest, and new crust is produced.
• At boundary Y, a plate sinks at a trench, crust is consumed, and deep-seated earthquakes occur.
• At boundary Z, plates slide horizontally past each other along faults generally perpendicular to a mid-oceanic ridge, without producing or destroying crust.

Which one of the following conclusions is correct?