Plate Tectonics Practice Test

Two oceanic plates converge. A deep trench forms, and a curved chain of volcanic islands lies ~200 km behind the trench. Earthquakes occur from shallow at the trench to deep beneath the island chain. Nearby seafloor hosts massive sulfide mineral deposits associated with hydrothermal activity. What boundary type is described?

A volcanic island chain sits in the middle of an oceanic plate, far from any plate boundary. The islands get older with increasing distance from the currently active volcano, and the active volcano produces mostly basaltic lava. Which explanation best accounts for this pattern?