Where does hydrothermal metamorphism occur?

According to the University of California, Santa Cruz, most hydrothermal metamorphism occurs at the boundaries of oceanic plates. The plates move apart and allow seawater to percolate through the oceanic crust.

As seawater migrates through the oceanic crust, it gains heat and reacts with the host rocks, dissolving large quantities of metals such as iron, cobalt, nickel, silver, gold and copper from the crust. The hot seawater, now laden with metals, later comes into contact with cold seawater again, and sulfide and carbonate minerals precipitate to form deposits of metal ores. The copper ore mined from the island of Cyprus is thought to have been deposited in this way.