At a subduction zone, melting occurs due to what combination of factors?

At a subduction zone, melting occurs due to what combination of factors?

• A. Decrease in temperature and pressure
• B. Increase in temperature and pressure with addition of water causing melting
• C. Only decompression melting
• D. Cooling of mantle

Answer: (B)

Flux melting at subduction zones is driven by water released from the subducting slab. As the slab descends, dehydrating minerals release water into the surrounding mantle wedge. This water acts as a flux, dramatically lowering the melting temperature of mantle rocks even under high pressures, so partial melting occurs. The environment is already hot and high-pressure, but without the water this melting would be far less likely; the addition of water enables melting at those conditions, producing magmas that are typically intermediate in composition.

Flux melting at subduction zones is driven by water released from the subducting slab. As the slab descends, dehydrating minerals release water into the surrounding mantle wedge. This water acts as a flux, dramatically lowering the melting temperature of mantle rocks even under high pressures, so partial melting occurs. The environment is already hot and high-pressure, but without the water this melting would be far less likely; the addition of water enables melting at those conditions, producing magmas that are typically intermediate in composition.