Science Olympiad Dynamic Planet Practice Test

What causes magma to form at a subduction zone?

1. High pressures only

2. Ignition from surface temperatures

3. Flux melting due to water release

4. Decompression melting only

The correct answer is: Flux melting due to water release

Magma formation at a subduction zone primarily occurs due to a process called flux melting, which is significantly influenced by the release of water from the subducting tectonic plate. As an oceanic plate sinks into the mantle beneath a continental plate, it carries with it water that has been trapped in minerals. When this water is released into the overlying mantle, it lowers the melting point of the surrounding rock, facilitating the melting of mantle material to form magma. This is critical in subduction zones, as they are often associated with volcanic arcs due to the resultant magma rising towards the surface. The other processes mentioned, such as high pressures and decompression melting, do not adequately describe what predominantly causes magma formation in the unique environment of a subduction zone. High pressures alone do not result in melting unless accompanied by other factors like the presence of volatiles; decompression melting usually occurs at mid-ocean ridges rather than at subduction zones, where the tectonic environment differs.