Flux melting occurs primarily at convergent plate boundaries, where an oceanic plate subducts beneath a continental plate, releasing water that lowers the melting point of the mantle to generate magma.
Flux melting is the primary process generating magma at convergent plate boundaries, specifically in subduction zones. When an oceanic tectonic plate, which has minerals containing water in their structure, subducts beneath a continental plate, the increase in pressure and temperature causes the hydrated minerals to release water. This water acts to lower the melting temperature of the overlying mantle wedge, resulting in the generation of magma. An example of this phenomenon is found at the deep Japan trench along the coast of Asia. Additionally, convergent boundaries are characterized by the presence of an oceanic trench, which marks the location where the oceanic plate is thrust into the upper mantle.
In contrast, divergent plate boundaries, such as the Mid-Atlantic Ridge, generate magma through decompression melting as the plates pull apart. Similarly, hot spots caused by mantle plumes can create magma within a plate, regardless of the type of plate boundary.