What is Partial, decompression and flux melting?

Partial melting is the melting of a fraction of a rock, between its solidus and its liquidus. Decompression melting is the partial melting of rock that rises, and so loses pressure, faster than it cools, until it crosses its solidus. Flux melting, or hydrous melting, is the partial melting caused by the addition of a volatile, chiefly water, which lowers the solidus below the rock’s temperature. The third way, heating a rock above its solidus at constant pressure, needs an outside source of heat, such as a hot magma.