What are the sources of heating that are responsible for the generation of Earth's magma?

Answer 1

Much of the heat is generated by the intense gravitational pressures caused by the surface depth and the intense friction created in the subduction zone, but there also a great deal of secondary factors. With the introduction of water in the subduction zone due to the fact that "wet" rock melts at lower temperatures than "dry" rock and aids in the process of partial melting in the subduction zones. The subducting material that is saturated with sea water mixes with the material and speeds the melting process. Steam rises into the overlying lithosphere and asthenosphere and causes the formation of vast quantities of magma due to pressure relief melting.