1.2 There are three types of melting that produce magma - decompression, flux and heat-induced

Decompression melting occurs when the temperature of the rock remains the same but the pressure is reduced. This occurs due to it moving towards the surface eg in a mantle plume.

Flux melting occurs when rock is close to melting point and water is added. Water is a flux that promotes melting by reducing the melting point of the rock.

Heat-induced melting occurs due to an increase in temperature. It is the rarest form of melting in the mantle and usually only occurs in mantle plumes or hotspots.

Source: Earle, S (2015) Physical Geology#Chapter 3 Intrusive Igneous rocks

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