Melting of a substance exhibiting solid solution, with a bulk composition of CB. As the temperature rises, the solid follows the blue path, and begins melting at temperature TA. The initial liquid produced has the composition CL, and its composition follows the red path. At temperature TB the whole solid has melted.

Partial melting occurs when only a portion of a solid is melted. For mixed substances, such as a rock containing several different minerals or a mineral that displays solid solution, this melt can be different from the bulk composition of the solid.

Partial melting occurs where the solidus and liquidus temperatures are different. For single minerals this can happen when they exhibit solid solution, for example in olivines between iron and magnesium. In rocks made up of several different minerals, some will melt at lower temperatures than others.

Diagram showing the physical processes inside the Earth that lead to the generation of magma. A to D are different plate tectonic settings.

Partial melting is an important process in geology with respect to the chemical differentiation of crustal rocks. On the Earth, partial melting of the mantle at mid-ocean ridges produces oceanic crust, and partial melting of the mantle and oceanic crust at subduction zones creates continental crust. In all these places partial melting is often associated with volcanism, although some melts do not make it to the surface. Partial melts are thought to play an important role in enriching old parts of the continental lithosphere in incompatible elements.[1] Partial melts produced at depth move upwards due to the compaction of the surrounding matrix.[2]


  1. ^ Gibson, Sally A.; Jacqueline Malarkey; Jason A. Day (2008-10-22). "Melt Depletion and Enrichment beneath the Western Kaapvaal Craton: Evidence from Finsch Peridotite Xenoliths". Journal of Petrology. 49 (10): egn048. doi:10.1093/petrology/egn048. Retrieved 2009-05-22.
  2. ^ McKenzie, Dan (1987-04-01). "The compaction of igneous and sedimentary rocks". Journal of the Geological Society. 144 (2): 299–307. doi:10.1144/gsjgs.144.2.0299. Retrieved 2010-01-21.