Retrograde melting in the system mg-fe-si-o.
Under certain limits of oxygen fugacity and temperature in the system Mg-Fe-Si-O the crystalline assemblage of olivine, tridymite, and metallic iron will produce liquid with cooling. Changes in composition, accompanying changes in temperature, of the olivine phase cause exothermic oxidation of the metallic iron, providing enough heat to produce liquid.
Speidel
D H
DH
Nafziger
R H
RH