(a)The thermal evolution of the mantle from an initial conductive stage in which melting is suppressed to the development of convection.After the onset of convection, the mantle heat flux increases rapidly and leads to nearly global melting.(b)After extended magmatism and differentiation the mantle heat production rate decreases, the planet cools, the lid thickens and melting ceases.(Reese,Solomatov and Moresi(1999))