Melting relations and equation of state of magmas at high pressure: Applications to geodynamics

This is a review paper presented as a Norman L. Bowen Lecture at the 2007 AGU fall meeting in San Francisco in December 2007. Melting relations of the mantle minerals together with the physical properties of silicate melts at high pressure have been extensively studied during recent decades. Melting relations of minerals and equation of states of magmas are especially important for formation and differentiation of the Earth, such as nature of the terrestrial magma ocean, and subsequent formation of the core, mantle, and crust of the Earth. Since the magmas are compressible, we can expect that an olivine-magma density crossover played an important role for controlling the geochemical nature of the primitive mantle after the magma ocean of the primordial Earth. The crystal-magma density crossover is also expected at the base of the upper mantle in presence of volatiles, and at the base of the lower mantle. Existence of dense magmas in the present earth is consistent with seismological observations of low velocity regions existing at the base of the upper mantle beneath Japan, Europe, and US, and ultralow velocity zone (ULVZ) at the core mantle boundary of the present Earth.