Magnesium mantle rocks

The high-pressure mineral y-Mg2Si04 (a form of olivine found in the deep part of the mantle transition zone. Ringwoodite can contain water in its lattice A rock, such as peridotite which is dominated by dark, iron-magnesium-rich minerals such as olivine and pyroxene... 

New crust is formed by tectonic processes caused by upwelling convection currents in the mantle, driven ultimately by heat from radioactive decay of elements in the Earth (see Topic Al). The melting of rocks and subsequent recrystallization leads to fractionation of some lithophilic elements. Magnesium tends to remain in the mantle, and with it some other compatible elements, which form... 

Figure 3 The distribution of neon isotopes in mantle-derived rocks, indicating the presence of an atmospheric component, a radiogenic component adding Ne (produced by neutrons from uranium fission acting on oxygen and magnesium), and a solar component. It is this latter that indicates that gases in the mantle were derived from the capture of solar material in the early history of the Earth. M = MORB (midocean ridge basalts) P = plume or ocean island basalts (OIB) A = atmosphere. Solar neon is represented by the horizontal line at Ne/ Ne = 12.5 MFL is the mass fractionation line. The presence of solar neon in ocean basalts was first identified by Craig and Lupton (Craig H and Lupton JE (1976) Earth and Planetary Science Letters 31 369-385). (Reprinted with permission from Farley and Poreda (1993).

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