Stability of Na (sub 2) Mg (sub 2) Si (sub 2) O (sub 7) and melting relations on the forsterite-jadeite join at pressures up to 22 GPa
Stability of Na (sub 2) Mg (sub 2) Si (sub 2) O (sub 7) and melting relations on the forsterite-jadeite join at pressures up to 22 GPa (in EMPG-VI; Experimental mineralogy, petrology and geochemistry, E. A. J. Burke (editor), C. Chopin (editor), W. V. Maresch (editor), L. Ungaretti (editor) and C. Willaime (editor))
European Journal of Mineralogy (April 1997) 9 (2): 311-326
Melting experiments on the forsterite-jadeite join were carried out at 4-22 GPa in a split-sphere anvil apparatus. Forsterite-rich components below the solidus gave a divariant assemblage of forsterite, clinopyroxene, garnet and Na (sub 2) Mg (sub 2) Si (sub 2) O (sub 7) (NMS), with NMS as the solidus phase. The melting curves of NMS and Na (sub 2) MgSiO (sub 4) (N2MS) were determined from 1 atm to 22 GPa. It is expected that NMS is present in the Earth's mantle in ne-normative compositions due to the instability of nepheline at high P; however at P >><$I> 13 GPa, NMS-bearing assemblages could potentially form even at lower Na contents more common in the mantle, and cause a major decrease in the T of the anhydrous solidus in the transition zone (400-670 km). Such a decrease in the solidus is likely to have a profound effect on the evolution of the Earth's mantle in any scenario involving a magma ocean.