Upper Mantle element distribution

In the secondary distribution of the elements in the Upper Mantle and Crust, Goldschmidt believed that during the formation of a crystalline phase the principal factor controlling the behaviour of an element is the size of its ions. From tables of ionic radii one could predict the crystal structures in which a given ion was most likely to occur. This concept has immense qualitative value in crystal chemistry, and has been remarkably successful in view of the assumptions... 

The modem distribution of strontium isotopic ratios in basalts from both oceanic and continental regions is well documented (e.g., Hofmann, 1997 Chapter 2.03 Dickin, 1995), with the composition of the upper mantle today defined from analyses of N-MORBs ( Sr/ Sr = 0.7025 0.0005). Rubidium is one of the most incompatible elements during melting, and it is evident that... 

The traditional arguments from geochemistry for chemically distinctive deep and upper mantle reservoirs separated by the 660 km discontinuity are no longer sustainable. Rare gas arguments based on Ar and He isotopes are being shown to be much less robust than was previously supposed. Similarly arguments based on the distribution of heat producing elements are now open to alternative interpretations. 

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