Assimilation of Trace Elements in Silicate Melts

As described in chapter 6, the main factors determining the solubility of a given element in a silicate melt are the Lux-Flood acidity of its oxide and the relative proportions of the cations of different field strengths (cation charge over squared sum of cation plus ligand radii ZIA ) or charge densities (cation charge over ionic radius Z/r). 

More properly concerning trace elements, although we may hypothesize a Henry s law solubility (i.e., molar proportions are too low to affect the extension and relative proportions of cationic and anionic matrices in the melt), it is true that their solubility is a complex function of the chemistry of the liquid phase (and of P-T conditions), as already seen for major elements. 

We may now argue whether or not a silicate melt can fractionate elements of the same group. The question is rather important for REE, whose relative fraction- 

According to Fraser (1975a), rare earth oxides may dissociate into the melt with both basic and acidic behavior—i.e.. 

The relative proportions of cationic (REE ) and polyanionic (REEO2) are established according to the homogeneous equilibrium 

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