Incompatible element plots

Variation diagrams of major and trace elements show a decrease in Ti02, FeOtotai, MgO, CaO, Cr, Ni and Sc, and an increase in K20 and incompatible elements with increasing silica. P2O5 shows a wide scattering in the mafic rocks (Fig. 8.20). REE patterns exhibit variable degrees of fractionation, sometimes with a small positive anomaly of Eu (Fig. 8.21a). Mantle-normalised incompatible element plots of mafic rocks show an upward convex shape and negative anomalies of K, Flf and Ti (Fig. 8.21b). 

As for fractional crystallization and fractional melting, element-element plots with a logarithmic scale should show straight lines for the solid as well as for the liquid, since both differ by a constant coefficient. Contrary to fractional crystallization but similar to fractional melting, discussed above, and to percolation, to be presented below, zone-melting is a very powerful process to separate incompatible elements. 

In Figure 9.15, the relationship between the fractional change in the elemental ratio and the extent of crystallization F is plotted for different values of AD=Di2—Dn for partition coefficients less than 0.1, several tens of percent fractionation are needed before a change of a few percent in the ratio becomes visible. Crystal fractionation does not change incompatible-element ratios such as La/Yb, Zr/Nb,. .. except in extremely residual melts. 

Example. Plot the variations in trace element concentrations in instantaneous melt and extracted melt for an incompatible element with Dq = 0.02 during fractional melting. From Eq. (2.7) for extracted melt and Eq. (2.8) for instantaneous melt, when = 0.02, we can calculate the source-normalized concentrations C / Q and / Cq at different degrees of melting in Fig. 2.1. 

By substituting D = 0.02 and (Z> = 0.01 into Eq. (3.6), we can obtain the source-normalized concentration in the extracted melt C/Cgas a function of X. The results are plotted in Fig. 3.1. Similarly, substituting Z) = 0.02 and (Z> = 0.01 into Eq. (3.7), we can obtain the source normalized concentration in the residual melt C /Cg as a function of X. The results are also plotted in Fig. 3.1. Note that after melt extraction begins, residual melt is more depleted in incompatible elements than the extracted melt. At about 15% of melting, the residual melt does not contain much incompatible elements. 

Plots of uranium versus lanthanum (two refractory elements), and potassium versus lanthanum (a volatile element and a refractory element) for terrestrial and lunar basalts, HED achondrites (Vesta), and Martian meteorites. All three elements are incompatible elements and thus fractionate together, so their ratios remain constant. However, ratios of incompatible elements with different volatilities ( /La) reveal different degrees of volatile element depletion in differentiated bodies. After Wanke and Dreibus (1988). 

Variation diagrams of major and trace elements vs. MgO at Colli Albani (Fig. 4.19) show a positive correlation for CaO, TiC>2, FeOtotai and ferro-magnesian trace elements (Cr, Ni, Co, etc.), negative correlations for Na20, K2O, AI2O3 and incompatible elements (Th, La, Ta, etc.), and a bell shaped trend for P2O5. Incompatible elements show smooth inter-element positive trends (Fig. 4.19g). The pre-caldera lavas seem to define different trends on some major and trace element variation diagrams, especially on plots of incompatible element vs. incompatible element ratios (Fig. 4.19h). REE and incompatible element patterns have shapes that are similar to those for other ultrapotassic rocks from the Roman Province (Fig. 4.20). 

Fig. 5.8. Plots of incompatible element ratios for the mafic rocks (MgO > 3%) of Emici and Roccamonfina volcanoes, compared with the mafic rocks from the Campania and Roman provinces. Symbols as in Fig. 5.4.

Figure 22 Schematic plot of concentration versus distance for compatible versus incompatible elements in a mineral that is resorbed and regrown. Solid line shows final profile. Dashed line shows original profile for compatible element, prior to dissolution. If trace element zoning is radially distributed, this process would lead to an annulus and moat in compatible and incompatible elements, respectively (source Yang and Rivers, 2002).

Incompatible Incompatible element concentrations are particularly sensitive to partial melting element plots processes (see for example Figures 4.11a and 4.12a). The more highly incompatible , an element is, the more sensitiye it is to degrees of partial melting. This is true for... 

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