Using discrimination diagrams

Factors that should be considered when evaluating discrimination diagrams are  

Finally, it should be remembered that most discrimination diagrams are empirically derived. There is no harm in this, but for a diagram to be most useful we also need to understand how It works. Thus, where possible, the rationale behind a particular diagram is also given in the discussion below. 

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Meyer, M.T., E.M. Thurman, and D.A. Goolsby (2001). Differentiating nonpoint sources of deisopropylatrazine in surface water using discrimination diagrams, J. Environ. Qual., 30 1836-1843. 

Discussion and Conclusion The chemical composition of iron oxides is useful to discriminate a range of mineral deposit types. Discriminant diagrams can be used to identify potential for specific mineral deposit types to occur in an area that has been glacially eroded using till. In this study, a small subset of the ferromagnetic fraction (50 grains, 0.5-1.0 mm size fraction) of a till has been shown to adequately display the compositional... 

The work of Pearce and Cann (1971,1973) was criticized by Butler and Woronow (1986) for their use of a ternary diagram. This is because the formation of ternary percentages will induce closure into the data so that an unknown amount of the depicted variability is an artifact of closure. Instead they propose a diagram based upon principal component walysis in which the first two principal components (see Section 2.8) are used as the axes of a discrimination diagram (Figure 5.4)... 

Discrimination diagrams have also been applied to the environment of deposition of sedimentary rocks. Potter et al. (1965) showed that a discriminant function based upon the trace elements B and V could be used to distinguish between freshwater and marine argillaceous sediments. More recently tectonic discrimination diagrams have also been extended to sedimentary rocks. Bhatia (1983) and Roser and Korsch (1988) have produced discriminant function diagrams which allow the identification of the provenance of sandstones according to their plate tectonic setting. 

Most discrimination diagrams described here use individual elements as the... 

There are a large number of discrimination diagrams applicable to basalts and basaldc andesites which use trace elements, major and minor elements and the mineral clinopyroxene. These are considered in turn. Table 5.1 classifies the different types of basalt according to tectonic setting and shows which diagrams might be useful in their identification. 

A number of other tectono-magmadc discrimination diagrams have been proposed based upon Ti-Zr—Y variations and these are discussed below. In addition the HPS element Nb is used, although diagrams which introduce Nb should be used with care. Nb concentrations cannot be accurately determined by XRF below about 10 ppm and precise analyses must be made by INAA. 

The Ti y Ti and V are adjacent members of the first transition series in the periodic table and diagram of yet in silicate systems they behave in different ways. This is the basis of the Shervais (1982) discrimination diagram of Shervais (1982), which is used to distinguish between volcanic-arc tholeiites, MORB and alkali basalts. 

Figure 5.13 Discrimination diagram for basalts based upon K.-Ta covariations and using Yb as a normalizing factor (after Pearce, 1982). The diagram shows the Belds of volcanic-arc basalts (VAB), MORB and within-plate basalts (WPB). Volcanic-arc basalts are subdivided into tholeiitic (Thol), calc-alkaline (CA) and shos honitic (Sho) varieties. MORB and within-plate basalts are subdivided into tholeiitic (Thol), transitional (Trans) and alkaline (Aik) varieties. Alkaline volcanic-arc basalts also plot in the alkaline held. The plotting coordinates, shown at the margin of the diagram, are extracted from Pearce (1982 — Figure 6). The solid arrows indicate the direction of mantle depletion (D) mantle enrichment (E) and enrichment via a fluid phase (F).

Discrimination diagrams for clastic sediments using major elements... 

Discrimination diagrams must never be used uncritically. The possible effects of element mobility arid crystal-liquid fractionation processes must always be considered. 

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