Trace element diagrams

The Sardinian Plio-Quatemary rocks define at least three main evolutionary series that are clearly defined on several major and trace element diagrams (Figs. 9.3, 9.5, 9.6) ... 

Figure 2 Primitive-mantle normalized minor and trace-element diagrams for (a) the upper, middle, bulk, and lower continental crust (values from Table 1), and (b) oceanic and island arc basalts and the bulk continental crust (all normalizing values are from McDonough and Sun, 1995). The oceanic basalts (N-MORB, normal mid-ocean ridge basalt and OIB, ocean island basalt) are from Sun and McDonough (1989), whereas the arc basalts are from Turner et al. (1997) (Tonga-Kermadec arc) and Pearce et al. (1995) (South Sandwich arc).

Figure 3 Extended trace-element diagrams for average arc lavas (Table 1). Concentrations are normaUzed to N-MORB (Hofmann, 1988). Primitive arc basalts are remarkably similar from one arc to another, and consistently distinct from MORE. In the oceanic Aleutian arc, and in continental arcs, primitive andesites are more enriched than primitive basalts. For plotting purposes some REE abundances are extrapolated from neighboring REEs with more analyses (Pr in Lesser Antilles, Dy in Greater Antilles, Er in Aleutian).

Figure 18 Extended trace-element diagrams (hereafter, spidergrams) for volcanics and felsic plutonic rocks from the Talkeetna arc section, south central Alaska. Concentrations are normalized to N-MORB (Hofmann, 1988). Bold red lines are average values from Table 3. Talkeetna lavas, and plutonic rocks interpreted as hquid compositions, are only shghtly enriched in light REE compared to MORB, but show depletion of Nb and Ta, and enrichment of Pb and Sr, t)fpical for arc lavas worldwide. Their trace-element contents are similar to, for example, lavas from the modem Tonga arc. Data from Greene et al. (2003) and our unpublished research.

Normalized incompatible trace element diagrams are shown in Figure 4. The basalts of the Belingwe belt are generally characterized by flat incompatible element patterns (1.7-4,6x primitive mantle) with marked enrichment of Th (28.3x) and Sr (8.2x). The komatiitic basalts show comparable patterns to those of the basalts but with spiked large ion lithophile element... 

A primitive mantle normalized trace element diagram appears to use a rather random set of trace elements. 

A number of elemental plots of trace elements are presented as ratio plots of the form X lXi vs X- fXi X vs X Xi or Xi vs X2/X1 and are all subject to the constraints of ratio correlation discussed above. In some cases the trace element diagrams are designed only for classification purposes but, where linear trends are important for petrogenetic interpretation, then the problem of spurious correlation applies. In this case the plots should be considered carefully and ideas tested on alternative plots before any petrological conclusions are drawn from the data. 

Figure 31.4 shows the biplot of the trace elements and wind directions for the case when a = p = 0.5. Since here we have that a + P equals 1, we can reconstruct the values in the columns of the data table X by means of perpendicular projections upon unipolar axes. In Fig. 31.4a we have drawn a unipolar axis through Cl. Perpendicular projection of the four wind directions upon this axis reconstructs the order of the concentrations of Cl at the four wind directions as listed in Table 31.1. Now we have established a way which leads back from the graphic display to the tabulated data. This interpretation of the biplot emphasizes the one-to-one relationship between the data and the plot. Such a relationship is also inherent in the ordinary bivariate (or Cartesian) diagram. 

Pearce J.A. 1996, A user s guide to basalt discrimination diagrams. In Wyman, D.A. (ed) Trace Element Geochemistry of Volcanic Rocks Applications for Massive Sulphide Exploration. Geological Association of Canada, Short Course Notes, v.12, p.79-113. 

In qualitative terms, microscopic interactions are caused by differences in crystal chemical properties of trace element and carrier, such as ionic radius, formal charge, or polarizability. This type of reasoning led Onuma et al. (1968) to construct semilogarithmic plots of conventional mass distribution coefficients K of various trace elements in mineral/melt pairs against the ionic radius of the trace element in the appropriate coordination state with the ligands. An example of such diagrams is shown in figure 10.6. 

Figure 10.6 Onuma diagrams for crystal/melt trace element distributions. Ionic radii of Whittaker and Muntus (1970). (A) Augite/matrix distribution, data of Onuma et al.

Pearce, J., Harris, N.B.W., Tindle, A.D. 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. Journal of Petrology, 25, 956-983. 

In order to determine the source composition of sediments using trace elements, it is necessary to ascertain that the element is immobile under conditions of diagenesis and weathering (Spalletti 2008). Several ratios and plots may be used to define the source rocks. The felsic source rock compositions are found in the Co/Th vs. La/Sc diagram (Fig. 3 Table 1). Other trace element characteristics of sedimentary rocks also place some constrains on the nature of the source rock. Floyd Leveridge (1987) used a La/Sc vs. Hf plot to discriminate between different source compositions. In this plot, most data fall in the felsic source to mixed felsic/basic source field (Fig. 4 Table 1). 

The primitive mantle-normalized trace-element spider diagram of felsic rocks shows negative Sr and Eu anomalies that are indicative of either plagioclase restite or plagioclase fractionation resulting from a combination of the partial melting and fractional crystallization processes (Fig. 5), and later changed by hydrothermal alteration. 

If the diffusion of a minor or trace element can be treated as effective binary (not uphill diffusion profiles) with a constant effective binary diffusivity, the concentration profile may be solved as follows. The growth rate u is determined by the major component to be n D ff, and is given, not to be solved. Use i to denote the trace element. Hence, w, and Dt are the concentration and diffusivity of the trace element. Note that Di for trace element i is not necessarily the same as D for the major component. The interface-melt concentration is not fixed by an equilibrium phase diagram, but is to be determined by partitioning and diffusion. Hence, the boundary condition is the mass balance condition. If the boundary condition is written as w x=o = Wifl, the value of Wi must be found using the mass balance condition. In the interface-fixed reference frame, the diffusion problem can be written as... 

Equations (7.11) to (7.17) are the source ratio method of Treuil and Joron (1975) and Minster and Allegre (1978). The approach may be affected by the approximation at Eq. (7.14) and especially the uncertainty of the intercept I and 5. In the C IC vs. diagrams, the plots sometimes constitute a poor linear relationship (Clague and Frey, 1982 Giannetti and Ellam, 1994), in part because the trace element concentration deviates from the batch melting model. This may result in large errors in the intercept value / and 5. 

Mafic Plio-Quatemary rocks in Italy show very variable trace element and isotopic compositions. Incompatible2 trace element abundances and ratios are best illustrated by mantle-normalised diagrams (spiderdiagrams), where concentrations of single elements in the rocks are divided by the abundances of the same elements in the mantle (Wood 1979). 

Fig. 1.6. Variation diagrams of incompatible trace element ratios and 87Sr/86Sr for mafic (MgO > 4 wt %) Plio-Quatemary volcanic rocks from Italy.

Fig. 2.3. Variation diagrams of MgO vs. selected major and trace elements and 87Sr/86Sr for magmatic rocks of the Tuscany Province. Symbols as in Fig. 2.2.

Fig. 4.6. Variation diagrams of selected major, trace elements and 87Sr/86Sr ratios vs. MgO for the Vulsini rocks. Symbols as in Fig. 4.4. Crosses indicate samples of uncertain location.

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. 6.5. Variation diagrams of selected major and trace elements vs. SiC>2 for Somma-Vesuvio rocks. For symbols see Fig. 6.4.

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