Crust elemental composition

Table 3.1 gives the local elemental composition of three different tubercles from three different systems formed under different chemical treatments. At the floor of each tubercle, the concentration of chlorine and sulfur is higher than in the crust. The concentration of most crust elements, except that of iron, also decreases near the tubercle floor. The crust contains traces of treatment chemicals including zinc, phosphorus, and silicon. Tubercle 1 contains up to 40% silicon in the crust, which strongly suggests accumulation of silt by settling of particulate. 

Table 8-2 Elemental composition by atoms of the Earth s crust"...

Relationship between the trace elemental composition of phytoplankton, continental crust and seawater. Phytoplankton and crustal abundances are normalized to phosphorus (ppm trace metal ppm P). Seawater trace elements abundances are normalized to phosphate (ppb trace metal ppb P as phosphate). Source-. From Quigg, A., et al. (2003). Nature 425, 291-294. 

The hazard of coal-related trace element pollution must be considered in conjunction with similar pollution from other sources. There is nothing toxicologically unique about the trace element composition of coal. It is geochemically similar to the makeup of the earths crust... 

FIGURE 1.1 Estimated elemental composition (by mass percent) of (a) the earth s crust and (b) the human body. Oxygen is the most abundant element in both. Only the major constituents are shown in each case small amounts of many other elements are also present. 

Correns (1969) has given a vivid description of the development of ideas concerning the elemental composition of the earth s crust and the discovery of the elements. Only 150 years ago (1821), the term chemistry of the earth was used by Berzelius, as synonymous with the term mineralogy . In the middle of the last century (1845 — 1854), G. Bischof published his three-volume work Lehrbuch der chemischen und physikalischen Geologie . Chemists (like Bunsen) and earth scientists became aware of the potential of a chemical approach to the problems of earth and hydrosphere. Clarke published the first edition of his Data of Geochemistry in 1908 and the fifth edition (1924) remained a standard reference for many years. Vernadsky (1863—... 

Table 2 Estimates of the trace-element composition of the upper continental crust. Columns 1-4 represent averages of surface exposures. Columns 5-8 are estimates derived from sedimentary and loess data. Column 9 is a previous estimate, where bracketed data are values derived from surface exposure studies. Column 10 is our recommended value (see Table 3). 

Figure 3 Comparison of different models for the trace-element composition of the upper-continental crust. All values normalized to the new composition provided in Table 3. Gray shaded field represents 20% variation from this value for all panels except (f), in which gray field represents a factor of two variation. Trace elements are divided into the following groups (a) transition metals, (b) high-field strength elements, (c) alkali, alkaline-earth elements, (d) REEs, (e) actinides and heavy metals, and (f) highly siderophile and chalcophile elements (note log scale). Data from Tables 1 and 2 lanthanum estimate from Eade and Fahrig (1973) is omitted from panel D.

Figure 9 Comparison of the major-element composition of the middle continental crust as determined by sampling of surface exposures (Shaw et al., 1994 Weaver and Tarney, 1984) and inferred from middle-cmstal seismic velocities combined with surface and xenolith samples (Rudnick and Fountain, 1995 Gao et al., 1998a). All values normalized to the new composition provided in Table 5 ( R G ), which is an average between tbe values of Gao et al.

Figure 17 Comparison of (a) rare-earth and (b) additional trace-element compositions of the upper, middle, and lower crust recommended here. Chondrite values from Taylor and McLennan (1985), mantle-normalizing values...

It has been known for over a century that the continental crust has an average composition approximating to andesite (when cast as an igneous rock type) (Clarke, 1889, Clarke and Washington, 1924). The myriad studies on continental crust composition carried out in the intervening years have refined our picture of the crust s composition, particularly for trace elements. 

McLennan S. M. (2001b) Relationships between the trace element composition of sedimentary rocks and upper continental crust. Geochem. Geophys. Geosys. 2 (article no. 2000GC000109). 

The preferred chemical estimates of the continental crust used throughout this chapter are listed in Table 1. The major element composition of the upper crust is well constrained, since this is the most accessible to sampling, both directly and via erosion and sedimentation, and different studies utilizing diverse databases have yielded remarkably similar results. Si02is —61%, and Mg number (Mg, molar Mg/(Mg - - Fe)) is — 55 for the bulk continental cmst, and so it is more differentiated than any magma in equilibrium with the upper mantle. Trace-element abundances are more variable, as are estimates for the composition and proportion of the middle and lower cmst. As we will see below, the latter are critical to any discussion of the mechanisms of cmst formation and differentiation. 

Variations in the major element composition of the crust are manifested in the proportions of rock-forming minerals. Many of the less common elements can be readily accommodated in these phases or is their commonly associated accessories. In some instances, the less common elements may prove to be anomalous in concentration, and a subset of these anomalies may be of economic interest. Much of the geochemical variation found in the crust conforms to this general motif in other cases, anomalous concentrations of the less common elements are expressed as the appearance of separate minerals or rock units, defining petrologic ally distinct geologic entities. When the anomalies can be... 

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