Lanthanide abundances normalization

As the first step in the analysis of our data, we divided each of the twenty-four distributions, element by element, by the average absolute mass abundance of the lanthanides in twenty chondrites (5) and plotted the ratios on a logarithmic scale against a linear scale of atomic number. A visual inspection of the normalized patterns indicated that at least eleven distributions, apart from diflFerences in total lanthanide abundance, were identical nearly all the other patterns diflFered only slightly from the eleven samples mentioned. The normalized pattern for one sample is shown in Figure 2. Obviously, the distributions of lanthanides in sea water are quite different from the pattern in chondrites. 

Lanthanide abundances in natural waters are extremely low (table 19, fig. 33). This observation is well illustrated by Haskin et al. (1966b), who calculated that the entire mass of lanthanides in the oceans is equivalent to that in about a 0.2 mm thickness of sediment of the same areal extent. The lanthanide patterns of normal ocean waters are significantly enriched in the heavy lanthanides relative to the light lanthanides, when compared to terrigenous sedimentary rocks. Ocean waters are relatively depleted in Ce a reflection of preferential incorporation of this element in... 

Fig. 38. Lanthanide abundance patterns for selected iron formations and iron-rich sedimentary rocks. Data are normalized to average shale values of the same period, Archean iron formation being normalized to average Archean shale (McLennan and Taylor 1984) and the others normalized to PAAS. In detail, iron formations exhibit considerable variability in lanthanide patterns. These samples illustrate the general feature of Eu enrichment, relative to contemporaneous upper continental crust, for Archean and early Proterozoic iron formations. The younger examples display no such Eu enrichment. This feature has been used to suggest that early Precambrian seawater was dominated by a hydrothermal signature, enriched in Eu (see fig. 30). (Data are from table 22.)...

Besides these discrepancies between crystallographic results and the instantaneous evidence obtained by spectroscopic measurements, there occurs another interesting discrepancy between classical physico-chemical and spectroscopic investigations. A very characteristic case is that of normal anion complexes and the outer-sphere ion-pairs in solution. This distinction is clear-cut in stable complexes (23) such as [Cr(H20)6]" S04 and [Cr(S04)(H20)4 or In the case of lanthanide chlorides, it is well-known that spectroscopic evidence (42, 75) for inner-shell complexes NdCl(H20)x indicates a formation constant hundreds of times smaller than that of the ion pair Nd(H20)g+ Cl . In organic solvents the inner complexes are relatively more abundant (2, 43). In certain cases, one also... 

Cook (1972) has recognized two different types of phosphorite in northwest Queensland pelletal and non-pelletal. The lanthanide distribution in the former is normal for marine phosphorites, whereas it is depleted in the latter type with the exception of the heavy lanthanides which are relatively more abundant. Pelletal types contain greater concentrations of elements which are known to substitute in the structure of apatite, whereas the other types contain components which probably are of detrital origin or are derived from weathering. 

To obtain the values of yi the logarithm of the normalized abundance of the i-th element was taken. That is, for a particular sample, the abundance of the i-th element is divided by the abundance of that element in the average lanthanide distribution (Table III), and the logarithm of this ratio is formed to give yi. 

When REE fractionation is discussed, it is common to normalize the data to the values in shale which are thought to be representative of the REEs in the upper continental crust. The shale-normalization not only helps to eliminate the well-known distinctive even-odd variation in natural abundance (the Oddo-Har-kins effect) of REEs but also visualizes, to a first approximation, fractionation relative to the continental source. It should be noted, however, that different shale values in the literature have been employed for normalization, together with the ones of the Post-Archean Australian Sedimentary rocks (PAAS) adopted here (Table 1). Thus, caution must be paid on the choice of the shale values if one ought to interpret small anomalies at the strictly trivalent lanthanides such as Gd and Tb. Alternatively, for detailed arguments concerning fractionation between different water masses in the ocean, it has been recommended that the data are normalized relative to the REE values of a distinctive reference water mass, for example, the North Pacific Deep Water (NPDW, Table 1). The NPDW-normalization eliminates the common features of seawater that appeared in the shale-normalized REE pattern and can single out fractionation relative to the REEs in the dissolved end product in the route of the global ocean circulation. 

Fig. 32. PAAS-normalized lanthanide patterns for early Proterozoic uranium deposits from the Pine Creek Geosyneline, Australia (data are from McLennan and Taylor 1979). Compared to the unmineralized host sedimentary roek, these deposits are extremely enriched in heavy lanthanides and depleted in light lanthanides. The abundances and amount of fractionation is related to the U content, suggesting the lanthanide mobility and U mineralization are directly related, thus helping to constrain the origin of the deposit. The fractionation of Sm and Nd during ore-formation allows dating by the Sm-Nd method.

Subscript N values may be obtained from isotope abundance data (e.g. see table) subscript S values, for the spike, are generally determined empirically. Typically, the amount of the lanthanide in the unknown is given in ppm by weight so that a factor consisting of the ratio of the atomic weight of normal and spike element must be applied. Hence ... 

Fig. 1. (a) The concentration of dissolved lanthanides in the surface waters of the Sargasso Sea. A composite of data measured by TIMS (Sholkovitz and Schneider 1991) and INAA (De Baar et al. 1983). Note classic sawtooth abundance pattern. Pm does not exist in nature, (b) Shale-normalized pattern of the composite seawater shown in (a) using shale concentrations of table 1. Tb, being inconsistent, probably reflects an incorrect concentration of the seawater. 

Fractionation of the lanthanides is often quantified by shale-normalized patterns. Normalization to shale represents an abundance relative to that of the upper crust of the continents. A flat shale pattern for river suspended particles would indicate a composition similar to that of averaged continental crust. To study fractionation in rivers, it is also instructive to normalize the dissolved composition to that of suspended particles on the assumption that the particles better represent the solids being weathered in the watershed. 

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