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100 MCO + 3 + M(CO 3 )- 2 rare earth element % total 80 60 40 20 MCO + 3 M(CO 3 ) - 2 M 3+ 0 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Figure 7. Speciation of the lanthanides in seawater at 25° C and 1 atmosphere pressure with 35.1 ‰ salinity and a total carbonate ion concentration [CO 3 2- ] of 1.39 x 10 -4 moles/kg. Figure adapted from Cantrell and Byrne (1987), and M refers to individual lanthanide elements. Hydroxide, chloride, fluoride, and sulfate REE complexes are not shown, as these are minor chemical species affecting REE behavior in seawater (Cantrell and Byrne, 1987). The carbonate anions binding to dissolved REY in seawater form either M(CO 3 ) + or M(CO 3 ) 2 - complexes, where M refers to the individual element. Monocarbonate M(CO 3 ) + complexes are more prevalent for light rare earth elements (LREE), and dicarbonate M(CO 3 ) - 2 complexes more so for heavy rare earth elements (HREE), with the relative proportions of these carbonate complexes roughly equal for middle rare earth elements (MREE) such as Gd and Tb. The calculated carbonate complexation constants are relatively unaffected by changes in temperature (Cantrell and Byrne, 1987), and it is surmised that the relative lanthanide distributions between mono- and dicarbonate complexes remains constant throughout the marine water column (Brookins, 1989). The solution complexation behavior of the REY strongly affects the process that controls the distribution of these elements in seawater, which is scavenging by particulate matter. The REY are readily adsorbed onto particle surfaces in natural 14
waters, as evidenced by the dominant association of the REY with Fe-organic colloids in river waters (e.g., Sholkovitz, 1995). The particle reactive nature of the rare earths was well exploited by early workers conducting seawater analyses, in which the REY were quantitatively removed and concentrated from seawater samples by coprecipitation with Fe-hydroxides (e.g., Goldberg et al., 1963; Høgdahl et al., 1968; Elderfield and Greaves, 1982). This scavenging by particulate matter is considered the primary removal process for the REY in seawater (e.g., de Baar et al., 1985a; Elderfield, 1988), and it appears that particle coatings consisting of organic films and Fe-Mn oxides are particularly important in this scavenging process (e.g., Byrne and Kim, 1990; Sholkovitz et al., 1994, and references therein). Experimental work indicates these scavenging reactions approach steady state within minutes (e.g., Byrne and Kim, 1990; Koeppenkastrop and De Carlo, 1993; Bau, 1999), suggesting that equilibrium conditions characterize REY partitioning between seawater and particle surfaces. The general shape of the REY patterns shown in Figs. 4-6, with a strong enrichment of the HREE over the LREE in seawater, can be attributed to the competition between carbonate complexation in solution and reactive particle surfaces. The exact process by which REY are adsorbed to particle surfaces is still a matter of study, and Piasecki and Sverjensky (2008) provide a review of proposed sorption mechanisms in addition to a triple-layer surface complexation model that is consistent with X-ray studies. However, to a first approximation, particle surface adsorption constants for individual REY can be described by their first hydrolysis constants (Erel and Morgan, 1991; Bau et al., 1996). Using such an approach, calculated partition coefficients between particle surfaces and seawater predict a preferential LREE enrichment for the adsorbed component (Erel and Stolper; 1993), consistent with LREE depletion in the solution phase and the observed REY patterns for world seawater. The 15
Page 1: Iron sedimentation and the neodymiu
Page 4 and 5: The process(es) by which IFs were d
Page 7: This thesis represents original and
Page 10 and 11: viii
Page 12 and 13: goal of the research is to discern
Page 14 and 15: Figure 1. Map of southern Africa sh
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Page 18 and 19: 100 10 MORB 1 0.1 raw data (mg/kg)
Page 20 and 21: 10 -2 hydrothermal fluid 10 -3 10 -
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Page 40 and 41: Elderfield H. and Greaves M.J. (198
Page 42 and 43: Haley B.A., Klinkhammer G.P. (2003)
Page 44 and 45: Lee J.H. and Byrne R.H. (1993) Comp
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Page 52 and 53: Abstract The benefits of inductivel
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Page 56 and 57: 1. Introduction The advent of induc
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Figure 5. Diagram depicting various
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20 18 basalt BHVO-2 (n=5) run preci
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The method precision for elements p
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Two approaches may be utilized to d
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For the more recent, full 32 elemen
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isotopic data for geologic CRMs, av
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Table 4. Interferences observed for
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value uncertainty (as %RSD) is repr
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1.50 FeR-4 (n=2) 1.25 JUB / referen
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1 IF-G/shale 0.1 0.01 La Ce Pr Nd P
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consistent (App. 1), and similar to
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1.50 SGR-1b (n=3) 1.25 JUB / refere
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1.50 JCh-1 (n=3) 1.25 JUB / referen
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1.50 JDo-1 (n=5) 1.25 JUB / referen
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determinations in carbonate rocks r
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1.50 JMn-1 (n=4) 1.25 JUB / referen
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eference value. The result is that
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eference value and the measured JUB
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the 32 analyzed elements, with Ti b
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Govindaraju K. (1995) 1995 working
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Appendix 1. Analytical data Appendi
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Appendix 1. Literature reference va
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Appendix 1 continued. Data in mg/kg
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the concentration of the major elem
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Potential interferences on monoisot
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1500 0.5 M HCl 4.0 interference on
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4000 0.40 0.20 3500 0.17 mg/kg 0.18
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interference on 95 Mo in sample sol
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Nd isotopes in 2.9 Ga Archean surfa
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Table 2 Trace element concentration
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Author's personal copy B.W. Alexand
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and preservation of oxide-facies IF
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TOP relative stratigraphic position
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The mechanism by which the alkali m
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6. Widdel, F. et al. Ferrous iron o
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82 PRESERVATION OF PRIMARY REE PATT
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ulk, open ocean seawater tended to
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