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Nd isotopes in 2.9 Ga Archean surface seawater 387 of the Mozaan IF samples (Fig. 4). The presence of positive Eu anomalies is clear evidence that REY from high-T hydrothermal inputs influenced the continental shelf environment that hosted the Mozaan IFs. For constraints on ancient hydrothermal fluxes, modern black smoker fluids offer the best analogs for the trace element compositions of high-T fluids which contributed to the REY distribution in Archean iron formations. For the Mozaan IFs, the magnitude of the positive Eu anomalies generally compare well with data for other IFs (Fig. 5). However, the general REY distributions of the Mozaan IFs are significantly different when compared to well studied examples such as the 3.7 Ga Isua IF of Greenland (Bolhar et al., 2004) and the 2.5 Ga Kuruman IF from South Africa (Bau and Dulski, 1996), though regardless of age, these iron formations display the seawater characteristics of marine chemical sediments (Fig. 5). Conservative mixing calculations indicate that a high-T hydrothermal fluid contribution of less than 0.1% is adequate for producing the Eu/Sm ratios observed within the Pongola and Kuruman IFs, and reasonably accounts for most of the Eu/Sm ratios observed in the Isua IFs REY/WMS 10 1 10 0 high-T hydrothermal fluid (x10 5 ) 10 -1 10 -2 10 -3 Isua IF (x2) Kuruman IF top/bottom IFs middle IFs
388 B.W. Alexander et al. / Geochimica et Cosmochimica Acta 72 (2008) 378–394 fluxes of trace elements would be expected to affect the REY distribution of the bottom water component, and though such fluxes are at best difficult to characterize, it can be ruled out that such low-T input would have displayed positive Eu anomalies. Y/Ho Y/Ho Sm/Yb 100 80 60 40 28 20 100 80 60 40 28 20 30 10 1 seawater hydrogenetic Fe-Mn crusts 0.1% hydrothermal fluid 1% hydrothermal fluid 5% hydrothermal fluid high-T hydrothermal fluids 0.1 1 10 Eu/Sm seawater 10 0.2 1 10 20 Sm/Yb hydrogenetic Fe-Mn crusts seawater hydrogenetic Fe-Mn crusts Pongola IF (2.9 Ga) Kuruman IF (2.5 Ga) Isua IF (~3.7 Ga) modern seawater modern hydrogenetic Fe-Mn crusts high-T hydrothermal fluids 1% hydrothermal fluid 0.1% hydrothermal fluid 5% hydrothermal fluid high-T hydrothermal fluids high-T hydrothermal fluids 5% hydrothermal fluid 1% hydrothermal fluid 0.3 0.1 1 10 Eu/Sm 5.2.3. Surface seawater input The major remaining REY input affecting the Mozaan IFs would be Archean surface seawater. Rare earth element distributions in modern seawater, while exhibiting local variability and distinct trends with depth, are generally consistent with the pattern shown in Fig. 5, and exhibit a (Sm/Yb) CN ratio of 0.8. A study by Elderfield et al. (1990) reported REY data for five coastal seas (salinity > 20‰) that exhibited (Sm/Yb) CN ranging from 0.70 to 1.24, consistent with coastal seawater from the East Frisian islands (North Sea) that displays (Sm/Yb) CN between 0.61 and 0.73 (Kulaksiz and Bau, 2007). Elderfield et al., 1990 also presented REY data for waters from six estuaries and 15 rivers. The estuarine waters (salinity < 10‰) displayed (Sm/Yb) CN that ranged from 0.63 to 4.74, while (Sm/Yb) CN of the river waters varied between 0.96 and 4.74. Much of the REY load transported by modern rivers is removed in estuaries by the settling of suspended detrital particles, and by the salinity-induced coagulation and settling of colloidal particles rich in the particle reactive REYs (e.g., Sholkovitz, 1994), processes that homogenize the widely varying REY distributions observed in modern rivers to produce the REY pattern typical of modern seawater. Elderfield et al. (1990) deduced that the colloidal fraction carried by many rivers would be enriched in the MREEs (shale-normalized) relative to the light and heavy REYs, similar to patterns observed for the Mozaan IFs sampled from the bottom and top of the sequence (Fig. 2), which represent iron formation deposited under the shallowest sea-level conditions. Studies of the Kalix river in Sweden demonstrated that colloidal particles dominate the transport and export of rare earth elements (Ingri et al., 2000), and these colloids consist of two fractions, one Fe-rich and another C-rich (Andersson et al., 2006). General enrichments in MREEs for Fe-rich organic colloids have been observed in the Hudson and Connecticut rivers (Sholkovitz, 1994), and the presence of MREE-enriched river waters has also been documented by Sholkovitz and Szymczak (2000) and Hannigan and Sholkovitz (2001). The speculation that riverine-derived colloidal particles enriched in the MREEs could exert a strong influence on REY distributions in the Mozaan IFs relies on similar processes controlling REY distributions in b Fig. 6. Elemental ratio plots for data sets presented in Fig. 5, with two-component conservative mixing lines for Eu/Sm, Sm/Yb, and Y/Ho (symbols for all plots defined in c): (a) Y/Ho versus Eu/Sm, showing that a 0.1% high-T hydrothermal (>350 °C, Bau and Dulski, 1999) fluid contribution to waters with shallow (
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Iron sedimentation and the neodymiu
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The process(es) by which IFs were d
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This thesis represents original and
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viii
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goal of the research is to discern
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Figure 1. Map of southern Africa sh
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appropriate to briefly discuss: 1)
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100 10 MORB 1 0.1 raw data (mg/kg)
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10 -2 hydrothermal fluid 10 -3 10 -
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seawater and returned to the sedime
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100 MCO + 3 + M(CO 3 )- 2 rare eart
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net effect of carbonate complexatio
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feature was not recognized in early
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sound geochemical basis for anomalo
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deviation of the 143 Nd/ 144 Nd rat
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available, it should be possible to
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modern and Archean oceans, as well
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Bau M., Möller P., and Dulski P. (
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Elderfield H. and Greaves M.J. (198
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Haley B.A., Klinkhammer G.P. (2003)
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Lee J.H. and Byrne R.H. (1993) Comp
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Piepgras D.J. and Wasserburg G.J. (
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Tosiani T., Loubet M., Viers J., Va
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Abstract The benefits of inductivel
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List of Figures Figure 1. Sample de
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1. Introduction The advent of induc
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Figure 1. Flow-chart diagram of the
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during decomposition (SiF 4 and CO
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Fractionation between the three iso
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cps, then 3000 cps must be subtract
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variety of ways. These range from r
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Table 3. Change in HFSE concentrati
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0.90, corresponding to an anomalous
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10 2 JDo-1 reference values 10 1 IF
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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
Page 90 and 91: 1.50 FeR-4 (n=2) 1.25 JUB / referen
Page 92 and 93: 1 IF-G/shale 0.1 0.01 La Ce Pr Nd P
Page 94 and 95: consistent (App. 1), and similar to
Page 96 and 97: 1.50 SGR-1b (n=3) 1.25 JUB / refere
Page 98 and 99: 1.50 JCh-1 (n=3) 1.25 JUB / referen
Page 100 and 101: 1.50 JDo-1 (n=5) 1.25 JUB / referen
Page 102 and 103: determinations in carbonate rocks r
Page 104 and 105: 1.50 JMn-1 (n=4) 1.25 JUB / referen
Page 106 and 107: eference value. The result is that
Page 108 and 109: eference value and the measured JUB
Page 110 and 111: the 32 analyzed elements, with Ti b
Page 112 and 113: Govindaraju K. (1995) 1995 working
Page 114 and 115: Appendix 1. Analytical data Appendi
Page 116 and 117: Appendix 1. Literature reference va
Page 118 and 119: Appendix 1 continued. Data in mg/kg
Page 120 and 121: the concentration of the major elem
Page 122 and 123: Potential interferences on monoisot
Page 124 and 125: 1500 0.5 M HCl 4.0 interference on
Page 126 and 127: 4000 0.40 0.20 3500 0.17 mg/kg 0.18
Page 128 and 129: interference on 95 Mo in sample sol
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Page 132 and 133: Nd isotopes in 2.9 Ga Archean surfa
Page 136 and 137: Table 2 Trace element concentration
Page 152 and 153: Author's personal copy B.W. Alexand
Page 166 and 167: and preservation of oxide-facies IF
Page 168 and 169: TOP relative stratigraphic position
Page 170 and 171: The mechanism by which the alkali m
Page 172 and 173: 6. Widdel, F. et al. Ferrous iron o
Page 178 and 179: 82 PRESERVATION OF PRIMARY REE PATT
Page 184: ulk, open ocean seawater tended to
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