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Nd isotopes in 2.9 Ga Archean surface seawater 381 lysed at the GeoForschungsZentrum, Potsdam, Germany. Major element concentrations were obtained by X-ray fluorescence (XRF), and mineral phase determinations were obtained by X-ray diffraction (XRD). Trace element concentrations were determined with a Perkin-Elmer/Sciex Elan Model 5000 inductively coupled plasma mass spectrometer (ICP-MS) following the procedures of Dulski (2001). Samarium and Nd concentrations were also determined using thermal ionization mass spectrometry (TIMS). Agreement between TIMS and ICPMS data is better than 2% for Nd (except shale WM2, 3.7%), and better than 4% for Sm (except shale WM2 and IF WM41, 6.1% and 6.0%, respectively). Iron-formation sample WM121 is atypical is displaying differences of 7.2% and 10.8% in respective Nd and Sm concentrations as determined by TIMS and ICPMS, yet Sm/Nd for WM121 differs by only 2.8% between the two analytical methods, and Sm/Nd comparisons between TIMS and ICPMS data never exceeds 5.3%, indicating that consistent REE ratios were determined regardless of the method used. Accuracy for other ICPMS analyses is conservatively estimated to be ±10%, and rare earth element ratios are estimated to be accurate within ±5%. Samples for Sm–Nd isotope determinations were spiked using a mixed 147 Sm/ 150 Nd spike, and processed at the Laboratory for Isotope Geology, Swedish Museum of Natural History. Samarium and Nd were separated using ion exchange techniques, and isotopic ratios were determined with a five collector Finnigan MAT 261 TIMS. Total analytical blank for Nd was approximately 40 pg, and Nd was analysed as NdO + in multidynamic mode, with the data being reduced assuming exponential fractionation and normalized to 146 Nd/ 144 Nd = 0.7219. External precision was obtained by repeated analyses of the La Jolla standard with 143 Nd/ 144 Nd = 0.511853 ± 0.000025 (2r, n = 10). Samarium was analyzed as an oxide in static mode and normalized assuming 149 Sm/ 152 Sm = 0.51686. Uncertainties in TIMS determination of Sm and Nd concentrations are estimated to about 1% Al 2 O 3 and almost 15% MnO and will be discussed in detail below. Unless otherwise noted, results refer only to the remaining 15 IF samples. Normative quartz and iron-oxides combined represent 96–99% (wt.) of the samples, with Fe ranging from 10% to 81%. Aluminium, Ca, Mg, Ti, and P are present only in trace amounts, and Na and K are absent or not measurable. Other than Si and Fe, only Mn is present in appreciable amounts of the major elements studied, and averages 1%. The mineralogy of the iron oxide component for all samples varies between magnetite and hematite, with the relative proportion of magnetite increasing with increasing Fe content. The absence of chlorite or secondary minerals indicates that the samples have experienced little alteration or weathering. Immobile trace element concentrations in the IF samples are low (
Table 1 Major element data for iron formation and shales, with mineral phase determinations for IF samples Iron-formation samples Shale samples a WM41 WM42 WM51 WM52 WM61 WM62 WM71 WM72 WM101 WM102 WM111 WM112 WM121 WM122 WM131 WM132 WM2 WM8 WM18 WM19 pelite b XRF (wt%) SiO 2 75.4 26.2 75.7 16.8 19.7 20.7 58.8 70.8 80.9 78.4 80.3 81.0 85.8 88.0 84.4 83.6 51.6 47.9 49.1 48.6 58 Al 2 O 3 0.13 1.22 0.18 0.07 0.67 0.39 0.21 0.02 0.52 0.22 nd nd 0.06 0.06 0.34 0.10 23.3 11.9 24.7 26.8 18.8 Fe 2 O 3 22.2 57.0 21.0 81.0 76.4 76.3 37.5 26.1 15.2 17.3 17.7 18.1 12.0 10.4 14.7 15.0 10.5 29.0 9.16 6.55 9.4 MnO 0.92 14.5 1.85 0.34 1.54 2.50 1.93 2.39 2.11 2.57 1.59 1.27 1.14 1.30 0.35 0.63 0.12 0.43 0.13 0.11 0.27 MgO 0.12 0.25 0.26 0.13 0.20 0.22 0.23 0.27 0.33 0.37 0.30 0.26 0.21 0.19 0.13 0.13 3.01 3.57 3.65 3.18 1.68 CaO 0.15 0.18 0.18 0.18 0.11 0.17 0.24 0.17 0.14 0.21 0.16 0.18 0.14 0.12 0.11 0.11
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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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THIS PAGE INTENTIONALLY LEFT BLANK
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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
Page 84 and 85: isotopic data for geologic CRMs, av
Page 86 and 87: Table 4. Interferences observed for
Page 88 and 89: 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
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ulk, open ocean seawater tended to
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