School of Engineering and Science - Jacobs University

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Figure 1. Map of southern Africa showing locations of major geologic features discussed in thesis. Ironformation units that provided samples for geochemical analyses were obtained from the Pongola Supergroup and the Pietersburg greenstone belt. environment, as well as from the 2.95 Ga Pietersburg greenstone belt, which is considered to represent a more open ocean, island-arc environment (Fig. 1). The hypothesis is that Sm-Nd isotopic signatures in IFs of similar age, yet from different depositional environments, might possess different Nd isotopic signatures that reflect the respective Nd sources to Archean seawater. 4
1.4. Research methods The research methods employed for this thesis consist of various techniques for obtaining geochemical analyses of rock samples. Three analytical techniques are used for performing elemental and isotopic measurements of the samples discussed. The first technique is X-ray fluorescence (XRF), which provided major element concentration data. The second analytical method is inductively coupled plasma mass spectrometry (ICPMS), which was used for trace metal concentration measurements. The third analytical method is thermal ionization mass spectrometry (TIMS), which was used for measuring Sm-Nd isotopic ratios. The XRF analyses were performed either at the GeoForschungsZentrum (GFZ) in Potsdam, Germany, or at the University of Johannesburg (South Africa) SpectRAU facility. The trace metal concentrations determined by ICPMS were provided either by the GFZ, for the initial research conducted for this thesis, or by the author using equipment within the Geochemistry Lab at Jacobs University Bremen (JUB). All Sm- Nd isotopic analyses were performed at the Laboratory for Isotope Geology at the Swedish Museum of Natural History in Stockholm, Sweden. Details of the XRF analyses are not discussed, as XRF techniques are well-developed and are only used for determining major element concentrations (e.g., Si, Al, Fe). A detailed description of the ICPMS analytical methods is provided in Chapter 2, and is applicable to data produced at both the GFZ and JUB. Descriptions of the Sm-Nd isotopic analyses are provided within the individual chapters where relevant. 1.5. Background and review of relevant literature The principle conclusions of this thesis rest upon the isotopic ratios of Nd in Archean seawater as inferred from Sm-Nd analyses of iron-formations. Therefore, it is 5
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 16 and 17: appropriate to briefly discuss: 1)
Page 18 and 19: 100 10 MORB 1 0.1 raw data (mg/kg)
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Page 52 and 53: Abstract The benefits of inductivel
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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
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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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School of Engineering and Science - Jacobs University

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