School of Engineering and Science - Jacobs University

More documents

Recommendations

Info

sound geochemical basis for anomalous behavior of Yb (e.g., electron configuration, etc.). Considering that the monocarbonate equilibrium constants for Yb are consistent with those of Er and Tm, and no discussion of ‘anomalous’ dicarbonate Yb complexation is provided by Luo and Byrne (2004), it is concluded that the slight positive Lu anomalies observed in seawater (see Fig. 6) likely represent real excursions of Lu concentrations from those predicted by extrapolation from Tm and Yb. 1.5.3. Sm-Nd isotopic signatures in the Earth’s crust and seawater Samarium and Nd each have several isotopes, and 147 Sm radioactively decays to stable 143 Nd with a half-life of 1.06 × 10 11 years. Even though both Sm and Nd have similar geochemical behavior, like all the lanthanides, fractionation between Sm and Nd does occur during differentiation of the Earth’s crust. Figure 10 presents complete REY patterns for evolved continental crust and MORB that have been normalized to chondrite (i.e., bulk silicate Earth), showing that crustal differentiation leads to distinctive Sm/Nd ratios. Upper continental crust is enriched in Nd relative to Sm and possesses a low Sm/Nd ratio of ~0.17, whereas MORB derived from a depleted mantle source possesses higher Sm/Nd ratios of ~0.32. As a result of different Sm/Nd ratios and the subsequent decay of 147 Sm to 143 Nd, Sm-Nd isotopic ratios will evolve differently in continental and oceanic crust. The Nd isotopic signature of a geologic sample is reported as the 143 Nd/ 144 Nd ratio, as 144 Nd is a stable isotope whose abundance does not change with time. The Sm- Nd isotopic system has been used extensively for dating geologic samples and a thorough review of the techniques and applications may be found in Faure (1986). The determination of radiomentric ages relies upon constructing an isochron using measured 147 Sm/ 144 Nd and 143 Nd/ 144 Nd ratios for a suite of cogenetic samples (e.g., minerals). 20
1000 chondrite-normalized 100 10 1 upper continental crust MORB La Ce Pr Nd PmSm Eu Gd Tb Dy Y Ho Er Tm Yb Lu Figure 10. Typical REY distributions in upper continental crust (data from Taylor and McLennan, 1995) and MORB (Niu et al., 1999) illustrating different Sm/Nd ratios. Light REE are strongly enriched in continental crust, which possesses negative Eu anomalies due to partitioning of Eu 2+ into plagioclase-rich residual material during intra-crustal partial melting and fractional crystallization. From the isochron an initial 143 Nd/ 144 Nd ratio may be determined, which allows the calculation of a geologic age for the samples. Alternatively, if the geologic age of a group of samples is already known, then measured Sm-Nd isotopic ratios in individual samples allow the calculation of initial 143 Nd/ 144 Nd ratios without the need for constructing an isochron. This is the approach used in this thesis, as the samples investigated are marine sediments, and not igneous rocks which can often be considered to have crystallized in a geologically instantaneous time period. The purpose of this research is not to date the sediments studied, but rather to examine any variations in their initial 143 Nd/ 144 Nd ratios, as these variations may shed light on sources of Nd to Archean seawater, as well as any isotopic variability in Archean oceans. Measured 143 Nd/ 144 Nd ratios in a geologic sample are typically expressed using the Є Nd (t) notation of DePaolo and Wasserburg (1976). The Є Nd (t) value describes the 21
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
Page 16 and 17: appropriate to briefly discuss: 1)
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 -
Page 22 and 23: seawater and returned to the sedime
Page 24 and 25: 100 MCO + 3 + M(CO 3 )- 2 rare eart
Page 26 and 27: net effect of carbonate complexatio
Page 28 and 29: feature was not recognized in early
Page 32 and 33: deviation of the 143 Nd/ 144 Nd rat
Page 34 and 35: available, it should be possible to
Page 36 and 37: modern and Archean oceans, as well
Page 38 and 39: Bau M., Möller P., and Dulski P. (
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
Page 46 and 47: Piepgras D.J. and Wasserburg G.J. (
Page 48 and 49: Tosiani T., Loubet M., Viers J., Va
Page 50 and 51: THIS PAGE INTENTIONALLY LEFT BLANK
Page 52 and 53: Abstract The benefits of inductivel
Page 54 and 55: List of Figures Figure 1. Sample de
Page 56 and 57: 1. Introduction The advent of induc
Page 58 and 59: Figure 1. Flow-chart diagram of the
Page 60 and 61: during decomposition (SiF 4 and CO
Page 62 and 63: Fractionation between the three iso
Page 64 and 65: cps, then 3000 cps must be subtract
Page 66 and 67: variety of ways. These range from r
Page 68 and 69: Table 3. Change in HFSE concentrati
Page 70 and 71: 0.90, corresponding to an anomalous
Page 72 and 73: 10 2 JDo-1 reference values 10 1 IF
Page 74 and 75: Figure 5. Diagram depicting various
Page 76 and 77: 20 18 basalt BHVO-2 (n=5) run preci
Page 78 and 79: The method precision for elements p
Page 80 and 81:
Two approaches may be utilized to d
Page 82 and 83:
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
Page 130 and 131:
THIS PAGE INTENTIONALLY LEFT BLANK
Page 132 and 133:
Nd isotopes in 2.9 Ga Archean surfa
Page 134 and 135:
Page 136 and 137:
Table 2 Trace element concentration
Page 138 and 139:
Page 140 and 141:
Page 142 and 143:
Page 144 and 145:
Page 146 and 147:
Page 148 and 149:
Page 150 and 151:
Page 152 and 153:
Author's personal copy B.W. Alexand
Page 154 and 155:
Page 156 and 157:
Page 158 and 159:
Page 160 and 161:
Page 162 and 163:
Page 164 and 165:
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 174 and 175:
Page 176 and 177:
Page 178 and 179:
82 PRESERVATION OF PRIMARY REE PATT
Page 180 and 181:
Page 182 and 183:
Page 184:
ulk, open ocean seawater tended to
show all

School of Engineering and Science - Jacobs University

Create successful ePaper yourself

Delete template?

Save as template?