School of Engineering and Science - Jacobs University
School of Engineering and Science - Jacobs University
School of Engineering and Science - Jacobs University
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1000<br />
chondrite-normalized<br />
100<br />
10<br />
1<br />
upper continental crust<br />
MORB<br />
La Ce Pr Nd PmSm Eu Gd Tb Dy Y Ho Er Tm Yb Lu<br />
Figure 10. Typical REY distributions in upper continental crust (data from Taylor <strong>and</strong> McLennan, 1995)<br />
<strong>and</strong> MORB (Niu et al., 1999) illustrating different Sm/Nd ratios. Light REE are strongly enriched in<br />
continental crust, which possesses negative Eu anomalies due to partitioning <strong>of</strong> Eu 2+ into plagioclase-rich<br />
residual material during intra-crustal partial melting <strong>and</strong> fractional crystallization.<br />
From the isochron an initial 143 Nd/ 144 Nd ratio may be determined, which allows the<br />
calculation <strong>of</strong> a geologic age for the samples.<br />
Alternatively, if the geologic age <strong>of</strong> a group <strong>of</strong> samples is already known, then<br />
measured Sm-Nd isotopic ratios in individual samples allow the calculation <strong>of</strong> initial<br />
143 Nd/ 144 Nd ratios without the need for constructing an isochron. This is the approach<br />
used in this thesis, as the samples investigated are marine sediments, <strong>and</strong> not igneous<br />
rocks which can <strong>of</strong>ten be considered to have crystallized in a geologically instantaneous<br />
time period. The purpose <strong>of</strong> this research is not to date the sediments studied, but rather<br />
to examine any variations in their initial 143 Nd/ 144 Nd ratios, as these variations may shed<br />
light on sources <strong>of</strong> Nd to Archean seawater, as well as any isotopic variability in<br />
Archean oceans.<br />
Measured 143 Nd/ 144 Nd ratios in a geologic sample are typically expressed using<br />
the Є Nd (t) notation <strong>of</strong> DePaolo <strong>and</strong> Wasserburg (1976). The Є Nd (t) value describes the<br />
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