School of Engineering and Science - Jacobs University

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148 B.W. Alexander et al. / Earth and Planetary Science Letters 283 (2009) 144–155
Table 2
Sm–Nd concentrations (mg/kg) and isotope ratios for Pietersburg IF.
Sample Sm Nd
147 Sm/ 144 Nd
143 Nd/ 144 Nd±2σ a Є Nd (0) Є Nd (t) Sm Nd
TIMS TIMS t=2.95 Ga ICPMS %RSD ICPMS %RSD
TIMS/ICPMS
TIMS/ICPMS
IF1 0.954 4.116 0.1401 0.511502±4 −22.2 −0.66 0.983 −3.0 4.24 −2.9
IF2 0.426 1.915 0.1344 0.511466±5 −22.9 0.83 0.393 8.4 1.80 6.4
IF3 1.525 6.694 0.1377 0.511464±4 −22.9 −0.48 1.55 −1.6 6.84 −2.1
IF4 2.029 8.862 0.1384 0.511485±3 −22.5 −0.35 2.02 0.4 8.84 0.2
IF4r b 2.035 8.874 0.1386 0.511486±3 −22.5 −0.39
IF5 0.847 3.725 0.1375 0.511499±3 −22.2 0.29 0.890 −4.8 3.91 −4.7
IF5r b 0.856 3.747 0.1381 0.511504±4 −22.1 0.14
IF6 0.424 1.922 0.1334 0.511455±5 −23.1 0.99 0.410 3.4 1.90 1.2
IF7 1.717 8.041 0.1291 0.511290 ±9 −26.3 −0.61 1.68 2.2 8.01 0.4
t=3.8 Ga
IF-G c 0.39 1.72 0.1371 0.511277 2.73
IF-G 0.383 1.687 0.1373 0.511258±4 2.25
BCR-2 d 6.574 28.64 0.1388 0.512628 ±2
a
b
c
2σ refers to last digit in the measured ratio.
r in sample name denotes a replicate digestion and analysis of the same sample, and these data are not discussed in the text.
Data from Stecher et al. (1986). IF-G distributed by GIT-IWG (Groupe International de Travail – International Working Group), Service d' Analyse des Roches et des Minéraux,
CRPG-CNRS, Vandoeuvre-lès-Nancy, France. Sample powder from the original IF-G processing run is no longer available, though a second batch of Isua IF-G iron-formation is
currently available from GIT-IWG. Data for this study, and presumably from Stecher et al. (1986) as well, are for IF-G powder from the original processing run.
d Average of 2 separate digestions of BCR-2 Columbia River basalt reference material (United States Geologic Survey).
the overall reproducibility (external precision) is 9 ppm as estimated
from the standards. Uncertainties in TIMS determination of Sm and Nd
concentrations are estimated as b1% and 2%, respectively.
Agreement between TIMS and ICPMS concentration data is better
than 4.7% for both Sm and Nd, except for sample IF2 where TIMS
values are respectively 8.4% and 6.4% higher relative to ICPMS data
(Table 2). Rare earth element ratios calculated from TIMS and ICPMS
data are significantly more consistent, with all samples displaying
Sm/Nd that varies by no more than 2.2% between the two analytical
methods. Therefore, we very conservatively estimate the accuracy for
ICPMS analyses as better than ±10%, and accuracy for rare earth
element ratios as better than ±5%.
Fig. 2. Selected trace element concentrations plotted as a function of Ti. Trends are similar regardless of elements affinity for felsic (Rb, Th) or mafic crust (Ni, Co). The excellent
correlation between Rb and more immobile metals such as Al and Ti argues against significant post-depositional mobility of trace metals following IF deposition.