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Science 17 December 2004:
Vol. 306. no. 5704, pp. 2077 - 2080
DOI: 10.1126/science.1104639
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Reports

Clues from Fe Isotope Variations on the Origin of Early Archean BIFs from Greenland

Nicolas Dauphas,1,2,3* Mark van Zuilen,4 Meenakshi Wadhwa,2,3 Andrew M. Davis,1,3 Bernard Marty,4,5 Philip E. Janney2,3

Archean rocks may provide a record of early Earth environments. However, such rocks have often been metamorphosed by high pressure and temperature, which can overprint the signatures of their original formation. Here, we show that the early Archean banded rocks from Isua, Akilia, and Innersuartuut, Greenland, are enriched in heavy iron isotopes by 0.1 to 0.5 per mil per atomic mass unit relative to igneous rocks worldwide. The observed enrichments are compatible with the transport, oxidation, and subsequent precipitation of ferrous iron emanating from hydrothermal vents and thus suggest that the original rocks were banded iron formations (BIFs). These variations therefore support a sedimentary origin for the Akilia banded rocks, which represent one of the oldest known occurrences of water-laid deposits on Earth.

1 Origins Laboratory, Department of the Geophysical Sciences, and Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA.
2 Department of Geology, The Field Museum, 1400 South Lake Shore Drive, Chicago, IL 60605, USA.
3 Chicago Center for Cosmochemistry, The University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA.
4 Centre de Recherches Pétrographiques et Géochimiques, CNRS 15 rue Notre-Dame des Pauvres, Boite Postal 20, 54501 Vandoeuvre-lès-Nancy Cedex, France.
5 Ecole Nationale Supérieure de Géologie, Rue du Doyen Marcel Roubault, Boite Postal 40, 54501 Vandoeuvre-lès-Nancy Cedex, France.

* To whom correspondence should be addressed. E-mail: dauphas{at}uchicago.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Microscale heterogeneity of Fe isotopes in >3.71 Ga banded iron formation from the Isua Greenstone Belt, southwest Greenland.
M. J. Whitehouse and C. M. Fedo (2007)
Geology 35, 719-722
   Abstract »    Full Text »    PDF »
Raman and ion microscopic imagery of graphitic inclusions in apatite from older than 3830 Ma Akilia supracrustal rocks, west Greenland.
K. D. McKeegan, A. B. Kudryavtsev, and J. W. Schopf (2007)
Geology 35, 591-594
   Abstract »    Full Text »    PDF »
Antiquity of the Oceans and Continents.
A. P. Nutman (2006)
Elements 2, 223-227
   Abstract »    Full Text »    PDF »
Geology, Age and Origin of Supracrustal Rocks at Akilia, West Greenland.
C. E. Manning, S. J. Mojzsis, and T. M. Harrison (2006)
Am J Sci 306, 303-366
   Abstract »    Full Text »    PDF »
Biominerals.
H. C. W. Skinner (2005)
Mineralogical Magazine 69, 621-641
   Abstract »    Full Text »    PDF »


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Science. ISSN 0036-8075 (print), 1095-9203 (online)