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Early Archaean Age for the Isua Iron Formation, West Greenland

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Abstract

SOME 150 km north-east of Godthaab, on the edge of the inland ice cap, a refolded syncline of mainly basic rocks containing banded ironstones and other rocks of supracrustal origin is enclosed by granitic gneisses (Fig. 1). These gneisses have yielded an Rb-Sr whole-rock isochron age of 3,700 ± 140 m.y., indistinguishable from that of the Amitsoq gneisses of the Godthaab area1. The present metamorphic grade of both the gneisses and the iron formation is upper greenschist to amphibolite facies. There is no published map of the area, but the following geological details are taken from reports by Keto2. The total succession of supracrustal rocks is 2 to 3 km thick. The lower part of the succession consists of quartzites and meta-greywackes. These are overlain by garnet–chlorite schists and banded iron formation, including both Fe-oxides and carbonates. The top of the succession consists of greenschist facies metabasites, Bridgwater et al.3 suggest that the Isua supracrustals may represent a shallow-water shelf facies.

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References

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Authors and Affiliations

  1. Department of Geology, University of Oxford,

    S. MOORBATH, R. K. O'NIONS & R. J. PANKHURST

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  1. S. MOORBATH
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  2. R. K. O'NIONS
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  3. R. J. PANKHURST
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MOORBATH, S., O'NIONS, R. & PANKHURST, R. Early Archaean Age for the Isua Iron Formation, West Greenland. Nature 245, 138–139 (1973). https://doi.org/10.1038/245138a0

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