146Sm–142Nd evidence from Isua metamorphosed sediments for early differentiation of the Earth's mantle

Guillaume Caro (), Bernard Bourdon, Jean-Louis Birck and Stephen Moorbath
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Guillaume Caro: Université Denis Diderot 4
Bernard Bourdon: Université Denis Diderot 4
Jean-Louis Birck: Université Denis Diderot 4
Stephen Moorbath: Oxford University

Nature, 2003, vol. 423, issue 6938, 428-432

Abstract: Abstract Application of the 147Sm–143Nd chronometer (half-life of 106?Gyr) suggests that large-scale differentiation of the Earth's mantle may have occurred during the first few hundred million years of its history1. However, the signature of mantle depletion found in early Archaean rocks is often obscured by uncertainties resulting from open-system behaviour of the rocks during later high-grade metamorphic events2. Hence, although strong hints exist regarding the presence of differentiated silicate reservoirs before 4.0?Gyr ago, both the nature and age of early mantle differentiation processes remain largely speculative3,4,5. Here we apply short-lived 146Sm–142Nd chronometry (half-life of 103?Myr) to early Archaean rocks using ultraprecise measurement of Nd isotope ratios. The analysed samples are well-preserved metamorphosed sedimentary rocks from the 3.7–3.8-Gyr Isua greenstone belt of West Greenland. Our coupled isotopic calculations, combined with an initial ɛ143Nd value from ref. 6, constrain the mean age of mantle differentiation to 4,460 ± 115?Myr. This early Sm/Nd fractionation probably reflects differentiation of the Earth's mantle during the final stage of terrestrial accretion.

Date: 2003
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DOI: 10.1038/nature01668

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