Sm-Nd studies of Archaean metasediments and metavolcanics from West Greenland and their implications for the Earth's early history |
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| Authors: | PJ Hamilton RK O&#x;Nions D Bridgwater A Nutman |
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| Institution: | 1. Department of Earth Sciences, Cambridge University, Downing Street, Cambridge, U.K.;2. Geologisk Museum, Oster Voldgade 5-7, 1350 København, Denmark;3. The Geological Survey of Greenland, Oster Voldgade 10, DK-1350 København, Denmark |
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| Abstract: | Metasedimentary and metavolcanic rocks from the Archaean of West Greenland have been examined for evidence of crustal components greater than 3.8 Ga in age and for their compatibility with the presently adopted bulk Earth Sm-Nd parameters. Sm-Nd isotopic data have been obtained for the garbenschiefer metagabbro unit, metasediments from the Isua supracrustal belt, gneisses interior to the Isua belt and metasediments from the Malene supracrustal belt.Using estimates of emplacement age (T) of between 3.77 and 3.67 Ga for the parental volcanics to the garbenschiefer unit, initial143Nd/144Nd ratios yield positiveεNdT values between +1.0 and +3.1 (relative to the CHUR parameters) for seven out of eight samples. Model Sm-Nd ages for the Isua gneisses and metasediments are only compatible with their estimated stratigraphic ages if their sources were ca.+2εNd relative to CHUR at those times. Similarly, model Sm-Nd ages for the Malene samples are only compatible with stratigraphic age constraints when based on a source evolution with positiveεNdT. Implications of these results for the early development of the Earth's mantle are discussed. |
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