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    The influence of melt infiltration on the Li and Mg isotopic composition of the Horoman Peridotite Massif

    Lai, Y.-J. and Pogge von Strandmann, Philip A.E. and Dohmen, R. and Takazawa, E. and Elliott, T. (2015) The influence of melt infiltration on the Li and Mg isotopic composition of the Horoman Peridotite Massif. Geochimica et Cosmochimica Acta 164 , pp. 318-332. ISSN 0016-7037.

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    Abstract

    We have analysed the Li and Mg isotope ratios of a suite of samples from the Horoman peridotite massif. Our results show that most Li and all Mg isotopic compositions of the Horoman peridotites are constant over 100 metres of continuous outcrop, yielding values for pristine mantle of δ7Li = 3.8 ± 1.4 ‰ (2SD, n = 9), δ25Mg = -0.12 ± 0.02 ‰ and δ26Mg = -0.23 ± 0.04 ‰ (2SD, n = 17), in keeping with values for undisturbed mantle xenoliths. However, there are also some anomalously low δ7Li values (-0.2 to 1.6 ‰), which coincide with locations that show enrichment of incompatible elements, indicative of the prior passage of small degree melts. We suggest Li diffused from the infiltrating melts with high [Li] into the low [Li] minerals and kinetically fractionated 7Li/6Li as a result. Continued diffusion after the melt flow had ceased would have resulted in the disappearance of this isotopically light signature in less than 15 Ma. In order to preserve this feature, the melt infiltration must have been a late stage event and the massif must have subsequently cooled over a maximum of ∼0.3 Ma from peak temperature (950°C, assuming the melts are hydrous) to Li closure temperature (700°C), likely during emplacement. The constant δ26Mg values of Horoman peridotites suggest that chemical potential gradients caused by melt infiltration were insufficient to drive associated δ26Mg fractionation greater than our external precision of 0.03 ‰.

    Metadata

    Item Type: Article
    School: Birkbeck Schools and Departments > School of Science > Earth and Planetary Sciences
    Depositing User: Philip Pogge von strandmann
    Date Deposited: 22 Oct 2015 10:53
    Last Modified: 28 Sep 2017 05:45
    URI: http://eprints.bbk.ac.uk/id/eprint/13144

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