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    Experimental determination of Li isotope behaviour during basalt weathering

    Pogge von strandmann, Philip and Fraser, W. and Hammond, S. and Tarbuck, G. and Wood, I. and Oelkers, E. and Murphy, M. (2019) Experimental determination of Li isotope behaviour during basalt weathering. Chemical Geology 517 , pp. 34-43. ISSN 0009-2541.

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    Abstract

    Silicate weathering is the primary control of atmospheric CO2 concentrations on multiple timescales. However, tracing this process has proven difficult. Lithium isotopes are a promising tracer of silicate weathering. This study has reacted basalt sand with natural river water for ~9 months in closed experiments, in order to examine the behaviour of Li isotopes during weathering. Aqueous Li concentrations decrease by a factor of ~10 with time, and δ7Li increases by ~19‰, implying that Li is being taken up into secondary phases that prefer 6Li. Mass balance using various selective leaches of the exchangeable and secondary mineral fractions suggest that ~12–16% of Li is adsorbed, and the remainder is removed into neoformed secondary minerals. The exchangeable fractionation factors have a Δ7Liexch-soln = −11.6 to −11.9‰, while the secondary minerals impose Δ7Lisecmin-soln = −22.5 to −23.9‰. Overall the experiment can be modelled with a Rayleigh fractionation factor of α = 0.991, similar to that found for natural basaltic rivers. The mobility of Li relative to the carbon-cycle-critical cations of Ca and Mg changes with time, but rapidly evolves within one month to remarkably similar mobilities amongst these three elements. This evolution shows a linear relationship with δ7Li (largely due to a co-variation between aqueous [Li] and δ7Li), suggesting that Li isotopes have the potential to be used as a tracer of Ca and Mg mobility during basaltic weathering, and ultimately CO2 drawdown.

    Metadata

    Item Type: Article
    Keyword(s) / Subject(s): Chemical weathering, Weathering experiments, Isotope fractionation, Basalt weathering
    School: Birkbeck Schools and Departments > School of Science > Earth and Planetary Sciences
    Depositing User: Philip Pogge von strandmann
    Date Deposited: 02 May 2019 09:49
    Last Modified: 31 Jul 2019 12:10
    URI: http://eprints.bbk.ac.uk/id/eprint/27380

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