Tracing Proterozoic arc mantle Hf isotope depletion of southern Fennoscandia through coupled zircon U–Pb and Lu–Hf isotopes

Andreas Petersson, Karolina Bjärnborg, Anders Scherstén, Axel Gerdes, Tomas Næraa

    Research output: Contribution to journalArticle

    Abstract

    Constraints on the composition of the depleted mantle Sm–Nd and Lu–Hf crust formation ages have a long history of scientific debate. When calculating mantle extraction ages, and constructing crustal growth models, a linear evolution of incompatible trace elements in a depleted mantle since > 4 Ga is routinely used. Mantle depletion however varies regionally and over time and subduction of sediments and oceanic crust renders a mantle-wedge variously enriched relative to a modelled depleted mantle. Here we show that primitive mantle-derived subduction related gabbroic intrusions from southern Fennoscandia have Hf isotope compositions that are enriched relative to a MORB-like linear depleted mantle evolution curve. Extrapolation of primitive Paleoproterozoic gabbro suites enables the construction of a regional mantle evolution curve, providing improved constraints on model ages, crustal residence times and the fraction of juvenile versus reworked continental crust. Convergent margins are assumed to be one of the main sites of continental crust growth, and using an overly depleted mantle source yield model ages that are too old, and hence cumulative crustal growth models show too much crust generation early in the Earth's history. The approach of using the Hf isotope composition of zircon from primitive subduction related gabbroic intrusions as a proxy for mantle Hf isotope composition, piloted in this study, can be applied to other convergent margins.

    Original languageEnglish
    Pages (from-to)122-131
    Number of pages10
    JournalLithos
    Volume284-285
    DOIs
    Publication statusPublished - 1 Jul 2017

    Fingerprint

    Isotopes
    Proterozoic
    zircon
    isotope
    mantle
    Chemical analysis
    Trace Elements
    Extrapolation
    convergent margin
    subduction
    Sediments
    Earth (planet)
    continental crust
    crust
    history
    mid-ocean ridge basalt
    gabbro
    mantle source
    oceanic crust
    residence time

    Cite this

    Petersson, Andreas ; Bjärnborg, Karolina ; Scherstén, Anders ; Gerdes, Axel ; Næraa, Tomas. / Tracing Proterozoic arc mantle Hf isotope depletion of southern Fennoscandia through coupled zircon U–Pb and Lu–Hf isotopes. In: Lithos. 2017 ; Vol. 284-285. pp. 122-131.
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    Tracing Proterozoic arc mantle Hf isotope depletion of southern Fennoscandia through coupled zircon U–Pb and Lu–Hf isotopes. / Petersson, Andreas; Bjärnborg, Karolina; Scherstén, Anders; Gerdes, Axel; Næraa, Tomas.

    In: Lithos, Vol. 284-285, 01.07.2017, p. 122-131.

    Research output: Contribution to journalArticle

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