Inclined K-Ar illite age spectra in brittle fault gouges: Effects of fault reactivation and wall-rock contamination

E. Torgersen, G. Viola, Horst Zwingmann, I.H.C. Henderson

    Research output: Contribution to journalArticle

    22 Citations (Scopus)

    Abstract

    © 2014 John Wiley & Sons Ltd. K-Ar clay fraction ages of brittle faults often vary with grain size, decreasing in the finer size fractions, producing an inclined age-grain-size spectrum. K-Ar ages and mineralogical characterization of gouges from two normal faults in the Kongsberg silver mines, southern Norway, suggest that inclined spectra derived from brittle fault rocks reflect the mixing of inherited components with authigenic mineral phases. The ages of the coarsest and finest fractions constrain faulting at c. 260-270 Ma and reactivation around 200-210 Ma, respectively. This study demonstrates how wall-rock contamination influences the K-Ar age of the coarsest size fractions and that authigenic illite and K-feldspar can crystallize synkinematically under equivalent conditions and thus yield the same K-Ar ages.
    Original languageEnglish
    Pages (from-to)106-113
    JournalTerra Nova
    Volume27
    Issue number2
    DOIs
    Publication statusPublished - 2015

    Fingerprint

    fault gouge
    wall rock
    reactivation
    illite
    grain size
    authigenic mineral
    normal fault
    effect
    contamination
    feldspar
    silver
    faulting
    clay
    rock

    Cite this

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    abstract = "{\circledC} 2014 John Wiley & Sons Ltd. K-Ar clay fraction ages of brittle faults often vary with grain size, decreasing in the finer size fractions, producing an inclined age-grain-size spectrum. K-Ar ages and mineralogical characterization of gouges from two normal faults in the Kongsberg silver mines, southern Norway, suggest that inclined spectra derived from brittle fault rocks reflect the mixing of inherited components with authigenic mineral phases. The ages of the coarsest and finest fractions constrain faulting at c. 260-270 Ma and reactivation around 200-210 Ma, respectively. This study demonstrates how wall-rock contamination influences the K-Ar age of the coarsest size fractions and that authigenic illite and K-feldspar can crystallize synkinematically under equivalent conditions and thus yield the same K-Ar ages.",
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    Inclined K-Ar illite age spectra in brittle fault gouges: Effects of fault reactivation and wall-rock contamination. / Torgersen, E.; Viola, G.; Zwingmann, Horst; Henderson, I.H.C.

    In: Terra Nova, Vol. 27, No. 2, 2015, p. 106-113.

    Research output: Contribution to journalArticle

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    AU - Torgersen, E.

    AU - Viola, G.

    AU - Zwingmann, Horst

    AU - Henderson, I.H.C.

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    N2 - © 2014 John Wiley & Sons Ltd. K-Ar clay fraction ages of brittle faults often vary with grain size, decreasing in the finer size fractions, producing an inclined age-grain-size spectrum. K-Ar ages and mineralogical characterization of gouges from two normal faults in the Kongsberg silver mines, southern Norway, suggest that inclined spectra derived from brittle fault rocks reflect the mixing of inherited components with authigenic mineral phases. The ages of the coarsest and finest fractions constrain faulting at c. 260-270 Ma and reactivation around 200-210 Ma, respectively. This study demonstrates how wall-rock contamination influences the K-Ar age of the coarsest size fractions and that authigenic illite and K-feldspar can crystallize synkinematically under equivalent conditions and thus yield the same K-Ar ages.

    AB - © 2014 John Wiley & Sons Ltd. K-Ar clay fraction ages of brittle faults often vary with grain size, decreasing in the finer size fractions, producing an inclined age-grain-size spectrum. K-Ar ages and mineralogical characterization of gouges from two normal faults in the Kongsberg silver mines, southern Norway, suggest that inclined spectra derived from brittle fault rocks reflect the mixing of inherited components with authigenic mineral phases. The ages of the coarsest and finest fractions constrain faulting at c. 260-270 Ma and reactivation around 200-210 Ma, respectively. This study demonstrates how wall-rock contamination influences the K-Ar age of the coarsest size fractions and that authigenic illite and K-feldspar can crystallize synkinematically under equivalent conditions and thus yield the same K-Ar ages.

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