Age intercalibration of 40Ar/39Ar sanidine and chemically distinct U/Pb zircon populations from the Alder Creek Rhyolite Quaternary geochronology standard

Tiffany Rivera, Michael Storey, M. D. Schmitz, J. L. Crowley

    Publikation: Bidrag til tidsskriftTidsskriftartikelForskningpeer review

    Resumé

    We report results from a 40Ar/39Ar sanidine and CA-TIMS 238U/206Pb zircon dating study of eruption and crystal residence timescales of the Alder Creek Rhyolite (ACR), California, extruded during the Cobb Mountain normal-polarity subchron (C1r.2n). A 40Ar/39Ar ACR sanidine date of 1.1850 ± 0.0016 Ma (2σ external uncertainty), determined relative to the astronomically dated A1 tephra sanidine, is interpreted as the ACR eruption age. This age is supported by CA-TIMS U–Pb zircon dating, guided by LA-ICPMS trace element analyses, titanium-in-zircon (TiZR) thermometry, and cathodoluminescence (CL) imaging. Using these data, two compositionally distinct zircon populations were revealed. “Pre-ACR” Group B zircon exhibit oscillatory zoning, large positive Ce and negative Eu anomalies, high incompatible trace element contents, TiZR temperatures of 650 °C–750 °C, and Th/U disequilibrium corrected 238U/206Pb dates of 1.38–1.24 Ma. These crystals are interpreted as antecrysts inherited from earlier intrusives in the Geysers–Cobb Mountain magma source region. “ACR-related” Group A zircon, present as discrete grains and overgrowths on Group B zircon, display less intense CL with diffuse zoning, and have less pronounced positive Ce and negative Eu anomalies, lower incompatible trace element contents, higher TiZR temperatures that range up to 840 °C, and significantly younger dates. The youngest Group A dates yield a weighted mean of 1.1978 ± 0.0046 Ma (2σ, including systematic uncertainties) that is interpreted as the mean age of zircon crystallization prior to eruption. The 13 ± 5 ka offset between the 40Ar/39Ar and 238U/206Pb dates can be attributed to zircon magma residence time. Recognition of a young population of ACR zircon is consistent with the 40Ar/39Ar eruption age, which coincides with the astronomical age estimate for the Cobb Mountain subchron determined by correlating the oxygen isotope record of the giant piston core MD972143 to the La93(1,1) orbital solution. On the basis of independent radio-isotopic and orbital forcing results, we propose the refined age of 1.1850 ± 0.0016 Ma (2σ external uncertainty) for the Quaternary ACR 40Ar/39Ar sanidine standard.
    OriginalsprogEngelsk
    TidsskriftChemical Geology
    Vol/bind345
    Sider (fra-til)87-98
    ISSN0009-2541
    DOI
    StatusUdgivet - 2013

    Emneord

    • Geochronology
    • EARTHTIME
    • Quaternary
    • Intercalibration
    • Pleistocene
    • Cobb Mountain

    Citer dette

    @article{c6b53f66bbf64b219006c2992622bc8e,
    title = "Age intercalibration of 40Ar/39Ar sanidine and chemically distinct U/Pb zircon populations from the Alder Creek Rhyolite Quaternary geochronology standard",
    abstract = "We report results from a 40Ar/39Ar sanidine and CA-TIMS 238U/206Pb zircon dating study of eruption and crystal residence timescales of the Alder Creek Rhyolite (ACR), California, extruded during the Cobb Mountain normal-polarity subchron (C1r.2n). A 40Ar/39Ar ACR sanidine date of 1.1850 ± 0.0016 Ma (2σ external uncertainty), determined relative to the astronomically dated A1 tephra sanidine, is interpreted as the ACR eruption age. This age is supported by CA-TIMS U–Pb zircon dating, guided by LA-ICPMS trace element analyses, titanium-in-zircon (TiZR) thermometry, and cathodoluminescence (CL) imaging. Using these data, two compositionally distinct zircon populations were revealed. “Pre-ACR” Group B zircon exhibit oscillatory zoning, large positive Ce and negative Eu anomalies, high incompatible trace element contents, TiZR temperatures of 650 °C–750 °C, and Th/U disequilibrium corrected 238U/206Pb dates of 1.38–1.24 Ma. These crystals are interpreted as antecrysts inherited from earlier intrusives in the Geysers–Cobb Mountain magma source region. “ACR-related” Group A zircon, present as discrete grains and overgrowths on Group B zircon, display less intense CL with diffuse zoning, and have less pronounced positive Ce and negative Eu anomalies, lower incompatible trace element contents, higher TiZR temperatures that range up to 840 °C, and significantly younger dates. The youngest Group A dates yield a weighted mean of 1.1978 ± 0.0046 Ma (2σ, including systematic uncertainties) that is interpreted as the mean age of zircon crystallization prior to eruption. The 13 ± 5 ka offset between the 40Ar/39Ar and 238U/206Pb dates can be attributed to zircon magma residence time. Recognition of a young population of ACR zircon is consistent with the 40Ar/39Ar eruption age, which coincides with the astronomical age estimate for the Cobb Mountain subchron determined by correlating the oxygen isotope record of the giant piston core MD972143 to the La93(1,1) orbital solution. On the basis of independent radio-isotopic and orbital forcing results, we propose the refined age of 1.1850 ± 0.0016 Ma (2σ external uncertainty) for the Quaternary ACR 40Ar/39Ar sanidine standard.",
    keywords = "Geochronology, EARTHTIME, Quaternary, Intercalibration, Pleistocene, Cobb Mountain",
    author = "Tiffany Rivera and Michael Storey and Schmitz, {M. D.} and Crowley, {J. L.}",
    year = "2013",
    doi = "10.1016/j.chemgeo.2013.02.021",
    language = "English",
    volume = "345",
    pages = "87--98",
    journal = "Chemical Geology",
    issn = "0009-2541",
    publisher = "Elsevier BV",

    }

    Age intercalibration of 40Ar/39Ar sanidine and chemically distinct U/Pb zircon populations from the Alder Creek Rhyolite Quaternary geochronology standard. / Rivera, Tiffany; Storey, Michael; Schmitz, M. D. ; Crowley, J. L.

    I: Chemical Geology, Bind 345, 2013, s. 87-98.

    Publikation: Bidrag til tidsskriftTidsskriftartikelForskningpeer review

    TY - JOUR

    T1 - Age intercalibration of 40Ar/39Ar sanidine and chemically distinct U/Pb zircon populations from the Alder Creek Rhyolite Quaternary geochronology standard

    AU - Rivera, Tiffany

    AU - Storey, Michael

    AU - Schmitz, M. D.

    AU - Crowley, J. L.

    PY - 2013

    Y1 - 2013

    N2 - We report results from a 40Ar/39Ar sanidine and CA-TIMS 238U/206Pb zircon dating study of eruption and crystal residence timescales of the Alder Creek Rhyolite (ACR), California, extruded during the Cobb Mountain normal-polarity subchron (C1r.2n). A 40Ar/39Ar ACR sanidine date of 1.1850 ± 0.0016 Ma (2σ external uncertainty), determined relative to the astronomically dated A1 tephra sanidine, is interpreted as the ACR eruption age. This age is supported by CA-TIMS U–Pb zircon dating, guided by LA-ICPMS trace element analyses, titanium-in-zircon (TiZR) thermometry, and cathodoluminescence (CL) imaging. Using these data, two compositionally distinct zircon populations were revealed. “Pre-ACR” Group B zircon exhibit oscillatory zoning, large positive Ce and negative Eu anomalies, high incompatible trace element contents, TiZR temperatures of 650 °C–750 °C, and Th/U disequilibrium corrected 238U/206Pb dates of 1.38–1.24 Ma. These crystals are interpreted as antecrysts inherited from earlier intrusives in the Geysers–Cobb Mountain magma source region. “ACR-related” Group A zircon, present as discrete grains and overgrowths on Group B zircon, display less intense CL with diffuse zoning, and have less pronounced positive Ce and negative Eu anomalies, lower incompatible trace element contents, higher TiZR temperatures that range up to 840 °C, and significantly younger dates. The youngest Group A dates yield a weighted mean of 1.1978 ± 0.0046 Ma (2σ, including systematic uncertainties) that is interpreted as the mean age of zircon crystallization prior to eruption. The 13 ± 5 ka offset between the 40Ar/39Ar and 238U/206Pb dates can be attributed to zircon magma residence time. Recognition of a young population of ACR zircon is consistent with the 40Ar/39Ar eruption age, which coincides with the astronomical age estimate for the Cobb Mountain subchron determined by correlating the oxygen isotope record of the giant piston core MD972143 to the La93(1,1) orbital solution. On the basis of independent radio-isotopic and orbital forcing results, we propose the refined age of 1.1850 ± 0.0016 Ma (2σ external uncertainty) for the Quaternary ACR 40Ar/39Ar sanidine standard.

    AB - We report results from a 40Ar/39Ar sanidine and CA-TIMS 238U/206Pb zircon dating study of eruption and crystal residence timescales of the Alder Creek Rhyolite (ACR), California, extruded during the Cobb Mountain normal-polarity subchron (C1r.2n). A 40Ar/39Ar ACR sanidine date of 1.1850 ± 0.0016 Ma (2σ external uncertainty), determined relative to the astronomically dated A1 tephra sanidine, is interpreted as the ACR eruption age. This age is supported by CA-TIMS U–Pb zircon dating, guided by LA-ICPMS trace element analyses, titanium-in-zircon (TiZR) thermometry, and cathodoluminescence (CL) imaging. Using these data, two compositionally distinct zircon populations were revealed. “Pre-ACR” Group B zircon exhibit oscillatory zoning, large positive Ce and negative Eu anomalies, high incompatible trace element contents, TiZR temperatures of 650 °C–750 °C, and Th/U disequilibrium corrected 238U/206Pb dates of 1.38–1.24 Ma. These crystals are interpreted as antecrysts inherited from earlier intrusives in the Geysers–Cobb Mountain magma source region. “ACR-related” Group A zircon, present as discrete grains and overgrowths on Group B zircon, display less intense CL with diffuse zoning, and have less pronounced positive Ce and negative Eu anomalies, lower incompatible trace element contents, higher TiZR temperatures that range up to 840 °C, and significantly younger dates. The youngest Group A dates yield a weighted mean of 1.1978 ± 0.0046 Ma (2σ, including systematic uncertainties) that is interpreted as the mean age of zircon crystallization prior to eruption. The 13 ± 5 ka offset between the 40Ar/39Ar and 238U/206Pb dates can be attributed to zircon magma residence time. Recognition of a young population of ACR zircon is consistent with the 40Ar/39Ar eruption age, which coincides with the astronomical age estimate for the Cobb Mountain subchron determined by correlating the oxygen isotope record of the giant piston core MD972143 to the La93(1,1) orbital solution. On the basis of independent radio-isotopic and orbital forcing results, we propose the refined age of 1.1850 ± 0.0016 Ma (2σ external uncertainty) for the Quaternary ACR 40Ar/39Ar sanidine standard.

    KW - Geochronology

    KW - EARTHTIME

    KW - Quaternary

    KW - Intercalibration

    KW - Pleistocene

    KW - Cobb Mountain

    U2 - 10.1016/j.chemgeo.2013.02.021

    DO - 10.1016/j.chemgeo.2013.02.021

    M3 - Journal article

    VL - 345

    SP - 87

    EP - 98

    JO - Chemical Geology

    JF - Chemical Geology

    SN - 0009-2541

    ER -