Research ArticleGEOCHEMISTRY

Argon constraints on the early growth of felsic continental crust

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Science Advances  20 May 2020:
Vol. 6, no. 21, eaaz6234
DOI: 10.1126/sciadv.aaz6234
  • Fig. 1 Observational constraints and the distribution of successful model solutions.

    Observational constraints used to select successful solutions are shown in orange. The 50th and 90th percentiles of successful solutions are shown in dark green and light green, respectively. (A) 40Ar/36Ar in the atmosphere. Orange bars are based on 40Ar/36Ar measurements of the Archean hydrothermal quartz by Pujol et al. (2), and the orange dot is the present-day 40Ar/36Ar from Lee et al. (16). (B) Mantle potential temperature. Orange dots are the Archean and Proterozoic mantle potential temperatures from Herzberg et al. (18). (C) Present-day cumulative distribution of crustal formation age. The orange line is from Korenaga (11). Ga, billion years. (D) Present-day cumulative distribution of crustal surface age. The orange line is based on the distribution of zircon U-Th crystallization ages (17).

  • Fig. 2 A posteriori distributions of crustal evolution parameters, based on ~2 × 104, ~2.5 × 104, and ~3 × 103 successful Monte Carlo solutions from stages 1, 2, and 3, respectively.

    Distributions from stages 1, 2, and 3 are shown in green, blue, and red, respectively. (A) Initial recycling rate, (B) present-day recycling rate, (C) decay constant for crustal recycling, (D) decay constant for crustal generation, (E) onset time for crustal formation, and (F) reworking factor.

  • Fig. 3 Net crustal growth and crustal generation and destruction rates based on ~3 × 103 successful Monte Carlo solutions.

    The middle 50 and 90% of our successful solutions are shown in dark green and light green, respectively. The medians of the successful solutions are shown in black dotted lines. (A) Net crust growth, (B) crustal generation rate, (C) crustal recycling rate, and (D) crustal reworking rate.

  • Fig. 4 Instantaneous and cumulative contributions of individual mass transfer rates to atmospheric 40Ar based on the median of ~3 × 103 successful Monte Carlo solutions.

    Mantle processing rates to generate continental crust (Kmc), oceanic crust (Kmo), and hot spot islands (Kmp) are shown in red, dark blue, and green, respectively. Crustal recycling (Krc) and reworking (Krw) rates are shown in orange and purple, respectively. (A) Instantaneous contributions and (B) cumulative contributions of individual mass transfer rates to atmospheric 40Ar.

  • Table 1 List of independent variables in the argon degassing model.

    ParameterDefinitionValueUnit
    tdTiming of
    sudden
    degassing
    0.05 to 0.1Ga
    FdSudden
    degassing
    fraction
    10 to 80%
    36Ar(t0)Initial amount
    of 36Ar in BSE
    2 × 1039 to 2 × 1040No. of atoms
    κrDecay constant
    of crustal
    recycling rate
    −3 to 3Ga−1
    κgDecay constant
    of crustal
    generation rate
    −1 to 30Ga−1
    RsInitial crustal
    recycling rate
    0 to 10 × 1022kg Ga−1
    RpPresent-day
    crustal
    recycling rate
    0 to 2 × 1022kg Ga−1
    tsCrustal growth
    starting point
    0.057 to 0.567Ga
    frwCrustal
    reworking rate
    factor
    0.1 to 0.8
    HBSE(tp)Present-day
    BSE heat
    production
    13 to 19TW
    HCC(tp)Present-day
    continental
    crust heat
    production
    5 to 10TW
    Qtotal(tp)Present-day
    total terrestrial
    heat flux
    43 to 49TW
    Qc(tp)Present-day
    core heat flux
    5 to 15TW
    ΔQcDifference
    between initial
    and present-
    day Qc
    2 to 5TW
    feffKmoIncomplete
    degassing
    factor for
    mid-ocean
    ridge degassing
    50 to 100%
    feffKmpIncomplete
    degassing
    factor for
    mantle plume
    degassing
    10 to 100%
  • Table 2 List of dependent variables in the argon degassing model.

    ParameterDefinitionCalculation
    Q(tp)Present-day mantle
    heat flux
    Q(tp) = Qtotal(tp) − HCC(tp)
    40KBSE(tp)Present-day 40K in the
    BSE
    Calculate according to HBSE(tp)
    40Kcc(tp)Present-day 40K in the
    continental crust
    Calculate according to HCC(tp)
    QcCore heat fluxQc(t) = ΔQc(tpt)/tp + Qc(tp)
    KmpHot spot island
    generation rate
    Kmp(t)=Kmp(tp)Qc(t)Qc(tp)feffKmp
    KmoOceanic crust
    generation rate
    Kmo(t)=Kmo(tp)Z(t)V(t)Z(tp)V(tp)feffKmo

Supplementary Materials

  • Supplementary Materials

    Argon constraints on the early growth of felsic continental crust

    Meng Guo and Jun Korenaga

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