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Preservation of Earth-forming events in the tungsten isotopic composition of modern flood basalts

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Science  13 May 2016:
Vol. 352, Issue 6287, pp. 809-812
DOI: 10.1126/science.aad8563
  • Fig. 1 μ182W values measured for the Baffin Bay and Ontong Java Plateau samples, the geological reference materials VE-32 and BHVO-1, and the Alfa Aesar W standard.

    The values are expressed as deviations, in parts per million (ppm), from the average value measured for the W standard. The gray shaded area represents 2σ for the average W standard value. Errors for each data point are 2σ.

  • Fig. 2 HSE abundances for the Baffin Bay and Ontong Java Plateau (OJP) samples.

    Abundances are normalized to the HSEs of carbonaceous chondrites (CI group) from (25). The gray shaded area shows the range of HSE abundances for type-2 Hawaiian picrites (26).

  • Fig. 3 Model for the creation of mantle reservoirs with distinct W isotopic compositions.

    (A) Early core formation leaves the proto-Earth’s mantle with a high Hf/W ratio that, with time, evolves to a high μ182W value (i). (B) The impact of a large body affects the Hf/W ratio and W isotopic composition of a portion of the proto-Earth’s mantle. (C) Evolution of the portion of the mantle (ii) affected by the impact of a large body, involving some degree of isotopic equilibration between the impactor materials and the mantle. The core of the impactor subsequently merges with the core of the proto-Earth. (D) Possible scenario after isostatic adjustment (27) and creation of a mantle with heterogeneous μ182W through impacts of large bodies. Mantle domains affected by impacts that occur after the extinction of 182Hf no longer generate radiogenic 182W, so their 182W/184W ratios can change only by mixing with other terrestrial reservoirs or with late-accreted chondritic material. (E) Late accretion, representing ~0.5% of Earth’s mass, decreases the 182W/184W ratio of all the earlier-formed reservoirs by ~15 ppm. This last accretion is responsible for endowing the modern mantle with chondritic relative abundances of the HSEs.

  • Table 1 Tungsten concentrations and isotopic compositions.

    Included are data from the Baffin Bay samples Pi-23a, Pi-23b, and Pd-2; the Ontong Java Plateau sample 192-1187A-009R-04R; the mid-ocean ridge glass sample VE-32; and the BHVO-1 basalt standard. Uncertainties are ±2σ. More details are given in (17) and table S2.

    LocalityGeodynamic
    context
    Sampleμ182W
    (ppm)
    ±2σ
    (ppm)
    W
    (ppb)
    Baffin BayFlood basaltPi-23a11.95.962
    Baffin BayFlood basaltPi-23b8.35.662
    Baffin BayFlood basaltPd-248.44.626
    Ontong Java
    Plateau
    Flood basalt192-1187A-
    009R-04R
    23.95.323
    East Pacific RiseMid-ocean
    ridge basalt
    VE-32–0.84.554
    HawaiiOcean island basaltBHVO-1–2.37.7274

Supplementary Materials

  • Preservation of Earth-forming events in the tungsten isotopic composition of modern flood basalts

    Hanika Rizo, Richard J. Walker, Richard W. Carlson, Mary F. Horan, Sujoy Mukhopadhyay, Vicky Manthos, Don Francis, Matthew G. Jackson

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods
    • Figs. S1 to S6
    • Tables S1 to S5
    • Full Reference List

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