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Shear deformation of bridgmanite and magnesiowüstite aggregates at lower mantle conditions

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Science  08 Jan 2016:
Vol. 351, Issue 6269, pp. 144-147
DOI: 10.1126/science.aad3113
  • Fig. 1 The rotational Drickamer apparatus (RDA) cell assembly used to reach the shallow lower mantle conditions.

    (A) The anvils, gaskets, and cell assembly for the RDA deformation experiment; (B) a side view of the cell assembly; and (C) a top view of the cell assembly. Diffracted x-ray comes mostly from one side of a sample closer to the x-ray detectors.

  • Fig. 2 A plot of the equivalent stress in bridgmanite and magnesiowüstite as a function of strain.

    Run conditions are given in Table 1. Stress in bridgmanite was estimated by using diffraction peaks (110) and (112). Stress in magnesiowüstite was estimated by using diffraction peaks (200) and (220). In both cases, the stresses shown here are the arithmetic average of stresses estimated from these planes. Some hint of strain weakening can be seen, particularly for bridgmanite (hatched regions are drawn to guide the eyes). Results from beta 74 are based on estimated strain (strain marker was not visible). Also, the pressure and temperature conditions for beta 74 are different from all others. Bars represent the errors. Errors are given for one standard deviation and are due to the uncertainties in the peak shift and the fitting errors to equation S1 (supplementary materials).

  • Fig. 3 SEM (scanning electron microscope) back-scattering images of the recovered sample from the run gamma 21.

    (A) A back-scattered electron image of the RDA cell assembly cut along the diameter. The sample position, alumina ring, and TiC central electrode are labeled for clarity. The layers of material above the sample are also identified (ZrO2, Al2O3, TiC+Diamond, BN). (B) A back-scattered electron image of the recovered sample from the run gamma 21, deformed up to 100% strain. The light gray grains are mangesiowüstite, and the dark gray grains are bridgmanite. An oblate shape shows a strain ellipsoid corresponding to the bulk strain of 100%. Arrows indicate the sense of shear. (C) A back-scattered electron image of an undeformed sample from the run gamma 23. This sample was annealed at 27.4 GPa and 2140 K and quenched after 1.5 hours.

  • Table 1 Summary of run conditions.

    The total strain is the equivalent strain, εE, including both axial compression strain (εU) and shear strain (εS) as Embedded Image.

    Run numberTemperature
    (K)
    Pressure
    (GPa)
    Total strain
    (%)
    Strain rate
    (×10−5 s−1)
    beta 74*2000 ± 10024.1 ± 0.5524.3
    gamma 21*2130 ± 10027.0 ± 0.51003.0
    gamma 222130 ± 10027.0 ± 0.555 ± 173.0 ± 0.9
    gamma 23**2140 ± 10027.4 ± 0.500
    gamma 242150 ± 10027.5 ± 0.523 ± 73.2 ± 1.0
    gamma 252150 ± 10027.5 ± 0.548 ± 153.6 ± 1.1

    *Strain marker was not visible in these runs. Strain was estimated from the angle of rotation of the anvil and the relationship between the angle of rotation and shear strain based on previous results. **After annealing, the furnace failed. No strain after annealing.

    Supplementary Materials

    • Shear deformation of bridgmanite and magnesiow??stite aggregates at lower mantle conditions

      Jennifer Girard, George Amulele, Robert Farla, Anwar Mohiuddin, Shun-ichiro Karato

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

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      • Materials and Methods
      • Figs. S1 to S5
      • References

      Additional Data

      Database S1

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