EGU2020-18346
https://doi.org/10.5194/egusphere-egu2020-18346
EGU General Assembly 2020
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Pressure dependence of olivine grain growth at upper mantle conditions

Filippe Ferreira1, Marcel Thielmann1, and Katharina Marquardt2
Filippe Ferreira et al.
  • 1Universitaet Bayreuth, Bayerisches Geoinstitut, Germany
  • 2Imperial College London, Department of Materials, United Kingdom

The convective motion of Earth’s upper mantle is controlled by two main deformation mechanisms: grain size-insensitive dislocation creep and grain size sensitive diffusion creep. Grain size thus plays a key role in upper mantle deformation, as it has a significant impact on the viscosity of the upper mantle. Moreover, grain size also affects seismic velocities as well as seismic attenuation.

Despite the importance of grain size and its evolution during deformation, there is still a lack of experimental data on grain growth of olivine at upper mantle pressures. For this reason, we here investigate olivine grain growth at pressures ranging from 1 GPa to 12 GPa and temperatures from 1200 to 1400ºC. The experiments were done using piston cylinder and multi-anvil apparatuses. We used as a starting material olivine aggregates with small amounts of pyroxene (<10%) produced via sol-gel method.

Our results indicate that grain growth is reduced at increasing pressures.  This suggests that the enhanced grain growth due to the temperature increase with depth may be offset, thus facilitating a change from dislocation to diffusion creep in the deep upper mantle. This might have an important impact on the dynamics of the upper mantle.

How to cite: Ferreira, F., Thielmann, M., and Marquardt, K.: Pressure dependence of olivine grain growth at upper mantle conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18346, https://doi.org/10.5194/egusphere-egu2020-18346, 2020

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  • CC1: Comment on EGU2020-18346, Lucan Mameri, 06 May 2020

    Hi, Filippe.

    Thank you very much for this very interesting contribution. I was wondering...

    1) Do you have any results/ideas about the effects on grain growth of olivine for a higher volume of PX? Lets say 30 or 40%. What about for an aggreagte with 100% olivine aggregate, the results are similar to the 4% PX  study-case you showed?

    2)  What if having thin layers of PX in your experiments instead of a random distribution? how do you think this can affect the grain growth rates as a function of pressure ?

    Looking forward for what's to come

    Regards

    • AC1: Reply to CC1, Filippe Ferreira, 06 May 2020

      Hi Lucan!

      1.  The limitation of having a larger amount of pyroxene is that longer duration of experiments (on the scale of weeks) might be necessary to actually measure grain growth, which can become unfeasible for high pressure experiments (especially for multi-anvil). From the results of Tasaka & Hiraga (2013, doi.org/10.1002/jgrb.50285), who investigated the effect of different volume fractions of enstatite on forsterite grain growth at 1 atm, I expect that our results at 10 vol.%of Px are comparable to 30- 40 vol% Px.  However, the effect of Px volume fraction on the olivine grain growth seems to be larger in the range of 0-10 vol% of Px. Thus, I would expect noticeable increase in the grain growth rate of olivine at 100 vol.% when compared to 96 vol.%.
      2. Interesting point. If there’s no phase mixing I would expect that grains of both phases would grow much faster, as there’s no pinning particles inhibiting grain growth. Would be interesting to test this experimentallly!

      Thank you for your questions,

      Filippe

      • CC2: Reply to AC1, Lucan Mameri, 09 May 2020

        Nice. Thank you Filippe.

        Keep the nice work man

        Regards

         

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