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Open AccessArticle

Pressure Dependence of Magnesite Creep

1
Department of Geosciences, University of Akron, Akron, OH 44325, USA
2
Department of Geology and Geophysics, Texas A&M University, College Station, TX 77843, USA
3
Department of Earth Environmental and Planetary Sciences, Brown University, Providence, RI 02912, USA
*
Author to whom correspondence should be addressed.
Now at Newmont Goldcorp, Winnemucca, NV 89414, USA.
Now at Southeastern North Carolina Regional Microanalytical and Imaging Consortium, Fayetteville State University, Fayetteville, NC 28301, USA.
§
Now at Department of Geology, Bowling Green State University, Bowling Green, OH 43403, USA.
Now at National Science Foundation, Alexandria, VA 22314, USA.
Now at Solar Testing Laboratories, Inc., Cleveland OH 44131, USA.
**
Now at OceanaGold, Kershaw, SC 29067, USA.
††
Now at Geological Institute, ETH Zurich, 8092 Zurich, Switzerland.
Geosciences 2019, 9(10), 420; https://doi.org/10.3390/geosciences9100420
Received: 29 July 2019 / Revised: 19 September 2019 / Accepted: 24 September 2019 / Published: 26 September 2019
(This article belongs to the Section Geophysics)
We determined the activation volumes (V*) for polycrystalline magnesite with grain sizes of 2 and 80 µm deforming by low temperature plasticity (LTP) mechanisms (kinking and dislocation glide), diffusion creep, and dislocation creep at temperatures of 500, 750, and 900 °C, respectively, and a strain rate of 1–2 × 10−5 s−1 at effective pressures of 2.9–7.5 GPa in a D-DIA and 0.76 GPa in a Griggs apparatus. In each set of experiments performed at a given temperature, the strength of magnesite increases with increasing pressure. Microstructures of fine-grained magnesite deformed at 500 °C and 750 °C are consistent with deformation by LTP mechanisms and diffusion creep, respectively. Microstructures of coarse-grained magnesite deformed at 900 °C are consistent with deformation by dislocation creep. Pressure dependencies of magnesite flow laws for LTP, diffusion creep, and dislocation creep are given by activation volumes of 34 (± 7), 2 (± 1), and 10 (± 5) × 10−6 m3/mol, respectively. Addition of these activation volumes to previously determined flow laws predicts magnesite strength to be much lower than the flow strength of olivine at all subduction zone depths of the upper mantle. Thus, subducting oceanic lithosphere that has been partially carbonated by reaction with CO2-bearing fluids may deform at lowered stresses where magnesite is present, possibly resulting in strain localization and unstable run-away shear. View Full-Text
Keywords: magnesite; deep focus earthquakes; activation volume magnesite; deep focus earthquakes; activation volume
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Millard, J.W.; Holyoke, C.W., III; Wells, R.K.; Blasko, C.; Kronenberg, A.K.; Raterron, P.; Braccia, C.; Jackson, N.; McDaniel, C.A.; Tokle, L. Pressure Dependence of Magnesite Creep. Geosciences 2019, 9, 420.

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  • Supplementary File 1:

    ZIP-Document (ZIP, 131582 KB)

  • Externally hosted supplementary file 1
    Link: https://works.bepress.com/caleb_holyoke/20/
    Description: All spectra and images used to calculate differential stresses, pressure, strain and strain rate. All spectra files are text files and images are tiff files.
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