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Pressure Dependence Of The Strength Of Magnesite Deforming By Low Temperature Plasticity, Diffusion Creep, Or Dislocation Creep

Millard, Joseph William

Abstract Details

2018, Master of Science, University of Akron, Geology.
Recent experiments by Holyoke et al. [2014] indicate that magnesite is weak compared to olivine possibly, leading to strain localization into magnesite-bearing horizons of downgoing subducting slabs, and causing intermediate depth (200 – 400 km) deep focus earthquakes (DFE). However, they did not determine the pressure dependence of the strength of magnesite. In order to determine the pressure dependence of magnesite deforming by low temperature plasticity (LTP) mechanisms (kinking and dislocation glide), diffusion creep, and dislocation creep, I deformed two natural magnesite aggregates (d ~ 3 and 80 µm) over a wide range of pressures (Peff = 0.76 – 7.5 GPa) at strain-rates of ~ 10-5/s and at temperatures T = 500, 750, and 900 °C, respectively. Triaxial deformation experiments were conducted in the D-DIA at Beamline 6-BMB at the Advanced Photon source at Argonne National Lab and in the Griggs apparatus at the University of Akron. Differential stresses in all sets of experiments increase with increasing pressure. Microstructures in experiments performed on fine-grained magnesite at 500 °C include flattened, angular grains, which were slightly reduced in size; microstructures in experiments performed on fine-grained magnesite at 750 °C include rounded grains, increased porosity and four-grain junctions; and microstructures in experiments performed on coarse-grained magnesite at 900 °C include elongated grains, patchy undulatory extinction, and recrystallized grains at grain boundaries. Based on these results and results obtained by Holyoke et al. [2014], the pressure dependence or activation volume, (V*) = 33.8 (±1), 2.2 (±0.7), and 10.3 (±2)*10-6 m3/mol, for LTP, diffusion creep, and dislocation creep, respectively. With the addition of the influence of pressure to the flow laws of Holyoke et al. [2014], the strength contrast between magnesite and olivine decreases. However, magnesite remains orders of magnitude weaker than olivine at all subduction zone depths which may lead to strain localization and generation of DFE.
Caleb Holyoke, Dr. (Advisor)
John Peck, Dr. (Committee Member)
James Thomka, Dr. (Committee Member)
60 p.

Recommended Citations

Citations

  • Millard, J. W. (2018). Pressure Dependence Of The Strength Of Magnesite Deforming By Low Temperature Plasticity, Diffusion Creep, Or Dislocation Creep [Master's thesis, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1526913343559104

    APA Style (7th edition)

  • Millard, Joseph. Pressure Dependence Of The Strength Of Magnesite Deforming By Low Temperature Plasticity, Diffusion Creep, Or Dislocation Creep. 2018. University of Akron, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1526913343559104.

    MLA Style (8th edition)

  • Millard, Joseph. "Pressure Dependence Of The Strength Of Magnesite Deforming By Low Temperature Plasticity, Diffusion Creep, Or Dislocation Creep." Master's thesis, University of Akron, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1526913343559104

    Chicago Manual of Style (17th edition)