Browsing by Subject "EBSD"

Now showing 1 - 4 of 4
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    Data for Grain Growth in Olivine + Ferropericlase Rocks Deformed to High Strains
    (2023-10-12) Wiesman, Harison S; Zimmerman, Marrk E; Kohlstedt, David L; wiesm010@umn.edu; Wiesman, Harison S; University of Minnesota Rock and Mineral Physics Lab
    We performed grain growth experiments on four samples of olivine (Ol) + periclase (Per); three samples contained volume fractions of fPer = 0.2, 0.5, 0.8 of Per100 while the fourth contained fPer = 0.2 of Per70, a Fe-bearing periclase. Prior to the grain growth experiments, these samples were deformed to shear strains of γ = 6 – 7, which resulted in a well-mixed, random distribution of grains of both phases among each other. After deformation, samples were statically annealed for 10 h and 100 h at T = 1523 K in a one-atmosphere furnace to facilitate grain growth. Almost all grain growth occurred within the first 10 h of annealing and only the sample containing fPer = 0.8 experienced additional, albeit limited, grain growth up to 100 h. Additionally, grain growth laws determined for single-phase samples of Ol and Per predict increases in grain size by factors of 4 and 5, respectively after 100 h of annealing, larger than observed in our experiments. We attribute the initial increase in grain size during the first 10 h of annealing to stored strain energy from deformation and/or Ostwald ripening, however the kinetics of grain growth are too slow in our samples to allow for grain growth over longer periods of time. The lack of significant grain growth in our study reaffirms the importance of Zener pinning in polymineralic rocks deformed to large strains, such that, once mixing is thorough, pinning along interphase boundaries is effective at maintaining a fine grain size.
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    EBSD data for sheared partially molten rocks (olivine + basalt)
    (2018-01-04) Qi, Chao; Kohlstedt, David L; qixxx063@umn.edu; Qi, Chao
    This data set contains the EBSD data for samples of olivine + basaltic melt deformed in torsion. The results are published in "Crystallographic preferred orientation of olivine in sheared partially molten rocks: The source of the 'a-c switch'" by Chao Qi, Lars Hansen, David Wallis, Ben Holtzman and David Kohlstedt on Geochemistry, Geophysics, Geosystems (G-cubed) 2018.
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    The Effect of Secondary-Phase Fraction on the Deformation of Olivine + Ferropericlase Aggregates (DATA)
    (2022-09-29) Wiesman, Harison S; Zimmerman, Mark E; Kohlstedt, David L; wiesm010@umn.edu; Wiesman, Harison S; University of Minnesota Rock and Mineral Physics Lab
    To study the mechanical and microstructural evolution of polymineralic rocks, we performed deformation experiments on two-phase aggregates of olivine (Ol) + ferropericlase (Per). Two-phase samples were prepared with periclase fractions (fPer) between 0.1 to 0.8. Additionally, single-phase samples of both Ol and Per were prepared to facilitate comparison between the mechanical and microstructural behavior of two-phase and single-phase materials under the same experimental conditions. Each sample was deformed in torsion at T = 1523 K, P = 300 MPa at a constant strain rate up to a final shear strain of γ = 6 to 7. Microstructural developments indicate differences in both grain size and crystalline texture between single- and two-phase samples. During deformation, grain size approximately doubled in our single-phase samples of Ol and Per but remained unchanged or decreased in two-phase samples. Zener-pinning relationships fit to the mean grain sizes in each phase demonstrate that the grain size of the primary phase is controlled by phase boundary pinning. The stress-strain data and calculated values of the stress exponent, n, indicate that Ol in our samples deformed by dislocation-accommodated sliding along grain-grain interfaces while Per deformed via dislocation creep. At shear strains of γ < 1, the strengths of samples with fPer ≥ 0.5 match those modeled by assuming both phases deform at the same stress, while the strengths of samples with fPer ≤ 0.5 are greater than predicted by instead assuming both phases deform at the same strain rate. Above γ = 4, however, sample strengths are greater than those predicted by either the uniform stress or the uniform strain rate bound. We hypothesize that these high strengths are due to the presence of phase boundaries throughout our two-phase samples, for which deformation is rate-limited by dislocation motion along interfacial boundaries.
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    Kinematic and thermochronologic studies of Cordilleran metamorphic complexes (Pioneer, Idaho; North Cascades, Washington)
    (2012-09) Alamdarie, Ahmadreza Malekpour
    This thesis addresses the exhumation of metamorphic rocks in two settings in the North American Cordillera: (1) exhumation of the Pioneer core complex rocks in Idaho, related to detachment activity for which the deformation kinematics are analyzed in detail in this thesis; (2) exhumation of rocks associated with incision of the Skagit Gorge and Ross Lake drainages, North Cascades, Washington state, as traced by fission-track age-elevation relations. In the first study, kinematic analysis was aimed at determining the relative contributions of pure and simple shear strain in the ~100 m thick quartzite-dominated detachment shear zone, using quartz microstructures (quartz ribbons and recrystallized grains) and crystallographic preferred orientation (measured by electron backscatter diffraction) as well as the shape preferred orientation of feldspar porphyroclasts. Results from quartz microfabric suggest a pure shear contribution of 0-70%, which likely reflects the spatial and temporal distributions of crustal thinning in this detachment system. Vorticity derived from feldspar shape fabrics indicates that an initial, pure-shear dominated fabric was overprinted by an increment of simple shear dominated strain (g ~ 1.0) that rotated feldspar clasts "in mass" out of their average orientation, likely during the formation of C' shear planes. In the second study, apatite fission-track ages were obtained from 13 samples from two subvertical profiles on the steep flanks of Skagit Gorge and Ross Lake in the North Cascades, in order to construct age-elevation relations. Results from this study are combined with previous apatite and zircon U-Th/He ages from the same samples to provide some new information about the cooling history. The Ross Lake traverse displays an enigmatic reversal of slope of age-elevation curves, possibly owing to thermal resetting from volcanic flows at ~15 Ma. The Skagit transect displays a steep age-elevation profile an provides an exhumation rate of 0.21 km/Myr, a value similar to that obtained from U-Th/He systems.