Browsing by Subject "olivine"
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Item Berkovich nanoindentation and FTIR data describing the effect of water on olivine plasticity(2023-08-28) Kumamoto, Kathryn, M; Breithaupt, Thomas, P; Hansen, Lars, N; Wallis, David; Li, Bo-Shiuan; Armstrong, David, EJ; Goldsby, David, L; Li, Yang; Warren, Jessica, M; Wilkinson, Angus, J; lnhansen@umn.edu; Hansen, Lars, N; Rock and Mineral Physics LabThis data set contains data collected as part of a study to determine the influence of dissolved hydrogen on the mechanical properties of olivine. Nanoindentation experiments were conducted to measure the hardness of both pristine olivine crystals and olivine crystals predoped with hydrogen. The hydrogen content of samples was assessed with Fourier-transform infrared spectroscopy (FTIR). This data set includes mechanical data from indentation experiments as well as spectra from FTIR measurements.Item 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 LabWe 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.Item EBSD data for sheared partially molten rocks (olivine + basalt)(2018-01-04) Qi, Chao; Kohlstedt, David L; qixxx063@umn.edu; Qi, ChaoThis 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.Item 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 LabTo 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.Item Experimental Deformation of Olivine Aggregates(2023-12) Meyers, CameronMechanical modeling of deformation in the Earth’s upper mantle relies on flow laws derived from deformation experiments on olivine aggregates. Olivine is the primary phase in Earth’s upper mantle and is thought to control its bulk mechanical behavior. In particular, it is critical to understand the dependence of strain rate on grain size, temperature, and stress. Additionally, as olivine rocks are deformed their microstructures evolve by dynamic recrystallization and formation of crystallographic preferred orientation (CPO), which influence their mechanical properties. In this thesis, we add to the large body of work attempting to understand the physics of high-temperature deformation of olivine aggregates by presenting new experimental data, using both hot-pressed olivine aggregates and naturally sourced dunite rocks as starting material. In Chapter 1, the thesis is broadly summarized in an introductory chapter. This is followed by the description and characterization of a new method for synthesizing fine-grained, nearly pore-free olivine aggregates by evacuated hot pressing of naturally sourced olivine powders in Chapter 2. In this chapter, the material is thoroughly characterized, densification kinetics are examined, and differences in grain growth kinetics between this new method and conventional methods are demonstrated. In Chapter 3, we examine data from experiments on evacuated hot-pressed aggregates that were deformed in torsion in a gas-medium deformation apparatus. These data are used to understand the microstructural evolution of olivine aggregates deformed to high strain. Microstructures were characterized by electron backscatter diffraction (EBSD) to investigate grain size and CPO evolution. This is followed, in Chapter 4, by the presentation of an experimental, wherein evacuated hot-pressed olivine aggregates were deformed in a deadweight creep apparatus at 1 atm confining pressure at conditions where diffusion creep was active. The data are examined to evaluate the diffusion creep flow law for olivine. Finally, in Chapter 5, we present an experimental study aimed at measuring the anisotropy in viscosity of naturally sourced dunite rocks with a preexisting CPO. These studies, together, represent a significant contribution to our understanding of the physics of olivine deformation, and in turn, mantle dynamics.Item The influence of hydrogen, deformation geometry, and grain size on the rheological properties of olivine at upper mantle conditions(2015-09) Tielke, JacobMany important geophysical processes, including mantle convection and the associated movement of Earth's tectonic plates, are strongly dependent upon the rheological properties of Earth's upper mantle. Olivine is the most abundant mineral in the upper mantle and therefore largely controls the mechanical behavior of this region of Earth's interior. Many experimental investigations have been carried out to study the rheological properties of olivine single crystals, synthetically produced aggregates, and naturally occurring mantle rocks at asthenospheric temperatures. In contrast, relatively few studies have focused on measuring the rheological properties of olivine deforming at lithospheric temperatures. Furthermore, there are several unanswered questions about the microphysical processes that control deformation of olivine at upper mantle conditions. One outstanding question in the field of rock and mineral physics is "Do different microphysical processes control the rate of deformation of olivine at asthenospheric compared to lithospheric mantle conditions?" To address this question we carried out direct shear experiments on olivine single crystals at temperatures that span the transition from lithospheric to asthenospheric mantle conditions. The results of these experiments, which are presented in Chapter 2, demonstrate that the dependence of strain rate upon stress transitions from a power-law relationship at high temperatures to an exponential dependence at lower temperatures. This transition in rheological behavior is consistent with deformation that is controlled by the climb of dislocations at high-temperature conditions and deformation that is controlled by the glide of dislocations at low-temperature conditions. Furthermore, the direct shear geometry allows for isolation of the (001)[100] and (100)[001] dislocation slip systems, which cannot be individually activated in triaxial compression. At high-temperature conditions, crystals oriented for shear on the (001)[100] slip system are observed to be weaker than crystals oriented for shear on the (100)[001] slip system. At low-temperature conditions the opposite relationship is observed: crystals oriented for shear on the (100)[001] slip system are weakest. Another important outstanding question is "Do the mechanisms of hydrolytic weakening in olivine differ at asthenospheric compared to lithospheric mantle conditions?" In Chapter 3 we report the results of experiments carried out on olivine single crystals under hydrous conditions at both asthenospheric and lithospheric temperatures. For crystals deformed at high-temperatures and under hydrous conditions, the dependence of strain rate on stress follows a power-law relationship with a stress exponent (n) of ~2.5, consistent with deformation that is rate limited by diffusion of silicon through the olivine lattice. In contrast, crystals deformed at high-temperatures and under anhydrous conditions yield n values of ~3.5, consistent with deformation that is rate limited by diffusion of silicon through the cores of dislocations. At low temperature conditions, the strain rate of both hydrous and anhydrous crystals are equally well described by the same exponential dependence of stress. These observations demonstrate significant hydrolytic weakening occurs at asthenospheric temperatures, but hydrolytic weakening cannot be resolved at lithospheric temperatures for our experimental conditions. Lastly, we address a question about polycrystalline deformation: "What deformation mechanism is responsible for grain-size sensitive (GSS) power-law creep of olivine aggregates?" In Chapter 4 we compare strain rates measured during deformation experiments on olivine aggregates to strain rates calculated from a micromechanical model of intragranular slip. The micromechanical model uses the measured stress from deformation experiments and grain orientations determined from post-deformation electron backscatter diffraction measurements to approximate the contribution of dislocation creep to the strain rate. Olivine aggregates deform up to a factor of 4.6 times faster than the maximum possible rates determined from the micromechanical model of intragranular slip. The ratio of experimentally determined strain rates to those from the micromechanical model is strongly dependent upon grain size, but is independent of stress and strength of lattice-preferred orientation. These observations indicate that GSS power-law creep occurs in both weakly and strongly textured olivine aggregates at the studied conditions. We consider three explanations for the observed rheological behavior, (1) a combination of diffusion and dislocation creep, (2) the operation of dynamic recrystallization creep, and (3) the operation of dislocation-accommodated grain-boundary sliding. Our analyses indicate that the microstructural and mechanical behavior of olivine aggregates deforming in the grain-size sensitive power-law regime are most consistent with the operation of dislocation-accommodated grain-boundary sliding at the studied experimental conditions.