The contribution of this dissertation is to expand the current knowledge of factors and mechanisms that influence the development of preferred orientation of minerlas and pores in different materials, ranging from rocks in Earth's crust to minerals in the deep Earth. Preferred orientation-a main contributing component to elastic anisotropy-is however very challenging to quantify. The overall focus of this thesis thus aims to (1) apply the capabilities of synchrotron X-ray techniques to determine preferred orientations of hexagonal metals and shales under different conditions and (2) enhance our understanding of their relationships to the elastic properties.

Lattice preferred orientation (LPO) or `texture' of hexagonal close-packed iron (hcp- Fe) crystals during deformation has been suggested as the cause of the elastic anisotropy observed in Earth's inner core. However, relatively little is known about LPO of other hcp metals. An investigation of a wide range of hcp metals (Cd, Zn, Os, and Hf) as analogs to hcp-Fe was thus undertaken to better understand deformation mechanisms at high pressure and temperature in Chapter 2. The diamond anvil cell in a radial geometry (rDAC) and the D-DIA multi-anvil apparatus, equipped with a heating system, were used to impose both pressure and stress on the samples. These state-of-the-art tools enable us to create extreme conditions similar to the Earth's interior. A synchrotron X-ray beam is then employed to record diffraction patterns of the deformed materials. Results show that all hcp metals preferentially align their c-axes near the compression axis during deformation but with considerable differences. The gradual texture evolution in Cd and Zn is mainly controlled by basal slip systems while a rapid texture development in Os and Hf at ambient temperature is due to a dominant role of tensile twinning, with some degree of basal slip. At elevated temperature, tensile twinning is suppressed and texturing is governed by combined basal and prismatic slip. Under all conditions, basal slip appears to be the main deformation mechanism in hcp metals at high pressure and temperature. These findings are similar to those of hcp-Fe and useful to better understand the deformation mechanisms of hcp metals and their implications for elastic anisotropy.

Besides the investigation of deep Earth materials, this dissertation also considers crustal rocks: particularly shales, which are among the most anisotropic rocks. Shale has increasingly received attention because of its significance in prospecting for petroleum deposits, as well as seals in the context of CO2 sequestration. Elastic anisotropy in shales is caused by the LPO of clay minerals as well as by shape preferred orientation (SPO) of pore, fractures, and the organic material (kerogen) network. However, due to the small grain size and poor crystallinity of swelling clays, the LPO of clays is difficult to quantify. In Chapter 3, a high-energy synchrotron X-ray diffraction technique was applied to characterize LPO and phase proportions of Posidonia Shale collected in the Hils Syncline from Germany, in order to examine the influence of clay content, burial depth, and thermal history. The samples used in this study had experienced different local temperatures during burial and uplifting, as established by the maturity of kerogen (0.68-1.45% vitrinite reflectance, Ro), but their constituent clay minerals, including kaolinite, illite-mica, and illite-smectite, show similar degrees of LPO in all samples, ranging between 3.7 and 6.3 multiple of random distribution (m.r.d.). These observations imply that the difference in local thermal history, which significantly affects the maturity of kerogen, at most marginally influences LPO of clays, as the alignment of clays was established early in the history.

In Chapter 4, the SPO of constituents phases in Kimmeridge Shale (North Sea, UK) and Barnett Shale (Gulf of Mexico, USA) was quantified to a resolution of ~1 μm by using synchrotron X-ray microtomography (SXMT) technique. Measurements were done at different facilities (ALS, APS, and SLS) to characterize 3D microstructures, explore resolution limitations, and develop satisfactory procedures for data quantification. Segmentation images show that the SPO of low density features, including pores, fractures, and kerogen, is mostly anisotropic and oriented parallel to the bedding plane. Small pores are generally dispersed, whereas some large fractures and kerogen have irregular shapes and remain aligned horizontally. In contrast, pyrite exhibits no SPO. The volume fractions and aspect ratios of low density features extracted from three synchrotron sources show excellent agreement with 6.3(6)% for Kimmeridge Shale and 4.5(4)% for Barnett Shale. A small variation is mainly due to differences of optical instruments and technical setups. The SXMT is proven to be a crucial technique to investigate 3D internal structures of fine-grained materials at high-resolution.

A relationship between LPO, SPO, and elastic anisotropy of the Qusaiba Shale from the Rub'al-Khali basin in Saudi Arabia is established in Chapter 5. The Qusaiba samples exhibit strong LPO of clay minerals (2.4-6.8 m.r.d.) due to their high total clay content and high degree of compaction. The SPO of pores, fractures, and kerogen here are also anisotropic and organized mainly parallel to bedding, with little connectivity of the flat pores normal to the bedding. The microscopic information (LPO) extracted from different synchrotron X-ray techniques is then applied in different averaging approaches (Voigt, Reuss, Hill, and Geometric mean) to calculate macroscopic properties of shales. A comparison of calculated elastic properties (Vp(max)=6.2 km/s, Vp(max)=5.5 km/s, and Vp ani.% =12%) with ultrasonic measurements (Vp(max)=5.3 km/s, Vp(max)=4.1 km/s, and Vp ani.% =27%) suggests some discrepancy as the distribution of kerogen and the orientation of the microfracture and porosity network are not included in the averaging model. These features reduce the strength of the matrix, enhancing the elastic anisotropy. Through linking the matrix and porosity components, a more comprehensive model of shale elastic properties is thus necessary for a further study.

Calcium silicate hydrate (C-S-H) is the main hydration product of Portland cement that mainly contributes to concrete's physical and mechanical properties. The porosity of C-S-H plays a vital role in the durability-based performance of concrete. Most of the information about the microstructure of C-S-H now is only in 2D due to the complex morphologies of hydration products. This dissertation aims to investigate synthetic C-S-H and C-A-S-H with various Ca/Si ratios and curing temperatures using Transmission Electron Microscope (TEM) tomography. The 3D reconstructions of all samples were done using the simultaneous iterative reconstruction technique (SIRT). The highest beam dose that doesn’t damage the samples for TEM tomography is 5000 e-/(nm2 s) for all samples. The 3D reconstructions and selected ROI analysis confirm that there are only foil-like structures for all C-S-H and C-A-S-H samples. Both CPSD and CMIP reveal that most of the pore sizes of all samples are below 40 nm. However, C-S-H at Ca/Si ratio 1.0 and 1.6 seem to have pore sizes larger than 100 nm. The curing temperature causes a lower porosity in the structure of both C-S-H and C-A-S-H. However, the porosity is not affected by chemical composition. Scanning transmission electron microscopy (STEM) is used to compare the results with TEM. The 3D results of both TEM and STEM tomography show no significant difference. Still, the continuous pore size distribution with CMIP simulations shows a remarkable difference. C-S-H at Ca/Si ratio 1.0 from TEM tomography has 3 dominant pore sizes at 22.2, 28.8 and 37.7 nm, while STEM tomography has only one dominant pore size at 6.0 nm. The pore network’s size of TEM_C-S-H 1.0 is significantly larger but less dense than STEM_C-S-H 1.0. A preliminary study of a fluid flow model has been accomplished. Both porosity and permeability increase with samples higher Ca/Si ratio, and higher equilibrated temperatures. The successful model will enhance the understanding of the relationship of mechanical properties and porosity of cement and concrete. TEM tomography combine with Xlib plugin in ImageJ shows the capability to determine the 3D nanostructure and pore networks of C-S-H and C-A-S-H. To determine the sustainability of cements and concrete, the understanding of the relationship of mechanical properties and porosity is needed. The resulting information of 3D nanostructure and pore analysis provide these critical information for developing a new generation of optimized green cement and concrete.

With the advent of x-rays in the late 1800s and crystal x-ray diffraction in the early 1900s, the field of crystallography took off and by now, the crystal structures of most minerals have been well-characterized. When subjected to stress, the response of the crystal is dependent upon the material properties. When an aggregate of randomly oriented anisotropic crystals is subjected to a differential stress, crystallographic preferred orientation can develop. Seismic anisotropy detected in areas of high deformation, such as proximal to subducting slabs and along the core-mantle boundary, has been attributed to the development of crystallographic preferred orientation (CPO), a process in which anisotropic crystals rotate into a similar alignment in response to differential stress, creating an anisotropic bulk aggregate. Stress can also distort the crystal lattice by creating defects in the lattice, such as point defects and dislocations, which create areas of localized elastic strain surrounding the defect. The orientation of the macrostress may affect the residual strain in the crystal lattice. And the evolution of this plasticity around a feature, such as a fracture, can provide information regarding fracture mechanics of the material, how the material responds to a free surface, and elucidate healing mechanics. In this dissertation, three experiments studying microstructure in geologic materials using synchrotron x-rays and their implications for Earth’s systems are explored.

In Chapter 1, the texture development of high-pressure hydrous trigonal phase D [MgSi2O4(OH)2], monoclinic phase Egg [AlSiO3(OH)], and orthorhombic δ-AlO(OH) are investigated using radial diamond anvil cell (DAC) x-ray diffraction. Phase D, synthesized from serpentine, developed an (001) maximum of 7.4 m.r.d, indicating basal slip, and aligning the basal planes perpendicular to the principal axis of compression. Phase Egg, synthesized from kaolinite, developed a strong (001) maximum of 10.3 m.r.d., also indicative of basal slip as the primary deformation mechanism. δ-AlO(OH) developed an (010) maximum of 3.0 m.r.d. parallel to the compression direction. For all phases, the sheet-like planes aligned themselves perpendicular to the compression axis. Visoplastic self-consistent polycrystal plasticity modeling confirmed that (001) slip in phase D at 50% strain produces a texture very similar to the texture observed in the deformed aggregate. The hydrous phases investigated here have P-wave anisotropy and shear-wave splitting values comparable or greater than other mantle phases. The stiffness coefficients of deformed bulk aggregate were also calculated.

In Chapter 2, scanning Laue microdiffraction is used to measure the residual strain in thin sections of natural and experimentally deformed quartzites from which the paleostress orientation is inferred. Samples with low levels of plastic deformation, which possess small, uniform diffraction peak shape return principal strain orientations reasonable with the known or expected deformation conditions, such as a vein quartzite from a hydrothermal structure in Hong Kong (HSM), showing the principal axis of compression perpendicular to the long axes of the grains, and rolled Ti, which shows the principal axis of compression parallel to the normal direction and principal axis of extension parallel to the rolling direction. In samples with high levels of plastic deformation, such as quartzite from a hydrothermal explosion structure in Hong Kong (Ko1) or quartzite deformed in a piston apparatus (H2), the principal strain axes of compression and extension show two maxima oriented along the vertical axis inclined at 45◦ to the Z-direction. This strain pattern, seen across four different rock samples, is believed to be an artifact that results from the inability to detect subpixel shifts in the peak position due to the non-Gaussian intensity distribution of the peak shape. However, the source of this exact strain pattern remains a point of investigation.

In Chapter 3, scanning Laue microdiffraction is used to measure the elastic strain around a Mode I crack along (10-14) in a slice of calcite in a time series of three consecutive scans over the course of 44 hours following load removal. An increasingly compressive strain perpendicular to the fracture surface that migrates and accumulates around the crack plane is observed. Correspondingly, an increasingly tensile strain coplanar to the fracture surface is also observed. Peak broadening is recorded in the areas showing high strain. This suggests the movement of plasticity such as defects toward the fracture surface over time, in addition to the increased compressive strain perpendicular to the crack plane with relaxation of the bulk of the crystal, indicative of healing. The orientation of common low-temperature glide planes r = {10-14} <20-2-1> and f = {-1012} <0-22-1> systems, and twinning on e = {-1018} <40-41> in calcite are oriented to intersect with the crack along (10-14) and could facilitate such movement.

The vast majority of rocks that constitute the Earth are composed of multiple mineral phases and complicated deformation conditions are found everywhere, yet little is known about plastic deformation of polyphase polycrystalline rocks, especially with low symmetry phases and highly contrasting mechanical properties. In particular, plastic deformation of mantle rocks is of interest for its connection to geophysical processes, such as mantle convection, slab subduction and upwelling plumes. Seismic observations show regions in the mantle where seismic waves encounter large scale anisotropy of the rocks they propagate in. Although there are many possible reasons for this large scale anisotropic signature of these particular regions, in the upper mantle it has been connected to the development of crystallographic preferred orientation, hereafter called texture, of the mineral olivine due to plastic deformation produced by specific geodynamical processes. Studies have also connected measured seismic anisotropy to texture in the minerals that compose the core mantle boundary region, in the mantle transition zone and in the core of the Earth. Deformation of lower mantle minerals is still poorly understood. Although large convective cells, upwhelling plumes and subducted slabs are expected, the bulk of the lower mantle remains seismically isotropic. The lower mantle is mainly composed of the mineral bridgmanite and ferropericlase, with a small volume fraction of Ca-Si-perovskite. Understanding plastic deformation of the bridgmanite and ferropericlase mineral aggregate can provide valuable information to better understand lower mantle dynamics, and to explain seismic observations. The objective of this dissertation is to explore plastic deformation of bridgmanite and periclase polycrystalline aggregates from both modeling and experimental approaches. In particular to understand the influence of microstructure in texture development and the role of deformation heterogeneities at the local grain scale.

A finite element framework is used in Chapter 2 to explore plastic deformation by dislocation glide of a virtual two phase polycrystal with a random microstructure. Aggregates are deformed up to 20% strain under uniaxial compression and two different simulations where performed using the FEpX code, one where the yield strength of both phases is the same, and the second where the yield strength of the bridgmanite phase is 8 times higher than the periclase. This approach enabled the investigation of the effects of yield strength contrast in the mechanical response of the phases under uniaxial compression. Trends in texture development, plastic deformation rates and intragranular misorientation distributions are analyzed. Single phase bridgmanite and single phase periclase simulations were also performed for comparison with their two phase counterparts. It is found that both the bridgmanite and periclase phase develop weak texture in both the single and two phase simulations. Distributions of the plastic deformation rate show that as the yield strength contrast is increased in the two phase simulations, heterogeneities in the distribution of the plastic deformation rate across the bulk of the sample increase drastically. However, a wider distribution of the plastic deformation rate is observed in the single phase bridgmanite simulation, than in the two phase simulation where both phases have the same yield strength. This indicates that deformation heterogeneities in bridgmanite are mainly due to the high anisotropy of its single phase mechanical properties. Misorientation of each element in a grain with respect to the grain average orientation is calculated and statistical trends of the grains of the bridgmanite phase and the periclase phase are analyzed separately and compared. While misorientation distributions for the bridgmanite phase remain very similar across the different simulations, misorientation distributions of the periclase phase become much wider and with a larger mean misorientation as the yield strength contrast is increased. In addition, the distribution of misorientations in the periclase phase when deformed on its own is the narrowest of them all, indicating that deformation heterogeneities in the periclase phase are introduced by deforming in the two phase scenario with a harder phase. Slip system activity calculations show most of the deformation by dislocation slip is carried by the periclase phase in the two phase simulation with large yield strength contrast.

A fast Fourier transform formulation implemented in the VPFFT code is used in Chapter 3 to study the effects of microstructure in texture development of a two phase polycrystalline aggregate composed of 75% bridgmanite and 25% periclase, and also single phase simulations for comparison. Using this approach, it is also found that bridgmanite and periclase develop weak texture, even when deformed as single phase aggregates. Furthermore, it is observed that there is little microstructure dependence of the texture and strain rate distributions for a microstructure where periclase is at the cores of bridgmanite grains, one where grains of both phases are randomly distributed across the aggregate and one where periclase grains are at triple junctions of the bridgmanite grains. A microstructure where periclase grains is percolating around bridgmanite grains is found to be the outlier of this study, it develops very strong texture in the bridgmanite phase and presents sharper distributions of the strain rate in this phase than the other tested microstructures, indicating a microstructure dependance of the deformation of bridgmanite in this case. Since grains are discretized into smaller elements, statistical trends in the distribution of strain rates of regions at grain boundaries and regions in interior of grains can be compared. It is found that in two phase simulations, regions at grains boundaries in grains of the periclase phase develop the widest distribution of strain rate values, suggesting that deformation heterogeneities are mainly concentrated in these regions.

High pressure diamond anvil cell experiments were performed on the bridgmanite + periclase two phase system to explore texture development at high pressure due to dislocation slip. Diamond anvil cell experiments were performed in synchrotron x-ray sources, where 2D diffraction patterns are collected and samples are laser heated to induce phase transformations at high pressures. The sample grains sizes that were previously possible to analyze using the traditional Rietveld technique were limited to grain sizes that produced smooth powder diffraction patters in order to analyze intensity variations along Debye rings and determine the texture developed in the sample. Recently the high pressure diamond anvil cell community has adopted a more novel multigrain data collection and analysis technique, where diffraction images with sharp diffraction spots originating from multiple grains can be indexed and clusters in orientation space are searched to correlate multiple diffraction spots with the particular grain they originate from. Applying this data collection technique presents challenges in the diamond anvil cell, in particular when non hydrostatic conditions are desired for texture development studies. The small rotation angle accessible to the diamond anvil cell, peak overlap due to plastic deformation in the grains and low intensity of diffraction spots due to weakly diffracting materials are some of the challenges encountered in these experiments. An overview of the implementation of this data collection and analysis technique to the diamond anvil cell for texture studies, together with some preliminary results, is presented in Chapter 4.