Evaluating quartz crystallographic preferred orientations and the role of deformation partitioning using EBSD and fabric analyser techniques (original) (raw)
Related papers
Journal of Structural Geology, 1993
Individual orientation determination of quartz grains by electron channelling in principle gives the complete orientation. However, in routine analysis the noise level in electron channelling patterns (ECPs) does not permit the determination of handedness of a quartz grain in a polycrystal. In practice, all quartz grains are arbitrarily indexed as right-handed. Hence, Dauphine twins can be identified, but not Brazil twins. This practice also means that only the centrosymmetric petrophysical properties can be determined from texture measurements. These include most geologically relevant properties (e.g. thermal conductivity, thermal expansion and elasticity). However, other properties (e.g. piezoelectricity) which are not centrosymmetric cannot be calculated from such texture measurements. Some texture-forming processes (e.g. dislocation glide) can also be considered to be centrosymmetric in quartz, whereas others (e.g. grain boundary migration) may not be.
Journal of the Geological Society of India, 2012
The lattice preferred orientation analysis of quartz c-axis has been used to study the fabric elements in deformed quartz. Application of X-ray texture goniometer attached with high resolution X-ray diffractometer is used to improve the quality of the studies related to texture analysis, which is difficult to observe under conventional optical microscopic method. A comparison is made in between the conventional optical microscope and XTG method using a quartz sample from Malanjkhand reef is used to demonstrate the difference obtained within fabric elements. In photomicrograph, only one fabric component is observed while pole figure analysis using XTG method depicts three components of deformation. This technique is also very useful in the study of polymineralic rocks as well as deformation induced in synthetic materials.
Journal of Structural Geology, 2016
We ask the question whether petrofabric data from anisotropy of magnetic susceptibility (AMS) analysis of deformed quartzites gives information about shape preferred orientation (SPO) or crystallographic preferred orientation (CPO) of quartz. Since quartz is diamagnetic and has a negative magnetic susceptibility, 11 samples of nearly pure quartzites with a negative magnetic susceptibility were chosen for this study. After performing AMS analysis, electron backscatter diffraction (EBSD) analysis was done in thin sections prepared parallel to the K 1 K 3 plane of the AMS ellipsoid. Results show that in all the samples quartz SPO is sub-parallel to the orientation of the magnetic foliation. However, in most samples no clear correspondance is observed between quartz CPO and K 1 (magnetic lineation) direction. This is contrary to the parallelism observed between K 1 direction and orientation of quartz c-axis in the case of undeformed single quartz crystal. Pole figures of quartz indicate that quartz c-axis tends to be parallel to K 1 direction only in the case where intracrystalline deformation of quartz is accommodated by prism slip. It is therefore established that AMS investigation of quartz from deformed rocks gives information of SPO. Thus, it is concluded that petrofabric information of quartzite obtained from AMS is a manifestation of its shape anisotropy and not crystallographic preferred orientation.
Double Crystal Topography Compensating for the Strain in Processed Samples
physica status solidi (a), 1985
An extension of double crystal topography and -diffractometry is presented. The new technique is especially dedicated for defect characterization in samples strained from technological processing. Its basic idea is to account for the curvature in such samples by a crystal collimator of tunable curvature. The capacity of this "curved collimator topography" (CCT) in revealing dislocations as well as in analysing the composition of the mixed crystal layers is demonstrated with examples from Gal -&l,As-double-hetero-epitaxy.
Journal of Structural Geology, 2018
Kinematic analysis of deformed rocks requires study of structures in a section parallel to the stretching lineation and perpendicular to the foliation, i.e., XZ section of the strain ellipsoid. However, presence of stretching lineation is more of an exception rather than a norm in naturally deformed rocks. This raises challenges for kinematic studies. In this study the authors advocate use of Anisotropy of Magnetic Susceptibility (AMS) to identify the three principal axes of AMS ellipsoid (K 1 >K 2 >K 3), which are equated with principal axes of the strain ellipsoid (X>Y>Z). This helps identify X direction of strain ellipsoid in deformed rocks that lack visible stretching lineations. It is proposed that a section prepared parallel to the K 1 K 3 plane of a deformed rock can be treated as equivalent to XZ section of strain ellipsoid, thus making it possible to perform kinematic studies in a rock that did not have stretching lineation. Use of this method is demonstrated on massive metavolcanic rocks of Hutti region (Dharwar Craton, South India), which is replete with quartz veins that contain gold. Crystallographic Preferred Orientation (CPO) of quartz veins is measured using SEM-EBSD studies of thin sections prepared parallel to K 1 K 3 plane of the host rock. Obtained data help recognize the presence of down-dip sense of movement as well as strain partitioning within veins, which are aspects that were not recognized in earlier studies. It is concluded that integration of AMS and SEM-EBSD studies will play an important role in kinematic studies in future.
Earth and Planetary Science Letters, 2019
Crystallographic preferred orientations (CPOs) in olivine are widely used to infer the mechanisms, conditions, and kinematics of deformation of mantle rocks. Recent experiments on water-saturated olivine were the first to produce a complex CPO characterised by bimodal orientation distributions of both [100] and [001] axes and inferred to form by combined activity of (001)[100], (100)[001], and (010)[100] slip. This result potentially provides a new microstructural indicator of deformation in the presence of elevated concentrations of intracrystalline hydrous point defects and has implications for the interpretation of seismic anisotropy. Here, we document a previously unexplained natural example of this CPO type in a xenolith from Lesotho and demonstrate that it too may be explained by elevated concentrations of hydrous point defects. We test and confirm the hypothesis that combined (001)[100], (100)[001], and (010)[100] slip were responsible for formation of this CPO by (1) using high-angular resolution electron backscatter diffraction to precisely characterise the dislocation types present in both the experimental and natural samples and (2) employing visco-plastic self-consistent simulations of CPO evolution to assess the ability of these slip systems to generate the observed CPO. Finally, we utilise calculations based on effective-medium theory to predict the anisotropy of seismic wave velocities arising from the CPO of the xenolith. Maxima in S-wave velocities and anisotropy are parallel to both the shear direction and shear plane normal, whereas maxima in P-wave velocities are oblique to both, adding complexity to interpretation of deformation kinematics from seismic anisotropy.
Crystallographic preferred orientation development by dissolution–precipitation creep
Journal of Structural Geology, 2000
Crystallographic preferred orientations (CPOs) in deformed rocks are commonly interpreted as resulting from crystal plastic deformation mechanisms, where deformation is achieved by the movement of dislocations. In this paper we investigate the possibility of CPO-development by dissolution±precipitation creep or pressure solution. A numerical model is presented, which simulates the development of a grain aggregate that deforms by reaction-controlled dissolution±precipitation creep. Grains are simulated as rectangular boxes that change their shape by growth, or dissolution of their surfaces, depending on the normal stresses acting on the individual surfaces. Grains can also rotate due to an applied vorticity (for non-coaxial deformation) and if they have a non-equidimensional shape. For each strain increment, stress that is applied to the grains is the same for all grains, while individual grains deform and rotate by different amounts. A variety of CPOs develop at moderate strains, depending on the reaction rates of the different crystal-surfaces and type of deformation (uni-axial shortening, plane strain pure shear and simple shear). The modelling results con®rm that dissolution±precipitation creep may play a role in CPO-development in rocks. q
Accurate quantification of quartz and other phases by powder X-ray diffractometry
Analytica Chimica Acta, 1997
The 33 parameters that affect accuracy of quantitative analysis by X-ray powder diffractometry can be grouped as (1) Instrumental or systematic, (2) Inherent properties of the analyte, or (3) Parameters related to preparation and mounting of powders. The effect of each on diffraction intensity is summarized. An optimal value or range is given for instrumental parameters. Evaluation of inherent parameters of the analyte and optimization of those related to preparation and mounting of powders are discussed. Published methods are briefly reviewed. Their reported detection limits for crystalline silica are well below what can be reliably determined in natural and industrial products if one or more critical parameters are neglected. as the size and shape of coherent diffraction domains. An addendum illustrates practical consideration of major parameters during routine analysis for quartz.
Quaternary International, 2017
Sequential experiments were performed with quartzite flakes with the main purpose of monitoring usewear formation processes. The two main objectives of this research were the construction of a wide reference collection to serve for future functional interpretations of the archaeological material and to achieve a better comprehension of the mechanical behaviour of quartzite when subjected to the stress applied in determined prehistoric tasks (e.g., sawing, scraping bone, wood, etc.). The two objectives are strictly related because the appearance of wear on the tool edges resulting from those tasks would be dependant on the mechanical behaviour of the rock in question. Concepts from tribology were used to provide an explanatory framework. As mechanical behaviour of solid materials always depends on their mechanical proprieties which are unique, each raw material should be treated individually in use-wear analysis. For this reason, there is an urgent need to create a reliable and objective system to identify and interpret wear due to use on quartzite. For data recording, we resorted to both optical and electron microscopes (OLM and SEM) to present a wide photographic documentation and to compare the adequacy and complementarity of those microscopic techniques for microwear studies. Furthermore, both the experimental residues of the worked materials and the rock particles detached from the active edges were analysed to understand their role as interfacial medium affecting use-wear formation. EDX (Energy-Dispersive X-ray spectroscopy) was used to document the presence of rock particles detached from the tools edges and then embedded in the residues of the worked materials. The results from analysing the experimental flakes allowed us to infer more closely the mechanical behaviour of quartzite. As a final point, the potential of OLM and SEM for analysing quartzite surfaces was evaluated and it emerged that the combination of the two techniques in an integrated approach is a feasible choice, though the application of SEM is always desirable in order to get more trustworthy results.
Integrated spatial and orientation analysis of quartz c-axes by computer-aided microscopy
Journal of Structural Geology, 1993
A new method for the complete determination of quartz c-axis orientations is proposed. Its primary aim is to integrate the analysis of crystallographic orientations and the spatial distribution of the lattice orientations within the fabric in the form of high resolution AVA (Achsenverteilungsanalyse). The method is based on standard mineral optics and image analysis techniques. It uses a slightly modified polarizing microscope, a surveillance camera and a computer (a universal stage is not necessary). The method has been developed for quartz but can be extended to the analysis of other uniaxial minerals. The primary results of the analysis consist of three logical images which represent: (a) the azimuth and (b) the inclination of the c-axes, and (c) the goodness-of-fit of the analysis at every pixel. Thus, the absolute c-axis orientation is defined at each point of the picture, and can be displayed in colour-coded form (= AVA image). From the azimuth and inclination images, further results are derived. Transferring the orientations to a stereogram, a volume-weighted pole figure is obtained. By calculating the angular mismatch between pixels, i.e. by performing a gradient-filtering in orientation space, high-and low-angle grain boundaries are discriminated. As a consequence, image segmentation, i.e. the identification of grains and grain boundaries, is based on c-axis orientation and not on visual bias. Simultaneous visualization of microstructure and crystallographic orientation greatly facilitates the analysis of deformation fabrics.