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The study of Quartz Textures in Multiphase rocks using Neutron Diffraction Texture Analysis at the JINR, Dubna JINR, Summer Student Practice, September 2009 G.F. Ndlovu 1, T.I. Ivankina 2, R.N. Vasin 2 1 Council for Scientific and Industrial Research (CSIR), Pretoria, South Africa 2 Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, Dubna, Russia

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Main topics Why Quartz Why measure texture Goals Methods Results Experimental Theoretical Conclusions Acknowledgements

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Why Quartz Most common compound in the Earth’s Crust (SiO2 ) and most useful Occurs in all environments and all rock types - sedimentary, metamorphic or igneous Its piezoelectric properties make it highly useful in modern technology Outokumpu Deep Drilling Project depth m OKU 818 Composition - quartz (~40%) - mica (~30-40%) - plagioclase (~20-30%)

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Why do geologists measure texture? The modelling of physical anisotropies (seismic wave velocities, heat conductivity, thermal expansion, magnetic, piezoelectric, etc.) of rocks Deconvolution of the deformation history of rocks on the basis of the symmetry of the mineral textures, which commonly reflect the symmetry of deformation Texture Property Rock sample (marble) Single crystal

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Crystallographic texture Many materials are polycrystalline bodies, i.e. they consist of grains (crystallites) with a different size and orientation. Crystallographic texture is the lattice (or crystallographic) preferred orientation of crystallites of the same phase (mineral) in the chosen coordinate system: LPO (or CPO). Random orientation: NO crystallographic texture Aligned grains: One-component crystallographic texture Multi-component crystallographic texture The properties of the polycrystal are anisotropic and depend upon texture

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Objectives Learn about the operation of the SKAT diffractometer –Measure the diffraction spectra of geological samples (quartz-bearing) Use AutoIndex, GeoTOF, Pole Figure plot and Beartex programs –Indexation of spectra –Extracted experimental pole figures from spectra –Obtain quantitative 3D orientation distribution function (ODF)- quantitative measure of texture

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Experimental using neutrons creates completely new possibilities, some of which are unique and inaccessible by x rays Main Advantages of Neutron Diffraction Technique low absorption of neutrons in matter »large sample volumes accessible TOF » complete diffraction patterns can be recorded application of multiple detectors » measurements are fast excellent spectral resolution » suitable for polyphase geological samples with many diffraction lines unique scattering angle 2 of all detectors » minimum of intensity corrections required Texture diffractometer SKAT operates in the beam of the reactor IBR-2 (JINR, Dubna, Russia). 19 detectors are placed completely on the assembly ring maintaining the axial symmetry with respect to the neutron beam SAAS S A Methods Schematic view of the SKAT’s detector system. 19 detector modules named from A to S, with S in the center of the pole figure. The line on the unit sphere corresponds to the scattering vectors of detector ring, line in the XY plane is its stereographic projection. The grid of the measured pole figure. Small circle corresponds to the plane projection of the scattering vectors, dots shown where the data on pole density are situated. Pole sphere Pole figure raster

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Mathematic description of the crystallographic texture: orientation distribution function (ODF) f(g), where (g) corresponds to the rotation to align the coordinate system of the sample K a with the coordinate system of the crystallite K b. XaXa ZaZa YaYa XbXb ZbZb YbYb β γ α Theoretical Methods ( X a,Y a,Z a ): K a – right-handed, Cartesian sample coordinate system. (X b,Y b,Z b ): K b – right-handed, Cartesian crystal coordinate system. Quantitatively the orientation of the certain crystallite (g) is described by three Euler angles g={α,β,γ}. All the possible orientations (0 ≤ α,γ ≤ 2π; 0 ≤ β ≤ π) form the orientation G-space. f (g) describes the volumetric fraction of crystallites with the orientation g+dg. It is normalized to 1: The traditional method for the representation of preferred orientations is pole figures, i.e.,stereographic projection of the normals to the planes (hkl). A pole figure gives an answer to the question:Which volume fraction of the sample have a orientation for which the lattice plane normal coincide with a sample direction Z Spherical coordinates of normal to crystalographic plane (001) ( pole P2) Neutron diffraction quartz PF (11-20) stereographic projection of pole Р 2

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Data processing Normalized diffraction spectra Experimental pole figures (measured simultaneously due to application of TOF-method) Calculation of the ODF (WIMV method) Recalculation of pole figures using the ODF (0001) - absent reflection (11-20), (10-11), (01-11) – overlapped. ODF characteriztion: texture index F 2, construction of the ODF-histogram and ODF-spectrum

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Crystallographic textures that are characteristic of quartzites Dauphine twins, type I : two crystals, one rotated around [0001] on 180°. Pole figures, stereographic projection, linear scale contours. Model texture, type II (type I + misorientation) Pole figures, stereographic projection, linear scale contours. A.N. Nikitin, T.I. Ivankina, K. Ullemeyer, R.N. Vasin, 2008, published in Kristallografiya, 2008, Vol. 53, No. 5, pp. 859–866 PFs exhibit strong, symmetrically dependent peaks of high pole density Differ from the first-type textures by diffused peaks and lower pole density

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Model texture, type III (rotation around normal to (02-23)) Pole figures, stereographic projection, linear scale contours, rotation axis direction: left to right. Model texture, type IV (rotation around normal to (02-21)) Pole figures, stereographic projection, linear scale contours, rotation axis direction: left to right. Analogous quartz textures in different rocks The (001) PF exhibits a diffused pole-density peak with a tendency to waist distribution of c axes along small-circle arcs

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Results (11-21) Experimental pole figures TOF-chanels Intensity, a.u (10-11) (10-10) (11-20) (10-12) Recalculation of pole figures using the ODF (11-21),(01-11) - absent reflection (10-11), (01-12) – overlapped Fig. 1. Diffraction spectrum and pole figures corresponding to indexed reflections for the OKU 818 quartzite sample The main objective of texture analysis is to obtain information on the crystal orientation distribution in the sample Incomplete pole figures and regions of the diffraction spectrum containing overlapping peaks

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Recalculated pole figures of the principle crystallographic planes The texture of a polycrystalline sample is a statistical ensemble of crystallites. A statistically representative number of crystallites or grains is needed to obtain reliable information. Obtaining reproducible pole figures requires 10 4 –10 5 grains

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Conclusions Experimental PFs were used to reconstruct ODFs, on the basis of which PFs were calculated for the principal directions in quartz bearing rock samples The rock sample under study exhibit a strong quartz texture (the maximum pole density > 1.56) Pole figure data processing yielded the complete texture for quartz In addition to the mineral textures factors like oriented, microcracks and grain boundaries control the elastic properties of rock samples Useful in studying how quartz grains interact with or are affected by other minerals during deformation Remarks –Improve the intensity/background ratio and increase the flux of thermal neutrons at the sample position

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Acknowledgements Many thanks to the following Organisations and Personnel – JINR, Dubna –FNL, JINR, Dubna Dr. Tatyana Ivankina Dr. Roman Vasin –The NRF Dr. Noel Jacobs –The CSIR & Univ of Free State Prof. Thembela Hillie Prof. Wiets Roos

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Thank You!

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