g.f. ndlovu 1 , t.i. ivankina 2 , r.n. vasin 2
DESCRIPTION
The study of Quartz Textures in Multiphase rocks using Neutron Diffraction Texture Analysis at the JINR, Dubna. G.F. Ndlovu 1 , T.I. Ivankina 2 , R.N. Vasin 2. 1 Council for Scientific and Industrial Research (CSIR), Pretoria, South Africa - PowerPoint PPT PresentationTRANSCRIPT
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. Ndlovu1, T.I. Ivankina2, R.N. Vasin2
1 Council for Scientific and Industrial Research (CSIR), Pretoria, South Africa2 Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research,
Dubna, Russia
Main topics • Why Quartz
• Why measure texture• Goals • Methods• Results
• Experimental• Theoretical
• Conclusions• Acknowledgements
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 - 2516 m
OKU 818Composition- quartz (~40%)- mica (~30-40%)- plagioclase (~20-30%)
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
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
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
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
SA ASS
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
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 Ka with the coordinate system of the crystallite Kb.
Xb
Zb
Yb
β
γ
α
Theoretical Methods
(Xa,Ya,Za): Ka – right-handed, Cartesian sample coordinate system.(Xb,Yb,Zb): Kb – 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
Data processingNormalized 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 F2, construction of the ODF-histogram and ODF-spectrum
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
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
Results(1
1-21
)
Experimental pole figures
TOF-chanels
Inte
nsity
, 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
001 110 101 011
0.3 1.6 0.5 1.3 0.6 1.3 0.6 1.6
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 104–105 grains
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
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
Thank You!