La diffraction neutronique appliquée à l'étude de l'orientation préférentielle de réseau dans les quartzites

Abstract

It is shown that lattice preferred orientation analysis by neutron diffraction can be successfully applied in the case of rocks, and particularly in the case of quartzites. Neutron diffraction gonio-metry is a technique similar to X-ray goniometry, already applied to cubic metals and recently to materials of hexagonal symmetry such as titanium. The main advantage of this technique results from the low absorption coefficient of neutrons for most materials, provided that their hydrogen content is limited : the recording is thus performed directly in transmission, simplifying the corrections ; it also allows the use of large samples (<- 1 cm3) and is therefore suitable for the analysis of aggregates with a large grain size (- 1 mm). The samples studied come from a quartzite sequence deformed along the Main Central Thrust of Nepal. The {1120} and {1010} pole figures compare well with previous diagrams obtained by X-ray diffraction. The orientation distribution function has been calculated in the case of one sample using seven pole figures, and taking into account the trigonal lattice symmetry. It allows the calculation of the (0001) pole figure, which is similar to the diagram obtained by U-stage measurements on a limited number of grains. All the diagrams display monoclinic symmetry, the foliation and the linéation being in no way symmetry elements for the pole figures : this is a very common feature in naturally deformed quartzites (and other rocks) indicating that the plastic flow regime was not coaxial, i. e. displaying a simple shear component. Rolled titanium produces diagrams having similarities with quartzite ones but with a higher symmetry, the rolling process being globally a coaxial deformation process. In that case the foliation (rolling plane) and the linéation (rolling direction) are symmetry elements for the pole figures.

Microfabrics of UHP metamorphic granites in the Dora Maira Massif, western Alps – no evidence of deformation at great depth

“…5b), the preferred orientation indicates the activation of prism <a> and rhomb <a> slip (Lister & Price, 1978; Hobbs, 1985; Law, 1990). For these samples, the single‐girdle c ‐axes patterns indicate simple shear (Burg & Laurent, 1978; Lister & Price, 1978; Bouchez et al. , 1979).…”

Kinematic and tectonic significance of microstructures and crystallographic fabrics within quartz mylonites from the Assynt and Eriboll regions of the Moine thrust zone, NW Scotland

“…In relation to these mylonites, the asymmetrical fabrics from the Allt nan Sleach mylonites could reflect either a greater degree of non-coaxiality associated with their entire deformation history, or a more advanced overprinting of coaxial by non-coaxial deformation. Bouchez (1978) and Bouchez et al (1979) have proposed that in simple shear deformation of a quartzite, the dominant crystallographic slip direction ((a)) will tend to become aligned parallel to the direction of bulk simple shear deformation. Thus for simple shear deformation, the dominant a-axis maximum would be interpreted as indicating the shear direction, and with increasing strain R. D. LAW, M. CASEY AND R. J. KNIPE (Ramsay & Graham 1970) one would expect the lineation lying within the foliation to be progressively rotated into alignment with this shear direction parallel a-axis maximum (Boullier & Quenardel 1981, fig.…”

The Fabric of Polycrystalline Ice Deformed in Simple Shear: Experiments in Torsion, Natural Deformation and Geometrical Interpretation

“…This is particularly clear for peridotites in which three behavioural domains of olivine can be distinguished with increasing temperature (Nicolas et Vialon, 1980). The behaviour of quartz is more complex and the experimental controls are less complete than for olivine, but it is believed that the (1120) slip direction prevails in natural quartz-tectonites (Christie et al, 1964;Bouchez et al, 1979), along with the (0001) basal plane at low-temperature (greenschists facies) and other planes in a zone around the (1120) direction for higher temperatures (Bouchez and Pcher, 1981).…”