Journal of Applied Crystallography

Volume 34, Part 4 (August 2001)

research papers

J. Appl. Cryst. (2001). 34, 442-453 [ doi:10.1107/S0021889801005635 ]

Rietveld texture analysis of Dabie Shan eclogite from TOF neutron diffraction spectra

H.-R. Wenk, L. Cont, Y. Xie, L. Lutterotti, L. Ratschbacher and J. Richardson

Abstract: Orientation distributions of garnet and omphacite in eclogite from the ultra-high pressure Dabie Shan belt in east-central China were determined from neutron diffraction data by the Rietveld method. Diffraction spectra were recorded in 16 sample orientations with seven detectors, with a kappa-geometry texture goniometer at the time-of-flight (TOF) neutron facility at the Intense Pulsed Neutron Source (IPNS). The textures of the two minerals were extracted simultaneously from 16 × 7 = 112 diffraction spectra, covering a large portion of the pole figure. The texture analysis was performed both with the Williams-Imhof-Matthies-Vinel (WIMV) method and the harmonic method, implemented in the program package MAUD. The incomplete pole-figure coverage introduced artificial oscillations in the case of the harmonic method. The discrete WIMV method produced better results, which illustrate a more or less random orientation distribution for cubic garnet. Apparently elongated grains turned out to be layers of randomly oriented crystals. Monoclinic omphacite displays a sharp texture, with [001] parallel to the lineation direction. The texture data obtained by neutron diffraction were verified with EBSP (electron backscatter pattern) measurements.

Keywords: texture analysis; Rietveld refinement; garnet; omphacite; time-of-flight neutron diffraction; orientation distribution function; pole figures.