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

Orientation distributions of garnet and omphacite in eclogite from the ultr a-high pressure Dabie Shan belt in east-central China were determined from neutron diffraction data by the Rietveld method. Diffraction spectra were r ecorded in 16 sample orientations with seven detectors, with a kappa-geomet ry texture goniometer at the time-of-flight (TOF) neutron facility at the I ntense Pulsed Neutron Source (IPNS). The textures of the two minerals were extracted simultaneously from 16 x 7 = 112 diffraction spectra, covering a large portion of the pole figure. The texture analysis was performed both w ith the Williams- Imhof-Matthies-Vinel (WIMV) method and the harmonic metho d, implemented in the program package MAUD. The incomplete pole-figure cove rage 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 elonga ted grains turned out to be layers of randomly oriented crystals. Monoclini c omphacite displays a sharp texture, with [001] parallel to the lineation direction. The texture data obtained by neutron diffraction were verified w ith EBSP (electron backscatter pattern) measurements.