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Preferred Orientation of Quartz in Metamorphic Rocks from the Bergell Alps

1
Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA
2
School of Urban Planning and Municipal Engineering, Xi’an Polytechnic University, Xi’an 710048, China
3
Material Science & Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
4
Joint Institute for Nuclear Research, 141980 Dubna, Russia
*
Author to whom correspondence should be addressed.
Minerals 2019, 9(5), 277; https://doi.org/10.3390/min9050277
Received: 7 March 2019 / Revised: 26 April 2019 / Accepted: 1 May 2019 / Published: 5 May 2019
(This article belongs to the Special Issue Texture and Microstructural Analysis of Crystalline Solids)
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Abstract

Crystal preferred orientation of 47 samples of quartzite and eight samples of associated marbles from the Bergell Alps have been analyzed with time-of-flight neutron diffraction and EBSD. The results show a clear distinction of texture types for quartzites transformed from Triassic sandstones and quartz layers in gneiss. Textures of Triassic quartzites are overall weak and display a maximum of c-axes perpendicular to the foliation or a crossed girdle perpendicular to the lineation. Pole figures for positive rhombs {10 1 ¯ 1} show a maximum perpendicular to the foliation and negative rhombs {01 1 ¯ 1} generally display a minimum. Based on polycrystal plasticity models this texture type can be attributed to a combination of basal and rhombohedral slip. Asymmetry of the distributions is attributed to simple shear and local strain heterogeneities. The relatively weak texture is partially caused by muscovite limiting dislocation motion and grain growth, as well as adjacent layers of marble that accommodate significant strain. Most quartz layers in gneiss, including mylonites, display a texture with a-axes parallel to the lineation and a c-axis maximum in the intermediate fabric direction. This texture type can be attributed to dominant prismatic slip. Many samples are recrystallized and recrystallization appears to strengthen the deformation texture. The study shows good agreement of neutron diffraction and EBSD. Neutron diffraction data average over larger volumes and maximum pole densities are generally lower and more representative for the bulk material. With EBSD the microstructure and mechanical twinning can be quantified. View Full-Text
Keywords: quartzite; preferred crystal orientation/texture; neutron diffraction; EBSD; Central Alps quartzite; preferred crystal orientation/texture; neutron diffraction; EBSD; Central Alps
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Wenk, H.-R.; Yu, R.; Vogel, S.; Vasin, R. Preferred Orientation of Quartz in Metamorphic Rocks from the Bergell Alps. Minerals 2019, 9, 277.

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