Abstract
Abstract. The crystallographic preferred orientations (textures) of three samples of Black Hills Quartzite (BHQ) deformed experimentally in the dislocation creep regimes 1, 2 and 3 (according to Hirth and Tullis, 1992) have been analyzed using electron backscatter diffraction (EBSD). All samples were deformed to relatively high strain at temperatures of 850 to 915 °C and are almost completely dynamically recrystallized. A texture transition from peripheral [c] axes in regime 1 to a central [c] maximum in regime 3 is observed. Separate pole figures are calculated for different grain sizes, aspect ratios and long-axis trends of grains, and high and low levels of intragranular deformation intensity as measured by the mean grain kernel average misorientation (gKAM). Misorientation relations are analyzed for grains of different texture components (named Y, B, R and σ grains, with reference to previously published prism, basal, rhomb and σ1 grains). Results show that regimes 1 and 3 correspond to clear end-member textures, with regime 2 being transitional. Texture strength and the development of a central [c]-axis maximum from a girdle distribution depend on deformation intensity at the grain scale and on the contribution of dislocation creep, which increases towards regime 3. Adding to this calculations of resolved shear stresses and misorientation analysis, it becomes clear that the peripheral [c]-axis maximum in regime 1 is not due to deformation by basal 〈a〉 slip. Instead, we interpret the texture transition as a result of different texture forming processes, one being more efficient at high stresses (nucleation or growth of grains with peripheral [c] axes), the other depending on strain (dislocation glide involving prism and rhomb 〈a〉 slip systems), and not as a result of temperature-dependent activity of different slip systems.
Highlights
Quartz textures, usually presented in the form of pole figures, are frequently used for the analysis of deformed rocks
We interpret the texture transition as a result of different texture forming processes, one being more efficient at high stresses, the other depending on strain, and not as a result of temperature-dependent activity of different slip systems
We suggest a model in which the texture transition can be explained (a) by the motion of [c] during subgrain rotation recrystallization (SGR) and dislocation glide towards the center of the pole figure along welldefined paths into the girdle and (b) by an additional process operating at high differential stress levels producing new grains with [c] at the periphery of the pole figure (Fig. 12a, b)
Summary
Quartz textures (crystallographic preferred orientation), usually presented in the form of pole figures, are frequently used for the analysis of deformed rocks. X-ray or electron backscatter diffraction (EBSD) data are widely considered to make interpretations about deformation kinematics such as shear senses (e.g., Berthe et al, 1979; Simpson, 1980; Kilian et al, 2011b), vorticity (e.g., Wallis, 1995; Xypolias, 2009) and progressive strain type (e.g., Price, 1985; Sullivan and Beane, 2010), deformation mechanisms (e.g., Behrmann and Mainprice, 1987; Song and Ree, 2007; Kilian et al, 2011a) or recrystallization processes (e.g., Knipe and Law, 1987; Stipp et al, 2002), the involved slip systems (e.g., Bouchez and Pecher, 1981; Schmid and Casey, 1986; Law et al, 1990), or even to estimate synkinematic temperatures (e.g., Kruhl, 1996; Morgan and Law, 2004; Thigpen et al, 2010).
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