Variation in Degree of Hornblende Grain Alignment within two Boudinage Structures

Abstract

The degree of preferred orientation of hornblende in two boudinage structures is analyzed by means of an X-ray texture goniometer. Relative values of reflected intensity for {110} are plotted on the stereographic net, and contoured at convenient intervals. As in conventional fabric diagrams for hornblende, {110} define a great-circle girdle whose breadth reveals the density of unimodal grouping of [001].The density of grouping of [001] varies throughout both boudinage structures. It decreases with increasing extension in structure A, and seems to have a similar trend in structure B, where the determined variation in degree of grain alignment is of doubtful statistical significance.The inverse relationship between the degree of preferred orientation and the magnitude of extension may be attributed to rotation of the principal directions of finite strain during syntectonic crystallization. Alternatively, reorientation of strained grains by annealing recrystallization may have produced the inverse trend.

Quantitative texture analysis of glaucophanite deformed under eclogite facies conditions (Sesia-Lanzo Zone, Western Alps): comparison between X-ray and neutron diffraction analysis

“…The texture is comparable with those described in amphiboles deformed at different pressure and temperature conditions: the [001]* and [110]* directions mainly lie parallel and perpendicular to the lineation respectively (e.g., Schwerdtner 1964;Schwerdtner et al 1971;Gapais & Brun 1981;Mainprice & Nicolas 1989;Kruhl & Huntemann 1991;Siegesmund et al 1994), where the [110]* orientation is a function of the fabric components (Gapais & Brun 1981). In the M26 glaucophanites, [100]* and [010]* directions scatter within the YZ-plane of the strain ellipsoid, and [001]* directions lie at an angle with respect to the lineation and foliation.…”

Current issues and new developments in deformation mechanisms, rheology and tectonics

“…They found that care was needed in quantitative texture analysis and that more than three individual pole figures must be measured to obtain accurate results for plagioclase. Schwerdtner et al 1971). In an attempt to further improve quantitative analysis, Zucali et al compared their results from neutron diffraction with spectra of X-ray diffraction summed from at least three slabs of the specimen.…”