COMPLETE TEXTURE ANALYSIS OF A DEFORMED AMPHIBOLITE - COMPARISON BETWEEN NEUTRON-DIFFRACTION AND U-STAGE DATA

This paper describes a new technique of analysing complex neutron diff raction patterns, allowing the quantitative texture analysis of each r ock-forming mineral up to triclinic lattice symmetry in polymineralic rocks. The method is demonstrated using hornblende and plagioclase fab rics in Alzenau amphibolite from the Spessart Mountains (Mid-German Cr ystalline Rise). Hornblende and plagioclase exhibit a pronounced shape preferred orientation with respect to the macroscopic fabric elements . For control purposes, crystallographic preferred orientations were a lso determined independently by individual grain measurements using a U-stage. From the neutron texture analyses we obtain only superposed p ole figures (hornblende and hornblende, hornblende and plagioclase, an d plagioclase with plagioclase) of low-indexed lattice planes. Therefo re, the critical crystallographic directions were recalculated by the orientation distribution function (ODF) which is given by texture comp onents. The optical and neutron-derived pole figures are in a good agr eement. All pole figures display strong preferred orientation, althoug h the plagioclase texture is less pronounced. The hornblende texture c onsists of a [001] maximum parallel to the stretching lineation, with [010] showing a tendency to develop a girdle around the lineation. [10 0]-axes are distributed with a clearly split maximum representing the monoclinic angle between [100] and [001]. The plagioclase texture is a rare one with (001) subparallel within the foliation and [100] orient ed subparallel to the lineation. [0101 of plagioclase is concentrated normal to lineation within the foliation. The technique outlined here is potentially the most useful one for texture analysis of polyphase r ocks, independent of crystal symmetry.