AN SEM ELECTRON-CHANNELING STUDY OF FLAME PERTHITE FROM THE KILLARNEYGRANITE, SOUTHWESTERN GRENVILLE FRONT, ONTARIO

Flame perthite from greenschist-facies mylonites in the Killarney gran ite, near Georgian Bay, in Ontario, have been examined using SEM back- scattered-electron (BSE) images and electron-channeling patterns (ECPs ). ECPs provide complete crystallographic orientation of a grain, or a part of a grain, as small as 5 mu m, and can be done anywhere within a polished section. Also, EC involves high-resolution BSE imaging, and can distinguish phases on the basis of mean atomic number rather than optical properties; it is therefore particularly useful in studying f eldspars. Using ECPs and BSE images, we determined (1) the relative cr ystallographic orientation of the host with respect to the flame, (2) the preferred growth-plane of the flames within the structure of the h ost K-feldspar, and (3) the orientation of the flames relative to the strain fabric in the host rock. This method gives more complete and mo re accurate information than the U-stage, and provides spatial informa tion that cannot be obtained with X-ray-diffraction texture analysis, The K-feldspar host and the albite flames share the same crystallograp hic orientation. The dominant plane along which flame growth has occur red within the K-feldspar structure is the same as that for perthite o f exsolution origin (i.e., parallel to the b axis and approximately 9 degrees from the c axis). Only in cases where multiple sets of flames are developed within a single crystal do other orientations occur. Rel ative to the rock fabric, flames are preferrentially oriented within a range subnormal to the C and S foliations; where two feldspar grains come in contact, flames also develop normal to their contact boundarie s. Therefore, K-feldspar grains that are crystallographically oriented with the perthite plane subparallel to the local maximum stress direc tion exhibit growth of abundant flames. Grains in other orientations d evelop only minor flames or none at all.