ON THE MEASUREMENT OF PLAGIOCLASE LATTICE PREFERRED ORIENTATIONS

There are two major difficulties in measuring plagioclase lattice pref erred orientations (LPOs) by U-stage. The first, which is caused by de pendence of the LPO determination on anorthite content, cannot be over come using the U-stage method at present. The second difficulty, which is caused by the dependence on orientation of thin sections, can be o vercome by measuring all twinned grains in any two orthogonal sections . Compared with previous methods published in the literature, the pres ent method using two rather than three orthogonal sections is more sta tistically meaningful and time-saving. In practice, this method was us ed for measuring LPOs of plagioclase (similar to An(50)) from a typica l anorthosite mylonite deformed under the granulite facies conditions in the Morin ductile shear zone within the Canadian Grenville Tectonic Province.