Progressive development of quartz fabrics in a shear zone from Monte Mucrone, Sesia-Lanzo Zone, Italian Alps

Abstract

Quartz c-axis fabrics are described from a shear zone in a jadeite — garnet bearing meta-granite from Monte Mucrone, in the Sesia-Lanzo Zone of the western Italian Alps. Quartz blebs in the meta-granitoid are progressively deformed into cigar shaped lenses, and are recrystallized. Fabrics measured from individual blebs show considerable variation resulting from an initial orientation effect, and are not very enlightening. A synoptic diagram, however, has a pole-free area which can be correlated with the extension direction, and an asymmetry which is consistent with the known sense of shear operating in the zone. Although the technique of preparing synoptic diagrams is rather painstaking, its use is advocated for complex fabric situations, as it may allow partial removal of problems associated with non-random initial orientation distributions.