A >5 km thick, north-dipping shear zone in the Pinal Peak map area, near Globe, Arizona, reveals contact metamorphism of the Pinal Schist through intrusion of the Proterozoic Madera Diorite. In Pinal Schist, sillimanite and rare andalusite occur in the metamorphic aureole around the diorite, but not elsewhere in this or adjoining map areas, where metamorphic grade is interpreted to be low greenschist facies. Deformation was synchronous in the schist and the diorite and is recorded by a well-developed, generally N- and NW-trending elongation lineation, Field interpretations of ductile deformation fabrics generally indicate top-to-the-south or reverse (present day coordinates) displacement. Microstructures in the Pinal Schist, the Madera Diorite, and the Pinal-Madera contact zone include S-C fabrics, mica ''fish,'' asymmetric sigma-type tails on porphyroclasts, and grain-shape and lattice-preferred mineral orientation, most of which indicate top-to-the-south (locally SE to SW) displacement, consistent with field interpretations. Some microstructures indicate top-to-the-north, or normal dip-slip, shear. Sillimanite is deformed into parallelism with other microstructures, indicating that it was involved in the deformation. Asymmetric double girdle quartz c-axis fabrics record dominantly top-to-the-south displacement, although top-to-the-north and sinistral fabrics are preserved locally. Symmetric girdles indicate deformation within the flattening (k < 1) field. The spatial distribution of symmetric and asymmetric girdles defines several structural domains within the shear zone. We interpret these domains to reflect large-scale strain partitioning. Equal area stereo plots of quartz c-axis data display clustering of maxima toward the center of the plots, suggesting activation of high-temperature slip systems. Coexistence of low-temperature deformation fabrics indicates continued deformation at progressively lower temperatures during pluton cooling. From this structural analysis we conclude that the Madera Diorite was pre-tectonic and that Pinal Schist and Madera Diorite were deformed synchronously, at relatively shallow crustal levels, in a contractional shear zone. The overall character of the shear zone reflects strain partitioning at a crustal scale.
