Deformational styles in the Proterozoic Pinal Schist, Pinal Peak, Arizona: microstructural and quartz c-axis analyses

A >5km 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. From microstructural and quartz c-axis analyses it is concluded 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. -from Authors