Geology of the Duncan Canal Shear Zone: evidence for Early to Middle Jurassic deformation of the Alexander Terrane, southeastern Alaska

The Duncan Canal Shear Zone, central southeastern Alaska, disrupts and penetratively deforms Devonian, Pennsylvanian, and Upper Triassic strata of the Alexander Terrane. The deformation is interpreted to have occurred within a regime of right-lateral shear during Early or Middle Jurassic time. Clastic and volcanic rocks correlated with the Upper Jurassic and Lower Cretaceous strata of the Gravina Belt lack the fabrics characteristic of the deformed Alexander Terrane strata and are inferred to unconformably overlie the shear zone. Deformational fabrics of mid-Cretaceous age observed in the Gravina rocks locally truncate and deform the shear-zone strata. Dextral stike-slip faults of Late Cretaceous and(or) Tertiary age that disrupt and modify fabrics of the shear zone are interpreted to accommodate some of the displacement observed on the Clarence Strait fault. The Duncan Canal shear zone extends southward to the Mosman Inlet region on Etolin Island where it projects beneath Jura-Cretaceous Gravina strata. In Duncan Canal and Mosman Inlet, the shear zone evolved within the Alexander Terrane and does not coincide with any recognized terrane boundaries. Since the Duncan Canal Shear Zone is restricted to the currently exposed eastern margin of the Alexander Terrane, the shear zone is interpreted to reflect deformation along the eastern margin of the Alexander Terrane. -Authors