The Tatshenshini shear zone extends from Klukshu Lake in southwestern Yukon, southward to the Yukon-British Columbia border. Deformation in the shear zone ranges from hundreds of meters to a few kilometers in width and is characterized by protomylonitic and mylonitic turbidites belonging to the Dezadeash Formation (Jurassic-Cretaceous) that are overlain by protomylonitic granodiorite of the Ruby Range Batholith (Late Cretaceous-Tertiary). The Dezadeash Formation-Ruby Range Batholith contact, bedding, and deformation and magmatic fabrics within the Tatshenshini shear zone are all coplanar, striking northwest-southeast and dipping moderately to the northeast. Kinematic indicators from the Dezadeash Formation and Ruby Range Batholith record a top-to-the-southwest sense of shear. Collision of the Insular superterrane with the Intermontane superterrane by the mid-Cretaceous resulted in the eastward directed underplating of Yukon-Tanana terrane-equivalent rocks by the Dezadeash Formation and the formation of the Tatshenshini shear zone. The Tatshenshini shear zone preceded and controlled emplacement of the Ruby Range Batholith, but magmatism, ending ~58--56 Myr ago, outlasted deformation. The results of this work support the correlation of the Ruby Range Batholith with the adjacent Great Tonalite Sill in southeastern Alaska. It also suggests a linkage between the Tatshenshini shear zone and the Coast shear zone in southeastern Alaska and along which the Great Tonalite Sill was emplaced. The Tatshenshini shear zone and the Coast shear zone represent the coda of long-lived tectonism along the Shakwak suture, the accretionary boundary between the Insular and Intermontane superterranes. ¿ 2000 American Geophysical Union