The Tally Ho shear zone is located along the western boundary of the Whitehorse Trough in southern Yukon, and separates the Stikine Terrane to the east and the Nisling Assemblage to the west. Complex geologic structures, Jurassic and Cretaceous plutonism and abundant Tertiary volcanism obscure the nature of this boundary and its relation to adjacent terranes. Pyroxenite, gabbro, marble, and highly strained volcaniclastic rocks form a 3-km-wide belt that is in intrusive and fault-contact with megacrystic granite and granodiorite, respectively. Structural relations in the field indicate that the ultramafic rocks in the Tally Ho shear zone are allochthonous, and have been thrust to their present position and subsequently folded in the Early Jurassic. Younger brittle and semi-brittle faulting occurred along the Llewellyn fault in the Late Cretaceous.
