STRUCTURAL DIVERGENCE AND TRANSPRESSION IN THE TESLIN TECTONIC ZONE, SOUTHERN YUKON-TERRITORY

The structural and tectonic evolution of the Teslin tectonic zone, a c omplex belt of ductilely deformed rocks forming the southern extension of the Yukon-Tanana terrane in the northern Canadian Cordillera, is e lucidated with new field data and by the reinterpretation of existing data. The zone includes greenschist to amphibolite facies metasediment ary and metaplutonic rocks of the Nisutlin and Anvil assemblages chara cterized by S and L-S tectonite fabrics. Primary contact relationships and ages show that most rocks in the zone were contiguous by Mississi ppian time. Mapping identified a number of strain domains which preser ve S fabrics dipping northeasterly or southwesterly, variable mineral lineation orientations, and a variety of shear directions including ea sterly and westerly vergent thrust shear, down-to-the-east and down-to -the-west normal shear, and dextral strike-slip shear. Regional constr aints and microstructures suggest that latest ductile deformation was Late Triassic to Early Jurassic in age. Structural characteristics are explained most effectively by convergent-dominated transpression in c ombination with tectonic wedging and associated back thrusting above a low-angle west dipping detachment. Oblique eastward and upward moveme nt of the rocks over the detachment, which may have coincided with the top of thinned North American continental crust, produced easterly ve rgent shear, and localized or widespread tectonic wedging and back thr usting produced westerly vergent shear. The transpressive deformation postdates formation of the Nisutlin assemblage by Mississippian time a nd subduction of the Slide Mountain Ocean beneath the Nisutlin assembl age in Permian to Early Triassic time. The western margin of the Tesli n tectonic zone was truncated by Cretaceous strike-slip faults and tra nslated northward. Rocks of the peraluminous orthogneiss assemblage of the Yukon-Tanana terrane in central Yukon acted as the tectonic wedge and were overthrust by rocks of the Nisutlin and Anvil assemblages in Early Jurassic time before unroofing by local extension in Cretaceous time.