Kilometre-scale folding in the Teslin zone, northern Canadian Cordillera, and its tectonic implications for the accretion of the Yukon-Tanana terrane to North America: Discussion

Abstract

Despite the often divergent opinions regarding the evolution of the Teslin suture zone (TSZ), previous tectonic models broadly agree that the TSZ comprises a ductile shear zone that constitutes a fundamental crustal boundary (e.g., Tempelman-Kluit 1979; Erdmer 1985; Hansen 1989; Stevens and Erdmer 1996; Hansen and Dusel-Bacon 1998). In contrast, de Keijzer et al. (1999) offer a radical model in which the TSZ is a rootless polydeformed nappe obducted onto North America. According to their interpretation the TSZ does not represent a shear zone. Although the influx of new ideas in science is always commendable, the methodology by which de Keijzer et al. (1999) arrive at their interpretation is scientifically flawed; they ignore or arbitrarily dismiss published TSZ data, and they fail to present evidence in support of key elements of their model. Although their data may be valid, we question: (1) their interpretation of linear fabric elements, (2) the existence of kilometre-scale folding, and (3) evidence for North American rocks in the western TSZ. de Keijzer et al. (1999) discard the interpretation of the TSZ as a complex ductile shear zone and assert that, apart from the western TSZ, most lineations represent crenulations and bedding–cleavage intersections. They state that they did not observe stretching lineations or fabric asymmetries. In contrast, previous workers (Erdmer 1985; Hansen 1989, Hansen et al. 1989, 1991; Stevens and Erdmer 1996; Oliver 1996; Hansen and Dusel-Bacon 1998) describe numerous structural domains within the TSZ and correlative L–S tectonites in east-central Alaska, based on elongation lineation orientation and microstructural asymmetry, which they attribute to widespread ductile shear across the entire TSZ. Thus, knowledge of whether or not the TSZ represents a zone of ductile shear deformation is critical to models of TSZ evolution. The presence and nature of quartz …