Backflow and margin-parallel shear within an ancient subduction complex

Lineated and foliated tectonics of the Teslin suture zone, Yukon, represent the deep-seated part of a west-dipping subduction complex that formed seaward of western North America in Permian-Triassic time. The tectonites were progressively underplated onto the hanging-wall plate during B-type subduction. With continued subduction and underplating, the boundary between the hanging wall and subduction channel migrated oceanward, resulting in "growth' of the hanging-wall plate at depth. These tectonites preserve a progressive record of backflow, dextral margin-parallel shear, and downflow within the subduction channel. Early Jurassic A-type subduction of the leading edge of western North America resulted in eastward overthrusting of the tectonites as a coherent block onto North American strata. These tectonites provide empirical evidence that backflow, margin-parallel displacement, and downflow can all occur within the deeper parts of subduction zones. -Author