Reconstructing deformation along the northwestern margin of the Tibetan Plateau is critical for evaluating the relative importance of microplate vs. continuum models of the Indo-Asian collision. Questions regarding the evolution of this margin are (1) what is the total offset along the sinistral Altyn Tagh strike-slip system, (2) how has that offset been absorbed in the western Kunlun Shan, and (3) why does the N-S width of the Tibetan plateau vary so dramatically along strike? I use new U-Pb zircon ages to determine if batholiths in the western and eastern Kunlun Shan belts correlate. Both areas show bimodal populations of ages with a belt of Cambrian to Devonian plutons in the north and a suite of Permian to Jurassic intrusion to the south. These data, in conjunction with regional geologic observations, define a discrete, east-west trending boundary between two plutonic and tectonic belts. This boundary has been offset along the Altyn Tagh system by 475±70 km. Kinematic arguments indicate that this offset cannot be the result of north-directed thrusting in the western Kunlun Shan. Therefore, we propose that south-directed faulting in the Tianshuihai thrust belt both offset the tectonic boundary and produced the asymmetry in the Tibetan plateau. Shortening appears to have been absorbed by thin-skinned thrusting in the upper crust, ductile flow in the lower crust, and N-dipping subduction in the mantle. Factors controlling the formation of the south-directed thrust system appear to be the contrast between the rigid Tarim and the weaker Songpan-Ganzi flysch belt and a north-dipping mantle suture inherited from Late Paleozoic subduction. The evolution of western Tibet leads to a view of continental deformation that integrates elements of the microplate model (e.g., plate-like mantle and crust-mantle decoupling) with aspects of the continuum model (weak crustal flow beneath the plateau).