There are currently two mutually exclusive views of continental deformation: either continents deform heterogeneously by breaking into microplates or they deform homogenously as continua. Distinguishing between these views centers on determining the extent to which intracontinental faults link to form microplate-boundary systems that remain active for tens to hundreds of millions of years. The Indo-Asian collision presents an excellent opportunity to understand the long-term evolution of fault linkages since it has been active throughout the Cenozoic and is cut by a number of major faults. The left-lateral Altyn Tagh fault is the largest of these structures, and has been active since the early stages of the collision. Understanding how this fault terminates is critical for determining if it has formed part of a long-lived microplate-boundary system. A field-based structural and thermochronologic study is testing the hypothesis that the western end of the Altyn Tagh fault linked with an early Cenozoic, south-directed backthrust belt. Field mapping and cooling histories derived from 40Ar/39Ar analyses of basement K-feldspars together indicate that three faults are key structures within this hypothesized south-directed backthrust belt. Whether the structural evolution of these three fault systems is consistent with predictions of the backthrust hypothesis, the following are are being determined for each fault system: 1) the geometry and history of motion, 2) the timing of deformation, 3) the total Cenozoic offset, and 4) how these faults link with the Altyn Tagh system. The study focuses on the Karakax, Yulung, and Loqzung systems. The Karakax fault is presently an active, north-dipping strike-slip fault but appears to have an earlier history of reverse/thrust motion. The Yulung fault system cuts Tertiary volcanics and may have uplifted a range of >6800 m peaks during south-directed thrusting. Within the Loqzung fault system, Cretaceous and Tertiary strata are locally deformed by south-directed structures. If the backthrust hypothesis is correct, the Altyn Tagh fault formed part of a microplate-boundary system that has existed since the earliest stages of the Indo-Asian collision. This result would support the microplate model for the Indo-Asian collision zone and contradict the idea that continental deformation is fundamentally homogeneous at long time scales.
