Eastward Propagation of the Kunlun Fault and Implications for Mechanics of the Tibetan Plateau

The role of strike-slip faulting in the tectonics of Tibet and the Himalayas remains uncertain. Models of deformation in Tibet fall between two contrasting scenarios; one of which views these fault zones as lithospheric block boundaries that promoted a stepwise, northward propagation of plateau uplift, and another that views these fault zones as only the brittle, upper-crustal manifestation of a broad shear zone in a ductile middle/lower crust. In the latter case, strike-slip fault zones in Tibet do not necessarily play a role in plateau uplift. Along the easternmost Kunlun fault, a major strike-slip fault zone in northeastern Tibet, we observe a gradient in slip-rates from 10 m/kyr at 99 E, to rates of less than 2 m/kyr that are accompanied by a fault termination at 102 E. Analysis of river long profiles and accompanying catchment erosion rates reveals a broad zone of increased rock uplift rates straddling this portion of the Kunlun fault. Preliminary elastic modeling indicates that this zone of uplift could be elastically supported by the slip-rate gradient, and yet this gradient would result in stresses that exceed a reasonable crustal strength after only 30-40 kyr. One interpretation of this result is that the Kunlun fault is relatively young east of 99 E and is propagating eastward. If so, slip along the fault would significantly post-date the 10 ma minimum age of uplift in the northeastern Tibetan plateau region estimated by a number of stratigraphic, structural, and thermochronologic proxies. Alternatively, if the slip-rate gradient is a long-lived feature, then the 10-12 m/kyr of left-lateral slip observed along the central Kunlun fault must be absorbed by more distributed shear in the east. If so, a significant change in the mechanical behavior of the crust is implied between the central and northeastern Tibetan Plateau.