2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 11
Presentation Time: 10:30 AM

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


HARKINS, Nathan, Department of Geosciences, The Pennsylvania State University, Deike Building, University Park, PA 16802, CRADDOCK, William, U. S. Geological Survey, Reston, VA 20192 and KIRBY, Eric, Department of Geosciences, Penn State University, University Park, PA 16802, nharkins@geosc.psu.edu

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.