HR: 17:50h
AN: T34C-10    [Abstracts]
TI: Slip-rate gradients along the eastern Kunlun fault: Implications for crustal strength in eastern Tibet
AU: * Harkins, N
EM: nharkins@geosc.psu.edu
AF: Department of Geosciences, The Pennsylvania State University, Deike Building, University Park, Pa 16802, United States
AU: Kirby, E
EM: ekirby@geosc.psu.edu
AF: Department of Geosciences, The Pennsylvania State University, Deike Building, University Park, Pa 16802, United States
AU: Shi, X
EM: xzs104@psu.edu
AF: Department of Geosciences, The Pennsylvania State University, Deike Building, University Park, Pa 16802, United States
AU: Wang, E
EM: erwang@mail.iggas.ac.cn
AF: Institute of Tibetan Plateau Research & Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100080, China
AB: The degree to which convergence between India and Eurasia is accommodated by slip on intra-continental strike-slip faults is central to the question of the strength of Tibetan crust/lithosphere. Although rapid, spatially uniform slip along these structures is often cited as evidence for a strong crust, recent recognition of displacement-rate gradients near the tips of these structures afford an opportunity to evaluate the relationship between fault slip and distributed deformation of the surrounding plateau. Here we present new estimates of slip rate from displaced geomorphic markers at 6 sites along the easternmost ~ 150 km of the Kunlun fault. We reconstruct displacement using high-resolution surveys of displaced landforms and combine these with a regional chronology derived from radiocarbon and cosmogenic isotopes. Collectively, these rate determinations reveal a systematic eastward decrease in slip-rates toward the fault tip. Offset, early Holocene glacial moraines at our westernmost site indicate rates of ~ 7 mm/yr near 99.6° E. These rates appear to decrease eastward to ~ 6 mm/yr at 100.4° E, ~ 5 mm/yr near 101° E, 3-4 mm/yr near 101.5° E, and finally to ~ 2 mm/yr near 102° E. Gradients in slip-rate are broadly matched by geodetic velocities, which show a similar decrease in the far-field shear across the Kunlun fault. If the fault tip has remained relatively stationary during the Holocene, then displacement gradients should reflect the constitutive properties of the crust (e.g., Barr and Houseman, 1996). Preliminary analysis indicates that while the long length- scale of the slip-rate gradient implies a relatively strong crust, the short length-scale over which distributed shear decays away from the fault tip implies a weak crust. Incorporation of our slip-rate data and the far-field surface motion rates into a 2D visco-elastic model should elucidate whether this gradient uniquely requires a fault tip in a strong crust, a weak crust, or neither.
DE: 1105 Quaternary geochronology
DE: 1150 Cosmogenic-nuclide exposure dating (4918)
DE: 8002 Continental neotectonics (8107)
DE: 8111 Continental tectonics: strike-slip and transform
DE: 8159 Rheology: crust and lithosphere (8031)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting