HR: 17:45h
AN: T34B-08    [Abstracts]
TI: Lateral Advection of Bedrock and Steady-State Convexo-concave Stream Longitudinal Profiles: Implications for the History of the South Tibetan Fault System
AU: * Miller, S R
EM: srmiller@geosc.psu.edu
AF: Pennsylvania State University, Department of Geosciences, University Park, PA 16802
AU: Slingerland, R L
EM: sling@geosc.psu.edu
AF: Pennsylvania State University, Department of Geosciences, University Park, PA 16802
AU: Kirby, E
EM: ekirby@geosc.psu.edu
AF: Pennsylvania State University, Department of Geosciences, University Park, PA 16802
AB: Recent geological studies and geodynamic models suggest that rock comprising the Higher Himalaya is extruded from beneath the Tibetan Plateau along the South Tibetan fault system and the Main Himalayan and Main Central Thrusts. If true, longitudinal profiles of Transhimalayan rivers should reflect the velocity field of extrusion. Longitudinal profiles of the Transhimalayan rivers are convexo-concave as they pass from the Tibetan Plateau through the Higher Himalaya to the Lesser Himalaya and Sub-Himalaya. Convex reaches, on the plateau and in the Higher Himalaya, are as long as 50 km. Does this convexo-concavity develop as a steady-state consequence of extrusion? Other possible explanations include transient knickzone migration due to changes in climate/base-level or spatial variations in lithology and sediment size. Using the CHILD coupled surface process-tectonics model, we demonstrate conditions under which steady-state convexo-concave profiles may occur on a plateau margin undergoing lateral crustal extrusion. Whereas stream-power law models of detachment-limited streams in equilibrium with vertical rock uplift and uniform climate and lithology produce typical concave stream profiles, the inclusion of lateral bedrock advection can produce steady-state convexo-concave profiles between an upper-bounding low-angle normal fault and lower-bounding thrust fault. The convexities in about half of the Transhimalayan rivers occur above the South Tibetan fault system, suggesting that a simple extrusion model alone does not satisfactorily explain the profiles of Transhimalayan rivers if they are in equilibrium with bedrock flux. Results are consistent with GPS measurements showing the southward displacement of Tibet relative to India and no appreciable modern activity on the South Tibetan fault system. An increase in precipitation in southern Tibet during the late Cenozoic associated with the Asian monsoon or a decrease in the rate of lateral extrusion are more likely causes of convexities north of the South Tibetan fault system.
DE: 9320 Asia
DE: 8102 Continental contractional orogenic belts
DE: 8107 Continental neotectonics
DE: 3210 Modeling
DE: 1824 Geomorphology (1625)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting