HR: 13:40h
AN: H33F-01 INVITED     [Abstracts]
TI: Transient Landscape Evolution of a Progressively Exhumed Basement-cored Uplift: Kyrgyz Range, Tien Shan
AU: * Oskin, M E
EM: oskin@unc.edu
AF: University of North Carolina at Chapel Hill, Department of Geological Sciences CB #3315, Chapel Hill, NC 27599 United States
AU: Burbank, D W
EM: burbank@crustal.ucsb.edu
AF: University of California at Santa Barbara, Department of Geological Sciences, Santa Barbara, CA 93106 United States
AU: Sobel, E E
EM: sobel@rz.uni-potsdam.de
AF: Institut für Geowissenschaften, Universität Potsdam Postfach 60 15 53, Potsdam, 14415 Germany
AB: Field examples that quantify the establishment, incision, and elaboration of stream channel networks in tectonically active mountain ranges illuminate transient channel characteristics and can potentially discriminate between competing process models. The Kyrgyz Range, located on the northern margin of the western Tien Shan, illustrates long-term (10⁶ - 10⁷ year) transient landscape evolution in response to uplift and erosion of an active basement-cored uplift. Eastward propagation of range uplift has progressively exhumed resistant bedrock capped by a tilted, (formerly) planar, pre-Cenozoic unconformity. Apatite fission track thermochronology records the exhumation history of this unconformity and progressively greater exhumation westward in response to bedrock incision. Bulk landscape characteristics, such as basin hypsometry and hillslope angles, evolve rapidly in response to the onset of mountain range uplift but only gradually approach spatially average conditions that could be considered steady state. Transient evolution of bedrock channels provide insight into processes that underlie the approach to steady state conditions. An analytic model, based on stream power, for exhumation of the unconformity as a geomorphic marker predicts the form of transient channel incision and confirms the utility of this surface for reconstruction of range uplift. Prominent knickpoints are not predicted to develop on main stem channels under these conditions but must develop at tributary junctions. Rapid glacial incision and cirque retreat overprints this transient landscape as the range crest rises into the zone of ice accumulation. In turn, glacial erosion sets up new boundary conditions for subsequent channel evolution. Initially, glaciation completely overwhelms the channel system with debris, shutting off fluvial bedrock incision downstream. Reestablishment of bedrock incision is sensitive to the balance between glacial till transport distance, till grain size, and discharge. Because all of these factors increase with catchment size, it is difficult to predict where bedrock incision may reoccur in the landscape. Once fluvial bedrock incision is reestablished, however, further adjustments take place to the channel networks pioneered by glaciation. Modeled transient bedrock channel incision predicts that tributary junctions will migrate to maximize the stream power expended upon the landscape. Examples of these adjustments are present within the landscape of the Kyrgyz Range even after several kilometers of exhumation.
DE: 1804 Catchment
DE: 1856 River channels (0483, 0744)
DE: 1862 Sediment transport (4558)
DE: 1863 Snow and ice (0736, 0738, 0776, 1827)
SC: Hydrology [H]
MN: Fall Meeting 2005