HR: 16:00h
AN: T32E-01 INVITED     [PDF]
TI: Drainage Divide Migration, Orographic Precipitation, and Uplift in the Southern Andes
AU: * Hilley, G E
EM: hilley@seismo.berkeley.edu
AF: University of California, 377 McCone Hall Department of Earth and Planetary Sciences University of California, Berkeley, CA 94720-4767 United States
AU: Blisniuk, P M
EM: peter@geo.uni-potsdam.de
AF: Universitaet Potsdam, Institut fuer Geowissenschaften Universitaet Potsdam, Potsdam, 14415 Germany
AU: Strecker, M R
EM: strecker@geo.uni-potsdam.de
AF: Universitaet Potsdam, Institut fuer Geowissenschaften Universitaet Potsdam, Potsdam, 14415 Germany
AB: Statigraphic and geomorphic evidence within the Patagonian Andes suggests that rapid uplift starting in lower to middle Miocene caused drastic changes of drainage and sediment transport patterns. In particular, capture of formerly E-draining channels by head-ward erosion of W-draining fluvial systems indicates that an eastward migration of the drainage divide took place in this area. We hypothesize that this migration was caused by the development of an asymmetry in the distribution of precipitation and erosion that progressively concentrated on the windward (western) side of the uplifting mountain belt. We coupled the bedrock fluvial power-law incision model to climatic models that consider the impact of relief on precipitation with constant base-levels on either side of the uplift zone. Forward models indicate that when rock uplift rates are low, relief remains relatively subtle within the orogen, the topography is approximately symmetric, and precipitation is uniformly distributed over the mountain belt. However, high rock uplift rates concentrate precipitation along the windward slopes of the orogen at the expense of the leeward slopes. The increase in erosional power on the windward slopes causes the drainage divide to migrate towards the leeward portions of the orogen. For high uplift rates, enough topography is constructed to completely starve moisture from the leeward portion of the orogen. This eliminates erosional power within the fluvial systems in these areas, preventing the development of steady-state topography. To apply this model to the southern Andes, we used topographic and precipitation data from this region to constrain the parameters in the precipitation and fluvial bedrock incision model. We found that an order-of-magnitude increase in rock uplift rates or decrease in the erosional efficiency during the lower to middle Miocene can explain the approximate magnitude of drainage divide migration observed. Therefore, we speculate that an increase in uplift rates within the southern Andes has concentrated precipitation along the western flanks of the mountain belt, reduced precipitation along the eastern flanks, and forced the drainage divide to the east.
DE: 0399 General or miscellaneous
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 8102 Continental contractional orogenic belts
DE: 8107 Continental neotectonics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting