SPATIAL PATTERNS OF CHANNEL STEEPNESS IN THE CENTRAL ROCKIES: DO RIVER PROFILES RECORD LANDSCAPE EVOLUTION FORCING BY YELLOWSTONE DYNAMIC TOPOGRAPHY?

Numerous investigations demonstrate that mantle convective processes affect the surface topography of the overriding plate. ‘Positive dynamic topography’ refers to the surface expression of mantle upwelling. An advecting wave of dynamic topographic surface uplift plate is thought to result from southwestward migration of North American relative to the Yellowstone hotspot. Advection of positive dynamic topography through an overriding plate disturbs the landscape by a combination of a change in surface uplift rate and tilting. Identification of dynamic topography from the Yellowstone landscape, however, is complicated by the polygenetic regional topography created by the overprinting effects of glaciation, plume-related bimodal volcanism, basin and range extension, early Cenozoic arc volcanism, and Laramide contraction. Our model, which is parameterized to Yellowstone but doesn’t include climate variations, suggests contribution of the dynamic topography erosional signal should decrease from 0.1mm/yr to 0.5 mm/yr at a 100km radius from the hotspot uplift source. The cosmogenic chronology that we are building to constrain spatial patterns of incision in the Bighorn Basin indicates that there is differential incision occurring in the Bighorn basin. Rates vary from 2.8mm/yr in the western basin, which is closer to Yellowstone to 1.1mm/yr in the eastern basin. The Quaternary has been a period dominated by river incision and net erosion for the Greater Yellowstone and central Rockies, global cooling and its effects at the Plio-Pleistocene transition is thought to be the dominant control on this erosional regime, however the magnitude of contribution from Yellowstone dynamic topography to the regional landscape evolution is still unknown because published incision rates lack the resolution to differentiate between incision forcing mechanisms. Analysis of river profiles in bedrock streams is powerful tool for determining spatial patterns of surface deformation. We compare results for normalized channel steepness indices across various basins in the Central Rockies and Greater Yellowstone area with known extent of glaciation, lithology, active faulting, and EarthScope mantle p-Wave velocity data to determine whether there is are regional steepeness patterns associated with the hotspot.