IS DYNAMIC TOPOGRAPHY ASSOCIATED WITH THE YELLOWSTONE HOT SPOT DRIVING LANDSCAPE AND DRAINAGE EVOLUTION OF THE BIGHORN BASIN?

The Yellowstone caldera is one surface manifestation of a mantle plume, however, translation of a lithospheric plate over a mantle plume creates dynamic topography that advects through the plate at the rate of plate motion with respect to the mantle. A wave of surface and rock uplift accompanies this advection of dynamic topography. Previous studies of the Yellowstone region have reached two differing conclusions as to whether the plume is expressed topographically. The first is that the high topography (Yellowstone Crescent of High Terrain ‘YCHT’), localized seismicity (the ‘tectonic parabola’), and a geoid high centered on Yellowstone are thought to represent plume forcing of late Cenozoic tectonics and landscape evolution. The second conclusion is that climate change is the principal driver of landscape evolution in this region. The Yellowstone plume topographic signal, however, is complicated by contributions from plume-related bimodal volcanism, basin and range extension, early Cenozoic arc volcanism, and Laramide contraction to the polygenetic regional topography. The Bighorn Basin, which formed during the Laramide orogeny, lies to the east of the present caldera, and was a depositional center for most of the Cenozoic. Previous work indicates the basin transitioned from subsidence and deposition to uplift and incision between 4-2 Ma. Flights of strath terraces in the basin reflect net downcutting and rock uplift with respect to the river since abandonment. This matches our model for advection of the swell that predicts an eastwardly decline of differential incision. Reconstruction of the erosional story of the Bighorn Basin permits us to identify differential rock uplift occurring within the basin; stream profile analysis reveals active disturbance of the upstream portions of the Bighorn’s tributaries. Key tests of dynamic topographic-forcing of the landscape include terrace dating to constrain the timing and rates of incision throughout the Bighorn Basin.