Yellowstone's tectonic parabola and lower-crustal flow: Application of the waterbed model for ductile lower crust

Upper mantle V_P anomalies align well with observed crustal anisotropy throughout the Pacific Northwest, suggesting that vertical traction from the mantle may be closely coupled to crustal dynamics. However, these observations suggest that central Idaho should have moderately subsided throughout the Cenozoic, where in fact a pulse of uplift has been occurring since the mid-Miocene. This uplift represents one segment of the larger Yellowstone "tectonic parabola," a broad region of uplift that surrounds the Yellowstone hot spot track. Prior studies have investigated the influence of dynamic topography associated with a flattening Yellowstone plume in generating this uplift, but have been unable to account for a majority of the uplift by that mechanism alone.

We propose that this uplift is primarily a consequence of lower crustal flow, forced away from the subsiding Snake River Plain and inflating the adjacent crust. This crustal flow is a response to two dynamic forcing mechanisms: density variations in the mantle that apply upward traction at the Moho (i.e. a component of the plume-flattening model), and propagating injection of a dense mid-crustal sill along the Yellowstone hot spot track that compresses the lower crust from above (much like fluid flow inside a waterbed). We numerically model crustal flow using geologically-constrained parameters that are reasonable for the Yellowstone area and show that this mechanism is sufficient to explain the amplitude and timing of recent uplift in central Idaho.