Brian Zurek

Position of the Snake River watershed divide as an indicator of geodynamic processes in the greater Yellowstone region, western North America

Tectonic processes, fl exure due to crustal loading, and dynamic mantle fl ow each impart a unique imprint on topography and geomorphic responses over time scales of 104 to 10 6 yr. This paper explores the mobility of regional drainage divides as a key geomorphic metric that can distinguish between the various processes driving crustal deformation in the greater Yellowstone region of the northwestern United States. We propose a new analysis that quantifi es the differences between the location of the presentday drainage divide from divides synthetically generated from fi ltered topography to determine the relative impact of tectonic and dynamic mantle infl uences on landscape development. The greater Yellowstone region is an opportune location for this investigation because contrasting models have been proposed to explain the parabolic shape of elevated topography and active seismicity that outline the imprint of hypothesized hotspot activity. Drainage divides synthesized from topography fi ltered at 50, 100, and 150 km wavelengths within the greater Yellowstone region show that the locations of the actual and synthetic Snake River drainage divides are controlled by both dynamic and fl exural mechanisms in the eastern greater Yellowstone region, but by fl exural mechanisms only in the western greater Yellowstone region. The location of the actual divide deviates from its predicted position in the fi ltered topography where tectonic controls, such as active faults (e.g., Centennial and Teton faults), have uplifted large footwall blocks. Our results are consistent with the notion of a northeastward-propagating greater Yellow stone region topographic and seismic parabola, and suggest that Basin and Range extension follows from, rather than precedes, greater Yellowstone region dynamic topography. Furthermore, our analysis suggests that eastward migration of the Snake River drainage divide lags behind the continued northeastward propagation of high-standing topography associated with the Yellowstone geophysical anomaly by 1–2 m.y.