T6 Heterogeneity in Geomorphic Systems: Driving Forces and Landscape Response

Sunday, 25 September 2016
8:00 AM - 12:00 PM
Room 405

MECHANICAL FEEDBACKS BETWEEN LANDSCAPE EVOLUTION, ROCK RHEOLOGY, AND ACTIVE DEFORMATION IN CANYONLANDS NATIONAL PARK, UTAH

Paper number: T6-13
Program: Technical Sessions
Time: 11:10 AM – 11:25 AM

Authors

Abstract

The Grabens within Canyonlands National Park is an active salt system primarily driven by differential unloading due to incision of the Colorado River. This results in an array of extensional faults, salt diapirs, and an anticline following the trace of the Colorado River and its tributaries. The system contains other spatially complex conditions in the region that can create feedbacks between active deformation and landscape evolution that vary both temporally and spatially. The gentle dip of the evaporite layer drives salt flow downdip. Unconfined salt within the Colorado River canyon, weaknesses in the overlying brittle plate, and topographic gradients on the scale of tens of meters to kilometers create a pressure gradient driving salt flow from areas of thicker to thinner sedimentary overburden. Three-dimensional numerical models were built to test the spatial scale at which salt responds to these parameters, how these parameters interact within a system, and where specific processes are likely to occur based on field observations. Model results show the topography has an influence on salt flow on both regional and local scales and predict the formation of existing structures on consistent spatial scales. The Colorado River canyon initiates salt flow and subsequent brittle extension, though weakening of the overburden, incision of tributaries, and exposure of salt within the Colorado River canyon all affect the development of the system over time. Weakening of the overburden initiates stronger coupling of salt flow and topography, where salt responds to smaller features, like the tributaries and the grabens and flows at higher rates. This has implications for the structural evolution of the grabens and incision of the tributaries. Tributary intersections with the Colorado River form a wider canyon that drives more rapid, localized uplift along the river anticline, resulting in salt diapirism. These features only locally alter direction and rates of salt flow within 2 km of the canyon wall. In contrast, where salt is exposed along the length of the canyon, downstream from the Grabens, salt flow is diverted towards the exposed salt 6 km beyond the canyon and displacement rates increase by a factor of 2-3. This predicts a shift in strain before and after incision of the river into the evaporite layer.

Geological Society of America Abstracts with Programs. Vol. 48, No. 7

doi: 10.1130/abs/2016AM-286492

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