EAPSI: Using 3D numerical models to understand deformation of an active salt system in Needles District, Utah

Kravitz Katherine A, Boulder CO

Investigators

Abstract

The landscape of eastern Utah, including Moab Valley, Arches, and Canyonlands National Parks, is influenced by flow and dissolution of a buried salt deposit. These deposits are some of the weakest rocks on Earth and flow plastically at shallow depths, deforming, breaking, and moving overlying sedimentary rock. The Needles District, located in southern Canyonlands National Park, Utah, is actively deforming due to salt flow into the large canyon incised by the Colorado River. To investigate how salt flow, failure of the overlying rock, and fluid transport through the Colorado River, three-dimensional numerical models will be produced. The focus of this study is to understand how faults develop and interact and how plastic flow of the salt is coupled to the brittle overlying sedimentary formations. This research will take place at GNS, Wellington, New Zealand, allowing access to a powerful modeling software and the expertise of landform modeler, Dr. Phaedra Upton. The Needles District exposes an array of actively creeping normal faults that accommodate gravity-driven extension above a plastically deforming substrate of evaporite deposits. This research will create three-dimensional mechanical models using Flac3D to understand the mechanics behind active deformation in the Needles District. Models will address how 1) preexisting weaknesses (i.e. joints) in the sedimentary units control fault expression, 2) heterogeneity in the salt layer affects deformation patterns, and 3) varying salt flow and dissolution rates influence the system. These models will yield mathematical and visual solutions of how salt deforms and it is coupled to brittle failure of the overburden. Modeling how plastic flow and brittle deformation are coupled as well as salt heterogeneity can create a more precise picture of rock mechanics that has yet to be explored and can potentially be applied to extensional tectonic settings in other regions. This NSF EAPSI award is funded in collaboration with the Royal Society of New Zealand.