FRACTURE PATTERNS RELATED TO METEORITE IMPACT AND SUBSEQUENT SALT MOVEMENT AT UPHEAVAL DOME, CANYONLANDS NATIONAL PARK, UTAH

Upheaval Dome is a ~5.5 km wide circular topographic depression in Canyonlands National Park, Utah. Upturned beds around the feature indicate that it is a structural dome located above salt layers in the Paradox formation. Its ambiguous origin, either as a salt diapir or a meteorite impact, has been debated for the last 75 years. Recently, planar deformation features (PDFs) were discovered at the dome. PDFs have been shown to be distinct from metamorphic features caused by tectonic processes and are now accepted as a strong diagnostic tool for meteorite impact. Although the discovery of PDFs may seem to be the end of the argument concerning the origins of the dome, post-impact salt flow beneath the crater may still have had an effect on the formation of the feature. Based on field and aerial photograph analysis, we have identified and characterized both dynamic and slowly-formed deformation features around the dome. Fractures with dendritic branching patterns are representative of dynamic fracturing, caused by a high growth velocity associated with a high energy event. Clastic dikes within siliciclastic rocks and fractures with lattice frameworks also imply a dynamic event at the dome. However, multiple sets of regular, planar fractures (joints and deformation bands) are common around the dome and pointing to a slow growth process. To determine if such fractures are nonetheless related to dome formation, we isolated local from regional deformation by removing three regional fracture sets from the overall dataset. Fracture orientations in tilted beds were back-rotated to determine original formation orientations. There are no clear local fracture trends (e.g., radial) when beds are back-rotated to horizontal, suggesting that some fractures may have formed after beds had already been deformed by the impact. Future petrographic studies will focus on any evidence of shock metamorphic features and microscopic characterization of the different fracture types. We advocate that strong evidence for a meteorite impact does not necessarily rule out salt diapirism as prominent deformation process at Upheaval Dome. The two models are not mutually exclusive.