DEFORMATION FEATURES AT UPHEAVAL DOME, UTAH, IMPLY BOTH METEORITE IMPACT AND SUBSEQUENT SALT DIAPIRISM

Upheaval Dome is a ~5.5 km-wide circular topographic depression in Canyonlands National Park, Utah. Upturned beds around the feature indicate a structural dome located above salt layers in the Pennsylvanian Paradox Formation. Its ambiguous origin, either as a result of an underlying salt diapir or a meteorite impact, has been debated since 1927. Recently, planar deformation features (PDFs) were discovered at the dome, which provide diagnostic evidence for meteorite impact. Although the presence of PDFs supports the meteorite impact hypothesis for the formation of Upheaval Dome, it does not rule out the possibility that the structural architecture of the dome was strongly influenced by post-impact salt flow.

In this study, a combination of field mapping and observation, aerial photograph interpretation, and petrographic analysis, is used to identify and characterize both dynamic and slowly-formed deformation features at Upheaval Dome. Shear fractures and deformation bands are both found in abundance at Upheaval Dome in both radial and concentric orientations that are separate from fractures created by the regional stress field. These two distinct forms of shearing deformation within the same lithology ostensibly reflect disparate formation conditions. They are differentiated by unique morphological characteristics, both in outcrop and in thin section. The high frequency, close spacing, and central slip surface of shear fractures suggest that they were formed dynamically; however, deformation bands that have distributed shearing, definable cross-cutting relationships, and regular spacing, are interpreted to have formed slowly through progressive shearing over time. The wide variety of different fracture types within specific rock units at Upheaval Dome suggest that different formation mechanisms and driving stresses existed at different points in time. The available evidence suggests that both meteorite impact and post-impact salt diapirism contributed to the development of Upheaval Dome, lending credence to both existing hypotheses for the creation of the structure. Ultimately, however, the dome is unlikely to have formed without a triggering meteorite impact event.