ANATOMY OF A CENTRAL UPLIFT OF A COMPLEX IMPACT CRATER: THE UPHEAVAL DOME STRUCTURE, UTAH

The internal structures of central uplifts of impact craters are among the most complex geologic features within the Earth’s crust. Upheaval Dome, Utah, is used as a reference and case study to display the internal geometry of a central uplift and to deduce mechanisms of uplift formation in impact craters within a sedimentary, siliciclastic target. Geological data gained from high resolution mapping of the central part of the structure were combined with topographic data in an ArcGIS database. A 3D-visualization of the geometry of faults and strata within the central uplift is shown and interpreted with respect to their deformation history. Central uplift formation is induced by an inward and upward directed convergent flow of the crater floor during collapse of the transient crater cavity. Radial folds and a concentric stacking of imbricated thrust slices are prominent deformation features and result from a constrictive strain pattern. The arrangement of structural elements in the inner part of the Upheaval dome roughly displays some bilateral symmetry, trending northwest. The dominance of northwest dipping reverse faults indicates a material transport of “top to the south-east” which may be caused by an oblique impact. Fault planes commonly dip steeply and are bent due to a passive distortion after activation. The macroscopic coherence of large target units and blocks and the anisotropy of the layered target causes remarkable deviations from an ideal convergent flow field. Stratified siliciclastic rocks are commonly deformed by localized brittle faulting, and massive sandstones may be deformed by a distributed cataclasis. During crater collapse, pervasively crushed sandstones will flow locally as a granular medium, resulting in the formation of dikes. Acting as lubricants, they accommodate the complex meso-scale folding and faulting of the neighboring strata. A standard numerical model of impact cratering was designed for comparison with the observed structures and to estimate impact parameters like initial crater size, amount of erosion, and the time of impact.