Structure and formation of a central uplift: A case study at the Upheaval Dome impact crater, Utah
Thomas Kenkmann, Andreas Jahn, Dirk Scherler, Boris A. Ivanov, 2005. "Structure and formation of a central uplift: A case study at the Upheaval Dome impact crater, Utah", Large Meteorite Impacts III, Thomas Kenkmann, Friedrich Hörz, Alex Deutsch
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The internal structures of central uplifts of impact craters are among the most complex geologic features within 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 and structural data gained from our high-resolution mapping of the central part of the structure were combined with topographic data in an ArcGIS database. A three-dimensional visualization of the geometry of faults and strata within the central uplift is presented 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 gravity-driven 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 southeast, 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 cause remarkable deviations from an ideal convergent flow field. Stratified siliciclastic rocks are commonly deformed by localized brittle faulting, and massive sandstones are deformed by a distributed cataclastic flow. 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 mesoscale 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. The best fit between model and field data is found when the White Rim Sandstone is buried ∼2000 m beneath the target surface. This most likely corresponds to an Upper Cretaceous age of Upheaval Dome during deposition of the Mancos shales. The initial diameter of the Upheaval Dome impact crater would have been ∼7–8 km.